Paulo Fernando Machado

Bulk tank milk composition from Brazilian herds distributed by its somatic cell count

A survey on the somatic cell count (SCC), fat, protein, lactose and total solids percentages on bulk tank milk samples, from December 1996to July 1998, was used to characterize the milk composition as determined by SCC. Data of 4785 from the database were classified according to the SCC, in four groups (Group 1, SCC 1.500 thousand cells/mL). A descriptive statistics, analysis of variance and multiple mean tests were applied to the groups. Increases on the group classes were associated with increases on concentration and standard deviation and decreases on protein and lactose concentrations. Despite of the no significance, the total solids tended to decrease as group classes increase. The bulk tank milk samples with higher SCC had greater fat percentages, lower protein and lactose percentages and the same total solids percentages. The significant changes in the milk component contents occur above 1.000.000 cells/ml for fat and 500 thousand cells/ml for protein and lactose. Bulk tank groups with greater SCC have greater variability in milk component compositions.

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.

Contagem de células somáticas e produção de leite em vacas holandesas confinadas

ABSTRACT - The relationship between milk somatic cells count (SCC) and milk yield has been the aim of countless researchesin several countries; however, in Brazil, the literature related to this subject is scarce. Therefore, the objective of this st udy is to verifyif the losses in milk yield due to SCC increase are proportional to the yield, or absolute (independent of it) and starting fro m which SCC,the losses become evident. For this study, 13.725 observations were used, collected monthly from 6 different herds, from Januar y/2001up to June/2002. The analysis model, for lactation curve, was based upon the incomplete gama function, considering the effects of lactationorder, herd and calving season. The SCC entered in that model in two ways: as multiplicative factor (representing relative loss es) andas addictive factor (representing absolute losses). The best model was chosen based on the information criteria of Schwarz (BIC ). It isconcluded that the losses are absolute, becoming evident from 17.000 cells/mL, and they are 238 and 868 mL/day for each increas e ofone unit in the natural logarithm scale, starting from that SCC, respectively, for primiparous and multiparous.Key Words: SCC, subclinical mastitis, bovine mastitis, milk yield

Random regression models using different functions to model test-day milk yield of Brazilian Holstein cows

We analyzed 152,145 test-day records from 7317 first lactations of Holstein cows recorded from 1995 to 2003. Our objective was to model variations in test-day milk yield during the first lactation of Holstein cows by random regression model (RRM), using various functions in order to obtain adequate and parsimonious models for the estimation of genetic parameters. Test-day milk yields were grouped into weekly classes of days in milk, ranging from 1 to 44 weeks. The contemporary groups were defined as herd-test-day. The analyses were performed using a single-trait RRM, including the direct additive, permanent environmental and residual random effects. In addition, contemporary group and linear and quadratic effects of the age of cow at calving were included as fixed effects. The mean trend of milk yield was modeled with a fourth-order orthogonal Legendre polynomial. The additive genetic and permanent environmental covariance functions were estimated by random regression on two parametric functions, Ali and Schaeffer and Wilmink, and on B-spline functions of days in milk. The covariance components and the genetic parameters were estimated by the restricted maximum likelihood method. Results from RRM parametric and B-spline functions were compared to RRM on Legendre polynomials and with a multi-trait analysis, using the same data set. Heritability estimates presented similar trends during mid-lactation (13 to 31 weeks) and between week 37 and the end of lactation, for all RRM. Heritabilities obtained by multi-trait analysis were of a lower magnitude than those estimated by RRM. The RRMs with a higher number of parameters were more useful to describe the genetic variation of test-day milk yield throughout the lactation. RRM using B-spline and Legendre polynomials as base functions appears to be the most adequate to describe the covariance structure of the data.

Influência de fatores de ambiente sobre a contagem de células somáticas e sua relação com perdas na produção de leite de vacas da raça Holandesa

Cumulative milk yield at 305 days (MY-305) and somatic cell count (SCC) from the first to the fifth lactation of Holstein cows were analyzed in this study. Somatic cell count was logarithmically transformed to somatic cell score (SCS) that was then included in the model not only as a dependent but also as an independent variable. Year, season, and parity order all significantly affected the average SCS in this study. Data of the effect of SCS on milk yield showed significant losses on MY-305 because of the observed negative linear relationship between these two variables. Somatic cell score affected differently MY-305 from different parity orders with greater effect after the 3rd parity. Although clinical mastitis seems to cause greater economic losses, prevention and control of sub-clinical mastitis deserve more attention due to its greater prevalence leading to significant reduction on herd productivity.Cumulative milk yield at 305 days (MY-305) and somatic cell count (SCC) from the first to the fifth lactation of Holstein cows were analyzed in this study. Somatic cell count was logarithmically transformed to somatic cell score (SCS) that was then included in the model not only as a dependent but also as an independent variable. Year, season, and parity order all significantly affected the average SCS in this study. Data of the effect of SCS on milk yield showed significant losses on MY-305 because of the observed negative linear relationship between these two variables. Somatic cell score affected differently MY-305 from different parity orders with greater effect after the 3rd parity. Although clinical mastitis seems to cause greater economic losses, prevention and control of sub-clinical mastitis deserve more attention due to its greater prevalence leading to significant reduction on herd productivity.

Short communication: Evaluation of an on-farm test to estimate somatic cell count

The objective of this study was to compare the results of an on-farm test, named Somaticell, with results of electronic cell counting and for milk somatic cell count (SCC) among readers. The Somaticell test correctly determined the SCC in fresh quarter milk samples. Correlation between Somaticell and electronic enumeration of somatic cells was 0.92 and kappa coefficient 0.82. Using a threshold of 205,000 cells/mL, the sensitivity and specificity for determination of intramammary infections were 91.3 and 96.0%, respectively. The SCC was greater for milk samples from which major mastitis pathogens were recovered. Minor variation among readers was observed and most likely associated with the mixing procedure. However, the final analysis indicated that this variation was not significant and did not affect the amount of samples classified as having subclinical mastitis. The on-farm test evaluated in this study showed adequate capacity of determining SCC on quarter milk samples and may be considered as an alternative for on-farm detection of subclinical mastitis.

Modelos de dimensão finita para a estimação de parâmetros genéticos para a produção de leite de primeiras lactações de vacas da raça Holandesa

Foram estimados parâmetros geneticos para producao de leite acumulada ate 305 dias (P305) e producao de leite no dia do controle (PLDC) de 50.171 controles mensais de 9.281 primeiras lactacoes de vacas da raca Holandesa. A P305 e as PLDC foram analisadas por meio de modelo animal uni e bicaracteristicas. Para a P305 o modelo incluiu como aleatorio, o efeito genetico e como efeitos fixos o grupo de contemporâneos e a covariavel idade da vaca ao parto. Para as PLDC foi usado o mesmo modelo descrito para a P305, incluindo como covariavel o numero de dias em lactacao. Os componentes de variância foram estimados pelo Metodo da Maxima Verossimilhanca Restrita. As estimativas de herdabilidade (h2) para as PLDC oscilaram entre 0,07 e 0,19 em analises unicaracteristicas e, de 0,12 a 0,22 nas bicaracteristicas. Para a P305, as h2 resultantes das analises uni-caracteristica e bicaracteristica foram 0,26 e 0,27, respectivamente. As correlacoes geneticas das PLDC com a P305 foram todas positivas e elevadas, variando de 0,63 a 1,00. As correlacoes geneticas entre as PLDC variaram de 0,30 a 1,00. A selecao para a P305 parece ser o melhor criterio de selecao a ser adotado, uma vez que proporciona maiores ganhos geneticos para as producoes de leite em, praticamente, todos os controles da lactacao.

Somatic cell count and production characteristics of lactating Holstein cows

Subclinical mastitis results in the decrease of milk and fat production. This disease is detected using somatic cell counts. The objective of this study was to quantify the relation of somatic cell levels, transformed into linear score (LS), and the production of milk and fat during 305 days of lactation, peak milk production, and the lactation duration time of Holstein cattle. Data were gathered concerning 147 closed lactations of Holstein cows (83 primiparous and 64 multiparous) from a confined herd in the state of Sao Paulo, Brazil. Statistical analyses were performed through the general linear model procedure. The productive characteristics of multiparous, but not primiparous cows, were affected acording to the linear score. An increase in the average linear score during lactation resulted in the decrease of fat and milk production in the 305 days of lactation. The increase in the average linear score at the beginning of the lactation period resulted in a decrease of milk production at the peak of lactation.

Efeitos genéticos e de ambiente sobre a produção de leite e a contagem de células somáticas em vacas holandesas

The objective of this study was to estimate the genetic and phenotypic relationships between somatic cell count (SCC) and milk yield and to evaluate the possibility of using SCC as a selection criteria in breeding programs of dairy cattle. Somatic cell count records were transformed into somatic cell score (SCS) using a logarithmic scale. Genetic parameters for milk yield (305 days) and average somatic cell score (ASCS) were estimated. The overall means for 305-day milk yield (MY305) and ASCS were, respectively, 7519.51 kg and 4.04. Heritability estimates for MY305 and ASCS, obtained from univariate analyses were 0.22 and 0.13, respectively. Similar results were obtained from bivariate analysis. The genetic correlation between MY305 and ASCS was -0.16. This result differs from most of those from the literature and suggests that selection for milk yield will not increase ASCS.

Short communication: Principal components and factor analytic models for test-day milk yield in Brazilian Holstein cattle.

A total of 46,089 individual monthly test-day (TD) milk yields (10 test-days), from 7,331 complete first lactations of Holstein cattle were analyzed. A standard multivariate analysis (MV), reduced rank analyses fitting the first 2, 3, and 4 genetic principal components (PC2, PC3, PC4), and analyses that fitted a factor analytic structure considering 2, 3, and 4 factors (FAS2, FAS3, FAS4), were carried out. The models included the random animal genetic effect and fixed effects of the contemporary groups (herd-year-month of test-day), age of cow (linear and quadratic effects), and days in milk (linear effect). The residual covariance matrix was assumed to have full rank. Moreover, 2 random regression models were applied. Variance components were estimated by restricted maximum likelihood method. The heritability estimates ranged from 0.11 to 0.24. The genetic correlation estimates between TD obtained with the PC2 model were higher than those obtained with the MV model, especially on adjacent test-days at the end of lactation close to unity. The results indicate that for the data considered in this study, only 2 principal components are required to summarize the bulk of genetic variation among the 10 traits.