Effect of live yeast culture supplementation on apparent digestibility and rate of passage in horses fed a high-fiber or high-starch diet

¹ INRA, UR1213 Herbivores, Site de Theix, 63122 Saint Genes Champanelle
² Alltech-France, 14 Place Marie-Jeanne Bassot, 92593 Levallois-Perret
³ Alltech-France, 14 Place Marie-Jeanne Bassot, 92593 Levallois-Perret; Etablissement National d'Enseignement Supérieur Agronomique de Dijon (ENESAD), 26 Boulevard Dr Petitjean, BP 87999, 21079 Dijon, France
⁴ Etablissement National d'Enseignement Supérieur Agronomique de Dijon (ENESAD), 26 Boulevard Dr Petitjean, BP 87999, 21079 Dijon, France

^* To whom correspondence should be addressed. E-mail: v.julliand{at}enesad.fr.

	Abstract

Eight crossbred male horses aged 12 ± 5 years and weighing 305 ± 18 kg were used in pairs in a 4 x 4 Latin square design with 4 ground and pelleted diets. Each pair included a cecum and right-ventral colon-fistulated animal and a cecal-fistulated animal. The 4 horse diets were: a high-fiber diet (HF+0), based on dehydrated alfalfa, a high-starch diet based on barley and wheat bran (HS+0), and either the HF or HS diet supplemented with Saccharomyces cerevisiae (SC) CBS 493.94 (HF+SC and HS+SC). The probiotic preparation contained 4.5 x 10⁹ cfu·g^-1 of live yeast mixed with the culture medium, and was top-dressed on to feed pellets at a rate of 10 g·d^-1, equally distributed between the 2 daily meals. All 4 diets were offered in the same quantities [18.0 g of pelleted feed DM + 3.5 g of long wheat straw·kg BW^-1·d^-1]. Each of the 4 experimental treatments was divided into a 21-d period of diet adaptation followed by a 10-d period of total fecal collection for digesta flow rate and apparent digestibility measurements. Three markers were used to measure mean retention time (MRT) of feed particles: Yb bound to the pelleted feeds for MRT in the whole digestive tract (MRT_Yb), Eu bound to the pelleted feeds, and Dy bound to the fecal particles for MRT in the hindgut (MRT_Eu and MRT_Dy). Apparent digestibilities of DM, OM, and CP were greater (P < 0.001) in the HS than HF diet, independently of SC supplementation; whereas, ADF digestibility was greatest in the HF diet (P = 0.035). Cellulolytic activity estimated through the in vitro disappearance rate of dietary ADF fraction (IVAD_ADF) was lesser (P < 0.001) in the HS than HF diet. There was no dietary effect on NDF digestibility due to the longer MRT_Eu of small particles in the hindgut (P = 0.036), which compensated for the lower fibrolytic activity expressed per unit of time in HS compared to HF diet. SC supplementation improved ADF digestibility (P = 0.038) and stimulated DM (P = 0.030) and NDF (P = 0.038) intakes, but had no effect on the MRT of solid digesta. The absence of any significant diet x SC interaction supports the strategy of using SC to stimulate cellulose digestion and improve the nutritional status of horses under both HF and HS diets.

Key Words: dietary effect, digestibility, fiber digestion, horse, live yeast, transit time