The orotic acid concentration in the blood, milk, and urine of dairy cows fed with urea supplemented diet

Response of renal orotic acid and creatinine to treatments affecting metabolic protein supply of ruminants

90 urine samples obtained in three lamb trials and one experiment using adult wethers were analyzed for their contents of orotic acid and creatinine. The average daily excretion of orotic acid accounted for 0.5 mg to 1.5 mg (35 micrograms to 130 micrograms/W0.75) with a high individual variation. Correlation coefficients between orotic acid and other urinary constituents were low indicating an entirely different response to metabolic variations. There was only a weak relationship to live weight, protein retention and rumen fluid traits. Defaunation reduced the orotic acid excretion (significant in the adult wethers) whereas the addition of rumen-protected lysine as well as the use of different dietary carbohydrate sources were without effect. The urinary excretion of creatinine increased with live weight and age from 0.4 g/d in the 20 kg lambs to 1.7 g/d in the adult 53 kg wethers. The correlations with live weight were close whereas the apparently negative correlation with protein retention was not real as could be evaluated by calculation of the partial correlations. There was a close correlation of creatinine with total N, urea and allantoin. Neither defaunation nor rumen-protected lysine and the kind of carbohydrate source had significant effects on creatinine. The use of orotic acid and creatinine as indicators of metabolic disorders were discussed. Easy application in practical diagnosis without quantitative urine collection might be possible by the determination of orotic acid in the milk of cows and of the creatinine/N ratio in urine.

[Purine and pyrimidine metabolites for the estimation of rumen metabolism: HPLC analysis in milk and blood plasma]

In milk and blood plasma samples of 6 German Simmental and 12 German Black and White heifers it was investigated, whether purine and pyrimidine compounds are suitable indicators of the microbial protein synthesis in the rumen. Therefore the secreted quantities in milk and the concentration in blood plasma are correlated with energy intake. The results indicated significant correlation coefficients for both the secretion quantity of allantoin in milk (r = 0.942) and the concentration of allantoin in blood plasma (r = 0.694). Other investigated compounds appeared more suitable for evaluating the mammary gland metabolism (uridine-lactose synthesis, pseudouridine-protein synthesis). In an experiment with 7 male castrated pigmy goats subjected to a four-day fasting period the decrease of plasma allantoin, which was already apparent after 12 hours of fasting, was closely correlated with the increase of plasma free fatty acids.