Developmental and reproductive characteristics of beef heifers classified by number of estrous cycles experienced by start of first breeding

Authors: Roberts, Andrew; KETCHUM, JACLYN - University Of Nebraska; FUNSTON, RICHARD - University Of Nebraska

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2018
Publication Date: 11/23/2018
Publication URL: https://handle.nal.usda.gov/10113/6473322
Citation: Roberts, A.J., Ketchum, J.N., Funston, R.N. 2018. Developmental and reproductive characteristics of beef heifers classified by number of estrous cycles experienced by start of first breeding. Translational Animal Science. 3(1):541-548. https://doi.org/10.1093/tas/txy118.
DOI: https://doi.org/10.1093/tas/txy118

Interpretive Summary: A retrospective analysis was conducted to evaluate effect of number of estrous cycles exhibited before breeding on growth and reproductive performance of replacement beef heifers. Heifers were assigned into groups by number of estrous cycles exhibited before start of breeding; 0 (non-pubertal), 1, 2, 3, or > 3. Heifers in the 0 cycle group were born 6 day later than heifers in the 1, 2 or 3 cycle groups, which born 4 day later than the > 3 cycle group. Weight of heifers at birth decreased as number of cycles increased. Weaning weight and ultrasound measures of loin area and fat thickness over the loin at 1 year age increased as number of cycles increased. Post-wean weight gain, hip height at 1 year age, and weights from start of breeding through pre-calving increased with cycle numbers. Pregnancy rate in the 0 cycle group was lower (84%) than the 1 (90%) or > 3 (94%) estrous cycles groups, and tended to differ from the 2 (88%) and 3 (89%) estrous cycle groups. Interval from start of breeding to calving was 3- to 5-day longer for the 0 cycle group (300 ± 1 day) than other groups. Proportion of heifers calving in the first 21 day was lower in the 0 or 1 cycle groups than other groups. Rebreeding pregnancy rates at 2-years of age were lowest for the 0 (73%) and 2 (79%) estrous cycle groups, than the 1 (85 %), 3 (90%), or > 3 (92%) estrous cycle groups. In summary, date of birth and rate of physical maturation (weight, height, and fat deposition) were associated with timing of puberty. Pregnancy rate was greater in heifers that exhibited estrus before start of breeding, but did not improve from having more than one estrous cycle. Proportion conceiving early was greater for heifers having 2 or more cycles before breeding.

Technical Abstract: A retrospective analysis was conducted to evaluate effect of number of estrous cycles exhibited before breeding on growth and reproductive performance of replacement beef heifers fed ad-libitum or restricted by 20% less than ad-libitum during post-weaning development over a 9-year period. Progesterone concentration in blood samples collected at 9- to 11- day intervals were used to assign heifers into groups by number of estrous cycles exhibited before start of breeding; 0 (non-pubertal; n = 395), 1 (n = 205), 2 (n = 211), 3 (n = 116), or > 3 (n = 249). Heifers (P < 0.01) in the 0 cycle group were born 6 day later than the 1, 2 or 3 cycle groups, which born 4 day later (P < 0.01) than the > 3 cycle group. Weight of heifers at birth decreased (P < 0.05) as number of cycles increased. Weaning weight and ultrasound measures of loin area and fat thickness over the loin at 1 year age increased as number of cycles increased (P < 0.01). Post-wean weight gain, hip height at 1 year age, and weights from start of breeding through pre-calving increased with cycle numbers in a quadratic fashion (P < 0.02), and were greater (P < 0.05) in ad-libitum than restricted fed heifers. Pregnancy rate in the 0 cycle group was lower (84%; P < 0.05) than the 1 (90%) or > 3 (94%) estrous cycles groups, and tended to differ (P < 0.1) from the 2 (88%) and 3 (89%) estrous cycle groups. Interval from start of breeding to calving was 3- to 5-day longer (P < 0.05) for the 0 cycle group (300 ± 1 day) than other groups. Proportion of heifers calving in the first 21 day was less (P < 0.05) in the 0 or 1 cycle groups than other groups. Pregnancy rates of 2-year old cows (n = 898) were lowest (P < 0.05) for the 0 (73%) and 2 (79%) estrous cycle groups, than the 1 (85 %), 3 (90%), or > 3 (92%) estrous cycle groups. Restricted level of feeding during post-weaning development resulted in greater (P < 0.05) proportion of heifers in 0 cycle group and lower (P < 0.05) proportion in > 3 cycle group, but reproductive performance was not influenced (P > 0.1) by level of feeding or interaction of feeding and estrous cycle grouping. In summary, date of birth and rate of physical maturation (weight, height, and fat deposition) were associated with timing of puberty. Pregnancy rate was greater in heifers that exhibited estrus before start of breeding, but did not improve from having more than one estrous cycle. Proportion conceiving early was greater for heifers having 2 or more cycles before breeding.