EFFECT OF VARYING TIME OF NUTRIENT INTAKE DURING TWO PRODUCTION STAGES ON PRODUCTIVITY OF TWO-YEAR-OLD BEEF HEIFERS (POSTPARTUM, MILK PRODUCTION, ENERGY)

Three experiments were conducted using medium frame crossbred heifers to study the effect of rate and time of weight gain during the last trimester of gestation and early lactation on the productivity of heifers. In experiments 1 and 2, heifers were fed to gain according to one of three treatments based on the National Research Council (NRC) 1984 recommendations for an approximate 90-d period prior to parturition: (1) 1.2 kg (.) head(\u27-1) (.) d(\u27-1) gain for 45 da followed by no gain for 45 d; (2) .6 kg (.) head(\u27-1) (.) d(\u27-1) gain for the entire period; (3) no gain the first 45 d followed by 1.2 kg (.) head(\u27-1) (.) d(\u27-1) gain for the last 45 d. Deuterium oxide dilution did not appear to be a reliable method for measuring condition in pregnant heifers. Heifers that gained at an accelerated rate for a short time produced more milk (P \u3c .05) in early lactation than heifers that gained at a slower rate. Reproductive performance was similar for all treatment groups. The effect of varying time of nutrient intake during the first 90 d of lactation was studied in the third experiment. Forty heifers were individually fed in three treatments for 90 d postpartum, (1) 130% of the 1984 NRC recommendations for energy and protein for 45 d followed by 70% of NRC for 45 d; (2) 100% of NRC for 90 d; and (3) 70% of NRC for 45 d followed by 130% of NRC for 45 d. Heifers fed 130% NRC maintained their weight during the first 45 d of lactation while the other heifers lost weight during this period. Calf weight gains did not reflect the differences in milk production and were unaffected (P \u3e .10) by dam nutrition. Reproductive performance was not different (P \u3e .10) among heifers. These results indicate that neither of the alterante feeding systems produced superior performance when compared to feeding at a constant level, therefore, feeding at a constant level remains the recommended procedure for feeding heifers during late gestation and early lactation