|Hutchison, Jana - Edwards|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2006
Publication Date: 2/1/2007
Citation: Norman, H.D., Hutchison, J.L., Wright, J.R., Kuhn, M.T., Lawlor, T.J. 2007. Selection on yield and fitness traits when culling Holsteins during the first three lactations. Journal of Dairy Science. 90(2):1008-1020.
Interpretive Summary: Producers have emphasized different yield and fitness traits when culling dairy cows. The most intense selection was on milk and protein yields with less emphasis on fat yield, days open, somatic cell score, and dystocia score. This information can help in selecting which progeny-test bulls to sample and which to return to active AI service. This information also can aid in developing software for culling guides based on an index for use in dairy management.
Technical Abstract: Traits emphasized when culling females from the herd should be similar to those considered when choosing bulls to progeny-test or to place in service. Emphasis by dairy producers since 1980 on various yield and fitness traits when culling cows was documented. Least-squares differences between cows retained for additional calvings and those culled were estimated for first-parity milk, fat, and protein yields; somatic cell score (SCS); days open (DO); and dystocia score (DS). Differences between traits were calculated on both a least-squares and a standardized basis. First-lactation milk yield of cows that survived for >=2 parities was 642 to 1283 kg more than that of cows culled prior to parity 2. The first lactation superiority for those having >=3 lactations compared to those with 2 was small. Cows kept for >=2 lactations had 0.34 to 0.62 lower first-lactation SCS than those kept for only one. Likewise, those kept for 3 or >=4 lactations had lower first-lactation SCS than those having <=2. Emphasis on milk yield has produced declines in fertility due to the negative genetic relationship, in spite of considerable direct selection for fewer DO when culling cows. Direct selection in the cow pathway for fertility has increased. In 1980, cows kept for only one calving had 18, 18, and 24 more DO in first lactation than those having 2, 3, and >=4, respectively. By 2000, these differences had increased to 34, 41, and 52 more DO. Dystocia score had a positive relationship with survival, but differences were small. On a standardized basis, the most intense selection during first lactation was for milk and protein, with less for fat (74 to 86% of that for milk), DO (18 to 74%), SCS (17 to 37%), and DS (7 to 15%). Second and third lactations analyses showed producers continued to emphasize these same traits when culling in later lactations. The emphases on these traits in culling reveals how producers value these, and could help determine how these should be emphasized when choosing bulls. This information could also be useful in dairy management for developing culling-guide software based on an index approach.