Evaluation of Cow Reproduction in the Pureline Foundation Phase of the Canadian National Dairy Cattle Breeding Project

Abstract

Five reproduction traits—number of inseminations per cow, days to first estrus, days open, calving interval, and culling rate for infertility—were studied on dairy cows from a long-term breeding project of the Agriculture Canada Research Branch. Five experimental farms maintained either Holstein line, Ayrshire line, or both. Traits were analyzed within each line by a model in which station, year, sire group (paternal parentage), and bull (cow's mate) were considered. Variation these factors caused was small; most represented less than 1% of the total sum of squares. Holstein cows at Lethbridge, Lennoxville, and Ottawa had 1.9, 2.3, and 2.0 inseminations per cow, 55.1, 63.9, and 51.2 days to first estrus, and 109.9, 125.2, and 112.4 days open. The same traits of Ayrshire cows at Charlotte-town, Normandin, and Ottawa were 2.3, 2.2, and 2.0; 53.3, 61.4, and 53.0 days; and 105.2, 129.2, and 114.5 days. All three traits were derived from records of all cows, including those that did not complete calving intervals. Calving interval at all five stations varied from 376.1 to 412.4 days. Intensity of culling for infertility differed between stations, e.g., 5% in one and 31% in another. About 24% of all disposed cows were culled in both lines for infertility.