José Valente

Parâmetros genéticos para produções de leite e gordura nas três primeiras lactações de vacas Holandesas

In this study 9,527 lactations of purebreed Holstein cows, calved between 1988 to 1997, from herds in the Minas Gerais State, were analysed. Two data sets were established: one with first lactations only and another with the first lactation until the third one. Milk and fat 305-day yields were analysed using a multivariate mixed model and restricted maximum likelihood procedure (REML). The milk and fat 305 days yields averages were respectively 5,870 ± 1,662 kg and 199 ± 55 kg for set I and 5,521 ± 1,523 kg and 187 ± 50 kg for set II in the first lactation, and 6,421 ± 1,789 kg and 215 ± 58 kg for the second lactation, and 7,045 ± 1,903 kg and 231 ± 60 kg for the third lactation, respectively. Heritabilities estimated for milk and fat yields in set I (first lactation) were .28 ± .04 and .20 ± .03 and using the set II, were .16 ± .09 e .9 ± .9 for milk and fat yields in the first lactation, .17 ± .11 and .20 ± .11 for second one, and .16 ± .10 and .10 ± .16 in third lactation, respectively. Genetic correlations were high and ranged from .86 to 1.0.

Heterogeneidade de variância e avaliação genética de bovinos da raça Holandesa no Brasil

Dados de 109.200 lactacoes foram utilizados para verificar o efeito da heterogeneidade de variância sobre a avaliacao genetica de vacas e touros da raca Holandesa criados no Brasil. A producao total de leite ajustada para idade adulta foi usada para classificar os rebanhos em tres classes de desvio-padrao fenotipico: baixo ( 1625 kg). Dados das primeiras lactacoes foram analisados considerando a producao total de leite ajustada para idade adulta (TOTAJU) e producao total de leite ajustada para idade adulta e para 305 dias de lactacao (TAJU305). As producoes de leite medias e os componentes de variância genetica, residual e fenotipica aumentaram com o aumento do desvio-padrao da classe. Para as classes de baixo e medio, baixo e alto e medio e alto desvios-padrao, as correlacoes geneticas foram 0,97; 0,89; e 0,91 para TOTAJU e 0,97; 0,92; e 0,96 para TAJU305, respectivamente. As correlacoes entre os valores geneticos para as classes de baixo, medio e alto desvios-padrao obtidos nas analises conjuntas (considerando como diferentes a expressao da caracteristica nas tres classes) e os obtidos na analise geral (todas as classes como unica caracteristica) foram proximas a unidade. Entretanto, os reprodutores apresentaram maiores valores geneticos em rebanhos das classes de alto desvio-padrao. Na avaliacao genetica, e importante considerar a variabilidade entre rebanhos, pois, sob selecao, as classes mais variaveis contribuiram com a maior parte dos animais, e a avaliacao genetica do animal poderia ser funcao nao apenas do seu potencial genetico, mas tambem do ambiente no qual suas progenies expressaram a caracteristica.

Tendência genética para a produção de leite e de gordura em rebanhos da raça Holandesa no Estado de Minas Gerais

The objective of this work was to estimate the genetic trends for milk and fat yields of Holstein Dairy Cattle, in Minas Gerais State, Brazil. The statistical analyses were made by means of mixed models, using restricted maximum likelihood and animal model. The fixed effects studied were: herd-year-season at calving and linear and quadratic effect of age at calving besides the animal and residual random effects. The genetic trends were obtained by regression of the breeding value on the year of birth of cows. Records used in the analyses were 18,482 first lactations of cows born from 1986 to 1996. The genetic trends for milk and fat yield were 18.4 and 0.6 kg, respectively. The average of milk and fat yields were 5083 ± 50 to 6876 ± 51 kg, and from 172.6 ± 1.7 to 228.5 ± 1.7 kg, respectively. The breeding values estimated were negative in 1986 and 1987, and positive thereafter, with accentuate increase in the last years. This is an indication that milk farmers of Minas Gerais State have been taking strategies in order to increase the milk productions.

Estimativas de herdabilidade e correlações fenotípicas, genéticas e de ambiente entre algumas características reprodutivas e produção de leite na raça Gir

Os objetivos deste estudo foram estimar herdabilidades e correlacoes fenotipica, genetica e de ambiente entre producao de leite (PL), idade ao primeiro parto (IPP) e intervalo de partos (IDP) na raca Gir, com emprego de analises uni e bicaracteres sob o metodo da maxima verossimilhanca restrita, por meio de algoritmo livre de derivadas (MTDFREML), ajustando modelos-animal. O modelo matematico para estudar a PL incluiu os efeitos fixos de rebanho-ano de parto e epoca de parto e idade ao parto como covariavel (linear e quadratica) e, alem do residuo, os efeitos aleatorios de animal e ambiente permanente. Para a IPP o modelo incluiu os efeitos fixos rebanho-ano de nascimento e epoca de nascimento, e efeito animal como aleatorio. O modelo adotado para estudar IDP contemplou os efeitos fixos rebanho-ano de parto e epoca de parto e idade da vaca ao parto como covariavel, e mais os efeitos aleatorios de animal, ambiente permanente e residuo. Por meio de analises bicaracteres, as estimativas de herdabilidade foram, respectivamente: PL1 e IPP = 0,25 e 0,18; PL1 e IDP1 = 0,27 e 0,07; PL2 e IDP2 = 0,20 e 0,05; PL3 e IDP3 = 0,17 e 0,05. As estimativas de correlacoes fenotipica, genetica e de ambiente foram, respectivamente: PL1 e IPP = 0,02, -0,29 e 0,11; PL1 e IDP1= 0,23, 0,52 e 0,19; PL2 e IDP2 = 0,26, 0,54 e 0,23; PL3 e IDP3 = 0,25, 0,13 e 0,27.

Ajustamento para Heterogeneidade de Variância para Produção de Leite entre Rebanhos da Raça Holandesa no Brasil

Data of 36,755 first lactation of Holstein cows, daughters of 866 sires, distributed in different states from 1980 to 1993, were stratified in herds according to the phenotypic standard deviation of the milk yield adjusted for adult age, in three levels: low (11,713 lactations), medium (12,764 lactations) and high (12,278 lactations). The total milk production adjusted for adult age and adjusted for adult age and for 305 days of lactation, within each class, and the base 10 logarithm transformations, square root, standardization and the division by class phenotypic standard deviation were analyzed. The averages of milk yield, the genetic, residual, and phenotypic variance components increased with the increase of the class mean standard deviation. The heritability did not have the same behavior, the heritability estimates of the traits of the class with high standard deviation were similar to the heritability of traits of class with low standard deviation, and both were smaller than the class with medium standard deviation, although the component of addictive genetic variance has been higher. The used transformations did not correct the existing heterogeneity of variance among the classes. The heritabilities of the unchanged characteristics varied from .25 to .35.

Interação genótipo-ambiente para a produção de leite em rebanhos da raça holandesa no Brasil: (I) modelo de touro

Records on 14.418 first lactations of Holstein cows sired by 324 bulls distributed in 181 herds in different States from 1981 to 1991, were used to study the effect of genotype-environment interaction on milk production. The data were distributed in three levels (low-B, medium-M, and high-A) according to the average of the herd milk production. (Co)variances components were estimated by REML using two sire models. The variance components of sire ranged from 116,879 to 274,871 were larger at the higher levels, the residuals ranged from 1,691,879 to 1,956,025, increasing with the production level of the herds and the interaction ranged from 66,854 to 149,972 with the highest value when the daughters performed at the extreme levels. The heritabilities ranged from 0.22 to 0.49 and the genetic correlations were 0.22, 0.46, and 0.69, respectivelly, among the levels low and high, low and medium, and medium and high.

Fatores de ajustamento para a produção de leite e gordura na raça Holandesa para rebanhos do Estado de Minas Gerais

The objective of this work was to calculate adjustment factors for milk and fat yield according to the cow age and calving season, for Holstein breeds herds from Minas Gerais State. The statistical analyses were made by means of mixed models, using Restricted Maximum Likelihood in an animal model. The fixed effects were herd-year, genetic composition and age classes-calving season, and as random effects of animal (cow, sire and dam) and error terms. Records used in the analysis were 49,666 lactations of 26,822 cows, being 17,354 from grades and 9,468 from purebred cows. Twenty-one age classes were made; with the small one constituted by cows that calving under 24 months and the large one by cow with more than 99 months of age, per six calving seasons. The adjustment factors attained for milk production, were which larger than for fat factors, tended to be smaller for purebred cows than the correspondent values estimated for grade cows. The average milk and fat production milk was higher for the productions beginning in the season corresponding to the dry season, mainly for cows with more than 30 months of age. The differences found among the estimated factors for the dry season in relation to the rainy season were minimal, not overpass 8%. The milk and fat productions were higher for younger cows.

Efeito do ajustamento para os períodos de serviço anterior e corrente sobre os valores genéticos de touros para produção de leite na raça Holandesa

Previous and present days open were fit simultaneously as fixed effects in a sire model for 305 day milk production (L305) containing yet the fixed effects of herd-year-season, level of Holstein blood, age of cow as covariant (up to 3rd degree) and the random effects of sire and cow. A relationship matrix including the bull, his sire and his dam was used. The same model without age of cow was used for 305-day mature age equivalent milk yield (PROAJU). The REML method was used to solve the equations by means of the MTDREML program. By the results, the obtained conclusion was that the PROAJU increased 902 kg when the previous days open ranged from 20 to 320 days. This increase was of 813 kg for the same range in the present days open. The sires breeding values for PROAJU were predicted in four data sets using the prior model with exclusion of previous and present days open periods. The production records were adjusted by multiplicative adjustment factors obtained for previous and present days open and the sires were reevaluated. Rank correlation among sire breeding values for adjusted and non-adjusted milk production were nearly 1. The means of the differences among sire breeding values with adjusted and non adjusted milk production for the days open were approximately zero, indicating that factors for days open were appropriate for the data.

Diferenças entre produções de leite e de gordura de vacas PC e PO da raçaHolandesa no Estado de Minas Gerais

Milk and fat production of purebred and grade Holstein dairy cows in Minas Gerais State, Brazil were analyzed by, mixed models methodology and restricted maximum likelihood in an animal model. The fixed effects were herd-year-season, genetic composition (purebred and grade) and the linear and quadratic effects of age at calving and the random effect was the animal. A total of 49,666 lactations of 26,822 cows from 380 herds, being 9,468 of purebred and 17,354 of grade were used. Two seasons, each with three classes of two months, dry season (April-May, June-July, August-September) and rainy season (October-November, December-January, February-March) were used. In order to estimate genetic gains, 18,482 records of cows in the first calving, being 8,938 of purebred and 9,544 of grade cows were used. The data were grouped in five classes: ≤4,000kg, from 4,000 to 6,000kg, from 6,000 to 8,000kg, from 8,000 to 10,000 and ≥10,000kg of milk production in 305 days. The overall milk and fat average were 5,865.54 and 196.85kg, respectively. The milk and fat averages for the same age classe were consistently larger for the purebred cows. The estimated genetic trend for milk and fat in each class of milk production were: 10.52 and 0.33kg, 8.31 and 0.25kg, 8.90 and 0.29kg, 11.00 and 0.36kg, 9.51 and 0.36kg by year, respectively. The average milk and fat production for cows of first calving were: 6,084.6 and 205.1kg, 5,739.5 and 191.8kg for purebred and grade cows. The estimated genetics trends of 8.7 and 9.6kg, for purebred and graded cows, although small, reflect an increasing in milk production potential from 1986 to 1996.

Influência dos períodos de serviço anterior e corrente e do período seco anterior sobre a produção de leite na raça holandesa

O objetivo deste trabalho foi avaliar os efeitos dos periodos de servico anterior e corrente e do periodo seco anterior ajustados simultaneamente como efeitos fixos em modelo de touro para producao de leite ate 305 dias, contendo ainda os efeitos fixos de rebanho-ano-estacao, grupo genetico e idade da vaca e os efeitos aleatorios de touro e vaca. Foi usada matriz de parentesco, que incluiu o touro, o seu pai e sua mae. O mesmo modelo com exclusao da idade da vaca foi usado para producao de leite ate 305 dias ajustada a maturidade. As solucoes nas analises foram obtidas usando-se o metodo da maxima verossimilhanca restrita e o algoritmo livre de derivada. Polinomios ortogonais foram ajustados para suavizacao das solucoes. Solucoes e valores previstos para producao ate 305 dias nao foram apresentados, por terem seguido mesma tendencia da producao ate 305 dias ajustada a maturidade. A producao ate 305 dias ajustada a maturidade aumentou 950 kg, quando o periodo de servico anterior variou de 20 a 300 dias. Este aumento foi de 802 kg para a mesma variacao do periodo de servico corrente. Vacas com periodo seco de 60 a 80 dias obtiveram a producao de leite mais alta na lactacao seguinte. Valores estimados da heritabilidade foram 0,02 para o periodo de servico e 0,08 para o periodo seco, quando a producao total foi considerada no modelo, e 0,12 quando foi excluida. Fatores multiplicativos foram estimados para o ajustamento da producao de leite para os efeitos de periodo de servico e seco.