Summary Intakes of milk and milk nutrients were determined for 8 foals at 11–18 days of age and for 10 foals at 30–44 days and 60–74 days of age while sucking grazing mares. Water intakes (sources other than milk) of the foals were determined at 30–44 days and 60–74 days of age. Five of the 10 mares were fed a protein supplement (24% crude protein) in addition to grazing during the stud season. The protein supplement did not influence foal intakes of milk and milk nutrients, milk composition, weight gains of the mares or the growth rate of the foals. Foal milk intakes increased (P<0.05) from 16.9 kg/day at 11–18 days to 18.1 kg/day at 60–74 days of age. The water intakes of the foals increased (P<0.01) from 3.9 kg/day at 30–44 days to 5.5 kg/day at 60–74 days of age. Total fluid intakes per kg foal liveweight were 246, 202 and 172 g at 11–18, 30–44 and 60–74 days of age, respectively. For each kg of weight gain, foals consumed 12.8, 15.7 and 16.4 kg milk at 11–18, 30–44 and 60–74 days of age. Stage of lactation had a significant effect on the total solids, lactose and protein content of milk. The fat and gross energy content of milk remained constant.

The dynamics of N metabolism in mature horses were investigated when they were fed on a low-N diet or the same diet supplemented with sufficient urea or soyabean meal to meet their theoretical N requirements. There were no differences in DM, organic matter or neutral-detergent-fibre digestibilities for the three diets. N digestibilities and digestible-N intakes were similar for the urea-and soyabeansupplemented diets and very low for the low-N diet. For all three diets plasma urea was degraded in the digestive tract to NH, which was utilized by the bacterial population as a N source. NH, was absorbed from the large intestine into the blood and converted to urea. NH, was also incorporated into plasma proteins. The horses fed on the low-N diet degraded a greater proportion of endogenous urea in the digestive tract than did horses fed on the urea-or soyabean-supplemented diets. However, the horses fed on the urea diet had the highest degradation rate of urea. The quantity of urea degraded in the digestive tract of horses fed on the urea-supplemented and the low-N diets could not compensate for a lack of dietary crude protein in these diets. The horses were in a negative N balance when fed on the low-N and urea-supplemented diets and a positive N balance when fed on the soyabean-supplemented diet. Dietary urea supplementation did not benefit the horses. Urea: Nitrogen metabolism: HorseThere is some debate concerning the horse's ability to utilize urea. At present it is not known if dietary urea supplementation has a place in the horse industry, particularly in the case of mature horses grazing poor quality pastures. It has been shown that endogenous urea is degraded in the large intestine and the proportion of endogenous urea degraded increases with low-protein diets (Houpt & Houpt, 1971;Prior et al. 1974). These results indicate that horses utilize some endogenous urea and therefore it is possible that supplementary urea may be of nutritional benefit.The aim of the present experiment was to investigate the utilization of urea in the large intestine of the mature horse and to provide further information on the dynamics of N metabolism in horses fed on low-and adequate-protein diets. METHODS AnimalsThree adult geldings, two Standardbreds and one Arabian (average weight 400 kg), aged between 5 and 7 years were each surgically fitted with two polyvinyl chloride (PVC) cannulas which had an outside diameter of 15 nun and an internal diameter of 10 mm. One

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