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Effect of Heat Treating Alfalfa Hay on Chemical Composition and Ruminal In Vitro Protein Degradation

Agricultural Research Service, USDA, US Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706

Conventional (unshredded) and shredded alfalfa hays were heated in either a forced-air oven or a steam pressure cooker at different times and temperatures to determine the effect of heat treatment on chemical composition and ruminal protein degradability. Rates of protein degradation and extents of protein escape were estimated using a ruminal inhibitor in vitro system. Both rates and extents were corrected for the proportion of total N in ADIN. Estimated net protein escape (total escape minus ADIN-bound CP) of unshredded and shredded hays was increased by oven or steam heating. Optimal oven treatments, as indicated by the greatest increase in net protein escape, were 120 min at 150°C and 60 min at 160°C. Net protein escapes of shredded hay were greater than unshredded hay when neither was heated and when hays were heated to the same extent. Equivalent protein protection was obtained by oven heating for 120 min at 140°C, 60 min at 150°C, and 30 min at 160°C, which gave net protein escapes of 55, 54, and 54% for shredded hay and 44, 45, and 43% for unshredded hay, respectively. Similar protein protection was obtained at lower temperatures and shorter times with steam heating. Nearly optimal net protein escapes were obtained with steam treatment for 30 to 120 min at 100°C or for 15 min at 110 or 120°C. Oven heating and, especially, steam heating of hays for the longer times increased ADIN to very high percentages. These data indicated that moderate heat treatment of alfalfa hay reduces ruminal protein degradation and improves protein utilization.

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