Heifer Body Weight Gain and Reproductive Achievement in Response to Protein and Energy Supplementation While Grazing Dormant Range Forage

Abstract

Heifers grazing winter range require supplemental nutrients to complement dormant forage to achieve optimal growth and performance. A study was conducted to evaluate nutritional environment and effect of different supplementation strategies for developing heifers grazing dormant winter range. Eighty-four Angus crossbred heifers were stratified by body weight at weaning, allocated to one of six replicated pastures, and randomly assigned one of three supplemental treatments: 1) 908 g/d of a control supplement providing 340 g · hd -1 · d -1 of CP with 130 g of rumen undegradable protein (RUP) and 614 MJ of ME (LRUP); 2) 908 g/d of a RUP supplement providing 340 g · hd -1 · d -1 of CP with 170 g of RUP and 567 MJ of ME (HRUP); or 3) 1814 g/d of a protein and energy supplement providing 340 g · hd -1 · d -1 of CP with 120 g of RUP + 100 g of propionate salt (NutroCal TM , Kemin Industries, Inc.) and 1222 MJ of ME (LRUP + E). Body weights were taken in November, with monthly 12 h shrunk BW from January thru April, and again in September (at time of pregnancy diagnosis). Heifer average daily gain was similar throughout the developmental period except from d125 to d159 where LRUP + E supplemented heifers had greater gains (P < 0.01) than LRUP and HRUP supplemented heifers (0.33, 0.04, and 0.14 ± 0.05 kg/d, respectively). LRUP + E heifers had a greater percentage (P = 0.04) of heifers pubertal at time of artificial insemination compared to LRUP and HRUP heifers (57, 29, and 30, respectively). However, no differences were detected in overall pregnancy rates (P = 0.40). This study indicated that feeding more supplemental energy (i.e., propionate salt, ground milo and corn) allowed lightweight heifers to achieve a greater rate of gain at a key period during development and achieved comparable reproductive success to heifers only receiving supplemental protein.