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Nitrogen Metabolism of Steers Fed Suncured Hay and Drum Dehydrated Alfalfa and Coastal Bermuda Grass

University of Georgia, Athens and US Department of Agriculture, Athens 30602

Abstract

Four ruminally- and abomasally-cannulated steers were used in a 4 x 4 Latin square design experiment to determine the influence of heat dehydration of Coastal Bermuda grass (CBG) and alfalfa (Alf) on: a) protein and fiber digestibility, b) quantity of protein and amino acids reaching the abomasum, c) microbial protein synthesis and d) digestibility of the nitrogen fraction(s) present in neutral and acid detergent fiber. Treatments were a) CBG-hay (CBG-H), b) CBG-dehydrated (CBG-D), c) Alf-hay (Alf-H) and d) Alf-dehydrated (Alf-D). Apparent digestion of dry matter (DM), acid detergent fiber (ADF) and cellulose were higher in CBG than in Alf and appeared to be related to differences in lignin content of the two forages. Total crude protein (CP) and forage protein recovered from abomasal digesta were greater (P<.05) in Alf-D and CBG-D than in the corresponding hays; CP equivalent from ammonia in the abomasal digesta was reduced in CBG-D and Alf-D (P<.05). Bacterial protein recovered from the abomasal digesta was decreased from steers receiving both dehydrated forages (P<.05). Total grams of all individual and total essential amino acids, except methionine and lysine, recovered from the abomasal digesta of steers fed CBG-H or Alf-H were significantly less than amounts fed; whereas for the dehydrated forages only the amounts of histidine, arginine and leucine from CBG-D and histidine, arginine, leucine and valine from Alf-D were reduced by rumen fermentation. Acid detergent insoluble nitrogen (ADIN) as a percentage of forage DM was higher in CBG-D (.27%) than in CBG-H (.12%), but no change was noted with alfalfa. Neutral detergent insoluble nitrogen (NDIN) was higher in CBG (1.1%) than alfalfa (.49%), but was also more digestible. Results indicate that heat dehydration of forages is an effective method for decreasing rumen degradation of the protein, increasing amino acid supply available for absorption and that digestibility of ADIN and NDIN may be closely related to fiber digestibility.

¹ Dept. of Anim. and. Dairy Sci.

² Richard B. Russell Agricultural Research Center, Athens, GA.