NUTRITIONAL MANAGEMENT OF REPLACEMENT BEEF HEIFERS - A REVIEW

Systems to produce replacement heifers to calve initially at 2 yr of a ge and at 12-mo intervals thereafter require integrated forage-animal management plans. The process of developing heifers as replacements mu st begin during the cow-calf production phase. Age and weight at puber ty are affected by several factors, including breed of livestock. Gene rally, breeds of a larger size at maturity are older and heavier when reaching puberty. Heifers that are kept as replacements must be weaned at relatively heavy weights in comparison to their expected mature bo dy size without becoming obese. Excessive adipose tissue in heifers du ring the preweaning phase may result in reduced subsequent performance of these animals. Several management techniques were reviewed that ca n be used both pre- and postweaning, including using anthelmintics, an abolic growth implants, and ionophores. Anabolic growth implants can i ncrease heifer rates of gain and increase pelvic size. In addition, th ere are indications that these implants may alter mammary gland develo pment, which may subsequently increase milk production. Ionophores wer e shown to increase growth rates, particularly in grazing heifers but more importantly to decrease age at puberty. Age and weight at puberty have been shown to be affected by level of nutrition. It is preferabl e for heifers to reach puberty one or two estrous cycles before the br eeding season, and the breeding season for heifers should begin greate r-than-or-equal-to 21 d before the breeding season of the mature cow h erd. This time difference allows for the generally longer postpartum i nterval for primiparous cows than for multiparous cows. Because of the limited opportunities (every 12 mo) for cows to calve, optimum effici ency must be pursued.