Behavioural adaptations of sheep to repeated acidosis challenges and effect of yeast supplementation

Abstract

<jats:p>This study aims to determine whether sheep modify their feeding and general behaviour when they undergo acidosis challenge, whether these modifications are maintained when acidosis challenges are repeated and whether yeast supplementation affects these modifications. Twelve rumen-cannulated wethers fed concentrate (wheat) and forage (hay) were exposed to three 28-day periods consisting of a 23-day recovery phase (20% of wheat) followed by a 5-day acidosis challenge (60% of wheat). Both diets limited food intake to 90% of<jats:italic>ad libitum</jats:italic>intake. Six sheep received a daily supplementation of a live yeast product, six received a placebo. Ruminal pH was recorded continuously. Daily consumption of wheat, hay, water and weekly consumption of salt were monitored. Behavioural observations were performed twice in each period: once under the recovery phase and once under acidosis challenge. These observations included video recordings over 24 h (time budget), social tests (mixing with another sheep for 5 min) and nociception tests (CO<jats:sub>2</jats:sub>hot laser). As expected, sheep spent more time with a ruminal pH below 5.6 during challenges than during recovery phases (12.5<jats:italic>v.</jats:italic>4.7 h/day). Sheep drank more water (3.87<jats:italic>v</jats:italic>. 3.27 l/day) and ingested more salt (16<jats:italic>v</jats:italic>. 11 g/day) during challenges. They also spent more time standing than during recovery phases, adopting more frequent alarm postures and reacting more slowly to the hot stimulus. More severe behavioural modifications were observed during the first challenge than the two other challenges. Significant concentrate refusals were observed during challenge 1: from days 3 to 5 of this challenge, sheep ate only half of the distributed concentrate. Sheep were also more active and more aggressive towards each other in challenge 1. These behavioural modifications disappeared as the challenges were repeated: no behavioural modifications were observed between challenges and recovery phases during periods 2 and 3, and furthermore, sheep rapidly ate all the concentrate distributed during the third challenge. Focusing on the effects of yeast, the only differences registered between the two groups concerned ruminal pH, that is, mean ruminal pH values in the supplemented group were lower during the first challenge (5.11<jats:italic>v</jats:italic>. 5.60) but higher during the third challenge (5.84<jats:italic>v</jats:italic>. 5.28). In conclusion, our experiment suggests sheep can adapt to acidosis challenges, especially with yeast supplementation. Otherwise, ruminal pH values remained low during challenges, indicating that the modifications of general and feeding behaviour in subacute ruminal acidosis situations are not due exclusively to low ruminal pH values.</jats:p>

Repeated acidosis challenges and live yeast supplementation shape rumen microbiota and fermentations and modulate inflammatory status in sheep

“…This suggests that a gradual adaptation of the microbiota happened from one challenge to another and that low pH-resistant microorganisms could have been selected during the repeated challenges with better digestive comfort as a consequence. This is in agreement with the feeding behaviour of these sheep that had an improved feed intake and no sign of digestive discomfort as evaluated by their behaviour (less aggressiveness, agitation, and pain sensitivity) during the last two challenges (Commun et al, 2012). In contrast, in lactating dairy cows (Dohme et al, 2008) and in non-productive cows (Monteils et al, 2012), repeated ACs increased the duration and severity of SARA.…”

“…The study also investigated whether live yeast supplementation modulates these parameters. Data on feeding and general behaviour of sheep from the same experiment are available in Commun et al, 2012. During the whole experiment, none of the sheep demonstrated any visually apparent sign of illness and none was excluded from the statistical analysis (Control group, n = 6; SC group, n = 6).…”

“…In addition, we investigated whether a live yeast additive could exert any beneficial effect during repeated acidosis. Modifications of behaviour (time budget, reactivity, feed intake) of the same sheep in response to repeated ACs have been described elsewhere (Commun et al, 2012).…”

“…SARA threshold definition based on pH varies largely in the literature. To define ruminal chronic acidosis in our study, we chose the cut-off point of the time spent under pH 5.6 according to several authors (Keunen et al, 2002;Commun et al, 2012). During ACs, rumen pH decreased and the rumen microbiota and fermentation end-products (VFA, lactate) were altered, indicating that acidosis was induced as expected.…”

“…Therefore, our aim was to investigate in sheep the impact of repeated acidosis challenges (ACs) on rumen fermentations, microbial ecosystem and inflammatory response, and to study the effect of live yeast supplementation on these parameters. Information on feeding and general behaviour of sheep from the same experiment has been published in Commun et al (2012).…”