Effect of seasons on days open of breeding cows

Abstract

The objective was to assess the effect of seasons on the calving interval and calving dates in cows at the Cristo Rey ranch over 15 years. Data from 15 years at the Cristo Rey ranch was collected, including calving dates, conception dates, and the date of the previous calving to calculate the calving interval. The information was classified based on the last calving date and the corresponding season: spring, summer, autumn, and winter; resulting in four calving groups with their respective calving intervals. Descriptive analysis of calving intervals, frequency distributions, and an ANOVA using InfoStat were conducted to determine if there was a difference in calving intervals between groups. A total of 985 calvings were recorded, with an average of 240 days open. Only 15.8% of the cows had a calving interval less than 103 days; the highest percentage was concentrated between 104 and 358 days; additionally, 17 cows took more than a year and a half to become pregnant. The analysis of variance showed a significant difference between seasons with a P-value of 0.0003 and α = 0.05, with winter being the season with the fewest days open (219). The calving intervals observed by season (in addition to nutritional, sanitary, and genetic factors) condition the date of conception and, therefore, the calving date, so the same cow can become pregnant or calve in different seasons of the year.