Relationship between calving interval and profitability of Brown Swiss cows in a subtropical region of Mexico.

Brown Swiss cattle have replaced Zebus in some dual-purpose farms in tropical and subtropical regions of Mexico, under extensive grazing management. There is limited information about the productive and reproductive performance of this breed under tropical conditions; the lack of records from small farms may be the main reason. The objectives of the study were to evaluate the relationship between calving interval (CI) and milk and beef (weaned male calves) profit in Brown Swiss cows from a dual-purpose farm under extensive management in a subtropical region of Mexico. Data from 156 cows calving from 2000 to 2014 were analysed with both a linear and a survival model. Mean CI was 438 ± 49 days, mean age at first calving was 40 ± 6 months and length of productive life was 7 ± 3 years. The effects of parity, calving year and calving season were significantly related to CI (P < 0.05), whereas the effect of calf sex was not. Cows calving in the autumn and winter had shorter calving intervals, probably because supplements received during the dry season months improved energy balance. The highest culling rate was 28% at 45 months of age. Milk yield and total profit increased as CI increased from 12 to 20 months; beef contribution to total profit decreased as CI and milk yield increased. Calving intervals of more than 12 and up to 20 months had a positive effect on the milk production and profitability of dual-purpose cows in a subtropical region of Mexico.