Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 10, 2009
Publication Date: June 15, 2009
Citation: Muliniks, J.T., Cox, S.H., Kemp, M.E., Endecott, R.L., Waterman, R.C., Vanleeuwen, D.M., Petersen, M.K. 2009. Impact of body condition score on reproductive performance in young postpartum range cows grazing native range. Western Section of Animal Science Proceedings 60:81-84. Interpretive Summary: Postpartum interval can have a major economic impact on cow/calf producers in the terms of cow productivity. Mature cows tend to be more resilient and have a shorter postpartum interval than young cows; therefore, a prolonged postpartum interval is more frequent in young cows because of the additional demands for continued growth combined with the stress of lactation. Thus, prepartum body energy reserves can be very important for the resumption of luteal activity and also be a useful indicator of nutritional status and reproductive efficiency (i.e., days to first estrus and pregnancy rates) in young cows. Guidelines suggest that young cows need to be in a BCS > 6 for optimal reproductive performance. Therefore, the objective was to determine the effects of BCS at calving on pregnancy rates, days to first estrus, nutrient status assessed by blood metabolites and calf BW change in 315, 2- and 3-yr-old cows grazing native range. Another objective was to determine the interaction of rainfall on reproductive performance, nutrient status, and calf BW in young beef cows. Body conditions score at parturition, in this study, was not a dominant factor influencing reproductive performance. However, body condition score did tend to interact with annual rainfall. All groups of BCS had a tendency to respond the same in years with above average annual rainfall; consequently in below average rainfall years, cows in a lower BCS tended to be more resilient from the increase in environmental stress which allowed for a decrease in days from parturition to first estrus. With the variability in annual rainfall pattern of arid climates in the southwestern United States, cows in a BCS 4.0 to 4.5 may be more practical to producers on the basis on being more reproductively efficient and more resistant to environmental changes than cows with a higher body condition.
Technical Abstract: Body condition score (BCS) is used as a management tool to predict reproduction of young beef cows. The objective was to determine the effects of BCS at calving on pregnancy rates, days to first estrus (DTFE), nutrient status assessed by blood metabolites and calf BW change in 315, 2- and 3-yr-old cows grazing native range over 5 yr at the Corona Range and Livestock Research Center, NM. Palpable BCS (1 – 9) were determined by experienced technicians prior to calving. Cows were assigned to one of four BCS treatments: Thin (T; BCS = 3.5 to 4.25), Thin-Moderate (TM; BCS = 4.5), Moderate-Fat (MF; BCS = 4.75 to 5.25), or Fat (F; BCS = 5.5 to 7.0). Postpartum supplementation was terminated each year when cows reached BW nadir. Cows were weighed weekly and serum was collected 2×/wk for progesterone analysis to estimate DTFE. Year effects were also evaluated, with years identified as either above (AA) or below (BA) average rainfall. Data were analyzed as a 4 × 2 factorial. A calving BCS × rainfall interaction occurred for DTFE (P = 0.01). In AA years, all BCS groups achieved DTFE within 86 d postpartum with F cows cycling the earliest at d 68 postpartum. In contrast, during BA years, cows with a higher BCS (MF and F) took up to 61 days longer postpartum to reach DTFE compared to cows in a thinner BCS (T and TM). Pregnancy rates did not differ between BCS (P = 0.45; 90, 95, 90, 90 for T, TM, MF, and F, respectively). Calf weights at birth (P = 0.19), branding (P = 0.27), weaning (205-d weight; P = 0.51) were not affected by cow BCS at calving. Results suggest that BCS interacts with rainfall and may not be a consistent indicator of reproductive performance in young beef cows.