Factors Influencing the Secretion of Nitrogen in Sheep Saliva

Abstract

SUMMARY.Qnantitative measnrements were made on the volume of saliva secreted hourly b>' the parotid glands of merino sheep over a period of 24 hours on three separate days. At the same time fluctuations in the concentration of urea and total nitrogen in the saliva were studied in relation to the production of ammonia in the rumen and changes in tlie level of blood nrea that occurred throughout the day.Both the rnmen ammonia and tlie blood urea levels followed a relatively simple cyclical pattem over each 24-hour period. However, two distinct pha.ses were apparent in the sahvary nitrogen cycle. The first, a short phase, followed the stimulation changes associated with eating. The second phase was prolonged and more complex. It was influenced by changes in the level of blood urea, bnt additional factors also operated in the second phase.Changes in the second pha.se of the salivary nitrogen cycle have been discussed in relation to fluctuations in the concentration of rumen ammonia and blood urea.INTRODUCTION.

Nitrogen metabolism in the ovine stomach: 1. The transfer of urea from the blood to the rumen

“…Saliva, therefore, would only have affected the results obtained with conscious sheep if the quantities secreted differed appreciably between animals given the chaffed hay and GGP diets. This was not evident from the experiments with anaesthetized sheep, although the rates of secretion were uniformly low in comparison with other studies (Kay, 1960;Somers, 1961), and may not be applicable to the experiments with conscious animals. Nevertheless, the plasma urea levels were generally higher in sheep maintained on the GGP diet, thereby enhancing the salivary contribution of urea to the rumen.…”

“…This relationship did not differ between sheep. In addition, no upper limit to the secretion of urea in saliva was evident which would compare with the limit indicated by the studies of Somers (1961) at plasma levels of 30 mgN/100 ml for ovine parotid secretions. Saliva, therefore, would only have affected the results obtained with conscious sheep if the quantities secreted differed appreciably between animals given the chaffed hay and GGP diets.…”

“…A number of factors may influence the level of ammonia in the rumen. Urea can be transported to the rumen in saliva (McDonald, 1948;Somers, 1961) and by direct passage across the epithelium (Houpt, 1959;Packett & Groves, 1965;Houpt & Houpt, 1968). XJrease activity in the rumen ensures that urea reaching this organ intact is rapidly hydrolysed to ammonia and carbon dioxide (Pearson & Smith, 1943), while ammonia can be absorbed into the blood (McDonald, 1948).…”

“…of urea into the organ. Urea can enter the rumen in saliva (McDonald, In the work now reported the effects of diet, 1948; Somers, 1961), and by transfer across the prevailing levels of rumen ammonia and plasma rumen wall (Houpt, 1959;Packett & Groves, 1965; urea, and starvation have been examined for their Houpt & Houpt, 1968). In recent years attention effects on the transfer of blood urea to the rumen, has been turned to factors which regulate this transfer Many studies have indicated that a limit EXPERIMENTAL PROCEDURE is set to the passage of urea into the rumen at high levels of blood urea Nineteen Clun Forest wethers of 1-3 years of age Vercoe, 1969; Thornton, and weighing 30-61 kg were used.…”

The origin of the metabolic fecal nitrogen in relation to protein requirements

“…Therefore, these data show that not only is there a back ground level of endogenous nitrogen in the gut, but also that there is The second source of nitrogen available to rumen microflora is from the blood system. As mentioned earlier, saliva enters the rumen in association with the actual feed, or due to a feeding reflex, but the nitrogen constituents did have the blood as their source (McDonald, 1948;Somers, 1961). Another route of nitrogen entry into the rumen is a direct transfer across the rumen wall as urea (Houpt, 1959;Packett and Groves, 1965;Houpt and Houpt, 1968).…”