Irineu Umberto Packer

Genetic parameters for test day milk yield of first lactation Holstein cows estimated by random regression using Legendre polynomials

Data comprising 263,390 test-day (TD) records of 32,448 first parity cows calving in 467 herds between 1991 and 2001 from the Brazilian Holstein Association were used to estimate genetic and permanent environmental variance components in a random regression animal model using Legendre polynomials (LP) of order three to five by REML. Residual variance was assumed to be constant in all or in some classes of lactation periods for each LP. Estimates of genetic and permanent environmental variances did not show any trend due to the increase in the LP order. Residual variance decreased as the order of LP increased when it was assumed constant, and it was highest at the beginning of lactation and relatively constant in mid lactation when assumed to vary between classes. The range for the estimates of heritability (0.27 - 0.42) was similar for all models and was higher in mid lactation. There were only slight differences between the models in both genetic and permanent environmental correlations. Genetic correlations decreased for near unity between adjacent days to values as low as 0.24 between early and late lactation. A five parameter LP to model both genetic and permanent environmental effects and assuming a homogeneous residual variance would be a parsimonious option to fit TD yields of Holstein cows in Brazil.

k -Casein, b -lactoglobulin and growth hormone allele frequencies and genetic distances in Nelore, Gyr, Guzerá, Caracu, Charolais, Canchim and Santa Gertrudis cattle

The genotypes for k-casein (k-CN), b-lactoglobulin (b-LG) and growth hormone (GH) were determined by polymerase chain reaction (PCR) and restriction enzyme digestion in seven breeds of cattle (Nelore, Gyr, Guzera, Caracu, Charolais, Canchim and Santa Gertrudis). k-Casein had two alleles with the A allele occurring at a higher frequency in Bos indicus breeds (0.93, 0.92 and 0.91% for Gyr, Guzera and Nelore, respectively). The b-lactoglobulin locus had two alleles in all of the breeds. European breeds had a higher frequency of the b-LG A allele than Zebu breeds. The GH locus had two alleles (L and V) in Bos taurus and was monomorphic (L allele only) in all of the Bos indicus breeds evaluated. The highest frequency for the V allele was observed in Charolais cattle. The markers used revealed a considerable similarity among breeds, with two main groups being discernible. One group consisted of Zebu and Santa Gertrudis breeds and the other consisted of European and Canchim breeds.

Parâmetros genéticos para as produções de leite no dia do controle e da primeira lactação de vacas da raça Holandesa

Covariance components for test day records and lactation milk yield using 263.390 records of 32.448 first lactation Holstein cows, were estimated using animal models by REML. Besides the lactation model, two alternative repeatability models (RM) were analyzed. Lactation model included fixed effects of herd-year-season and age of cow with linear and quadratic terms, and random effects of animal and error. The first model for test-day yield (RMF) included the same effects, but fixed effect of contemporary group, defined as herd-year-month of test. Alternatively another model for test-day yield (RMF) used a logarithmic polynomial sub-model for the shape of the lactation curve. Heritability for lactation yield (0.27) was smaller than those estimated by RMF and RMS, 0.30 and 0.43, respectively. Heritability estimates for univariate (0.22-0.36) and bivariate models (0.23-0.33) for test day milk yields were found to be smallest during early and late lactation. Heritability estimate for lactation milk yield when estimated by univariate model (0.27) was smaller than estimates obtained by bivariate models (0.27-0.30). Genetic correlations were higher between consecutive test days than between test days in the beginning and end of lactation. Larger heritability estimates for test day models and large genetic correlations between test day and lactation yield (0.86-0.99) indicate a potential use of test day records in genetic evaluations.

Efeitos da seleção para peso pós-desmame sobre características de carcaça e rendimento de cortes cárneos comerciais de bovinos

Data from 44 bulls of the genetic groups Selection Nellore (NeS), Control Nellore (NeC) and Caracu (Ca) herds born in 1999 were used to evaluate the effects of selection for post weaning weight on carcass traits and meat cuts yields at 378 days of age (P 378). The animals were randomly distributed into two experimental classes: restricted feeding (AR) and ad libitum feeding (AL) including 8 animals from the NeS and Ca groups and 6 animals from the NeC group. Animals of each class were slaughtered in pairs when the animals AL group reached 4 mm of ultrasonic fat thickness on Longissimus dorsi muscle, between the 12th and 13th ribs. The interaction between genetic group and feeding class was not significant for most of the traits evaluated. The genetic group effect was significant. Animals of the Ca and NeS groups were heavier at slaughter and Ca animals required longer feedlot period to reach the desired fat thickness. Higher slaughter weights of these animals changed their carcass, hindquarter, forequarter and spare ribs weights. The selection for P 378 in the Nellore group resulted in heavier weights at slaughter, heavier carcasses and primary cuts, but lower meat tenderness, although within reasonable values of shear force (below 5.0 kgf).

Meta-análise para estimativas de herdabilidade para características de crescimento em bovinos de corte

A meta-analysis was conducted to summarize published heritability of estimates growth traits of zebu beef cattle of 186 reports. The factors affecting weighed heritability estimates were analyzed by the least square means method for a model including fixed effects. Breed and estimation method were the significant factors in the four traits (birth weight, weaning weight, weight at 365 days and weight at 550 days). Estimation method is always recommeded to summarize these estimates. The pooled heritability estimates for birth weight, weaning weight, weight at 365 days old and weight at 550 days old were 0.30±0.01, 0.23±0.01, 0.27±0.01 and 0.31±0.01, respectively. Meta-analysis techniques were recommended for polling of genetic parameters of zebu beef cattle.

Parâmetros genéticos para a produção de leite de controles individuais de vacas da raça Gir estimados com modelos de repetibilidade e regressão aleatória

Data comprising 8,183 test day records of 1,273 first lactations of Gyr cows from herds supervised by ABCZ were used to estimate variance components and genetic parameters for milk yield using repeatability and random regression animal models by REML. Genetic modelling of logarithmic (FAS), exponential (FW) curves was compared to orthogonal Legendre polynomials (LP) of order 3 to 5. Residual variance was assumed to be constant in all (ME=1) or some periods of lactation (ME=4). Lactation milk yield in 305-d was also adjusted by an animal model. Genetic variance, heritability and repeatability for test day milk yields estimated by a repeatability animal model were 1.74 kg2, 0.27, and 0.76, respectively. Genetic variance and heritability estimates for lactation milk yield were respectively 121,094.6 and 0.22. Heritability estimates from FAS and FW, respectively, decreased from 0,59 and 0.74 at the beginning of lactation to 0.20 at the end of the period. Except for a fifth-order LP with ME=1, heritability estimates decreased from around 0,70 at early lactation to 0,30 at the end of lactation. Residual variance estimates were slightly smaller for logarithimic than for exponential curves both for homogeneous and heterogeneous variance assumptions. Estimates of residual variance in all stages of lactation decreased as the order of LP increased and depended on the assumption about ME. Estimates of genetic and permanent environment variances did not show any trend due to the increase in the order of LP. Genetic correlation estimates between TD were largest for LP and larger for FW than for FAS. Except for FAS, a similar pattern in genetic correlation estimates was observed for all curves decreasing from values close to unity between adjacent TD at early lactation to negative values for TD in the beginning and the end of lactation. The Legendre polynomial of order five and the FAS under ME4 best fitted the data. There is a potential for using random regression to model animal genetic and permanent environmental effects using test day information of Gyr cows.

Curvas de crescimento em vacas de corte de diferentes tipos biológicos

The objective of this study was to select the best growth curve model, and to evaluate the influence of environmental and genetic group effects on the estimated parameters of the model. Five nonlinear models, Brody, Gompertz, Logistic, Von Bertalanffy and Richards, were adjusted to age‑weight data measured in 316 cows, obtained from four genetic groups: G (Nellore, ½Canchim + ½Nellore, ½Angus + ½Nellore, and ½Simmental + ½Nellore), from birth to 100 months of age; in two calving seasons: E (spring and fall). The cows were submitted to two levels of concentrate (S) during four months, after weaning. The models were adjusted by ordinary least squares using inverse‑variance weighted and unweighted mass. The Brody and Von Bertalanffy models converged for all genetic groups; however, the Brody model had a better fit. Estimates for asymptotic weight (A) and maturing rate (k) of the weighted Brody model were analyzed by a mixed model, which included overall effect and fixed effects of G, E, and S, and respective interactions. Parameter A was influenced by the effects of G and E, while k was influenced by S, indicating that improvements in feeding management result in less variation in the shape of growth curves and in increased rates of maturity.

Quality of colostral passive immunity and pattern of serum protein fluctuation in newborn calves

Immunity acquired by newborn animals is known as passive immunity, and for ruminants, antibody acquisition depends on the ingestion and absorption of adequate amounts of immunoglobulins from colostrum. This study relates different initial levels of acquired passive protection and serum total protein (TP) and immunoglobulin G (IgG). Serum immunoglobulin concentration and total protein were evaluated for female Holstein calves in the first sixty days of life. Animals were separated into three groups according to their initial level of passive immunity: group 1- animals with a low level of passive immunity (below 20 mg mL-1); group 2- animals with a medium level (between 20 and 30 mg mL-1), and group 3- animals with a high level (above 30 mg mL-1). Serum total protein was determined through the biuret method and IgG was determined by radial immunodiffusion. Data were analyzed as a completely randomized, split-plot statistical design. Fluctuation of the variables along the experimental period was determined through non-linear regression by the DUD method (PROC NLIN - Non Linear SAS). Animals with low antibody acquisition started to produce antibodies earlier, reflecting a compensatory synthesis. On the other hand, animals having adequate levels exhibited an extended period of immunoglobulin catabolism and the beginning of the endogenous phase was delayed. Regardless initial levels, the fluctuations in IgG contents occurred around adequate physiological concentrations, ranging from 20 to 25 mg mL-1.

Dias ao Parto de Fêmeas Nelore de um Experimento de Seleção para Crescimento: I - Modelo de Repetibilidade

Registros de datas de entrada na monta e respectiva data do parto, referentes a 1.247 femeas Nelore dos rebanhos experimentais da Estacao Experimental de Zootecnia de Sertaozinho (IZ - SP), selecionadas para altos (selecao e tradicional) e para medios (controle) pesos ao sobreano foram usados para obter a variavel dias ao parto, a fim de estudar o efeito da selecao para crescimento sobre o desempenho reprodutivo. Arquivos de novilhas e de vacas e novilhas foram analisados incluindo e nao incluindo as nao paridas. Nenhuma diferenca significativa foi detectada entre os registros provenientes das vacas dos rebanhos selecionados e do controle, apesar das vacas do rebanho selecao apresentarem as maiores medias de dias ao parto na maioria dos arquivos estudados. Concordando com os resultados obtidos para o efeito de rebanho, o peso a selecao foi significativo somente para as vacas e novilhas, considerando as nao paridas, com tendencia das mais pesadas a selecao apresentarem menores valores para dias ao parto. Modelos nos quais nao foi considerado o peso a selecao forneceram os mesmos resultados para o efeito de rebanho. As herdabilidades variaram de 0,02 a 0,16, sendo as mais altas obtidas em arquivos nos quais foram incluidos os registros das nao paridas, indicando que a observacao de caracteres de reproducao somente das femeas ferteis contribui para mascarar as diferencas geneticas entre os animais, e quando esta variabilidade e re-introduzida, designando-se penalidades as femeas que nao pariram, as diferencas geneticas entre os animais aparecem. Existem evidencias que a selecao para peso nao comprometeu o desempenho reprodutivo das femeas, mesmo sendo criadas em condicoes ambientais similares.

Produção de leite e comportamento de amamentação em cinco sistemas de produção de gado de corte

Foram estudados a producao de leite de vacas Nelore e o comportamento de amamentacao em diferentes sistemas de producao: NR-Nelore Referencia, sob manejo extensivo (manejo tradicional); NI-Nelore, sob manejo intensivo; e tres cruzamentos CN-Canchim x Nelore, AN-Angus x Nelore e SN-Simental x Nelore, sob manejo intensivo. Em tres momentos da lactacao (60, 120 e 180 dias apos o parto), foram medidos, nos bezerros, o numero e a duracao das mamadas, o ganho diario de peso (kg/dia) e o peso a desmama. O momento da lactacao e a interacao sistema de producao x momento da lactacao apresentaram efeito significativo sobre a producao de leite. A producao de leite nao apresentou corrrelacao com o comportamento de amamentacao nem com o ganho de peso dos bezerros dos diferentes sistemas de producao. Condicoes deficientes de alimentacao nao resultaram em menores producoes de leite de vacas Nelore, mas sim em acentuadas perdas de peso (80 kg) durante a estacao de monta no sistema NR. O tempo diario de amamentacao apresentou diminuicoes significativas no sistema extensivo com o decorrer da lactacao, enquanto os sistemas intensivos nao mudaram ou aumentaram os minutos de amamentacao por dia. Para as condicoes nas quais o experimento foi desenvolvido, os bezerros cruzados apresentaram os melhores desempenhos durante a fase pre-desmama, em comparacao com os bezerros Nelore.