Cattle need physically effective fiber to promote rumination and maintain rumen health, but research suggests that economics favor the use of low-roughage feedlot diets.
Gwinyai Chibisa, Karen Beauchemin and Karen Koenig with Agriculture & Agri-Food Canada's Lethbridge Research & Development Center and Gregory Penner with the University of Saskatchewan recently investigated the optimum barley silage proportion in barley-based finishing diets for beef cattle. They published their study in the Journal of Animal Science.
The researchers used eight ruminally fistulated crossbred beef heifers in a replicated 4 x 4 Latin square design with 28-day periods. Dietary treatments were 0%, 4%, 8% and 12% of dietary dry matter as barley silage, with diets containing 80%, 76%, 72% and 68% barley grain, respectively.
Chibisa et al. measured apparent total-tract digestibility (four-day total fecal collection), chewing behavior (six-day video recording), ruminal pH (six-day indwelling pH recording) and fermentation (one day with sampling at 0, 3, 6, 12 and 18 hours post-feeding), short-chain fatty acid (SCFA) absorption, gastrointestinal tract barrier function and blood variables.
According to Chibisa et al., increasing the proportion of barley silage decreased dietary starch content from 49.0% to 43.1% of dry matter, while neutral detergent content increased from 22.7% to 25.1% of dry matter. Silage proportion had no effect on dry matter intake, Chibisa et al. reported, but apparent dry matter digestibility decreased quadratically: 86.0%, 82.1%, 81.1%, 79.5% for the four diets, respectively (P < 0.001).
Although silage proportion had no effect on eating activity, the researchers said rumination time increased quadratically (P = 0.04). Increased silage proportion also increased minimum (quadratic, P = 0.011) and mean (quadratic, P = 0.007) ruminal pH, and there was a quadratic (P ≤ 0.047) decrease in duration and area under the pH acidosis threshold curves, Chibisa et al. said.
According to the researchers, increasing the proportion of barley silage in the diet decreased ruminal acidosis but did not completely eliminate it, even with a diet containing 12% silage dry matter.
Chibisa et al. explained that diet did not affect SCFA concentration in the ruminal fluid, but silage proportion quadratically (P ≤ 0.088) increased the ruminal acetate-to-propionate ratio.
The researchers added that they did not observe any effects of diet on absolute or fractional rates of absorption of acetate, propionate, butyrate or total SCFA nor on gastrointestinal barrier function or blood measurements.
Chibisa et al. concluded that responses to roughage level in their study were mostly quadratic, with the greatest improvements in acidosis variables between 0% and 4% barley silage and incremental improvements with further increases in silage levels.
They said the study showed a trade-off between maximizing diet digestibility and energy intake to promote animal performance in the feedlot and minimizing the risk of ruminal acidosis.