Bias in Genetic Evaluations by Records of Cows Treated with Bovine Somatotropin

Abstract

Records from Dairy Records Management Systems in Raleigh were used to estimate effects of bovine somatotropin (bST) treatment and to predict breeding values for milk production traits. The data comprised 5245 test-day records of bST-treated cows and 126,223 test-day records of untreated cows in first lactation for milk, fat, and protein yields. Fixed effects of bST treatment were estimated from test-day animal models with herd-test-date as another fixed factor. Percentage increases due to bST treatment ranged from 7 to 8% for test-day milk, fat, and protein yields. Random regression coefficients for additive genetic and permanent environmental effects were included in the model. To assess the potential for bias in genetic evaluations when some and not all cows are treated with bST, breeding values predicted by the test-day model with and without effects of bST treatment were compared for cows and sires. Correlations between breeding values predicted from models with and without effects of bST treatment were 0.99. However, relatively large bias was found for individual animals. This result suggests that bias in genetic evaluation caused by ignoring bST treatment may be significant. (Key words: dairy cattle, milk yield, breeding values) Abbreviation key: DRMS = Dairy Records Management Systems, MAD = maximum absolute difference, MAE = mean absolute errors, PBV = predicted breeding value, TD = test day.

Genetic Parameters for Yield Traits of Cows Treated or Not Treated with Bovine Somatotropin

“…Burton et al (1990) reported that bST can enhance milk yields without an apparent effect on mammary gland or general cow health. Collier et al (2001), in a study on the effect of using bST on the health of cows in commercial dairy cattle herds that were chosen randomly from different regions of the United States, showed that health problems in cows treated by bST were the same as Tsuruta et al (2000) reported estimates of heritability of 0.19 and repeatability of 0.39 for milk yield for cows treated with bST.…”

“…AlJumaah (2001) obtained estimates of heritability of 0.18 and of repeatability of 0.43 for milk yield with bST and of 0.13 and 0.39 for untreated cows. Tsuruta et al (2000) reported estimates of heritability of 0.19 and repeatability of 0.39 for milk yield for cows treated with bST.…”

“…Repeatability estimates were 0.50 and 0.43. Tsuruta et al (2000) reported Estimates of variance components, heritability, and repeatability for protein yield for lactations 1, 2, and later are shown in Table 5. Heritability estimates were 0.13, 0.17, and 0.12 for records of cows with bST, with a repeatability estimate for later lactations of 0.52.…”

“…AlJumaah (2001) showed that SCS were slightly less in bST herds. Tsuruta et al (2000) reported no significant difference for SCS between records of cows with or without bST. Hartnell et al (1991) found significant effects for bST for milk yield traits, but not for SCS or for percentages of fat and protein.…”

Impacto da utilização da somatotropina bovina (bST) sobre a produção de leite e a avaliação genética de bovinos da raça Holandesa

“…MORBECK et al (1991), por sua vez, observaram médias de 8.350 ± 562 kg, 8.348 ± 515 kg, 9.571 ± 515 kg e 9.070 ± 515 kg respectivamente para avaliação de quatro dosagens de aplicação de bST (0 mg, 5,15 mg, 10,3 mg e 16,5 mg). TSURUTA et al (2000) encontraram efeito significativo no tratamento com bST sobre a produção de leite. Neste estudo os autores verificaram que a aplicação deste hormônio elevou a produção em 7,2%.…”