Nitrogen conservation by ponies fed a low -protein ration
Houpt, T.R.; Houpt, K.A.
American Journal of Veterinary Research 32(4): 579-588
1971
ISSN/ISBN: 0002-9645 PMID: 5110116 Document Number: 42197
Two mature female ponies of Shetland type, initially weighing 110 kg and 136 kg, were used to measure retention of urea N. During most of the experiments they were fed on wheat straw supplemented with sucrose. Both ponies lost weight slowly and plasma urea concentration decreased. Urea balance was estimated in the first pony after 7.8 g urea N in 0.5% NaCl solution had been given by intravenous injection; a recovery period followed the administration of urea. Twenty-four hours after injection, 6.8 g urea N was excreted in urine, 2.1 g remained in body fluids, and 1.1 g was unaccounted for and presumed to be utilised in protein synthesis by the pony. A series of 7 similar experiments were done with this pony with different feeding and water intakes. Utilisation of urea was less when the pony was given straw to appetite or when the amount of straw was severely reduced, and best when moderate amounts of straw with sucrose were given. With a ration of hay and oats there was little or no utilization of urea N. Restricting water intake gave considerably better utilization of urea N than with unrestricted water. Single-injection experiments with the second pony were done by injecting intravenously, in 5 to 20 min, 20 to 45 g urea as a 25% solution in 0.5% NaCl. Urea utilization hour by hour also was measured in the second pony while urea was infused continuously. The experiments were done while the pony was fed on straw plus sucrose, or a full ration of hay and oats. In another experiment water intake was restricted, while a further study was after oral administration of alimentary antibacterial agents. In the single injection experiments a low-protein ration of straw and sucrose promoted utilization of urea N to the extent of 0.6 g/h; this fell to 0.4 g/h on full feeding with hay and oats and rose to 0.8 g/h after water deprivation. Antibacterial treatment completely inhibited utilization of urea N. The continuous injection of urea when the pony was given the low-protein ration gave utilization of 0.5 g urea N/h.