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Effect of Supplementation of Wheat Straw Diets Twice a Day on Rumen Ammonia, Volatile Fatty Acids and Cow Performance¹

Washington State University^,2, Pullman 99164

Abstract

Effects of low quality roughage, multiple feeding of supplement and various energy intakes on ruminal characteristics and beef cow performance were examined in related trials. In trial 1, four rumen-fistulated cows were fed four diets in a Latin square design. The diets were: (1) smooth brome-alfalfa hay; (2) wheat straw (WS); (3) WS + pelleted supplement fed once daily and (4) WS + pelleted supplement fed twice daily. Diet affected (P<.05) ruminal ammonia, VFA concentrations and pH. Mean ruminal ammonia was 2.7, .0, 7.6 and 14.5 mg/dl with treatments 1, 2, 3 and 4, respectively. Mean concentration of total VFA was 102, 65, 75 and 83 µmol/ml, respectively. Mean values for ruminal pH were 6.37, 7.15, 6.93 and 6.71, respectively. In trial 2, diets 1, 3 and 4 were fed to 61 dry pregnant beef cows at three energy intakes: (100) 100% TDN requirement; (80 to 100) 80% TDN requirement through d 255 of gestation period, then raised to 100% TDN and (80) 80% TDN requirement. On d 275 of gestation, cows were assigned to either 100% gestation or 100% lactation energy requirements and maintained on these diets until 30 d postcalving. Precalving average daily gain (ADG) was lowest (P<.05) for cows receiving 80% of their TDN requirement. Diet affected precalving ADG, with values of .54, .11 and .29 kg for cows fed hay, straw + supplement once daily and straw + supplement twice daily respectively. In addition to precalving ADG, hay fed cows had a lower (P<.05) weight loss 48 h postcalving, higher (P<.05) milk production 30 d postcalving, higher calf weights at 30 and 60 d and a shorter interval to conception. There were no interactions between diet type and energy intake on precalving and postcalving treatments.

¹ Scientific Paper No. 5896. College of Agriculture Research Center, Washington State Univ. Work conducted under Project 0414 and 0464.

² Dept. of Anim. Sci.

³ The authors wish to thank D. J. Coonrad, Beef Herdsmanager, for care of the animals and assistance in data collection and Dr. C. T. Gaskins for help with the statistical analysis.