Abstract
Four Holstein steers fitted with cannulae in the rumen and duodenum were grazed on orchardgrass (Dactylis glomerata L.) pasture to examine the effect of pre-grazing sward length and daily herbage allowance on ruminal nitrogen (N) digestibility and duodenal non-ammonia nitrogen (NAN) supply. Pasture maintained at two levels of daily herbage allowance of 50 and 100gDM/per kg BW of steers and two levels of sward length (35 and 25 cm) were allocated to four treatments in a 2×2 factorial design. N content of herbage did not significantly differ between sward lengths but declined when the daily herbage allowance was high (P<0.01). N intake increased in the short sward pasture than in the long sward pasture (P<0.05). However, the duodenal NAN flow was greater in the long sward pasture than in the short sward pasture (P<0.01), because the microbial N synthesis in the rumen and the ruminally undegraded N flow to the duodenum significantly increased in steers grazing on the long sward pasture (P<0.01). The amount of post-rumen N disappearance increased when steers grazed the long sward pasture compared with the short sward pasture (P<0.01).
