Title: Relationship between body condition score at calving and reproductive performance in young postpartum cows grazing native range Authors
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 2012
Publication Date: June 4, 2012
Citation: Mulliniks, J.T., Cox, S.H., Kemp, M.E., Endecott, R.L., Waterman, R.C., Van Leeuwen, D.M., Petersen, M.K. 2012. Relationship between body condition score at calving and reproductive performance in young postpartum cows grazing native range. Journal of Animal Science 90:2811-2817. Interpretive Summary: In this study, variation in body condition score at parturition was not useful in predicting reproductive success within a herd. With variability in annual precipitation of semi-arid climates and the practice of extensive management in the western United States, managing cows to a target body condition score of 4 to 4.5 rather than 5 at calving may have both financial and management benefits. Extensive and strategic range cow herd management that is implemented over time may set lower body condition score thresholds for reproductive success.
Technical Abstract: Body condition score is used as a management tool to predict competency of reproduction in beef cows. Therefore, a retrospective study was performed to evaluate association of BCS at calving with subsequent pregnancy rate, days to first estrus, nutrient status (assessed by blood metabolites), and calf BW change in 351, 2- and 3-yr-old cows grazing native range over 6 yr at the Corona Range and Livestock Research Center, Corona, NM. Cows were managed similarly prior to calving without manipulation of management to achieve predetermined BCS at parturition. Palpable BCS (1 to 9) were determined by 2 experienced technicians prior to calving. Cows were classified to 1 of 3 BCS groups prior calving: BCS 4 (mean BCS = 4.3 ± 0.02), 5 (mean BCS = 5.0 ± 0.03), or 6 (mean BCS = 5.8 ± 0.06). Cows were weighed weekly and serum was collected 2×/wk for progesterone analysis to estimate days to first estrus. Year effects also were evaluated, with years identified as either above or below average precipitation. Days to first estrus was similar among BCS groups (P = 0.93). Pregnancy rates were not influenced by calving BCS (P = 0.83; 92, 91, 90 % for BCS 4, 5, and 6, respectively). Days to BW nadir was not influenced by BCS at calving (P = 0.95). Cow BW were different at all measuring points (P < 0.01) with BCS 6 cows having the heaviest BW and cows in a BCS 4 the lightest. Cows in a BCS 4 and 5 lost more (P = 0.06) BW from the initiation of the study to the end of breeding than cows in a BCS 6. However, BW change at all other measurement periods was not different (P >/= 0.49) among BCS groups. Serum glucose and NEFA concentrations were not influenced by calving BCS (P >/= 0.51). Calf weights at birth (P = 0.60), branding (55-d weight; P = 0.76), weaning (205-d weight; P = 0.60) were not impacted by cow BCS at calving. Results suggest that variation in BCS among similarly managed animals may not be a consistent indicator of reproductive performance in young beef cows. Body condition score did not influence overall pregnancy rates, indicating that young cows can be in a lower BCS and still be reproductively punctual.