title: Calving intervals in beef cows at 2, 3, and 4 years of age when breeding is not restricted after calving.
abstract: The objective of this study was to evaluate calving intervals and repeatability of calving intervals of young beef cows when breeding seasons were initiated immediately after calving. Average calving date at 2, 3, and 4 yr of age was recorded, and duration of calving interval between the first and second and second and third parities was compared in 178 crossbred beef cows calving between 1981 and 1988. Cows were placed in paddocks with intact bulls immediately after calving so they had the opportunity to conceive at the estrus associated with the initial estrous cycles after calving. Average Gregorian date of calving for cows was progressively earlier with older age (March 9, March 5, and February 14 at 2, 3, and 4) yr of age, respectively). Repeatability of calving 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 calving interval was low and negative during 5 of the 6 yr. In young beef cows, year and parity interact to influence calving interval, and this average interval is less than 365 d when initiation of the breeding season is not restricted after calving.
authors.affiliation: Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Werth
authors.forename: S M
authors.initials: SM
authors.lastname: Azzam
authors.forename: J E
authors.initials: JE
authors.lastname: Kinder
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001947:Breeding; D002417:Cattle / Q000502:physiology*; D004971:Estrus / Q000502:physiology; D005260:Female; D007743:Labor, Obstetric / Q000502:physiology; D010298:Parity / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D013997:Time Factors