Heifer Development

Health and Reproduction

Abstract

Replacement heifer development is a critically important area for veterinarians to offer production medicine advice to their beef-producing clients. Productivity for beef cattle herds has been shown to increase when a high percentage of heifers become pregnant early in the first breeding season.⁵⁵ A producer's heifer development program should result in most heifers in the replacement pool reaching puberty at least 42 days prior to the start of breeding because the conception rate to first service is lower on the pubertal estrus compared to the third estrus.^14,80 Many producers put additional pressure on heifers to reach puberty at a young age by breeding them 3 to 4 weeks earlier than the mature cow herd. The stress of calving is greater on heifers than older cows, and more likely accompanied by calving difficulty. Thus, breeding replacement heifers essentially one heat cycle earlier than the mature cows allows the producer to concentrate on the heifers at calving. In addition, the length of time from calving to the resumption of cycling is longer in heifers than in cows.⁹⁸ Therefore, calving heifers earlier than mature cows gives the heifers the extra time they need to return to estrus and be cycling at the start of the subsequent breeding season.

In order for heifers to reach puberty by 12 to 13 months of age they must receive adequate nutritional intake to signal the body that the "luxury" of reproduction is attainable. Once puberty is attained, nutrition must be at a level that allows the heifer to continue cycling, ovulate a viable oocyte, and establish pregnancy. Nutritional demands of heifers during pregnancy exceed that of mature cows because the heifer is partitioning nutrients for her own growth as well as fetal growth and development. This increased demand for nutrients continues through early lactation, when the beef female has her highest nutritional requirements. Deficiency of energy or protein for extended periods in any production phase during the first two and one-half years of life will impact negatively on fetal development, calf viability, milk production and/or rebreeding for the next pregnancy.