Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
2420757 | Animal Feed Science and Technology | 2008 | 21 Pages |
The effect of increasing grass regrowth interval (RI) (28 days vs. 38 days (d)) on zero-grazed intake, rumen fermentation, in situ degradability, rumen digesta kinetics and nutrient flow to the omasum, was determined in six ruminally cannulated Holstein-Friesian steers in a 2 × 2 cross-over design experiment. Digesta kinetics was determined using the rumen evacuation technique and omasal flow was estimated using Co-EDTA, Yb-acetate and indigestible neutral detergent fibre (INDF) as digesta flow markers and purine bases as microbial markers. Increasing RI had no effect (P>0.05) on dry matter intake (DMI), total volatile fatty acid (VFA) concentration or molar proportions of VFA in the rumen but reduced (P<0.05) rumen ammonia nitrogen (N) concentrations. Rumen digestion and flow to the omasum of organic matter (OM), neutral detergent fibre (NDFom) and N did not differ (P>0.05) between the RI treatments. A higher proportion (P<0.05) of NDFom digestion occurred in the rumen with the 28 d than the 38 d RI treatment. There was no effect (P>0.05) of RI on microbial N flow or on efficiency of microbial nitrogen synthesis but the flow of non-ammonia non-microbial N was reduced (P<0.05) with the 38 d compared to the 28 d RI treatment. The digestion rate (kd), derived from the rumen evacuation technique, of DM and OM (P<0.05), and NDFom and DNDFom (P<0.01) decreased with increased RI. These results indicate that increasing the RI of a perennial ryegrass-based sward by 10 d from 28 to 38 d in spring/early summer had relatively little or no adverse effects on DMI, rumen fermentation and rumen or total tract digestion of OM and NDFom of growing beef cattle but reduced ammonia N levels in the rumen, potentially reducing nitrogen excretion to the environment.