|Van vleck, Lloyd|
Submitted to: Journal of Dairy Science
Publication Type: Abstract only
Publication Acceptance Date: 11/17/2006
Publication Date: 6/1/2007
Citation: Geha, M., Keown, J.F., Van Vleck, L.D. 2007. Statistical analysis of the effect of bovine somatotropin on reproduction and calving ease in commercial holstein herds [abstract]. Journal of Dairy Science. 90(6):3074-3075. (Abstract #69) Interpretive Summary: No interpretive summary is required.
Technical Abstract: Records involving 134 Holstein herds, having both bovine somatotropin (BST) treated and non treated cows, totaling approximately 100,000 cows in their second, third and fourth lactations from 1994 to 2002, were used to analyze the effect of BST on reproduction and calving ease. Using SAS MIXED and GLIMMIX procedures, records of cows in the same lactation with herd by year, season and milking frequency as a random factor, were analyzed for number of days open (DO), number of services (NS) and culling for reproductive problems (CRP). Similarly, records of cows, with herds by year treated as a random factor, were analyzed for calving ease (CE). The analyses showed that for all lactations, there was a significant treatment by year interaction (P<.05) for DO and NS, with noticeably greater estimates for the years 1994-1997 compared to later years, which could be interpreted as how long it took management practices to adapt to requirements of treated cows, rather than as a direct impact of the treatment itself. For all lactations, treated cows had more days open and more services per breeding cycle than non treated cows. Year by treatment interaction was significant for CRP for lactation 2 (p<0.01) with slightly higher probabilities of problems for BST treated cows, but with no significant differences for later lactations. This result can be interpreted as a negative response of younger cows to higher production stress on their reproductive performance as compared to older cows. Culling frequencies seemed to drop after 1997 which may also indicate management adjustment. For calving ease, there was no direct treatment effect, but rather the sex of the calf had the greatest impact with twin calves having most calving difficulty followed by bull and heifer calves. Because of lack of data, it was not possible to look at the effect of BST on the size of the calf born.