Genetic analyses of days to calving and their relationships with other traits in a Canchim cattle herd

Heritabilities and genetic correlations in a Canchim beef cattle herd were estimated using data on the following traits: male scrotal circumference at twelve months (SC12); days to first calving (DFC) for heifers; days to calving (DC) for cows; male and female weight (W) at twelve months (W12); heifer weight at the start of the first breeding season (WFBS) and at first calving (WFC); and cow weight at the start of the breeding season (WBS) and at calving (WC). Analyses of the DFC and DC traits were carried out excluding and including penalized (DFC P and DC P) non-calving females. The restricted maximum likelihood method was used, applying one-trait models for the DFC and DC analyses and two-trait models for analyses of DFC and DC combined with the other traits studied. Statistical models included fixed and additive direct random effects for all traits, maternal permanent environmental random effect for SC12 and W12, and the animal permanent environmental random effect for DC P, WBS and WC. We found that DFC and DC values can be improved by selecting for an increase in the SC12. Genetic correlations between DFC and W12 and between DC and W12 indicated that selection for increased W12 may increase DFC but does not produce significantly correlated responses in DC. Associations of the other body weight traits with DC and DFC suggest that heavier females experience lower reproductive performance.

Artificial infestation of Boophilus microplus in beef cattle heifers of four genetic groups

Resistance of beef cattle heifers to the cattle tick Boophilus microplus was evaluated by artificial infestation of 66 beef cattle heifers of the following genetic groups: 16 Nelore (NE), 18 Canchim x Nelore (CN), 16 Angus x Nelore (AN) and 16 Simmental x Nelore (SN). The animals, with a mean age of 16.5 months, were maintained with no chemical tick control in a Brachiaria decumbens pasture. Four artificial infestations with 20,000 B. microplus larvae were carried out 14 days apart and from day 18 to day 22 of each infestation the number of engorged female ticks (> 4.5 mm) was counted on the left side of each heifer. Data were analyzed as the percentage of return (PR = percentage of ticks counted relative to the number infested), transformed to (PR)», and as log10 (Cij + 1), in which Cij is the number of ticks in each infestation, using the least squares method with a model that included the effects of genetic group (GG), animal within GG (error a), infestation number (I), GG x I and the residual (error b). Results indicated a significant GG x I interaction, because AN and SN heifers had a higher percentage of return than CN and NE heifers, while CN heifers showed a higher percentage of return than the NE heifers only in infestations 3 and 4. Transformed percentages of return were NE = 0.35 ± 0.06, AN = 0.89 ± 0.06, CN = 0.54 ± 0.05 and SN = 0.85 ± 0.06.

Molecular marker heterozygosities and genetic distances as correlates of production traits in F1 bovine crosses

Several studies have investigated the relationship between heterozygosity, genetic distance and production traits. The objective of the present study was to evaluate the influence of the degree of heterozygosity and genetic distance on growth, carcass and reproductive related features in F1 bovine crosses. We tested 10 polymorphic markers in 330 purebred cattle (Nelore, Canchim, Aberdeen Angus and Simental) and 256 crossbred cattle belonging to four crossbred groups. Individual heterozygosities (Hi) and multilocus genetic similarity (Dm) were estimated and used in correlation analysis against individual phenotypic measurements. Significant (p < 0.05) Hi effects occurred for birth weight, 15 to 18 month weight, hot carcass weight and longissimus rib eye area. The extent to which increased heterozygosity (deltaH) in F1 crosses can be predicted from the genetic distance of parental breeds was also investigated using Nei's standard genetic distance (Ds) and standard heterozygosity (Hs). High correlations were found between deltaHi, deltaHs and the Ds of the parental breeds. Our results suggest that heterozygosity of the ten molecular markers used in this study may affect live weight during at least one growth phase. Parental genetic distance was a suitable predictor of the degree of progeny heterozygosity.

Association of GH and IGF-1 polymorphisms with growth traits in a synthetic beef cattle breed

The Canchim beef cattle (5/8 Charolais + 3/8 Zebu) has been selected for meat production in Brazil since late 1950. In the present work the effects of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) polymorphisms were investigated in 688 animals born between 1998 and 2000. These animals belonged to two genetic groups, i.e., traditional and new lineages. Genotype effects on expected breeding values for birth weight (BW), weaning weight (WW) and yearling weight (YW) were investigated by the least square method. Significant effects were found for GH genotype on YW (p < 0.05), with positive effects associated with the LV (leucine/valine) genotype. For IGF-1 genotypes, significant effects were found on BW (p < 0.01) and YW (p < 0.01). Average substitution effects for IGF-1 alleles estimated by regression analysis suggested a positive effect of the IGF-1 225 bp allele on BW and of the 229 bp allele on YW.

Genetic analysis of the infestation of females of the Caracu cattle breed by Horn Fly (Haematobia irritans irritans) L. (Diptera, Muscidae)

The objective of this study was to evaluate environmental factors that affect infestation of Caracu cattle breed by horn fly (Haematobia irritans) and to estimate genetic parameters for level of infestation. Infestation was evaluated on females from two herds in two consecutive years. Total number of flies on animals (FC) was counted, an infestation score (FS: 1 to 5) was recorded according to the estimated number of flies on animals, and number of parasites in photographs (FF) taken when the animals were evaluated was also counted. On each animal from one to eight observations were taken. A total of 3,836, 2,751 and 3,754 records from 718 animals were obtained for FC, FF and FS, respectively. The incidence of flies was lower during winter and higher during summer, and the thicker the hair coat of the animal the greater the infestation. Heritabilities and repeatabilities were equal to 0.10 and 0.10, 0.08 and 0.12, and 0.06 and 0.08, for FC, FF and FS, respectively. Findings indicate that selection for FC will result in low genetic progress and that animals should be evaluated more than once for selection purposes.

Tendência genética em pesos de bovinos da raça Nelore Mocha no Brasil / Genetic trends for body weight of polled Nellore cattle in Brazil

Uma amostra de 5924 animais, progênies de 28 touros, da raça Nelore Mocha, distribuídos em 3 regiões geográficas do Brasil (Sudeste, Nordeste e Centro-oeste), nascidos no período de 1981 a 1992, foi objeto deste estudo, no qual foram avaliadas as mudanças fenotípicas, genéticas e de meio sobre o peso aos 205 (P205), 365 (P365) e 550 (P550) dias de idade, para os conjuntos das regiões. A mudança fenotípica anual foi de 0,475 kg, 0,258 kg e 0,188 kg, respectivamente, para P205, P365 e P550. As mudanças genéticas estimadas foram de 1,518 kg/ano (P205), 2,206 kg/ano (P365) e 3,142 kg/ano (P550). As estimativas de mudanças de ambiente foram de -1,043 kg/ano (P205), -1,948 kg/ano (P365), e -2,254 kg/ano (P550).

Biometria testicular de touros Nelore (Bos taurus indicus) e touros cruzados Nelore-europeu (Bos taurus indicus x Bos taurus taurus) aos 20 e 24 meses de idade / Testicular biometry of Nellore (Bos taurus indicus) and crossbred bulls (Bos taurus indicus x Bos taurus taurus) at 20 and 24 months of age

O objetivo deste trabalho foi estudar os efeitos da idade, do grupo genético e da interaçäo entre idade e grupo genético, sobre as biometrias testiculares (circunferência escrotal e consistência testicular) Foram avaliados, aos 20 e 24 meses de idade, 190 touros Nelore e 447 touros cruzados Nelore-europeu. Aos 24 meses os exames foram repetidos. A circunferência escrotal e a consistência testicular foram influenciadas pelo grupo genético, idade e interaçäo grupo genético x idade. Foram encontradas maiores médias de circunferência escrotal e menores de consistência testicular em cruzados que em Nelore, tanto aos 20 quanto aos 24 meses. Correlaçöes entre circunferência escrotal As correlaçöes entre circunferência escrotal e idade, observadas no presente experimento, foram baixas para os touros Nelore aos 20 meses e aos 24 meses assim como para os cruzados aos 20 meses e aos 24 meses, entretanto, as correlaçöes entre circunferência escrotal e peso corporal foram maiores. As correlaçöes entre consistência testicular e idade e entre consistência testicular e peso corporal foram baixas para a maioria dos cruzados, para os cruzados em conjunto e para os Nelores

Avaliaçäo de sêmen congelado de bovinos. Provas lenta e rápida de termo-resistência: efeitos sobre a fertilidade / Evaluation of frozen bull semen. Quick and slow thermoresistance tests: effects on fertility

O objetivo do presente trabalho foi avaliar a eficiência de sêmen congelado, submetido às provas rápida (45 §C/1 hora) e lenta (38 §C/5 horas) de termo-resistência, sobre a fertilidade de fêmeas da espécie bovina. Cento e dezenove vacas foram selecionadas e divididas em 2 tratamentos. No tratamento 1 foram incluídos 6 grupos de 10 fêmeas, inseminadas com material cuja análise laboratorial revelou motilidade espermática progressiva superior ou igual a 20//, na prova rápida e valor menor a 20//na prova lenta. O tratamento 2 (controle) utilizou 59 vacas distribuídas em 5 grupos de 10 e um grupo de 9, inseminadas com material que, na prova lenta, apresentou 20//de motilidade espermática progressiva e qualquer valor na prova rápida. Apenas uma palheta foi utilizada por estro, tolerando-se até 3 repetiçöes de cio. O diagnóstico de gestaçäo foi realizado por palpaçäo retal, cerca de 60 dias após a última inseminaçäo artificial. Resultados satisfatórios foram alcançados nas taxas de prenhez (TTR/R = 0,793 ñ 0,05 e TTR/L = 0,875 ñ 0,05), näo havendo diferença estatística (P>0,05) quanto ao tipo de provas do termo-resistência. Näo houve diferença significativa (P>0,05) de prenhez de fêmeas inseminadas com material submetido ao teste de termo-resistência rápido, quando a motilidade espermática variou de 20 a 50//