Flow of thiamin to the duodenum in dairy cows fed different rations

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Abstract
SUMMARY: Four lactating Friesian cows with cannulae in the rumen and in the proximal duodenum were subjected to each of four different dietary treatments. Treatments differed with respect to concentration of crude protein, supply of urea nitrogen and frequency of feeding. The rations used consisted of hay, maize silage and concentrates and were offered to the animals according to milk yield.During the last 5 days of each experimental period (5 weeks), ingesta flow at the proximal duodenum was estimated by Cr-EDTA. Samples were taken from the duodenum at 2 h intervals and were analysed for thiamin, total nitrogen and microbial nitrogen. Labelling of microbial N was achieved by continuous infusion of 16N-urea into the rumen.With treatment 2 (26% less N than with treatment 1) thiamin net synthesis in the forestomachs and total thiamin entering the duodenum were significantly reduced whereas treatment 3 (substitution of 26% plant N by urea-N) and treatment 4 (six times instead of twice feeding daily) had no effect on synthesis and flow of thiamin to the small intestines. There were significant linear regressions between flow of microbial N and flow of thiamin to the duodenum and between organic matter digested and flow of thiamin.

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