"EFFECT OF CALVING SEASON ON PRODUCTIVE AND REPRODUCTIVE PERFORMANCE OF A DAIRY HERD IN LOS RIOS REGION"

Abstract

Calving season, be it fall or spring, is a particularly important factor which allows the prediction of productive and reproductive performance and provides information regarding influential factors on the dairy business. The objectives of this research were to describe calving distribution of a dairy farm and quantify the effect of calving season on productive and reproductive performance. Multiple linear regression was used to study the following dependant variables: milk yield and composition, and calving interval. The analyzed data corresponded to 1,433 lactations registered from 1989 to 2007 in a dairy farm of southern Chile. Descriptive results showed two clearly distinguishable calving seasons, fall and spring, with calving incidences of 50 and 37%, respectively. Milk yield and composition were significantly affected by calving season, however, calving interval was not statistically associated with calving season. Regarding milk yield, lactations initiated during the fall were significantly more productive than those started in spring. Also, fall calving was significantly more productive in terms of milk fat which can be explained as a consequence of feeding changes across seasons. Protein yield was significantly higher for spring calving which is associated to spring grass nutrient composition.