Effects of partial replacement of soybean meal with other protein sources in diets of lactating cows.

The protein nutrition of dairy cows is of great importance because of its direct influence on milk production, reproductive efficiency, and feeding cost. Eight first-lactation Holstein cows were randomly assigned to two contemporary 4 × 4 Latin squares in a 2 × 2 factorial design to evaluate the effects of replacing soybean meal with yeast-derived microbial protein (YMP) as a protein source (0% or 1.5% of dry matter (DM)) and its combination with slow-release urea (SRU; 0% or 0.75% of DM) on DM intake and milk production and composition, as well as blood parameters and nitrogen balance. Each experimental period lasted 28 days, with 21 days of adaptation and 7 days of data collection. The diets were formulated to attend the nutritional recommendations of the National Research Council and consisted of 49% forage (47% corn silage and 2% Tifton hay) and 51% concentrate, with 16.8% CP and 1.6 Mcal net energy for lactation/kg DM. For diets without YMP, the inclusion of SRU decreased DM intake, milk production as well as N intake and balance, but did not affect efficiency of production, milk composition or most of blood parameters. On the contrary, for diets with YMP, DM intake and milk production were increased by inclusion of SRU, while minor effects were observed for milk efficiency and composition, blood parameters as well as N intake, excretion and balance. When diets with SRU were compared, the inclusion of YMP increased DM intake, 4% fat-corrected milk, and N intake and balance (P<0.05), with no differences in milk production (kg/day), milk energy, efficiency of milk production or most of the blood parameters. For diets without SRU, YMP inclusion decreased DM intake, milk production, milk energy, N intake, fecal N and N balance (P<0.05), with no effects on milk efficiency and composition, or most of blood parameters. In conclusion, the use of YMP, SRU or both as partial substitutes of soybean meal in the diet of lactating cows has no negative effects on productivity parameters.

Effects of immunocastration and a ß-adrenergic agonist on retail cuts of feedlot finished Nellore cattle.

Immunocastration (ImC) has been proposed as an animal welfare-friendly alternative to reduce sexual and aggressive behavior and to increase carcass fat deposition with positive effects on meat quality. The ß-adrenergic agonists (ß-AA) are known as repartitioning agents that acts increasing lean tissue deposition. The combined use of these technologies can positively affect meat quality and increase retail cuts yield. Thus, this research was conducted to evaluate the combined effects of ImC and ß-AA (zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RH)) on retail cuts, bones, and fat trim of feedlot finished Bos indicus (Nellore) cattle. No interaction was observed between sexual condition and diet for any trait. The ImC decreased cold carcass, hindquarter (HQ), forequarter (FQ) and combined brisket, short ribs and flank (BSF) weights. The ImC also showed smaller weights of retail cuts and bones on the HQ and on the FQ than non-castrated (NoC). Fat trim weights did not differ from ImC and NoC. The most of subprimal cuts were heavier in NoC than in ImC. Feeding ß-AA did not affect cold carcass weight; however, animals fed ZH had higher weights of HQ and retail cuts in HQ when compared with RH and control (CO) group, with no differences between RH and CO for both traits. The weights of FQ, BSF, retail cuts in FQ, as well as bones and fat trimmings were not affected by ß-AA. In summary, ImC decreases carcass and retail cut weights, whereas ZH supplementation leads to an improvement in carcass lean tissue and retail cuts.

Monensin and a blend of castor oil and cashew nut shell liquid used in a high-concentrate diet abruptly fed to Nellore cattle.

Monensin and functional oils (FO) were supplemented to a high-concentrate diet abruptly fed to 12 ruminally cannulated Zebu steers to study their effects on rumen fermentation, blood metabolites, and , , and relative population. A randomized complete block design with repeated measures over time within 2 experimental periods of 21 d each was used. Treatments were a control (CTR; with no additives), FO (included at 400 mg/kg), and monensin included at 30 mg/kg (M30) or 40 mg/kg (M40). All steers were fed the same high-concentrate basal diet, which consisted of 92.25% concentrate. The first 60 h after transition showed a treatment and hour interaction for ruminal propionate proportion ( = 0.028), and no change in acetate molar proportion ( = 0.633), rumen pH ( = 0.370), and time the rumen pH remained below 5.6 ( = 0.242) were observed. The acetate:propionate ratio decreased ( = 0.020) when monensin was fed in both concentrations (2.30 for the M30 treatment and 2.32 for the M40 treatment) compared with when the CTR was fed (2.85), without being different when the FO (2.71) treatment was fed. Only the M30 treatment did not show pH below 5.2 (P=0.047) over the 60 h after the abrupt transition. Within the entire period, DMI ( = 0.008) and mean ruminal pH ( = 0.040) as well as molar proportions of propionate ( = 0.034) and valerate ( = 0.031) had significant interactions between treatment and day. Total VFA concentration was greater ( = 0.017) for the M30 (117.36 m) and CTR treatments (115.77 m) compared with the M40 treatment (105.02 m), without being different for the FO treatment (111.55 m). Treatments did not change feed behavior parameters. Blood HCO ( = 0.006) and total carbon dioxide ( = 0.003) were greater for the M30 (27.8 and 29.3 mmol/L, respectively) and FO treatments (28.3 and 29.7 mmol/L, respectively) compared with the CTR treatment (25.7 and 26.9 mmol/L, respectively). ( < 0.0001) and ( < 0.0001) decreased their population throughout days, whereas ( = 0.026) increased its population. Independent of ciliated protozoa genera, the greatest ( < 0.0001) protozoa counts were observed for the CTR treatment (52.7 × 10/mL), intermediate for the FO treatment (35.3 x10/mL), and least for steers fed monensin in both concentrations (15 × 10/mL for the M30 treatment and 14 × 10/mL for the M40 treatment). Feed additives had different effects to reduce the subacute acidosis. The use of the FO and M40 treatments did not change most of the rumen fermentation variables, especially in the first week after abrupt transition, when the M30 treatment provided higher protection against acidosis.

Effects of immunocastration and ß-adrenergic agonists on the performance and carcass traits of feedlot finished Nellore cattle.

ß-Adrenergic agonists (ß-AA) are non-hormonal growth promoters which promote muscle hypertrophy in supplemented animals. The effects of two ß-AA in combination with the immunocastration technique on the performance and carcass traits were evaluated using 96 feedlot Nellore males in a randomized complete block design with two sex conditions (immunocastrated (IC) v. non-castrated (NC)) and three treatments: CON (no ß-agonists added), RH (300 mg of ractopamine hydrochloride/day, for 33 days) or ZH (80 mg of zilpaterol·hydrochloride animal/day for 30 days, removed 3 days for required withdrawal period). The trial was carried for 100 days where in the first 70 days animals did not receive ß-AA (phase 1) and during the last 30 days they were treated with ß-AA (phase 2). The performance and ultrasound measurements of longissimus muscle area (LMA), backfat thickness (BFT) and rump fat thickness (RFT) were evaluated in both phases. No sex condition v. treatment interactions were observed for any trait. The NC animals had higher average daily gain (ADG) and final BW than the IC animals, but they did not differ in dry matter intake (DMI) and feed efficiency (gain to feed). The NC animals showed greater LMA (P=0.0001) and hot carcass weight (P=0.0006), and smaller BFT (P=0.0007), RFT (P=0.0039) and percentage of kidney, pelvic and heart fat (P<0.0001) when compared with IC animals. The animals fed ZH showed greater ADG (P=0.0002), G : F (P<0.0001) and dressing per cent (P=0.0136) than those fed RH and CON diets. No differences in BW and DMI were observed. A interaction between treatment and time on feed was observed for LMA and BFT, in which the animals fed ZH diet showed greater LMA (P<0.01) and lower BFT (P<0.01) at 100 days than the animals fed RH and CON diets, whereas RH and CON diets did not differ. Immunocastration decreases muscle development and increases carcass finishing. In contrast, ß-AA increases muscle and decreases fat deposition. The ZH has a higher action on the muscle metabolism than animals fed RH diet. However, RH diet achieves a better balance because it has an intermediary performance between non-supplemented and ZH animals and does not decrease the carcass fat.

Effect of flint corn processing method and roughage level on finishing performance of Nellore-based cattle.

This study was conducted to evaluate the effects of flint corn processing method (CPM) and level of NDF from roughage (rNDF) on performance, carcass characteristics, and starch utilization by finishing Nellore-based cattle fed high-concentrate, flint corn-based diets. In this study, 112 Nellore type bulls (initial BW 384.07 ± 29.53 kg and 24-36 mo of age) were individually fed using Calan gates or individual pens. The animals were used in a randomized complete block design in a 2 × 4 factorial arrangement with 2 CPM, high-moisture flint corn (HMC) or finely ground dry flint corn (FGC), with 1 of 4 levels of rNDF, 3, 8, 13, and 18% (DM basis), using sugarcane silage (SS) as roughage. Bulls were adapted to the finishing diet over a 21-d period and fed for a total of 81 d. Fecal starch (FS) concentration was determined on d 46 and 74 of the feeding period. There was a quadratic effect of rNDF on final BW ( < 0.01) and ADG ( = 0.01). Optimal concentrations of rNDF were estimated using the first derivative of second order polynomials, indicating that final BW and ADG were maximized with 13.3 and 13.0% rNDF, respectively. An interaction was observed between CPM and rNDF ( = 0.05) for DMI, with peak DMI occurring at 11.3 and 13.7% rNDF with FGC and HMC, respectively. Cattle fed HMC had 13.9% greater G:F ( < 0.01) compared with those fed FGC (0.172 vs. 0.151, respectively). There were quadratic effects of rNDF on HCW ( = 0.04) and ME intake ( < 0.01); heaviest carcass weights were estimated, in both cases, to be achieved with 12.8% rNDF. A quadratic effect of rNDF for renal, pelvic, and inguinal fat weight ( = 0.04) was observed, with a peak estimated to occur at 12.6% rNDF. An interaction between CPM and rNDF also was observed for FS ( < 0.05). Bulls fed FGC with 3% rNDF had greater FS content, and FS linearly decreased as concentration of rNDF increased. For bulls fed HMC, FS was 3.0% of DM and was unaffected by rNDF in the diet. Lower FS from bulls fed HMC suggests that availability of starch from flint corn was greater than that of FGC. For Nellore-based cattle fed a flint corn-based diet containing SS and 8% whole lint cottonseed, performance was optimized with 12.8% rNDF. In the absence of cottonseed addition to diets, optimal performance would be expected with about 14.5% rNDF.

A genomewide association mapping study using ultrasound-scanned information identifies potential genomic regions and candidate genes affecting carcass traits in Nellore cattle.

The aim of this study was to identify candidate genes and genomic regions associated with ultrasound-derived measurements of the rib-eye area (REA), backfat thickness (BFT) and rumpfat thickness (RFT) in Nellore cattle. Data from 640 Nellore steers and young bulls with genotypes for 290 863 single nucleotide polymorphisms (SNPs) were used for genomewide association mapping. Significant SNP associations were explored to find possible candidate genes related to physiological processes. Several of the significant markers detected were mapped onto functional candidate genes including ARFGAP3, CLSTN2 and DPYD for REA; OSBPL3 and SUDS3 for BFT; and RARRES1 and VEPH1 for RFT. The physiological pathway related to lipid metabolism (CLSTN2, OSBPL3, RARRES1 and VEPH1) was identified. The significant markers within previously reported QTLs reinforce the importance of the genomic regions, and the other loci offer candidate genes that have not been related to carcass traits in previous investigations.

Genome-wide association study for feedlot average daily gain in Nellore cattle (Bos indicus).

The genome-wide association study (GWAS) results are presented for average daily gain (ADG) in Nellore cattle. Phenotype of 720 male Bos indicus animals with information of ADG in feedlots and 354,147 single-nucleotide polymorphisms (SNPs) obtained from a database added by information from Illumina Bovine HD (777,962 SNPs) and Illumina BovineSNP50 (54,609) by imputation were used. After quality control and imputation, 290,620 SNPs remained in the association analysis, using R package Genome-wide Rapid Association using Mixed Model and Regression method GRAMMAR-Gamma. A genomic region with six significant SNPs, at Bonferroni-corrected significance, was found on chromosome 3. The most significant SNP (rs42518459, BTA3: 85849977, p = 9.49 × 10(-8)) explained 5.62% of the phenotypic variance and had the allele substitution effect of -0.269 kg/day. Important genes such as PDE4B, LEPR, CYP2J2 and FGGY are located near this region, which is overlapped by 12 quantitative trait locus (QTLs) described for several production traits. Other regions with markers with suggestive effects were identified in BTA6 and BTA10. This study showed regions with major effects on ADG in Bos indicus in feedlots. This information may be useful to increase the efficiency of selecting this trait and to understand the physiological processes involved in its regulation.

Protein synthesis and degradation gene SNPs related to feed intake, feed efficiency, growth, and ultrasound carcass traits in Nellore cattle.

We looked for possible associations of SNPs in genes related to protein turnover, with growth, feed efficiency and carcass traits in feedlot Nellore cattle. Purebred Nellore bulls and steers (N = 290; 378 ± 42 kg body weight, 23 months ± 42 days old) were evaluated for daily feed intake, body weight gain (BWG), gross feed efficiency, feed conversion ratio, partial efficiency of growth, residual feed intake (RFI), ultrasound backfat, rump fat, and ribeye area. Genotypes were obtained for SNPs in the growth hormone receptor (GHR-1 and GHR-2); calpain (CAPN4751); calpastatin (UoGCAST); ubiquitin-conjugating enzyme 2I (UBE2I-1 and UBE2I-2); R3H domain containing 1 (R3HDM1-1, -2, -3, and -4), ring finger protein 19 (RNF19); proteasome 26S subunit, non-ATPase, 13 (PSMD13); ribosomal protein, large, P2 (RPLP2); and isoleucine-tRNA synthetase 2, mitochondrial (IARS2) genes. Allelic substitution, additive and dominant effects were tested and molecular breeding values were computed. CAPN4751, GHR-1 and -2, IARS2, R3HDM1-4, and UoGCAST were found to be normally segregating polymorphisms. Additive and dominance effects were observed on BWG, feed efficiency and carcass traits, although dominant effects predominated. Significant allelic substitution effects were observed for CAPN4751, GHR-1 and -2, and UoGCAST on BWG, gross feed efficiency, RFI, and carcass traits, under single- or multiple-marker analyses. Correlations between molecular breeding values and phenotypes were low, excepted for RFI, based on allelic substitution estimates obtained by stepwise linear regression. We conclude that SNPs in genes related to protein turnover are related to economically important traits in Nellore cattle.

Exigências líquidas de energia e proteína de tourinhos Santa Gertrudes confinados, recebendo alto concentrado / Energy and protein requirements of Santa Gertrudis young bulls in feedlot, fed high concentrate diets

Com o objetivo de determinar as exigências de energia e proteína para ganho de tourinhos Santa Gertrudes, 33 tourinhos, com idade de 12 meses e peso inicial médio de 314,6±33,2kg, foram confinados durante 115 dias, após 56 dias de adaptação. Seis animais foram abatidos após adaptação, para determinação da composição química corporal inicial. Os animais receberam dietas contendo 80% de concentrado, avaliando-se a inclusão de 0; 4,5; e 9,0% do subproduto concentrado da produção de lisina na matéria seca. As exigências de energia líquida de ganho (ELg) foram estimadas em função do peso de corpo vazio (PCVZ) e do ganho de PCVZ (GPCVZ), e as exigências líquidas de proteína para ganho (PLg) foram estimadas em função do GPCVZ e da energia retida (ER). As equações obtidas para ELg e PLg foram: ELg (Mcal/dia) = 0,0061×PCVZ0,75×GPCVZ0,578; e PLg (g/dia) = 208,1×GPCVZ - 1,0868×ER. A exigência de energia líquida encontrada para ganho de 1kg de PV foi de 3,93; 4,88 e 5,76Mcal, e a exigência de proteína metabolizável foi de 367,81; 393,59 e 391,63g, respectivamente, para animais com 300, 400 e 500kg de peso corporal. O valor de exigência líquida para mantença foi obtido por meio da regressão do logaritmo da produção de calor (PC), em função da ingestão de energia metabolizável, chegando-se ao valor de 75,6kcal/PVz0,75/dia. Concluiu-se que, devido ao aumento do teor de gordura na composição do ganho, animais de maior peso de corpo vazio apresentam maiores exigências líquidas de energia.

The objective of this study was to determine the energy and protein requirements for gain of Santa Gertrudis young bulls. Thirty-three 12-month-year-old animals, with initial body weight of 314.6±33.2kg, were kept in individual pens during 115 days, after 56 days of adaptation. Six animals were slaughtered after adaptation and determined the chemical composition of initial body. The concentrate proportion in the diet was 80%, on dry matter basis, and the levels of LPB studied were: 0, 4.5 or 9.0%. It was verified that the net energy requirement observed for weight gain of 1kg was 3.93, 4.88 and 5.76Mcal, and the metabolizable protein requirement was 367.81, 393.59 and 391.63g, respectively, for animals with 300, 400 and 500kg of body weight. The estimated maintenance energy requirement observed was 75.6kcal/LW0.75/day. The conclusion was thatbecause of the fat content in the gain composition, animalswith higher EBW have higher net energy requirements.

Carcass quality of feedlot finished steers fed yeast, monensin, and the association of both additives / Qualidade de carcaça de novilhos terminados com dietas contendo levedura, monensina e associação de ambos aditivos

To evaluate the effects of the supplementation of feed additives on carcass quality in beef cattle, 72 Nellore steers (339.5kg, 20-month old) were feedlot finished and fed for 91 days one of the following diets: 1) control with no additives; or added of 2) live yeast culture; 3) monensin; or 4) the association of both additives. After slaughter, renal, pelvic, and inguinal fat and hot carcass weights were recorded and carcass was split into muscle, bone, and trimmable fat. Carcass Longissimus muscle area and subcutaneous fat thickness at the 12th rib were measured and steaks of Longisimus muscle were taken to determine meat color, shear force, drip, and cooking losses. Yeast increased carcass dressing percentage but there were no effects on hot carcass weight, Longissimus area, subcutaneous fat thickness, percentage and weight of retail cut yield and trimmings. Feed additives had no effect on carcass pH, meat color, fat content, shear force, and drip losses. Supplementation of yeast, monensin or the association of both additives had no important effects on carcass traits and on meat quality of feedlot finished steers.

Avaliaram-se os efeitos da suplementação de aditivos alimentares sobre a qualidade de carcaça em bovinos de corte. Usaram-se 72 novilhos Nelore com média de peso de 339,5kg e 20 meses de idade, terminados em confinamento e alimentados por 91 dias com uma das quatro dietas: 1) dieta controle sem aditivos, ou com a adição de 2) leveduras vivas, 3) monensina ou 4) associação entre ambos aditivos. Após o abate, os pesos da gordura renal, pélvica e inguinal e da carcaça foram medidos e a carcaça dividida em músculos, ossos e aparas. Foram mensurados a área de olho de lombo e a espessura de gordura subcutânea sobre o músculo Longissimus na região da 12ª costela e foram obtidos bifes para a determinação da cor, força de cisalhamento e perdas por cocção e cozimento da carne. A levedura aumentou o rendimento de carcaça, mas não houve efeito dos tratamentos sobre o peso de carcaça, porção comestível e aparas. Os aditivos não influenciaram o pH da carcaça, a cor, a gordura intramuscular, a força de cisalhamento e as perdas por exsudação da carne. A suplementação, com levedura e com monensina em associação ou separadamente, não teve efeito importante sobre a qualidade da carcaça em novilhos terminados em confinamento.

Preweaning performance and body composition of calves from straightbred Nellore and Bos taurus x Nellore crosses.

The objectives were to evaluate preweaning performance, body composition, and efficiency of calves representing straightbred Nellore (NL), F(1), and 3-breed-cross systems. Energy requirements, milk production, and efficiency of 39 cow-calf pairs were recorded from straightbred NL calves from NL cows (10), crossbred (Angus-sired) calves from NL cows (ANL: 9), and crossbred calves (CC; Canchim-sired: 5/8 Charolais, 3/8 Zebu) from ANL (10) and Simmental x NL (10) cows. Cows and their respective calves were individually fed from birth to weaning (17 to 190 d postpartum). At 38 d of age, corn silage (7.8% CP, 2.19 Mcal of ME/kg of DM) was available to calves ad libitum. Milk production at 42, 98, 126, and 180 d postpartum was recorded by weighing calves before and after suckling. The ratio between GE and ME of milk was considered 1:0.93. Calves were slaughtered at weaning and the 9th-, 10th-, and 11th-rib section was removed for body composition estimation. The ANL calves were lighter (P < 0.01) at birth than the CC calves; the NL calves were intermediate. At weaning, the CC calves were heavier (P = 0.04) than the NL and ANL calves (230 +/- 5.5 vs. 172 +/- 8.1 and 209 +/- 8.6 kg, respectively). The ANL calves had greater (371 +/- 27 Mcal; P = 0.01) silage intake than the NL (270 +/- 25 Mcal) and CC (279 +/- 17 Mcal) calves. Milk energy intake was greater for the CC calves (970 +/- 38 Mcal of ME; P = 0.005) than the NL (670 +/- 57 Mcal of ME) and ANL (743 +/- 61 Mcal of ME) calves. The ANL calves compensated for the reduced milk production of the NL cows, which supplied less of their energy requirement for growth by increased silage intake. Calves from crossbred cows received a greater proportion of their total energy intake from milk. Crossbred calves had greater (P < 0.03) retained energy (retained energy = weaning body energy - birth body energy) than the NL calves (388 +/- 23 for ANL, and 438 +/- 15 for CC vs. 312 +/- 22 Mcal for NL calves). Percentages of water (P = 0.74) and chemical fat (P = 0.51) were similar among groups (63.7 +/- 0.6 and 14.3 +/- 0.7% for ANL calves, 63.1 +/- 0.4 and 14.7 +/- 0.5% for CC calves, and 63.3 +/- 0.6 and 13.7 +/- 0.7% of empty BW for water and chemical fat, respectively, for NL calves). Energetic efficiency (kcal of retained energy/Mcal of ME intake) was similar (P = 0.52) among groups (358 +/- 22 for ANL calves, 355 +/- 14 for CC calves, and 327 +/- 22 for NL calves). The greater BW gains and the differences in empty body composition at weaning were not enough to compensate for the greater ME intake of crossbreds. In this study, the crossbreeding systems evaluated increased preweaning calf performance but did not affect gross or energetic calf efficiency.

Digestibilidade aparente de dietas com níveis crescentes de concentrado em novilhos Brangus e Nelore / Apparent digestibility of diets with increasing concentrate levels in Brangus and Nellore steers

Determinou-se a digestibilidade aparente, pela coleta total de fezes, de dietas contendo 20, 40, 60 ou 80 por cento de concentrado para novilhos Brangus e Nelore. Oito animais, quatro de cada raça, foram utilizados em delineamento quadrado latino 4x4, com cinco dias de adaptação e cinco dias de coleta de fezes, em cada período. A idade e o peso iniciais dos Brangus e Nelore foram 13 meses e 248kg e 30 meses e 403kg, respectivamente. Houve efeito do nível de concentrado (P<0,01) sobre os coeficientes de digestibilidade da matéria seca (MS), proteína bruta (PB), extrato etéreo, fibra bruta, fibra em detergente neutro, extrativo não-nitrogenado (ENN), matéria orgânica (MO) e nutrientes digestíveis totais (NDT). A dieta com 80 por cento de concentrado apresentou maior digestibilidade da MS, PB e NDT. A digestibilidade do ENN e da MO e a ingestão de MS foram diferentes entre raças (P<0,05); os Brangus tiveram maior ingestão de MS e NDT (P<0,01). Houve interação entre raças e níveis de concentrado quanto à ingestão de MS e NDT (P<0,01), com maior ingestão pelos Brangus, nos níveis mais altos de NDT. Os Nelore foram menos adaptados às dietas ricas em concentrado em relação aos Brangus.

The apparent digestibility of diets with 20, 40, 60 or 80 percent of concentrate fed Brangus and Nellore steers was determined through total fecal collection. Eight animals, four of each breed, were used in two 4 x 4 Latin square design with five days of adaptation to the diets and five days of collection in each period. The initial age and body weight of Brangus and Nellore steers were 13 months and 248 kg, and 30 months and 403kg, respectively. Concentrate levels affected (P<0.01) the digestibility coefficients of dry matter (DM), crude protein (CP), ether extract, crude fiber, neutral detergent fiber, nitrogen free extract (NFE), organic matter (OM) and total digestible nutrients (TDN). The diet with 80 percent of concentrate showed higher DM, CP and TDN digestibilities. The digestibility of NFE, OM and the dry matter intake were different according to the breeds (P<0.05). Brangus showed higher DM and TDN intake. The DM and TDN intake showed interaction (P<0.01) breed by concentrate level, with higher intake for the Brangus at higher TDN diets. The Nellore steers were less adapted to diets rich in concentrate than Brangus steers.

Energy requirement for maintenance and growth of Nellore bulls and steers fed high-forage diets.

Data from three comparative slaughter experiments with individually fed Nellore bulls (n = 31) and steers (n = 66) were utilized to determine their NEm and NEg requirements when fed high-forage diets. The experimental design provided ranges in ME intake, BW, and ADG for the development of regression equations to predict NEm and NEg requirements. The Nellore bulls (Trial 1) were divided into two intake levels (ad libitum and 65% of the ad libitum). The steers (Trials 2 and 3) were allocated to three intake levels (ad libitum and 55 and 70% of the ad libitum). In both trials, there were three slaughter groups within each intake level. The three end points for the bulls were different days on treatment (100, 150, and 190 d and 130, 180, and 200 d, respectively, for older and younger animal subgroups). The steers were slaughtered when animals of the ad libitum treatment reached 400, 440, and 480 kg shrunk BW (SBW) on average for the first, second, and third group, respectively. For all body composition determinations, whole empty body components were weighed, ground, and subsampled for chemical analysis. In each of the trials, initial body composition was determined with equations developed from a baseline slaughter group, using SBW and empty BW (EBW), fat (EBF), and protein (EBP) as variables. The NEm was similar for bulls and steers; NEm averaged 77.2 kcal/ kg0.75 EBW. However, the efficiency of conversion of ME to net energy for maintenance was greater for steers than for bulls (68.8 and 65.6%, respectively), indicating that bulls had a greater ME requirement for maintenance than steers (5.4%; P < 0.05). Our analyses do not support the NRC (2000) conclusion that Nellore, a Bos indicus breed, has a lower net energy requirement for maintenance than Bos taurus breeds. An equation developed with the pooled data to predict retained energy (RE) was similar to the NRC (2000) equation. A second equation was developed to predict RE adjusted for degree of maturity (u): RE = (6.45 - 2.58/u) x EWG x e(0.469) x u), where u = current EBW/final EBW in which final EBW was 365 kg for steers and younger bulls and 456 kg for older bulls at 22% EBF, respectively.

Analysis of 47Ca kinetics in normal subjects by means of a compartmental model with a non-exchangeable plasma calcium fraction.

1. 47Ca kinetic studies were performed in eight normal young adult males. Plasma, urinary and faecal stable and radioactive calcium and whole-body radioactivity were measured for up to 40 days after intravenous administration of the tracer. 2. The plasma radioactivity data could be fitted to the sum of four exponentials corresponding to a four-compartment model, but this model did not account for the consistently greater 47Ca specific radioactivities in plasma relative to those in urine at the same time in five of the subjects. 3. A non-exchangeable fraction of plasma calcium estimated as 5% of the mass in the plasma compartment was postulated to account for this finding. 4. An estimate of the insensible losses of calcium was obtained from the whole-body radioactivity counting data.