Proportional hazard model applied to study factors affecting days open in Argentinian dairy herds.

PICCARDI, M.; BALZARINI, M.; CAPITAINE FUNES, A.; BÓ, G.

Manhattan, Kansas.

Conferencia; 23 Conference on Applied Statistics in Agriculture.; 2011

Kansas University

The purpose of this study was to estimate, through proportional hazard models, the relative contribution of factors which affect the speed in which cattle become pregnant in Argentinian dairy herds. The factors considered were milk production level, lactation number, calving season and reproductive biotechnology used (artificial insemination, natural breeding using bulls, or combined). A total of 152.928 lactations corresponding to 292 dairy herds were analyzed. Three hazard models were adjusted to explore days open (DO). The first model just contemplated the level of production; in the second model, we added the rest of the variables mentioned and to the last model, we added the interaction between type of service and level of production. In order to compare the models, the likelihood ratio test (LRT) was used. The third model turned out to be the best. Cows of less production (< 5850 lts. 305EM) have a 26% more of risk to get pregnant in a particular moment than those animals of higher production (>8710 lts. 305EM). The DO were increased linearly with the number of lactation. The autumn-winter calving significantly shorten the period of empty cows over the summer. The impact of the type of service was not independent of the production level. Even if pregnancy rate does not increase with AI, compared to natural service, it is possible to increase significantly the speed of pregnancy in animals of high productive levels. The results of this observational study suggest that new reproductive management designs developed for specific productive levels could increase the overall reproductive efficiency.