– Steve Boyles, OSU Beef Extension Specialist
Net calf crop or number of calves weaned per cow exposed is an important calculation for commercial cow-calf producers. A 9-point system is commonly used to condition score beef cows. The importance of body condition at calving on subsequent reproductive performance has been documented extensively. Cows should have an optimum Body Condition Score (BCS) of 5 to 6 at calving that should be maintained through breeding to ensure optimal reproductive performance. The most important factor influencing pregnancy rate in beef females is body energy reserves at calving. In addition, low energy intake before calving appears to be the major culprit to reduced reproductive performance during the subsequent breeding season. Body condition score is a better indicator of the nutritional program than is body weight.
Calving Interval and Profitability: One of the major constraints in the improvement of reproductive efficiency of beef cows is the postpartum interval (PPI), defined as the period from calving until cows resume estrus activity. Calving interval, defined as the period between the birth of one calf until the birth of the next calf, is significantly affected by the postpartum interval. If a cow is to calve on a 365-day interval, with a 283-day gestation length, she has to conceive within 82 days of calving. It takes approximately 40 days for the uterus of a well managed cow to recover after calving, and this leaves a 42-day window in which to conceive. Cows that conceive within 80 days of calving tend to have a lower breakeven cost of production per pound of calf weaned than those that take more than 80 or 90 days to return to estrus.
Each time a cow is not bred during a 21-day heat cycle, it can cost up to 39 lbs of weaning weight (assuming an average daily gain on calves of 1.85 lbs/day. What do you expect for your calving season? Is it 60-25-10-5 (e.g. 60% of cows calving in first 21 days of calving season, 25% calving from day 22 to 41, 10% calving between day 42 and 62 and 5% open)? Open cows don’t produce a calf but they can at least be sold. Do the lighter calves in the 10% calved between day 42 and 62 make you money?….maybe?….. but not as much as the heavier/earlier born calves.
| Effect of body condition score (BCS) at calving on postpartum interval (PPI) | |
| BCS | PPI – Days |
| 3 | 88.5 |
| 4 | 69.7 |
| 5 | 59.4 |
| 6 | 51.7 |
| 7 | 30.6 |
| Adapted from Houghton et al., 1990 | |
Rule of Thumb #1: The recommendation is to target a body condition of 5 at calving for mature cows and 5.5 to 6 for young cows. Routinely feeding cows to achieve condition scores greater than 6 is not cost effective. A cow calving in a BCS of 5 will return an income of approximately $100 more than a cow calving in a BCS of 4.
Compared to a maintenance diet, a cow needs approximately 160 Mcal of NEg to change from a BCS 4 to a BCS 5. Corn has approximately 1 Mcal of NEg per pound; therefore, approximately 160 pounds of corn supplementation would be needed. In this example, if corn is valued at $3.00, $5.00, or $7.00 per bushel, then the added cost above maintenance to change body condition from 4 to 5 would be $8.57, and $20.00, respectively. This is far less money spent on feed than would be lost if cows were allowed to stay in a BCS of 4.
Rule of Thumb #2: It takes about 80 pounds of actual cow body weight for a mature cow to change one (±) BCS. First-calf heifers, on the other hand, require about 150 pounds to increase one BCS. The difference in weight required to change one BCS can be explained by the fact that first-calf heifers must continue to grow before they can begin improving BCS by depositing fat.
Next week we’ll explore the Effect of Energy and Protein Supplementation on Body Condition Score and Reproduction
Literature Citied
Cow-Calf Production In The U.S. Corn Belt. 2011. Midwest Plan Service. MWPS-66
Nutrient Requirements of Beef Cattle E-974. Oklahoma State University.
Rasby, R. and R. Funston. 2016, Invited Review: Nutrition and management of cows: Supplementation and feed additives. The Professional Animal Scientist 32 (2016):135–144.
OSU Beef Team. Library. https://u.osu.edu/beefteam/resource-library/