Amino acid digestibility of canola meal estimated with pulse-dose in dairy cows or roosters.

Intestinal digestibility of ruminally undegraded feed protein (RUP) is needed to formulate dairy rations adequately. Thus, our objective was to compare estimates of amino acid (AA) intestinal digestibility of canola meal rumen residues (CMr) using a pulse-dose in dairy cows or caecectomised roosters. Four cows received a pulse-dose of 40 g 15N-labelled CMr (15N-CMr) into the duodenum. The faeces were collected continuously for 28 hours. The digestibility was estimated from cumulative fecal recovery of 15N-AA. In parallel, caecectomised roosters were used to determine the intestinal digestibility of 15N-CMr. All intestinal digestibility coefficients estimated using the pulsed-dose method were lower than when estimated with the roosters (Table 1). For the pulse-dose method, only His had digestibility greater than 75% whereas none of the coefficients were below this value for the rooster method. The relatively large standard deviation associated to the pulse-dose method could indicate the technical difficulty associated to the use of large animals, especially to collect all the feces excreted, given that the IE was less variable between animals. On the other hand, coefficient of digestibility obtained with the caecectomised roosters method could be inflated by the assumption that the endogenous secretion is similar between fasted and fed birds. Nevertheless, both methods indicated that the RUP intestinal digestibility of 75% used by NRC (2001) seems an adequate digestibility of the rumen CMr. The reason for the reduction of the estimated MP supply when CM substitutes another protein source is therefore not caused by the low digestibility of RUP used by NRC (2001).