Studies in ruminant nutrition with particular reference to non-protein-nitrogen utilization

Section 1 of this thesis gives a review of the use of urea as a non-protein-nitrogen source in ruminant nutrition together with a description of the major biochemical reactions in the ruminant associated with an increase in the dietary intake of urea. The potential toxicity of urea is discussed. In Section 2 the analytical methods available for the determination of ammonia in biological tissues (blood, rumen fluid and milk) are reviewed and the analytical techniques used have been described and evaluated. In particular, a modified technique involving the use of an ion-exchange resin was found to be the best procedure for the analysis of large numbers of blood samples. Section 3 describes the formulation and manufacture of a molassed sugar beet pulp nut containing added urea, phosphate, trace elements and vitamins and containing about 17% crude protein and about 0.5% P considered suitable for a wide range of purposes in ruminant feeding, A series of experiments indicated that the rate of release of urea in the rumen from such a product was slower and caused a reduced degree of ammonia production than was the case for a barley nut containing an equivalent amount of urea. Section 4 describes the use of this supplemented sugar beet product as a major component of the milk production concentrate fed to dairy cows. In four of five trials where the material was used in 25-50% substitution of a barley/vegetable protein mixture entirely comparable yields of milk of similar composition were obtained. The product was shown to be completely non-toxic and was well accepted by cattle. In Section 5 a series of experiments describe the results of trials where the supplemented sugar beet pulp formed 50% of an all-concentrate diet fed to growing cattle. When compared with the more normal 85% cereals + 15% protein supplement type of diet virtually identical daily liveweight gains were recorded but there was a reduction of some 5% in food conversion efficiency. In Section 6 three experiments with housed ewes are described. Inclusion of urea in the sugar beet nut was shown to give improved and fully satisfactory liveweight gains in ewes during pregnancy, fully adequate birthweights in lambs and satisfactory liveweight gains. Balance trials were conducted to assess the extent of utilization of dietary urea in late pregnancy. The performance of the ewes and their lambs was shown to be related to the changes in plasma urea and free fatty acid concentrations recorded during the period of the trials. Section 7 describes a number of investigations concerning experimentally induced urea toxicity in sheep. Starvation was found to have an important effect on increasing the potential toxicity hazard. Investigations were conducted to assess the effects of certain combinations of amino acids when administered intravenously for both the protection and alleviation of urea toxicity in sheep. When the liver function of sheep was progressively impaired by oral administration of either carbon tetrachloride or copper sulphate over a long period, the sheep were demonstrated to be increasingly susceptible to urea toxicity