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United States Department of Agriculture

Agricultural Research Service

Title: Genetic parameters for yield traits of cows treated or not treated with bovine somatotropin

Authors
item Al-Seaf, A. - UNIV. OF NEBRASKA-LINCOLN
item Keown, Jeffrey - UNIV. OF NEBRASKA-LINCOLN
item Van Vleck, Lloyd

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 9, 2006
Publication Date: January 1, 2007
Citation: Al-Seaf, A., Keown, J.F., Van Vleck, L.D. 2007. Genetic parameters for yield traits of cows treated or not treated with bovine somatotropin. Journal of Dairy Science. 90:501-506.

Interpretive Summary: Bovine somatotropin (bST) is widely accepted and used as a management tool to enhance dairy cow productivity. Of nearly 9 million dairy cows in the United States, approximately one-third are in herds which use bST. The Food and Drug Administration approved use of bST for increasing milk production in dairy cows in 1993. Since then, records from cows treated with bST have accumulated at the Dairy Records Processing Center (DRPC). More data were available for this study than previous studies for cows treated with bST, and for records of treated cows for lactations 3, 4 and 5. The objective of this study was to examine the effect of bST treatment on estimates of genetic parameters for yield traits and SCS from lactation records of cows treated or untreated with bST and especially to estimate the genetic correlation between traits for cows defined as treated or not treated with bST. After editing, records for registered cows were divided into three subsets by lactation number: lactation one, lactation two, and later lactations (lactations three, four and five). The subsets contained (4,337 and 48,765), (3,730 and 37,796) and (3,645 and 33,957) records, respectively for bST treated and untreated cows. A two-trait animal model was used to estimate variance and covariance components and genetic parameters for yield traits and somatic cell scores for lactations 1, 2 and 3. Records from cows with or without bST treatment were considered to be two different traits. The estimates of additive genetic variance were slightly greater for records of cows without bST. However, estimates of phenotypic and permanent environmental variances were greater for records of cows receiving bST. Overall, estimates of phenotypic variance for milk yield, fat and protein yield and SCS for all data sets were greater for records of cows treated with bST than for records of cows untreated with bST. In contrast, estimates of genetic variance for milk, fat, and protein yields were slightly greater for records of cows untreated with bST. Estimates of genetic and environmental correlations between treated and untreated cows for the three yield traits and SCS and were large and positive for the three data sets. The estimates of genetic correlations between milk yields with and without bST for the three data sets were 0.99, 0.99, and 0.99. Estimates were slightly less for genetic correlations between fat yields for all data sets (0.96, 0.96, and 0.96). Estimates of genetic correlations between protein yields for all data sets were 0.96, 0.96, and 0.96. Finally, estimates of genetic correlation between SCS of treated and untreated cows for all data sets were near unity (0.99 0.99, and 0.99). Estimates of genetic correlations were large enough to support the conclusion of considering a single trait analysis for records of treated and untreated cows with bST treatment as a fixed effect.

Technical Abstract: Records from the Dairy Records Processing Center at Raleigh, NC were obtained for study. The records for registered cows were divided into three sets: (1) first lactations, (2) second lactations and (3) lactations from three to five. About 10% of the records for each set were for cows treated with bovine somatotropin (bST). The numbers of records for treated and untreated cows in each set were (4,337 and 48,765), (3,730 and 37,796) and (3,645 and 33,957), respectively. A multiple trait animal model with records of cows treated or untreated with bovine somatotropin as different traits was used to estimate genetic parameters for milk production traits and somatic cell score (SCS) for the three sets of records. Cows treated with bovine somatotropin produced more milk than untreated cows in all data sets by (10.0, 9.6 and 7.7 kg/100), respectively. The differences between records of treated and untreated cows for fat and protein yields for three data sets were (4.5, 4.0 and 3.6 kg/10) and (2.3, 2.8 and 2.0 kg/10), respectively. Cows receiving bovine somatotropin had smaller or equal mean somatic cell scores (SCS) than cows not receiving bovine somatotropin (-0.4, 0.00 and 0.00), respectively. Estimates of heritability for milk yield for records of treated and untreated cows were (0.13, 0.16 and 0.09) and (0.18, 0.18 and 0.14), respectively. Corresponding estimates of repeatability from data set 3 were (0.50 and 0.41) for records of treated and untreated cows, respectively. Estimates of heritability for fat yield for records of treated and untreated cows were 0.31, 0.16 and 0.12 and 0.27, 0.21 and 0.16, respectively, with estimates of repeatability of 0.45 and 0.40 for data set 3. Estimates of heritability for protein yield for records of treated and untreated cows were 0.13, 0.17 and 0.12 and 0.20, 0.23 and 0.16, respectively, with estimates of repeatability of 0.52 and 0.46. Estimates of heritability for milk yield traits were less for lactations three to five than for first and second lactations of both treated and untreated cows. Estimates of heritability for somatic cell score for treated and untreated cows were 0.09, 0.15 and 0.13 and 0.11, 0.13 and 0.13, respectively. Estimates of repeatability for later lactations were 0.52 and 0.45. Estimates of genetic correlations between milk yields with and without bovine somatotropin treatment for lactation one, lactation two and lactations three to five were large (0.99, 0.99 and 0.99), respectively. Estimates of genetic correlations for fat and protein yields were similar for all data sets (0.96). Estimates of genetic correlations for somatic cell score were 0.99 for lactations one and two and for later lactations. All estimates of genetic correlations between treated and untreated cows were large enough to conclude that records of treated and untreated cows could be considered to be one trait with treatment as a fixed effect to account for differences in means.

Last Modified: 7/30/2014
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