With the current price of replacement cattle, we must maximize the number of heifers that become productive cows. I am making the big assumption that at this stage in the game everything has gone right (the heifers weighed at least 65 percent of mature weight at breeding, they were bred to proven low-birth-weight bulls, they were culled on poor structure and small pelvic area, they were provided with adequate nutrition up to this point, etc.). But your job as a manager and caretaker of these heifers is still far from done. Heifer performance from this point forward will be determined by how well the heifer is managed up to and after the time she has her first calf.
A common statement we livestock specialists hear this time of year is, "I don't want to over-supplement these heifers or their calves will be too big, and I will have increased calving difficulty."
A University of Wyoming study (L. R. Corah, et al., Univ. of Wyoming. 1975. J. Anim. Sci. 41:819) illustrated the effects of level of nutrition on the calving performance of first-calf heifers. Heifers were divided into two groups 100 days prior to calving. One group received a ration meeting National Research Council (NRC) requirements for energy (TDN), and the other group received 65 percent of NRC requirements for TDN. Both rations were formulated to meet protein requirements. After calving, both groups received TDN and protein that met the NRC requirements. In the low-level TDN group, birth weights were reduced by about 5 pounds, but there was no reduction in calving difficulty (Table 1). Calf losses at birth were higher in the low TDN group. Weaning weight was 28 pounds heavier for the calves out of the heifers fed the higher-energy ration. The take-home message here in terms of calf production is obvious: There are more live calves with higher weaning weights produced from the heifers fed the higher TDN ration. This in itself should make the decision to supplement your heifers at an adequate energy rate an easy one to make. However, in addition to the increase in calf production, when the researchers examined the return to estrus after calving, those first-calf heifers receiving adequate energy prior to calving also came into heat sooner, allowing them the opportunity to breed earlier in the calving season. Evan Whitley, in his April 2001 NF Ag News and Views article Spring Clean Your Breeding Program, illustrated the importance of heifers and cows calving early in the breeding season.
To further illustrate the importance of nutritional status of the bred two-year-old heifer in the last trimester of pregnancy, consider that the heifer must continue to grow and gain body weight during this 90-day period. The weight of the fetus, fetal fluids, membranes, etc., will increase almost one pound per day. Therefore, to sustain her growth and the growth of the fetus she is carrying, the heifer needs to gain about 1 to 1.5 lbs. per day. The typical heifer will lose 100 to 125 lbs. when she calves (weight of the calf, fetal membranes and fluids). This weight represents about 10 to 14 percent of her body weight; therefore, she must be prepared nutritionally to handle this stress. She also must be managed differently and separately from the mature cow herd. Heifers that calve late typically breed back late. To ensure them a chance to rebreed in a timely manner and remain in your herd, separate them and feed them additional supplement as compared to your mature cow herd, or provide them with the highest-quality pasture you have available. If you have questions on heifer management, contact one of the Noble Research Institute's livestock specialists at (580)224-6501.