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Washington State University,2, Pullman 99164
Abstract
Two trials were initiated to evaluate the proportions of wheat straw that could be used successfully in winter diets of dry, pregnant beef cows. In addition, barley and(or) soybean meal-urea supplements to replace alfalfa hay as a supplement of wheat straw-diets was studied. In trial 1, 92 Angus cows, 3 yr old or older, in the final third of gestation, were randomly assigned to one of the following treatments: (1) 100% alfalfa hay (17.0% crude protein); (2) 67% alfalfa hay + 33% wheat straw (3.4% crude protein); (3) 33% alfalfa hay + 67% wheat straw, and (4) 75% wheat straw + 25% barley-urea (22.6% crude protein). Average daily dry matter intakes/cow during the 100-day wintering trial were 6.8, 6.9, 6.7 and 7.4kg for treatment groups 1, 2, 3 and 4, respectively. Cows wintered on diet 1 lost less weight (P<.05) from the beginning of the trial to 48 h postcalving than cows on treatments 3 or 4. After calving, all cows were fed 11.7 kg alfalfahay/d until they were placed on spring pasture. Cows were bred by artificial insemination at each observed estrus for 90 d postpartum. There were no differences (P>.05) attributable to winter treatment in days to first estrus or postpartum interval to conception. Cows wintered on diet 2 had a higher (P<.05) conception rate than cows on diets 3 and 4. Conception rates were 81.8, 90.5, 59.1 and 64.0% for cows fed diets 1, 2, 3 and 4, respectively. In the second trial 60 Angus cows were wintered on the following treatments: (1) 67% smooth bromegrass-alfalfa hay (9.1% crude protein) + 33% wheat straw; (2) 87% wheat straw +13% soybean meal, barley, urea supplement (53.3% crude protein); (3) 33% bromegrass-alfalfa hay + 67% straw and (4) 75% wheat straw + 25% barley-urea (12.7% crude protein). The first three diets were formulated to supply 80% and diet 4 to supply 100% of the cows' TDN requirements. Average daily dry matter intakes/cow were 6.8, 6.9, 7.4 and 8.8 kg for groups 1, 2, 3 and 4, respectively. Cows wintered on diets 2 and 4 gained more (P<.05) weight precalving than cows fed diet 3. Weight loss to 48 h postcalving was greater (P<.05) for cows wintered on diet 3 than for cows fed diets 1 and 4. Cows fed diet 3 took longer (P<.05) to reach first estrus than cows fed diet 4 (50.4 vs 36.1 d). Conception rates for cows fed the four diets were 54.6, 80.6, 66.5 and 78.8%, respectively, and they were not different (P>.05). There were no differences in calf performance in either trial. Dietary crude protein did affect (P>,01) in vitro dry matter disappearance (DMD). Higher crude protein diets had higher in vitro DMD. TDN intakes calculated from these in vitro DMD were 91, 77, 64 and 75% of suggested requirements for cows fed the four diets in trial 1 and 61, 64, 57 and 86% for those fed the four diets in trial 2. Weight changes up to 48 h postcalving were related (P<.05) to apparent digestible dry matter intakes (DDM). The relationship (R2 = .41) is described by the equation, weight change = -97.1 + 20.7 DDM. On the basis of these results, a daily crude protein requirement of at least .65 kg is suggested for 460 to 480 kg cows wintered on high wheat straw diets.
1 Scientific Paper No. 5744. College of Agriculture Research Center, Washington State Univ. Work conducted under Project 0414.
3 The authors wish to thank D. J. Coonrad, Beef Herdsmanager, for care of the animals and assistance in data collection.
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