Protein and starch digestion in steers fed feedlot diets differing in extent of protein degradation

Abstract

Twelve steers fistulated in the rumen and duodenum were allocated to one of three diets and fed 80 g DM/kg WO.75/d. The diets consisted of about 80% maize meal, 11% cottonseed hulls and either 1.44% urea (Treatment A), 0.96% urea (Treatment B) or 0.47% urea plus 5.6% fish-meal (Treatment C) as protein supplements. Passage and apparent digestion of protein and starch in the digestive tract were studied using Co-EDTA and Na-dichromate as fluid and particulate markers, respectively. A higher (P ~ 0.05) proportion of the dietary protein and starch was apparently digested post-duodenally in steers on Treatment C than in steers on Treatments A and B. Also, duodenal lysine flow was greatest with Treatment C. It is suggested that the supply of amino acids to the small intestine may be inadequate on diets with a UDP content of less than 35 to 40% of crude protein (Treatment C).

Twaalf osse toegerus met rumen- en duodenale fistels is toegeken aan een van drie diete en is teen 80g DM/kg WO.75 / d gevoer. Die diete het uit ongeveer 80% mieliemeel, 11% katoensaaddoppe en onderskeidelik 1.44% ureum (Behandeling A), 0.96% ureum (Behandeling B) en 0.47% ureum plus 5.6% vismeel (Behandeling C) as proteYensupplemente bestaan. Deurvloei en skynbare verteerbaarheid van proteYenen stysel in die spysverteringskanaal is bestudeer met behulp van onderskeidelik Co-EDTA en Na-dikromaat as vloeistof- en partikulere merkers. Meer proteYenen stysel (P ~ 0.05) is skynbaar mi die duodenum in osse op Behandeling C verteer as in osse op Behandelings A en B. Voorts was die vloei van lisien na die duodenum in osse op Behandeling C ook hoer. Die afleiding is gemaak dat aminosuurvoorsiening na die dunderm onvoldoende kan wees op diete waar die NDP-inhoud minder as 35 tot 40% van ruproteYenis (Behandeling C).