Analysis of Factors Affecting Calving Intervals of Dairy Cows

Abstract

Forty Dairy Herd Improvement Holstein herds selected for their long or short calving intervals, were visited to determine factors affecting calving intervals and breeding efficiency. Twenty-one herds with calving intervals of 360 to 374 days (S), and 19 herds with calving intervals of more than 405 days (L), based upon the 1969 Dairy Herd Improvement summary, were compared in a 2-year study.The L group had a 28-day longer interval (P<.01) from parturition to first service. The intervals between services were also longer (P<.01) for the L group. Twenty-four per cent of S group had first services by 60 days postpartum, 73% by 90 days, and 92% by 120 days compared with 13, 50, and 74% for the L group. Conception rates of the two groups did not differ at first service or after three services.Cows in the S group received more concentrates, but that was not considered a factor in their shorter breeding interval because more S than L herds had suboptimal nutrient intake. Nutritional deficiencies appeared to affect reproduction adversely in only one herd.Heat detection was a problem in several herds due to inadequate observation and failure to recognize some heat signs. Reproductive consciousness of the S operators was higher in that they were breeding cows earlier after parturition and had fewer problems detecting heat. Many operators need additional training to detect heat and on maintaining complete, individual-cow, health records.