Nilson Milagres Teixeira

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.

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.

Avaliação genética de bovinos da raça holandesa usando a produção de leite no dia do controle

153,963 test day milk yield records and 13,273 first lactations of Holstein cows calving between 1989 and 1998, were used with the objective of estimating genetic, phenotypic and environmental parameters for test day milk yield (PLDC) and 305 day milk yield (P305) and to study the convenience of using test day yields in genetic evaluations to replace P305. Four models were used. Models 1 and 2 differed according contemporary grouping and monthly milk records were considered as repeated measures. In model 1 (PLDCM01) records were grouped by herd-year-season of test day yield and in model 2 (PLDCM02) by herd-year-season of calving. In a third (model 3), monthly yield records were analyzed as individual traits (C01 to C10); and the fourth (model 4) was the traditional 305-day model. Restricted Maximum Likelihood methodology was used with the MTDFREML system. The estimates of heritability for PLDC, using model 1, model 2 and for P305 were 0.27, 0.15 and 0.25, respectively. Heritabilities for monthly milk records ranged from 0.11+0.02 (C01) to 0.21+0.03 (C08), with the largest values occurring beginning in the fourth month. Genetic correlation estimates between monthly records and P305 ranged from 0.76 to 1.00, with the highest correlations occurring in the middle lactation. It was concluded that using test day milk yield is promising and that selecting for middle lactation records could have advantages over 305-day milk yield.

Influência de fatores de meio ambiente na variação mensal da composição e contagem de células somáticas do leite em rebanhos no Estado de Minas Gerais

A total of 102,098 individual monthly-test-day records of Holstein cows from 189 herds of the state of Minas Gerais from January 1999 to December 2001 were used to evaluate the effects of environmental factors on the composition and somatic cell counts (CCSs) of milk. The CCSs were transformed to somatic cell scores (SCSs). Unadjusted means and standard deviations for milk yield, fat and protein percentages, and SCSs were, respectively, 22.87 and 7.35kg, 3.56 and 0.72%, 3.15 and 0.37%, 3.07 and 2.33 for first parity and 24.99 and 9.33kg, 3.57 and 0.76%, 3.14 and 0.38%, 4.23 and 2.3 for later parities. Least squares methodologies were used and the analyses were separated within lactation age group as first and later parities. Effects of herd-year, month of calving, days in milk, season of calving, age at calving and breed group were considered in order to explain total variations. In both data sets, except for protein percentage, for which days in milk was the most contributing effect for the variation, herd-year was responsible for most of the variation, followed by days in milk. The effect of herd-year was also the most important to explain the variation of SCSs, respectively, 19.0 and 34.6% for first and later parities, followed in importance by days in milk, respectively, 4.4 and 4.0% of the total variation. Milk fat and protein percentages were high early in the lactation, decreased to a minimum near 50 days followed by a steady increase to the end of the lactation while milk yield decreased. Fat and protein percentages were highest in winter and lowest in summer months. Seasonal variations of these components followed opposed trends of milk yield. The SCSs were high in the first 10 days of lactation decreasing to a minimum value respectively, from 50 to 60, and from 30 to 40 days for first and later parities and then increasing with similar rates to the end of the lactation. The variation of SCSs with month was similar for first and later parities. SCSs increased from February to June, and then decreased to a minimum in October. The increase of SCSs with cow age was curvilinear in first and linear in later lactations.

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.

Source of variation and genetic parameters of days open and days dry in Holstein dairy cattle in Minas Gerais State

The objective of this work was to evaluate the effect of some environmental factors on days open (DO) and days dry (DD), as well as to estimate genetic parameters for these traits in Holstein breed cows. A total of 6,485 records of DO and DD were used. The database were analyzed using a model that included the fixed effects of dairy group farmers, calving year, calving season, production level (PL), genetic group (GG), calving age class (CA) and the first order interactions between PL, GG and CA, and the random effect of bulls. The means, standard error and coefficients of variation for DO and DD were 121.21 (0.69) days, 46.10% and 92.27(0.59) days, 51.71%, respectively. For DO, effects of bull, dairy group farmers, calving year, calving season , PL were significant and was observed interaction between PL and GG. For DD, the effects of dairy group farmers, calving year, calving season, PL, CA and the interaction between PL and GG and for bull were significant. Genetic group did not affected the studied variables and a reduction in DO and DD with year was observed. The heritability estimate in univariate and bivariate analyses were 0.052 and 0.027 for DO, and 0.004 and 0.0001 for DD, respectively. The repeatabilities for DO and DD were 0.06 and 0.03, respectively. It was observed that the environmental effects are the most important on these traits. The genetic, phenotypic and environmental correlations between DO and DD (0.55, 0.72 and 0.73, respectively) show that cows with higher DO had greater days dry.

Estimação de tendência genética para produção de leite na raça Holandesa no estado de Minas Gerais

Production records from 75,567 lactations of 40,941 Holstein cows in 561 herds from 1980 to 2002 were used. Predicted cow and sire breeding values from an animal model were used to estimate genetic trend considering the four selection paths connecting two generations. The variance component estimates and breeding value predictions were obtained using the MTDFREML program package. The model of analysis accounted for the fixed effects of herd-year-season of calving, genetic group, age of calving as covariate (linear and quadratic) and the random effects of animal, permanent environment and error. The greatest annual genetic gain estimate was 57.7kg/yr for the path of sires of bulls from 1986 to 1991. For the path of dams of bulls, estimates were negative and for dams of cows changed from negative from 1970 to 1985 to 16.9kg/yr, from 1986 to 1999. When all paths of selection were combined, estimated annual genetic gain from 1970 to 1999 was 6.71± 3.78kg, corresponding to 0.1% of the average production. Estimates of genetic trend were much less than theoretically possible.

Parâmetros genéticos para características lineares de úbere: escore final de tipo, produção de leite e produção de gordura na raça Holandesa

Data on 3,063 linear classification records from 2,593 cows, from 1997 to 1999, were used in these analyses. A multiple trait animal model for three simultaneous trait was used to obtain correlations between pairs of the linear udder traits, final score, and milk and fat yields. Averages for udder traits ranged from 3.79 for fore teat placement to 5.81 for fore udder height. The average of final score was 80 and for milk and fat yields were 7,019±1,817 kg and 236±60kg, respectively. Repeatabilities ranged from 0.46 for udder depth to 0.76 for final score and heritabilities ranged from 0.11 for udder cleft to 0.40 for final score. Genetic correlations among linear udder traits were generally high and positive. The highest genetic correlation for linear udder traits occurred between udder height and udder cleft (0.71), followed by the correlation between fore udder attachment and udder cleft (0.69). Genetic correlation that included production and udder traits showed that the highest value was 0.46 between milk yield and rear udder width. Fat yield was moderately correlated with rear udder width (0.23). Some negative relationships were found. Estimates of phenotypic correlations were generally lower in absolute values than their corresponding genetic correlations.

Age of calving and region adjustment factors for milk and fat yields for graded and purebred Holstein in Minas Gerais State, Brazil.

Adjustment factors were estimated for milk and fat yields for Holstein herds according to age of cow at calving, genetic group (purebred or graded cows) and region of recorded milk yield (nucleus) in Minas Gerais State. Statistical analyses used mixed model methodologies by restricted maximum likelihood using animal model. Herd-year, season of calving, age of cow classes, genetic group, and region of recorded milk records were used as fixed effects, and cows and residuals as random effects. Analyses used 46,971 records of 26,822 cows being 17,354 classified as graded Holstein and 9,468 as purebred. In five regional nuclei, namely 1545, 2585, 5565, 35 and 75, cows were grouped in 21 age classes. The youngest one was formed by cows with less than 24 months and the oldest one by cows with 99 months of age or more. For purebred cows the age adjustment factors for milk and fat yields were lower than the correspondent ones for graded cows; however, the variability were higher for purebred cows compared to those of graded cows in 75, 2585 and 5565 regional nuclei. The age adjustment factors for young cows were higher than the correspondent factors for older cows. The fat yield adjustment factors were higher than milk yield adjustment factors in both purebred and graded cows. It is recommended to use specific factors for milk and fat yields estimated within nucleus and within genetic group.

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.