Indole and skatole are products of amino acid degradation in the rumen which could be useful to monitor protein utilisation in grazing ruminants. Two groups ("1970s" strain and "current" strain) of mixed age Holstein Friesian cows were housed indoors and fed cut pasture for 21 days. Concentrations of indole and skatole in milk fat and of milk urea nitrogen were determined. No significant differences were observed between strains of cow for indole and skatole concentration in milk fat, but they were different (P<0.01) between sampling dates. Both indole and skatole had moderate positive (r ~0.50) correlation with the rumen degradable protein (RDP) balance, whilst skatole had a weaker (r ~0.30) correlation with crude protein intake, metabolisable protein supply and RDP supply. Indole and skatole concentrations in milk fat were more closely correlated to the estimated RDP balance in the rumen than milk urea. A large proportion of individual animal variation in milk metabolites remains unaccounted for by protein intake, and may relate to individual differences in detoxification and elimination of indole and skatole.
Proceedings of the New Zealand Society of Animal Production, Volume 68, Brisbane, Australia, 23-26, 2008
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