Production performance of beef cows raised on three different nutritionally controlled heifer development programs.

Abstract

The objective of this study was to determine primiparous heifer performance following three different heifer development strategies that were the result of timed nutrient limitation. Two hundred eighty-two spring-born MARC III heifers were weaned at 203+/-1 d of age and 205+/-1 kg BW. The experiment was conducted on two calf crops with 120 heifers born in 1996 and 162 heifers born in 1997. Treatments consisted of different quantities of the same diet being offered for a 205-d period. Heifers in the HIGH treatment were offered 263 kcal ME/(BWkg)0.75 daily. Heifers in the MEDIUM treatment were offered 238 kcal ME/(BWkg)0.75 daily. Heifers in the LOW-HIGH treatment were offered 157 kcal ME/(BWkg)0.75 daily the first 83 d and 277 kcal ME/(BWkg)0.75 daily for the remainder of the 205 d. Treatments differed in total ME intake (P < 0.001); heifers on the HIGH treatment consumed 3,072+/-59 Mcal/heifer, those on the MEDIUM treatment consumed 2,854+/-21 Mcal/heifer, and those on the LOW-HIGH treatment consumed 2,652+/-19 Mcal/ heifer. At the beginning of breeding, heifers on the HIGH treatment were taller at the hips (P = 0.01) and weighed more (P < 0.001) than heifers in the other two treatments. The percentage of heifers that calved expressed as a fraction of the cows exposed did not differ among treatments (89.7%; P = 0.83). The age of heifer at parturition (P = 0.74) and the time from first bull exposure to calving (P = 0.38) did not differ among treatments. Birth weight of calves (P = 0.80) and the calves' weaning weight (P = 0.60) did not differ among the treatments. Calf survival rate on the LOW-HIGH treatment (73%) was lower than that on the moderate treatment (89%; P = 0.007) but did not differ from that on the HIGH treatment (81%; P = 0.26). The second-calf pregnancy rate (92.8%) for cows with a nursing calf at the start of breeding did not differ between treatments (P = 0.83). These findings suggest that as long as heifers are growing and meet a minimal BW before mating, patterns of growth may be altered in the post-weaning period without a decrease in the ability of the heifer to conceive or a decrease in calf growth potential. However, limit-feeding heifers may decrease first-calf survival. These alterations in postweaning gain through monitoring the amount of feed offered can be used to optimize feed resources.