CALVING INTERVALS IN BEEF-COWS AT 2, 3, AND 4 YEARS OF AGE WHEN BREEDING IS NOT RESTRICTED AFTER CALVING

The objective of this study was to evaluate calving intervals and repe atability of calving intervals of young beef cows when breeding season s were initiated immediately after calving. Average calving date at 2, 3, and 4 yr of age was recorded, and duration of calving interval bet ween the first and second and second and third parities was compared i n 178 crossbred beef cows calving between 1981 and 1988. Cows were pla ced in paddocks with intact bulls immediately after calving so they ha d the opportunity to conceive at the estrus associated with the initia l estrous cycles after calving. Average Gregorian date of calving for cows was progressively earlier with older age (March 9, March 5, and F ebruary 14 at 2, 3, and 4 yr of age, respectively). Repeatability of c alving intervals within individual, cows was also evaluated. There was an interaction between year and parity on calving interval between 2 and 3 (P < .001) and 3 and 4 (P < .004) yr of age. Repeatability of ca lving interval was low and negative during 5 of the 6 yr. In young bee f cows, year and parity interact to influence calving interval, and th is average interval is less than 365 d when initiation of the breeding season is not restricted after calving.