Culling in Quebec Holstein Herds. 1. Study of Phenotypic Trends in Herd Life

A total of 206 963 official lactation records and 128 182 owner sampler lactation records from the Programme d'Analyse des Troupeaux Laitiers du Québec herds were used to estimate survival rates of Holstein cows up to different parities by milk recording option and year of first calving. Survival up to a given parity was computed only for cows having the opportunity to reach that parity. Average productive herd life up to and including the eighth parity was computed for cows calving for the first time from 1981 to 1985. The overall productive herd life was 33.13 mo for owner sampler herds and 32.97 mo for official herds, and the respective replacement rates per year were 36.22% and 36.40%. Average herd composition in Quebec Holstein herds was: 33.4% of cows in parity 1, 24.2% in parity 2, 17.1% in parity 3, 11.4% in parity 4, 7.0% in parity 5, 3.9% in parity 6, 1.9% in parity 7, and 1.1% in parity 8. Cows in official herds had longer calving intervals than those in owner sampler herds. First calf heifers have been culled by official producers earlier in lactation than by owner sampler producers. Survival rates decreased from 1981 to 1992, and trends for official and owner sampler herds were very similar. Key words: Herd life, survival, Holstein, Quebec, culling