Impact of replacing protein pellets with soybean grain on nutrient utilization and the rumen and blood parameters of feedlot cattle under tropical conditions.

The aim of this study was to explore the effect of replacing protein pellets with soybean grain in high-concentrate diets with or without the addition of silage, on the intake, digestibility, and rumen and blood parameters of feedlot cattle in tropical regions. Four cannulated, crossbred steers were used, 4.5 ± 0.5 years old, with an average weight of 685.55 ± 111.78 kg. The steers were distributed in a 4 × 4 Latin square, in a 2 × 2 factorial scheme (two sources of protein: protein pellets or whole soybean grain, with or without added dietary bulk). There was no effect (P ≥ 0.109) from the interaction between the source of protein and the addition of silage to the diet on dry matter (DM) and nutrient intake, or the digestibility (P ≥ 0.625) of DM or crude protein (CP). However, both factors affected (P ≤ 0.052) the intake of DM, neutral detergent fiber (NDF), and non-fiber carbohydrates (NFC), as well as the independent digestibility (P ≤ 0.099) of fat, NFC, total carbohydrates (TC), and total cholesterol concentration. There was an effect (P ≤ 0.053) from the interaction between the source of protein and the addition of silage to the diet on the digestibility of NDF and total digestible nutrients (TDN), as well as on the glycose concentration (P = 0.003). Blood parameters (i.e. protein, albumin, creatinine, triglycerides, aspartate aminotransferase (AST), and alanine aminotransferase (ALT)) were not affected (P ≥ 0.139) by the source of protein, the addition of silage, or their interaction. Lastly, including 150 g/kg silage DM in a high-grain diet, and using soybean grain as a source of protein in substitution of protein pellet could be a suitable nutritional strategy to ensure adequate DM and nutrient intake and digestibility, with no detrimental effects on rumen and blood parameters of feedlot cattle in the tropics.

Genotype-by-gestational thermal environment interaction and its impact on the future performance of tropical composite beef cattle offspring.

With global warming, there are growing challenges for raising taurine and composite beef cattle populations in tropical regions, including elevated temperatures, limited forage availability, parasite infestation, and infectious diseases. These environmental factors can trigger specific physiological responses in the developing fetus, which may have long-term implications on its performance. Therefore, the main objective of this study was to assess the influence of naturally induced thermal stress during the gestation period on the subsequent performance of tropical composite beef cattle progeny. Furthermore, we aimed to investigate the impact of genotype-by-gestational thermal environment interaction (G×Eg) on traits under selection pressure in the breeding population. A total of 157,414 animals from 58 farms located in various Brazilian states were recorded for birth weight (BW), preweaning weight gain (PWG), yearling weight (YW), hip height (HH), scrotal circumference (SC), and days to first calving (DFC). We first applied a linear regression model to the BW data, which revealed that the last 40 d of gestation were suitable for calculating the mean temperature humidity index (THIg). Subsequent regression analyses revealed that for every 10-unit increase in THIg, detrimental effects of approximately 1.13% to 16.34% are expected for all traits evaluated. Genetic parameters were estimated through a reaction norm model using THIg as the environmental descriptor. The posterior means of heritability estimates (SD) were 0.35 (0.07), 0.25 (0.03), 0.31 (0.03), 0.37 (0.01), 0.29 (0.07), and 0.20 (0.09) for the direct effect of BW, PWG, YW, HH, SC, and DFC, respectively. These estimates varied along the range of THIg values, suggesting a variable response to selection depending on the thermal environment during gestation. Genetic correlation estimates between more divergent THIg values were low or negative for YW, PWG, and DFC, indicating that the best-performing individuals at low THIg values may not perform as well at high THIg values and vice versa. Overall, thermal stress during gestation impacts the future performance of beef cattle offspring. Our results indicate the need for developing effective breeding strategies that take into account G×Eg effects and the re-ranking of breeding animals along the THIg scale, particularly for traits such as DFC that are highly sensitive to thermal stress.

With global warming posing increasing challenges in tropical regions, this study aimed to assess the impact of thermal stress during gestation on the performance of composite beef cattle offspring. Environmental factors such as high temperatures, humidity, limited forage availability, and parasite infestation can elicit physiological responses in the developing fetus, affecting its long-term performance and welfare. Using the temperature humidity index (THIg) of the late gestation as a measure of thermal environment, a reaction norm model was applied to analyze the birth weight, preweaning weight gain, yearling weight, hip height, scrotal circumference, and days to first calving (DFC). Results revealed that increasing THIg values were associated with a detrimental effect in these traits. Genotype-by-environment interaction was found to significantly influence trait variability, with DFC showing the strongest effect. Negative genetic correlations were observed between divergent THIg values, suggesting that individuals performing well in mild thermal environments may not excel in high thermal stress conditions. The heritability estimates varied along the THIg scale, indicating that selection response may vary depending on the thermal environment during gestation. These findings emphasize the need for breeding strategies that account for genotype-by-environment effects and consider the impact of thermal stress on cattle performance.

Lifetime milk production of Holstein cattle in the humid tropics compared to Holstein-Gyr and Holstein-Brahman crosses.

Crossbred cattle are commonly used for milk production in the tropics, combining the potential benefits of pure breeds with the heterosis effects of the offspring. However, no comprehensive assessment of lifetime productivity for crossbred versus purebred cattle in low-altitude tropical environments has been carried out. The present study compares the lifetime productivity of purebred Holstein (HO, n = 17,269), Gyr (GY4, n = 435), and Brahman (BR4, n = 622) with crossbreds Gyr × Holstein (GY × HO, n = 5521) and Brahman×Holstein (BR × HO, n = 5429) cows from dairy farms located in low and medium altitude tropical regions in Costa Rica. The production traits of interest were age at first calving (AFC), days open (DO), milk production per lactation (TMP), lactation length (LLEN), age at culling (ACUL), and number of lactations (NLAC). Estimates of heterosis were also calculated. The AFC for GY × HO crosses (33-34 months) was not significantly different (p > .05) from HO (33.8 months). For BR × HO crosses, a significant (p < .05) decrease in AFC (BR3HO1 35.6 months, BR2HO2 34.5 months, and BR1H03 33.3 months) was observed as the fraction of HO breed increased. Estimates of heterosis for AFC were favourable for both crosses, of a magnitude close to 3%. The DO for F1 crosses (GY2HO2 94 days; BR2HO2 96 days) was significantly (p < .05) lower than HO (123 days). Estimates of heterosis for DO were also favourable and above 15% for both crosses. The TMP and LLEN were higher for HO (TMP = 5003 kg; LLEN = 324 days) compared with GY × HO (TMP = 4428 to 4773 kg; LLEN = 298 to 312 days) and BR × HO (TMP = 3950 to 4761 kg; LLEN = 273 to 313 days) crosses. Heterosis for TMP was favourable but low for both crosses, with a magnitude below 3.0%. The NLAC for HO (4.6 lactations) was significantly (p < .05) lower than F1 (GY2HO2, 5.8 lactations; BR2HO2, 5.4 lactations). Heterosis for NLAC was above 6.0% for both crosses. Overall, estimates of lifetime income over feed costs per cow on average were USD 2637 (30.3%) and USD 734 (8.4%) higher in F1 GY × HO and BR × HO, respectively, compared to HO. In conclusion, crossbred animals, specifically those with Gyr and Brahman genetics, extend the productive lifespan, increasing economic returns.

Reproductive Activity of Socorro Island Merino Ewes and Their Crosses with Pelibuey under Heat Stress Conditions.

An experiment was carried out to evaluate the effect of spring and autumn seasons on the reproductive activity of Merino Socorro Island ewes and their crosses with Pelibuey under heat stress (HS) conditions in the tropics. All ewes (n = 80) were randomly assigned to one of two breeds during the first and second periods, respectively: (1) Twenty Socorro Island Merino ewes (SIM) and (2) 20 Pelibuey Crossbred ewes (PBC). Animals were fed the same diet and given water ad libitum. All statistical analyses were performed using SAS statistical software 9.12 procedures. In both seasons, a mean of more than 80 U of maximum THI was obtained, while in spring and autumn, the minimum THI exceeded 30 and 40 U, respectively. All animals were in oestrus and ovulated in both seasons. The frequency of animals in spring during the first 48 h of oestrus expression was greater (p < 0.05) than 48-55 h but similar (p > 0.05) than 55-65 h; in autumn during the first 48 h and 48-55 h were similar (p > 0.05), but different (p < 0.05) than 55-65 h. The duration of oestrus expression was longer in the spring than in the autumn (p < 0.05). The frequency of animals was higher (p < 0.05) in SIM than in PBC ewes during the first oestrus cycle (1-17 d) and was also higher (p < 0.05) in PBC than in SIM ewes during the second oestrus cycle (18-35 d). The SIM ewes produced more (p < 0.05) progesterone (P4) than the PBC ewes. During the sampling days of the oestrus cycle, more P4 was created in autumn than in spring (p < 0.05). Both breeds showed severe HS. In the future, ewes treated under assisted reproductive programs in the tropics may improve reproductive efficiency.

Comparison of ruminal microbiota, IL-1ß gene variation, and tick incidence between Holstein × Gyr and Holstein heifers in grazing system.

Introduction: The variation in bacterial communities among breeds has been previously reported and may be one of the reasons why Holstein × Gyr dairy heifers have better development in grazing systems in tropical conditions. This study aimed to explore the ruminal microbiota composition, the IL-1ß gene variation, tick incidence, and blood parameters of Holstein × Gyr (½ Holstein × ½ Gyr) and Holstein heifers grazing intensely managed Guinea grass (Panicum maximum Jacq. cv. Mombaça). Methods: Sixteen heifers were divided into two groups consisting of 8 Holstein × Gyr and 8 Holstein heifers. The experimental period was comprised of 3 periods of 21 days. Ruminal samples were taken via the stomach tube technique. The sequencing of the V4 hypervariable region of the 16S rRNA gene was performed using the Illumina MiSeq platform. Counting and collection of ticks were conducted each 21 days. Blood and skeletal muscle tissue biopsies were performed at the end of the experiment. Results: Firmicutes were the most abundant phyla present in both breed rumen samples and Bacteroidota showed differences in relative abundance between breed groups, with greater values for Holstein heifers (p < 0.05 with FDR correction). The 10 most abundant unique OTUs identified in each breed included several OTUs of the genus Prevotella. Holstein heifers had a greater tick count and weight (9.8 ticks/animal and 1.6 g/animal, respectively) than Holstein × Gyr (2.56 ticks/animal and 0.4 g/animal, respectively). We found nucleotide substitutions in the IL-1ß gene that might be related to adaptation and resistance phenotypes to tick infestation in Holstein × Gyr heifers. Blood concentrations of urea, albumin, insulin-like growth factor 1, triiodothyronine, and thyroxine were greater in Holstein × Gyr than in Holstein heifers. Conclusion: Adaptations in Holstein × Gyr heifers such as ruminal microbiota, tick resistance, nucleotide substitutions in IL-1ß gene, and hormone concentration suggest a better energy metabolism and thermoregulation resulting in better performance in tropical grazing systems.

Intake, digestibility, energy and nitrogen utilisation, and enteric methane emission in Holstein and Girolando-F1 cows during the transition period.

This study aimed to evaluate intake, energy and nitrogen balance as well as methane emission in Holstein and ½ Holstein ½ Gyr (Girolando-F1) cows during the transition period. Twenty-four cows (12 Holstein and 12 Girolando-F1) were used to evaluate feed intake, apparent digestibility, heat production and methane emission, carried out in two periods: from 28 to 19 days pre-calving and from 15 to 23 days post-calving. A completely randomised design was used and data were analysed by ANOVA within periods (pre- and post-calving) considering the main effect of genetic groups. Girolando-F1cows presented greater body condition score (BCS) compared with Holstein. During pre-calving, there were no differences between genetic groups, except for highest heat production per kilogram of metabolic body weight for Holstein cows. After calving, Holstein cows had greater intake of DM, nitrogen, NDF per kg of BW and produced more heat per kg of metabolic body weight. Holstein cows yielded more milk and fat-corrected milk (FCM4%) compared with Girolando-F1 cows. Holstein cows presented higher methane emission per unit of BW and of metabolic weight. Emissions of enteric methane per kilogram of milk and per kilogram of FCM4% tended to be lower for Holstein compared with Girolando-F1 cows. Nitrogen and energy retention were similar for both Holstein and Girolando-F1 at pre- and post-calving. Despite differences in BCS, DMI, and milk yield, Girolando-F1 and Holstein cows present overall similar energy efficiency, albeit Holstein cows tended to present less methane emission per kg of eligible product (milk).

Effects of Duration of Calcium Propionate Supplementation in Lambs Finished with Supplemental Zilpaterol Hydrochloride: Productive Performance, Carcass Characteristics, and Meat Quality.

Forty-five male non-castrated crossbred Dorper lambs (40.17 ± 0.35 kg body weight, BW) were employed in a completely randomized design with five treatments to investigate the effects of the duration of calcium propionate (CaPr) supplementation (10 g CaPr/lamb/d for 0, 14, 28, or 42 d before slaughter) on lambs finished with zilpaterol hydrochloride (ZH, 7.2 mg/lamb/d for a fixed period of 28 d before slaughter) regarding their productive performance, carcass characteristics, and meat quality. Treatments consisted of the following: (1) No additives (CTL), (2) 0 days on CaPr plus 28 d on ZH, (3) 14 days on CaPr plus 28 d on ZH, (4) 28 days on CaPr plus 28 d on ZH, and (5) 42 days on CaPr plus 28 d on ZH. When compared with CTL, ZH lambs exhibited a similar average daily gain (ADG) but had lower dry matter intake (DMI), leading to increased feed efficiency. Supplementing with ZH alone did not affect carcass traits, visceral mass, whole cuts, or meat quality. Lambs that received both CaPr 28 d and ZH exhibited quadratic increases (p < 0.05) in final body weight (FBW), ADG, and dressing percentage (D%). These increases were optimal at estimated inclusion durations of 26 d for FBW, 30 for ADG, and 39 d for D%. The ADG:DMI ratio and the longissimus muscle area (LMA) both exhibited quadratic increases (p < 0.05). The optimal duration of CaPr supplementation for ADG:DMI ratio was found to be 28 d, while for LMA, it was 14 d. As the period of CaPr supplementation increased, there was a linear increase (p < 0.05) in hot carcass weight, leg circumference, and whole cuts of breast IMPS209 and shoulder IMPS207. Cook loss percent increased quadratically (p < 0.05), and was higher when CaPr was included for an estimated duration of 26 d. As the duration of CaPr supplementation increased, the purge loss percentage (PRL) also increased linearly (p < 0.05). In conclusion, including CaPr in the diet for a duration of 28 d in lambs improved the response to ZH supplementation on the productive performance, carcass weight, and some whole cuts. However, it can also have a negative effect on PRL%.

The impact of pig breed on stress levels and meat quality: a study on mangalita purebred and Duroc x Landrace crossbred pigs in Romania / [O impacto da raça suína nos níveis de estresse e na qualidade da carne: um estudo em porcos Mangalita puro-sangue e Duroc x Landrace cruzados na Romênia]

ABSTRACT This study aimed to investigate the impact of pig breed on stress levels and meat quality in two commercial pig farms in the north-eastern part of Romania. One farm raised 52 Mangalita pure-bred pigs and the other 82 Duroc x Landrace crossbred pigs. Serum cortisol, a biomarker of stress, and serum glucose were measured before and after slaughtering, while meat pH was measured at 45 minutes and 24 hours post-mortem. Results showed that the Duroc x Landrace crossbred pigs had higher serum cortisol and glucose values before and after slaughtering compared to the Mangalita purebred pigs. The meat pH values of the two breeds were similar, with the pH45 and pH24 values being 6.67 and 5.48 for Duroc x Landrace crossbred and 6.53 and 5.52 for Mangalita purebred, respectively. These results suggest that pig breed can have an impact on stress levels and meat quality, with Duroc x Landrace crossbred pigs showing higher stress levels and meat quality being not affected by the breed of pig. Further research is needed to confirm these findings and to understand the underlying mechanisms.

RESUMO Este estudo teve como objetivo investigar o impacto da raça suína nos níveis de estresse e na qualidade da carne em duas fazendas comerciais de suínos, no nordeste da Romênia. Uma fazenda criou 52 suínos puros Mangalita, e a outra 82 suínos mestiços Duroc x Landrace. O cortisol sérico, um biomarcador de estresse e a glicose sérica foram medidos antes e após o abate, enquanto o pH da carne foi medido aos 45 minutos e 24 horas post mortem. Os resultados mostraram que os suínos mestiços Duroc x Landrace apresentaram valores séricos de cortisol e de glicose mais elevados, antes e após o abate, em comparação com os suínos puros Mangalita. Os valores de pH da carne das duas raças foram semelhantes, sendo os valores de pH45 e pH24 de 6,67 e 5,48 para o mestiço Duroc x Landrace e de 6,53 e 5,52 para o puro sangue Mangalita, respectivamente. Esses resultados sugerem que a raça suína pode ter um impacto nos níveis de estresse e na qualidade da carne, com os porcos mestiços Duroc x Landrace apresentando níveis mais altos de estresse e a qualidade da carne não sendo afetada pela raça do porco. Mais pesquisas são necessárias para confirmar esses achados e entender os mecanismos subjacentes.

Nutritional Quality of Milk Fat from Cows Fed Full-Fat Corn Germ in Diets Containing Cactus Opuntia and Sugarcane Bagasse as Forage Sources.

We evaluated the performance, milk composition, and milk fatty acid profile of cows fed diets composed of cactus cladodes (Opuntia stricta [Haw.] Haw), sugarcane bagasse and increasing levels of full-fat corn germ (FFCG). We hypothesized that ground corn can be effectively replaced by FFCG when cactus cladodes and sugarcane bagasse are used as forage sources. The cows were randomly distributed into two 5 × 5 Latin Squares and fed five diets in which ground corn was progressively replaced with full-fat corn germ (FFCG; 0%, 25%, 50%, 75%, or 100% of substitution). Adding FFCG to the diet increased milk production and milk fat content and reduced milk protein content. Overall, FFCG reduced the proportion of saturated FAs and increased mono- and polyunsaturated FAs in milk, including CLA isomers. In addition, activity indices of stearoyl-CoA desaturase were reduced by increasing levels of FFCG. We conclude that the substitution of corn for FFCG in diets based on cactus cladodes and sugarcane bagasse positively modifies the FA profile of milk and could add commercial value to milk products (e.g., CLA-enriched milk). In addition, the milk fat response indicates that the basal diet was favorable to the rumen environment, preventing the trans-10 shift commonly associated with milk fat depression.

Fluctuations of antibody serum titers for Toxoplasma gondii and Neospora caninum in naturally infected crossbred cows during gestation.

This study aimed to assess the fluctuations of antibody serum titers for Toxoplasma gondii and Neospora caninum in naturally infected crossbred cows during gestation and to investigate transplacental transmission of T. gondii; 51 cows were monitored during pregnancy by monthly serologic testing by indirect fluorescent antibody test. 33 cows were seronegative for both N. caninum and T. gondii, 10 were seropositive only for N. caninum, 5 were seropositive only for T. gondii, and 3 were seropositive for both N. caninum and T. gondii. In both protozoan infections, great variation in antibody levels in pregnant cows was observed, and there was significant increase (p<0.05) in the comparison between the averages of serological titration per trimester. There was a significant correlation (p<0.05) between month and probability of seropositivity for T. gondii. We conclude that pregnancy influences antibody titers of crossbred cows naturally infected with N. caninum and/or T. gondii, and that serologic testing for T. gondii in pregnant cows from the sixth month of gestation onward may decrease the number of false negative results.

O objetivo deste estudo foi avaliar a flutuação dos títulos séricos de anticorpos para Neospora caninum e Toxoplasma gondii em vacas mestiças naturalmente infectadas durante a gestação e investigar a transmissão transplacentária desses protozoários. 51 vacas foram monitoradas durante a gestação, através de sorologia mensal pela Reação de Imunoflorescência Indireta. 33 vacas foram soronegativas para N. caninum e T. gondii, 10 foram soropositivas somente para N. caninum, 5 somente para T. gondii e 3 para N. caninum e T. gondii. Em ambas as infecções, observou-se grande variação nos níveis de anticorpos em vacas gestantes, e houve um aumento significativo (p<0.05) na comparação entre as medias da titulação sorológica por trimestre. Houve correlação significativa (p<0,05) entre os meses e a probabilidade de soropositividade para T. gondii. Conclui-se que a gestação influencia os títulos de anticorpos de vacas mestiças naturalmente infectadas por N. caninum e/ou T. gondii e que testes sorológicos para T. gondii em vacas gestantes a partir do sexto mês podem diminuir o número de resultados falsos negativos.

Ingestive behavior of Holstein × Zebu cows managed on deferred supplemented pasture

This study aimed to evaluate the ingestive behavior of F1 Holstein × Zebu cows grazing on deferred pasture receiving different supplementation strategies. The experimental design was completely randomized, in a 3×4 factorial, with three supplementation strategies and four evaluation periods. The ingestive behavior of 24 cows divided into three groups of supplementation provided at milking was observed, and two of these groups received protein in the pasture. Ingestive behavior was monitored every 10 minutes for 24 hours and analyzed in the form of periods (morning, afternoon, night, and dawn) and total time. The animals remained longer grazing during the afternoon when the BGHI presented values of 83.8. Protein consumption did not influence grazing time but interfered with forage consumption. For the total grazing time, the animals in group 2 spent less time grazing. The groups of animals presented no difference concerning the time spent on rumination and idleness. During night and dawn, when the climate was characterized as thermal comfort, the animals spent more time ruminating. The climatic conditions did not influence the ingestive behavior, as the grazing peak was observed at times of higher BGHI. However, supplementation of the animals in group 2 modified the ingestive behavior of F1 H × Z cows.

Morphometric measurements and carcass characteristics of Black Australorp, Naked Neck, and Rhode Island Red crossbreds under alternative production systems / Medições morfométricas e características de carcaça de Black Australorp, Naked Neck e Rhode Island Red crossbreds sob sistemas de produção alternativos

The present trial explained the effect of alternative production systems on growth, morphometric and carcass traits of four different chicken genotypes. The second generation of two genotypes RNN (Rhode Island Red × Naked Neck) and BNN (Black Australorp × Naked Neck) obtained by two self-crosses (RNN × RNN = RR and BNN × BNN = BB) and two reciprocal crosses (RNN × BNN = RB and BNN × RNN = BR) were evaluated in three alternative production systems (conventional cages, enriched cages, and aviary). At the 6th week of age after sexing, a total of 600 birds, comprising 150 from each crossbred with a total of 300 pullets and 300 cockerels were divided into conventional cages, enriched cages, and aviary systems having 200 birds in each.Birds were organized into 3×4 factorial arrangements under Completely Randomized Design (3 production systems × 4 genotypes × 2 sexes × 25 birds = 600 birds). Regarding genotypes, RB and BR males showed higher (p < 0.01) carcass yield, drumstick weight, breast weight, and thigh weight than BB and RR genotypes. Females of BR genotype showed higher (p < 0.01) breast weight, thigh weight and drumstick weight. As far as production systems are concerned, higher (p < 0.01) liver weight, heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight were observed in the males reared in enriched cages compared with conventional cages and aviary system. Females reared in enriched cages showed higher (p < 0.01) heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight when compared with those reared in conventional cages and aviary. It is concluded that chickens (both sexes) of BR and RB genotypes had better morphological measurements and carcass traits than those of RR and BB genotype chickens. Among alternative production systems, chickens reared in enriched cages had better traits than those of reared in conventional cages and aviary during the growing phase.(AU)

O presente estudo explicou o efeito de sistemas alternativos de produção sobre o crescimento, características morfométricas e carcaças de quatro genótipos de frango diferentes. A segunda geração de dois genótipos RNN (Rhode Island Red × Naked Neck) e BNN (Black Australorp × Naked Neck) obtida por duas autocruzes (RNN × RNN = RR e B ANN × BNN = BB) e duas cruzes recíprocas (RNN × BNN = RB e BNN × RNN = BR) foi avaliada em três sistemas de produção alternativos (gaiolas convencionais, gaiolas enriquecidas e aviário). Na 6ª semana de idade após o sexo, um total de 600 aves, compostas por 150 de cada raça cruzada com um total de 300 pullets e 300 galos, foi dividido em gaiolas convencionais, gaiolas enriquecidas e sistemas aviários com 200 aves em cada. As aves foram organizadas em 3×4 arranjos fatoriais sob projeto completamente randomizado (3 sistemas de produção × 4 genótipos × 2 sexos × 25 aves = 600 aves). Em relação aos genótipos, os machos RB e BR apresentaram maior rendimento de carcaça (p < 0,01), peso da baqueta, peso mamário e peso da coxa do que os genótipos BB e RR. As fêmeas do genótipo BR apresentaram maior (p < 0,01) peso mamário, peso da coxa e peso da baqueta. No que diz respeito aos sistemas de produção, maior (p < 0,01) peso hepático, peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa foram observados nos machos criados em gaiolas enriquecidas em comparação com gaiolas convencionais e sistema aviário. As fêmeas criadas em gaiolas enriquecidas apresentaram maior (p < 0,01) peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa quando comparadas com as criadas em gaiolas convencionais e aviárias. Conclui-se que as galinhas (ambos os sexos) dos genótipos BR e RB apresentaram melhores medidas morfológicas e traços de carcaça do que os de frangos genótipos RR e BB. Entre os sistemas de produção alternativos, [...].(AU)

Morphometric measurements and carcass characteristics of Black Australorp, Naked Neck, and Rhode Island Red crossbreds under alternative production systems / Medições morfométricas e características de carcaça de Black Australorp, Naked Neck e Rhode Island Red crossbreds sob sistemas de produção alternativos

The present trial explained the effect of alternative production systems on growth, morphometric and carcass traits of four different chicken genotypes. The second generation of two genotypes RNN (Rhode Island Red × Naked Neck) and BNN (Black Australorp × Naked Neck) obtained by two self-crosses (RNN × RNN = RR and BNN × BNN = BB) and two reciprocal crosses (RNN × BNN = RB and BNN × RNN = BR) were evaluated in three alternative production systems (conventional cages, enriched cages, and aviary). At the 6th week of age after sexing, a total of 600 birds, comprising 150 from each crossbred with a total of 300 pullets and 300 cockerels were divided into conventional cages, enriched cages, and aviary systems having 200 birds in each.Birds were organized into 3×4 factorial arrangements under Completely Randomized Design (3 production systems × 4 genotypes × 2 sexes × 25 birds = 600 birds). Regarding genotypes, RB and BR males showed higher (p < 0.01) carcass yield, drumstick weight, breast weight, and thigh weight than BB and RR genotypes. Females of BR genotype showed higher (p < 0.01) breast weight, thigh weight and drumstick weight. As far as production systems are concerned, higher (p < 0.01) liver weight, heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight were observed in the males reared in enriched cages compared with conventional cages and aviary system. Females reared in enriched cages showed higher (p < 0.01) heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight when compared with those reared in conventional cages and aviary. It is concluded that chickens (both sexes) of BR and RB genotypes had better morphological measurements and carcass traits than those of RR and BB genotype chickens. Among alternative production systems, chickens reared in enriched cages had better traits than those of reared in conventional cages and aviary during the growing phase.

O presente estudo explicou o efeito de sistemas alternativos de produção sobre o crescimento, características morfométricas e carcaças de quatro genótipos de frango diferentes. A segunda geração de dois genótipos RNN (Rhode Island Red × Naked Neck) e BNN (Black Australorp × Naked Neck) obtida por duas autocruzes (RNN × RNN = RR e B ANN × BNN = BB) e duas cruzes recíprocas (RNN × BNN = RB e BNN × RNN = BR) foi avaliada em três sistemas de produção alternativos (gaiolas convencionais, gaiolas enriquecidas e aviário). Na 6ª semana de idade após o sexo, um total de 600 aves, compostas por 150 de cada raça cruzada com um total de 300 pullets e 300 galos, foi dividido em gaiolas convencionais, gaiolas enriquecidas e sistemas aviários com 200 aves em cada. As aves foram organizadas em 3×4 arranjos fatoriais sob projeto completamente randomizado (3 sistemas de produção × 4 genótipos × 2 sexos × 25 aves = 600 aves). Em relação aos genótipos, os machos RB e BR apresentaram maior rendimento de carcaça (p < 0,01), peso da baqueta, peso mamário e peso da coxa do que os genótipos BB e RR. As fêmeas do genótipo BR apresentaram maior (p < 0,01) peso mamário, peso da coxa e peso da baqueta. No que diz respeito aos sistemas de produção, maior (p < 0,01) peso hepático, peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa foram observados nos machos criados em gaiolas enriquecidas em comparação com gaiolas convencionais e sistema aviário. As fêmeas criadas em gaiolas enriquecidas apresentaram maior (p < 0,01) peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa quando comparadas com as criadas em gaiolas convencionais e aviárias. Conclui-se que as galinhas (ambos os sexos) dos genótipos BR e RB apresentaram melhores medidas morfológicas e traços de carcaça do que os de frangos genótipos RR e BB. Entre os sistemas de produção alternativos, [...].

Morphometric measurements and carcass characteristics of Black Australorp, Naked Neck, and Rhode Island Red crossbreds under alternative production systems

Abstract The present trial explained the effect of alternative production systems on growth, morphometric and carcass traits of four different chicken genotypes. The second generation of two genotypes RNN (Rhode Island Red × Naked Neck) and BNN (Black Australorp × Naked Neck) obtained by two self-crosses (RNN × RNN = RR and BNN × BNN = BB) and two reciprocal crosses (RNN × BNN = RB and BNN × RNN = BR) were evaluated in three alternative production systems (conventional cages, enriched cages, and aviary). At the 6th week of age after sexing, a total of 600 birds, comprising 150 from each crossbred with a total of 300 pullets and 300 cockerels were divided into conventional cages, enriched cages, and aviary systems having 200 birds in each.Birds were organized into 3×4 factorial arrangements under Completely Randomized Design (3 production systems × 4 genotypes × 2 sexes × 25 birds = 600 birds). Regarding genotypes, RB and BR males showed higher (p 0.01) carcass yield, drumstick weight, breast weight, and thigh weight than BB and RR genotypes. Females of BR genotype showed higher (p 0.01) breast weight, thigh weight and drumstick weight. As far as production systems are concerned, higher (p 0.01) liver weight, heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight were observed in the males reared in enriched cages compared with conventional cages and aviary system. Females reared in enriched cages showed higher (p 0.01) heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight when compared with those reared in conventional cages and aviary. It is concluded that chickens (both sexes) of BR and RB genotypes had better morphological measurements and carcass traits than those of RR and BB genotype chickens. Among alternative production systems, chickens reared in enriched cages had better traits than those of reared in conventional cages and aviary during the growing phase.

Resumo O presente estudo explicou o efeito de sistemas alternativos de produção sobre o crescimento, características morfométricas e carcaças de quatro genótipos de frango diferentes. A segunda geração de dois genótipos RNN (Rhode Island Red × Naked Neck) e BNN (Black Australorp × Naked Neck) obtida por duas autocruzes (RNN × RNN = RR e B ANN × BNN = BB) e duas cruzes recíprocas (RNN × BNN = RB e BNN × RNN = BR) foi avaliada em três sistemas de produção alternativos (gaiolas convencionais, gaiolas enriquecidas e aviário). Na 6ª semana de idade após o sexo, um total de 600 aves, compostas por 150 de cada raça cruzada com um total de 300 pullets e 300 galos, foi dividido em gaiolas convencionais, gaiolas enriquecidas e sistemas aviários com 200 aves em cada. As aves foram organizadas em 3×4 arranjos fatoriais sob projeto completamente randomizado (3 sistemas de produção × 4 genótipos × 2 sexos × 25 aves = 600 aves). Em relação aos genótipos, os machos RB e BR apresentaram maior rendimento de carcaça (p 0,01), peso da baqueta, peso mamário e peso da coxa do que os genótipos BB e RR. As fêmeas do genótipo BR apresentaram maior (p 0,01) peso mamário, peso da coxa e peso da baqueta. No que diz respeito aos sistemas de produção, maior (p 0,01) peso hepático, peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa foram observados nos machos criados em gaiolas enriquecidas em comparação com gaiolas convencionais e sistema aviário. As fêmeas criadas em gaiolas enriquecidas apresentaram maior (p 0,01) peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa quando comparadas com as criadas em gaiolas convencionais e aviárias. Conclui-se que as galinhas (ambos os sexos) dos genótipos BR e RB apresentaram melhores medidas morfológicas e traços de carcaça do que os de frangos genótipos RR e BB. Entre os sistemas de produção alternativos, as galinhas criadas em gaiolas enriquecidas tinham características melhores do que as criadas em gaiolas convencionais e aviárias durante a fase de cultivo.

Morphometric measurements and carcass characteristics of Black Australorp, Naked Neck, and Rhode Island Red crossbreds under alternative production systems / Medições morfométricas e características de carcaça de Black Australorp, Naked Neck e Rhode Island Red crossbreds sob sistemas de produção alternativos

Abstract The present trial explained the effect of alternative production systems on growth, morphometric and carcass traits of four different chicken genotypes. The second generation of two genotypes RNN (Rhode Island Red × Naked Neck) and BNN (Black Australorp × Naked Neck) obtained by two self-crosses (RNN × RNN = RR and BNN × BNN = BB) and two reciprocal crosses (RNN × BNN = RB and BNN × RNN = BR) were evaluated in three alternative production systems (conventional cages, enriched cages, and aviary). At the 6th week of age after sexing, a total of 600 birds, comprising 150 from each crossbred with a total of 300 pullets and 300 cockerels were divided into conventional cages, enriched cages, and aviary systems having 200 birds in each.Birds were organized into 3×4 factorial arrangements under Completely Randomized Design (3 production systems × 4 genotypes × 2 sexes × 25 birds = 600 birds). Regarding genotypes, RB and BR males showed higher (p < 0.01) carcass yield, drumstick weight, breast weight, and thigh weight than BB and RR genotypes. Females of BR genotype showed higher (p < 0.01) breast weight, thigh weight and drumstick weight. As far as production systems are concerned, higher (p < 0.01) liver weight, heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight were observed in the males reared in enriched cages compared with conventional cages and aviary system. Females reared in enriched cages showed higher (p < 0.01) heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight when compared with those reared in conventional cages and aviary. It is concluded that chickens (both sexes) of BR and RB genotypes had better morphological measurements and carcass traits than those of RR and BB genotype chickens. Among alternative production systems, chickens reared in enriched cages had better traits than those of reared in conventional cages and aviary during the growing phase.

Resumo O presente estudo explicou o efeito de sistemas alternativos de produção sobre o crescimento, características morfométricas e carcaças de quatro genótipos de frango diferentes. A segunda geração de dois genótipos RNN (Rhode Island Red × Naked Neck) e BNN (Black Australorp × Naked Neck) obtida por duas autocruzes (RNN × RNN = RR e B ANN × BNN = BB) e duas cruzes recíprocas (RNN × BNN = RB e BNN × RNN = BR) foi avaliada em três sistemas de produção alternativos (gaiolas convencionais, gaiolas enriquecidas e aviário). Na 6ª semana de idade após o sexo, um total de 600 aves, compostas por 150 de cada raça cruzada com um total de 300 pullets e 300 galos, foi dividido em gaiolas convencionais, gaiolas enriquecidas e sistemas aviários com 200 aves em cada. As aves foram organizadas em 3×4 arranjos fatoriais sob projeto completamente randomizado (3 sistemas de produção × 4 genótipos × 2 sexos × 25 aves = 600 aves). Em relação aos genótipos, os machos RB e BR apresentaram maior rendimento de carcaça (p < 0,01), peso da baqueta, peso mamário e peso da coxa do que os genótipos BB e RR. As fêmeas do genótipo BR apresentaram maior (p < 0,01) peso mamário, peso da coxa e peso da baqueta. No que diz respeito aos sistemas de produção, maior (p < 0,01) peso hepático, peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa foram observados nos machos criados em gaiolas enriquecidas em comparação com gaiolas convencionais e sistema aviário. As fêmeas criadas em gaiolas enriquecidas apresentaram maior (p < 0,01) peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa quando comparadas com as criadas em gaiolas convencionais e aviárias. Conclui-se que as galinhas (ambos os sexos) dos genótipos BR e RB apresentaram melhores medidas morfológicas e traços de carcaça do que os de frangos genótipos RR e BB. Entre os sistemas de produção alternativos, as galinhas criadas em gaiolas enriquecidas tinham características melhores do que as criadas em gaiolas convencionais e aviárias durante a fase de cultivo.

Economic viability of different diets for F1 Holstein x Zebu cows in milk production systems / Viabilidade econômica do uso de diferentes ofertas de dietas para vacas F1 Holandês x Zebu no sistema de produção de leite

The aim of this study was to evaluate different levels of feed restriction in the diet for F1 Holstein x Zebu cows during the winter on performance and economic viability. Data from Zootechnical book keeping, and from experiments conducted in the Experimental Field of Felixlândia, belonging to EPAMIG, were used. Total lactation of sixty F1 Holstein x Zebu cows receiving different diets was analyzed, by 2.00%, 2.25%, 2.50%, 2.75% body weight (BW), and a control group (3.4%; no feed restriction), allowing 5% leftovers in relation to the dry matter supplied, distributed in a completely randomized design. Data on milk production and feed cost were collected, evaluating the different periods that characterize the lactation of an animal. The highest milk production was found in the diet levels 3.4 %, and 2.75% BW, 3,636.00, and 3,271.50 kg, respectively. Lower milk production was observed at levels of 2.50%; 2.25%; 2.00% BW, respectively. The highest feed cost was verified without feed restriction followed by the levels of 2.75%, 2.50%, 2.25%, and 2.00% BW. The supply of the no feed restriction diet resulted in a performance superior to levels 2.75; 2.50; 2.25; 2.00% BW. The items profit, profitability were similar between all treatments, indicating that, when there is occasional feed shortage, a restriction in the diet supply of up to 2% BW provides economic security to the rural producer.

Objetivou-se por meio deste estudo avaliar diferentes níveis de restrição alimentar da dieta de vacas F1 Holandês x Zebu durante o inverno sobre o desempenho e viabilidade econômica. Foram utilizados dados da escrituração zootécnica e de experimentos realizados no Campo Experimental de Felixlândia, pertencente à EPAMIG. Foi analisada a lactação total de sessenta vacas F1 Holandês x Zebu submetidas a diferentes ofertas de dieta, em 2,00%, 2,25%, 2,50%, 2,75% do peso corporal (PC) e um grupo controle com alimentação à vontade (3,4%), permitindo 5% de sobras em relação à matéria seca fornecida, distribuídos em delineamento inteiramente casualizado. Os dados de produção de leite e custo alimentar foram coletados, avaliando os diferentes períodos que caracterizam a lactação de um animal. A maior produção de leite foi verificada nos níveis de dieta 3.4% e 2,75% PC, sendo 3.636,00 e 3.271,50 kg, respectivamente. Produção de leite inferiores foram verificadas nos níveis de 2,50%; 2,25%; 2,00% do PC. O maior custo com alimentação foi verificado no nível de alimentação à vontade seguido dos níveis de 2,75%; 2,50%, 2,25% e 2,00% do PC. A oferta da dieta sem restrição teve um rendimento superior aos respectivos 2,75 níveis; 2,50; 2,25; 2,00% do PC, respectivamente. Os itens lucro, lucratividade e rentabilidade foram semelhantes entre todos os tratamentos, demonstrando que, quando há escassez eventual de alimento, a restrição no fornecimento da dieta de até 2% do PC oferece segurança econômica ao produtor rural que utiliza vacas em seu sistema F1 Holandês x Zebu.

Factors affecting the lactation curve parameters of crossbred dairy ewes in a flock of the highlands of Mexico.

Sheep milk production is incipient in Mexico with scarce knowledge on the performance of dairy ewes from different breeds. The objective of this study was to evaluate the effect of breed (Awassi (Aw), East Friesian (EF) and other (Ot)), parity number (1, 2 and 3 or more (+ 3)), litter size (1 and 2 or more (+ 2)) and lambing season (spring-summer (SS) and autumn-winter (AW)) on day of peak yield (DP), peak yield (PY), persistency (P), total milk yield (TMY), 305-day milk yield (TMY305d), 150-day milk yield (TMY150d) and lactation length (LL) of crossbred dairy ewes in a flock of the central highlands of Mexico. A total of 4312 weekly milk yield records collected from 2014 to 2015 were used to model 133 lactations using a random regression model with a fifth-order orthogonal polynomial. Flock mean values of curve parameters were 42 days at DP, 1.2 kg/day at PY, - 3.5 g/day of P, 190 kg TMY, 189 kg TMY305, 124 kg TMY150 and 269 days of LL. Multiparous ewes had significantly higher (P < 0.05) PY and TMY than primiparous ewes. Ewes that lambed in AW had 15% higher PY and produced 14% more TMY than ewes that lambed in SS (P < 0.05). Correlations among curve parameters were significant except for the correlation between PY and LL and between P and TMY150d. TMY was strongly correlated with LL (0.91). Predominantly Awassi crossbred ewes had lower curve parameter values than predominantly East Friesian and other crossbred ewes.

Performance, Feeding Behavior and Immune Response in Nellore and Angus × Nellore Steers Fed Whole Shelled Corn Diets with or without Fiber.

This study aimed to evaluate performance, to evaluate performance, carcass traits, feeding behavior, and humoral immune response in Nellore and Angus × Nellore steers fed whole shelled corn diets. Sixteen Nellore and 16 Angus × Nellore steers with 353 ± 25.3 kg were randomly assigned into 2 feeding groups, whole shelled corn without forage (WSC) or whole shelled corn and sugarcane bagasse (WSCB). The data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC, USA). Angus × Nellore steers had greater final BW, DMI, ADG, and subcutaneous fat thickness than Nellore. Moreover, Nellore steers had lower neutral detergent fiber (NDF) intake but spent more time ruminating and had a greater rumination rate of NDF. Regarding the diets, steers fed the WSCB had greater DMI and spent more time chewing and ruminating. Nellore × Angus steers had a greater haptoglobin concentration. The concentration of D-Lactate tended to be greater in the Nellore steers regardless of diet. In conclusion, the use of sugarcane bagasse in WSC diets increases DMI and ADG without affecting feed efficiency or the carcass traits of the steers. Although Angus × Nellore steers have increased haptoglobin concentration, this effect was not enough to reduce the performance of these animals.

Models to predict live weight from heart girth in crossbred beef heifers.

The objective of this study was to develop and evaluate linear, quadratic, and exponential mathematical models to predict live weight (LW) from heart girth (HG) in crossbred heifers raised in tropical humid conditions in Mexico. Live weight (363.32 ± 150.88 kg) and HG (166.83 ± 24.88 cm) were measured in 400 heifers aged between 3 and 24 months. Linear and non-linear regression was used to construct the prediction models. The goodness of fit of the models was evaluated using the Akaike information criterion (AIC), the Bayesian information criterion (BIC), coefficient of determination (R2), mean squared error (MSE), and root MSE (RMSE). In addition, the developed models were evaluated through internal and external cross-validation (k-folds) using independent data. The ability of the fitted models to predict the observed values was evaluated based on the root mean square error of prediction (RMSEP), R2, and mean absolute error (MAE). The correlation coefficient between LW and HG was r = 0.98 (P < 0.001). The quadratic model showed the lowest values of MAE (736.57), RMSEP (27.13), AIC (3783.95), and BIC (3799.91). Additionally, this model exhibited better goodness-of-fit values regarding external and internal validation criteria (higher R2 and lower RMSEP and MAE), thus having better predictive performance. The RMSE represented about 8% of the observed LW. Heart girth is highly correlated (r = 0.98) with LW. The quadratic model showed a high predictive capacity for crossbred heifers kept in tropical conditions.

Effect of the percentage of Bos taurus inheritance on the fertility of Holstein×Zebu and Brown Swiss×Zebu cows in the Mexican tropics

Background: No dairy breed or crossbreed has superior overall performance in all environments; therefore, it is necessary to determine which crossbreed is the most suitable for the Mexican tropic and what proportion of European breed is optimum for reproduction. Objective: To assess the effect of the proportion of Bos taurus (Bt) genes on reproductive performance of Holstein×Zebu (HZ) and Brown Swiss×Zebu (BZ) cows, and compare reproductive performance of these genotypes in a dual- purpose production system. Methods: Cows were maintained in a rotational grazing system on African star grass (Cynodon plectostachyus) in Veracruz, Mexico. Cows were milked twice daily. Calves were kept tied to the side of their dams while the cows were milked. Results: The percentage of Bt genes did not affect (p>0.05) fertility traits (age at first calving, days to first service after calving, services per conception, conception rate at first service, days open until conception, gestation length, and calving interval) of BZ cows. In contrast, HZ cows with less than 75% Holstein (H) genes were 0.3 years younger (p<0.05) at first calving and had 39.8 fewer days open (p<0.05) than HZ cows with 75% H genes or more. In addition, the calving interval of HZ cows with less than 75% H genes was 44.8 days shorter (p<0.05) than that of HZ cows with 75% H genes or more. The HZ cows had five fewer days pregnant and were 22.8 kg heavier at calving (p<0.05) than BZ cows. Conclusions: The effect of the percentage of Bt genes on cow fertility depends on the dairy breed used. In general, BZ and HZ cows present similar reproductive performance.

Antecedentes: Ninguna raza lechera o cruce tiene un desempeño general superior en todos los ambientes; por lo tanto, es necesario determinar cuál cruce lechero es más apropiado en el trópico mexicano y qué proporción de raza europea es óptima para la reproducción. Objetivo: Evaluar el efecto de la proporción de genes Bos taurus (Bt) en el desempeño reproductivo de vacas cruzadas Holstein×Cebú (HC) y Pardo Suizo×Cebú (PC), y comparar el desempeño reproductivo de estos dos genotipos en un sistema de producción doble propósito. Métodos: Las vacas se mantuvieron en un sistema de pastoreo rotacional en zacate Estrella de África (Cynodon plectostachyus) en Veracruz, México. Las vacas se ordeñaron dos veces al día. Los becerros se mantuvieron atados, a un costado de sus madres mientras éstas se ordeñaron. Resultados: El porcentaje de genes Bt no afectó (p>0,05) ninguna característica de fertilidad (edad a primer parto, días a primer servicio después del parto, servicios por concepción, tasa de preñez a primer servicio, días abiertos a la concepción, duración de la gestación, e intervalo entre partos) de las vacas PC. En contraste, las vacas HC con menos de 75% de genes Holstein (H) fueron 0,3 años más jóvenes (p<0,05) al primer parto y tuvieron 39,8 días abiertos menos (p<0,05) que las vacas HC con 75% de genes H o más. Además, el intervalo entre partos de las vacas HC con menos de 75% de genes H fue 44,8 días más corto (p<0,05) que el de las vacas HC con 75% de genes H o más. Las vacas HC tuvieron cinco días de gestación menos y fueron 22,8 kg más pesadas al parto (p<0,05) que las PC. Conclusiones: El efecto del porcentaje de genes Bt sobre la fertilidad de la vaca depende de la raza lechera usada. En general, las vacas PC y HC tienen similar desempeño reproductivo.

Antecedentes: Nenhuma raça ou cruza leiteira tem desempenho geral superior em todos os ambientes; portanto, é necessário determinar qual cruza leiteira é mais apropriada no trópico mexicano e qual proporção da raça europeia é ideal para a reprodução das vacas. Objetivo: Avaliar o efeito da proporção de genes Bos taurus (Bt) no desempenho reprodutivo de vacas Holandês×Zebu (HZ) e Pardo Suíço×Zebu (PZ), e comparar o desempenho reprodutivo desses dois genótipos em sistema de produção de dupla aptidão. Métodos: As vacas foram mantidas em sistema de pastoreio rotacional em capim Estrela de África (Cynodon plectostachyus) em Veracruz, México. As vacas foram ordenhadas duas vezes por dia. Os bezerros foram mantidos ao lado de suas mães enquanto eram ordenhadas. Resultados: A porcentagem dos genes Bt não afetou (p>0,05) nenhuma característica de fertilidade (idade ao primeiro parto, número de dias para o primeiro serviço pós-parto, serviços por concepção, taxa de prenhes no primeiro serviço, dias abertos, período de gestação e intervalo entre partos) das vacas PZ. Em contraste, vacas HC com menos de 75% dos genes Holandês (H) eram 0,3 anos mais jovens (p<0,05) no primeiro parto e tiveram 39,8 dias abertos a menos (p<0,05) do que as vacas HZ com 75% ou mais dos genes H. Além disso, o intervalo de parto das vacas HZ com menos de 75% dos genes H foram 44,8 dias mais curtos (p<0,05) do que as vacas HZ com 75% ou mais de genes H. As vacas HZ tiveram cinco dias de gestação a menos e foram 22,8 kg mais pesadas no parto (p<0,05) do que as PZ. Conclusões: O efeito da porcentagem de genes Bt na fertilidade da vaca dependeu da raça leiteira utilizada. Em geral, as vacas PZ e HZ tiveram desempenho reprodutivo semelhante.