Effect of breed group and age at first calving on the number of calvings during the lifetime of Zebu cows

Abstract

The objective of the study was to determine the effect of breed group (BG) and age group at first calving (AFC) on the number of calvings during the lifetime of the cows in a production system localised in the state of Yucatan, Mexico. Data included information gathered from 65 cows of the Brahman (Br, n = 313) and Nellore (Ne, n = 184) breeds, and commercial Zebu (CZ, undefined crosses of Brown Swiss and Zebu (n = 268) born from 1981 to 2002. Out of the total number of cows, 391 had been culled and 374 remained in the ranch (censured data). The stayability (number of calvings) of the cows in the herd was evaluated by BG and AFC using Kaplan Meier methodology. The survival curve for CZ had the fastest decline, which suggests a greater culling rate for this group in comparison with the Ne and Br cows. The survival curves for the cows that had their first calving before 2.5 years and between 2.5 and 3 years of age show that they had a lover lower chance of culling. In conclusion, BG and EFC had an effect (P < 0.05) on the survival curves; Nellore cows had a higher probability of more calvings. Cows that were younger than 3 years old at first calving had a higher probability of having more calvings during their lifetime when compared to those being older at first calving.