Rebreeding efficiency comes down to three key words: body condition score.
Body condition score (BCS) is a numeric estimate of the amount of fat on the cow’s body. BCS ranges from 1 to 9; 1 is emaciated, while 9 is extremely obese. A change in a single BCS, 4 to 5 for example, is usually associated with about a 75 lb. change in body weight. Evaluating BCS prior to calving, and from calving to breeding, is important to ensure reproductive success.
Rebreeding performance of cows is greatly influenced by BCS at calving. Cows that are thin (with a BCS score of less than 5) at calving take longer to resume estrous cycles, and therefore are delayed in their ability to rebreed. Females with a pre-calving BCS of less than 5 tend to have production cycles greater than one year. South Dakota research shows the influence of pre-calving BCS on the percentage of cows that initiated estrous cycles after calving. The trial demonstrated that the percentage of thin cows that were cycling in the first month of the breeding season was considerably lower than for cows that were in more moderate body condition. During the second month of the breeding season, 55% of the cows with a BCS score of 4 still had not initiated estrous cycles while more than 90% of the cows in more moderate condition had begun to cycle. Thin cows need a longer breeding season, resulting in more open cows in the fall. Their lighter weight might also result in lighter calves at selling time next year because the calves will be born later in the calving season.
Managing BCS after calving also impacts rebreeding efficiency. Maintenance requirements for energy and protein increase 25%–30% for most beef cows after calving. Plan supplementation to match or exceed the increased nutrient requirement. Rebreeding efficiency is enhanced in cows that calved thin if their energy intake is increased.
While the best management plan is to calve cows in a BCS of 5+, increasing the energy to cows that are thin at calving can boost reproductive performance.