I recommend starting the breeding season for heifers about one month ahead of the mature cows. Assuming most replacements are selected from heifers born in the first two months of the calving season, the heifer breeding season will start when they are 12 to 14 months of age.

Age and body weight are the two most important drivers for the onset of puberty. Most Angus heifers can reach puberty by 1 year of age if they attain 55-60% of their mature weight. Some heifers will reach puberty at a lighter weight, but to be on the safe side, I recommend aiming to have heifers weigh 60% of their expected mature weight by 12 months of age. For heifers that will have a mature weight of 1,200 pounds (lb.), they will need to weigh 720 lb. Heifers that mature at 1,400 lb. will need to weigh approximately 840 lb. in order to reach puberty.

Depending on weaning weight and mature weight, heifers typically need to gain between 1.25 and 1.75 lb. per day (some will require up to 2.25 lb. per day) between weaning and breeding to reach their target weight. While heifers don’t need to be fed a high-concentrate diet to reach these required gains, heifers grazing dormant forage or being fed good-quality hay will need to be supplemented with some grain or byproduct feeds in order to meet targeted weight gains.

The two greatest obstacles to reach puberty in a timely manner are poor quality forage and severe winter weather. When these two factors occur in the same year, weight gains from weaning to breeding can be less than necessary to have a high percentage of heifers become pregnant early in the breeding season. While short-term nutritional challenges associated with isolated storms are not likely to have negative effects, longer-term nutritional challenges from poor quality or quantity of forage or several weeks of wet and cold temperatures can delay the onset of puberty.

To ensure heifers are ready to breed at the start of the breeding season, I recommend at least a subset be weighed at least once (and preferably more often) between weaning and yearling age. If the heifers are not meeting their targeted weight gains, the ration should be adjusted to allow them to reach 60% of their mature body weight by 12 months of age.

Once puberty is attained, nutrition must be at a level that allows the heifer to continue cycling, ovulate a fertile egg and establish pregnancy. Nutritional demands of heifers during pregnancy exceed that of mature cows because the heifer is also using nutrients for her own growth as well as fetal growth and development. Deficiency of energy or protein for extended periods of time during any production phase will have a negative effect on fetal development, calf viability, milk production, and/or rebreeding for the next pregnancy.

Proper nutritional development of heifers from weaning to breeding is essential to ensure that a high percentage of heifers become pregnant early in their first breeding season. For spring-calving herds in much of the United States, that time coincides with winter weather and dormant forage. These constraints call for producers to carefully monitor heifer growth and to be ready to adjust rations if necessary to meet target breeding weights.

Editor’s note: Robert L. Larson is a professor of production medicine and executive director of Veterinary Medicine Continuing Education at Kansas State University in Manhattan, Kan.