Factors affecting calving interval in a beef cattle herd in Tennessee

A seven year study, involving 194 cows and 828 calving intervals,was conducted at the University of Tennessee Atomic Energy CommissionAgricultural Research Laboratory, Oak Ridge, Tennessee.

This study was designed to evaluate the following effects on calving interval: source of dam, age of dam, radiation treatment of dam, weight change of,dam during breeding season, previous parity of dam, sex of current calf, current calf's performance traits (unadjusted pre weaning average daily gain and pre weaning condition score) andsire of the calf for the following year.

Source, age of dam, and irradiation level of dam did not have a significant effect on calving interval.

Dam's weight change during the breeding season did exert influence on calving interval. Calving interval increased with the increase weight gain of the dam during the breeding season.

Previous parity of the dam had a pronounced effect on calving interval. Cows open the previous year had longer calving intervals and cows pregnant the previous year had shorter calving intervals.

Calf's pre weaning average daily gain and condition score were an important source of variation in calving interval. Average daily gain of the calves had a,negative response while condition score had a positive response on calving interval. Cows with calves with the highest average daily gain had the shortest calving interval; conversely, cows with calves with the highest condition score had the longest interval.

Sires used in "breeding herd the first two years had a nonsignificant effect on calving interval while the sires used thereafter were highly significant. Confounding of age of dam apparently causes the difference between the sire groups.