Suitability of live yeast addition to alleviate the adverse effects due to the restriction of the time of access to feed in sheep fed only pasture.

The effect of yeast addition on intake and digestive utilization of pasture was studied in ovines under restricted time of access to forage. Eighteen wethers housed in metabolic cages and fed fresh forage (predominantly Lotus corniculatus) were randomly assigned to three treatments: forage available all day (AD); forage available only 6 h/day (R) and forage available only 6 h/day plus live Saccharomyces cerevisiae yeast (RY). Feed intake and digestibility, feeding behaviour, kinetics of passage, ruminal pH and ammonia concentration, nitrogen balance and microbial nitrogen synthesis (MNS) were determined in vivo, and ruminal liquor activity of animals was evaluated in vitro. Restricted animals consumed less than those fed all day but achieved more than 75% of the intake and spent less time ruminating (p = 0.014). Although animals without restriction consumed more feed, they had a lower rate of passage (p = 0.030). The addition of yeast did affect neither intake nor feeding behaviour, but increased digestibility. Organic matter digestibility tended to increase 11% by yeast addition (p = 0.051), mainly by a rise in NDF (27%, p = 0.032) and ADF digestibility (37%, p = 0.051). Ingested and retained N was lower in restricted animals, as MNS (p ≤ 0.045). The use of yeasts did not significantly change the N balance or MNS, but retained N tended to be higher in supplemented animals (p = 0.090). Neither ruminal pH nor ammonia concentrations were affected by the restriction, but restricted animals had a lower ruminal activity evidenced by a lower volume of gas (p = 0.020). The addition of yeast overcame this limitation, noted by a higher volume of gas of inocula from supplemented animals (p = 0.015). Yeast addition emerged as a useful tool to improve digestibility of forage cell walls in ovines under restricted time of access to forage.