Effect of Age at First Calving on First Lactation Milk Yield in Holstein Cows from Costa Rican Specialized Dairy Herds

Abstract

In order to determine the effect of age at first calving (AFC) at 305-d milk yield, a historical prospective longitudinal study of 46,029 pure specialized dairy Costa Rican Holstein animals was carried out between 2000 and 2010. Data on purebred specialized dairy Holstein cows enrolled in the program VAMPP Bovino 3.0 were included. Information was analyzed by using descriptive statistics and mixed linear models. The effect of the AFC was adjusted to the ecological zone, season of birth, year of birth, inbreeding index, and type of parturition and parity number of the dam at birth. The average AFC for the animals that were part of the study was 30.7 mo (SD: 6.8, 95% CI: 30.6 - 30.7). The average total milk production in the first lactation was 5188.0 kg. (95% CI: 5153.4 - 5223.2), whereas the 305-dcorrected milk yield resulted in 5288 kg (95% CI: 5253.7 - 5323.2). Cows with AFC less than 26 mo and between 26.0 and 33.6 mo, produced −354.8 kg/305-d (P < 0.0001) and −105.6 kg/305-d (P = 0.0117) respectively, compared with cows calving over 33.6 mo. It is likely that the observed effect of the AFC on the topmost dairy lactation affects the productive life of the cow within the herd. Further studies are required to prove this hypothesis.