Effect of Live Yeast and Mannan-Oligosaccharides on Performance of Early-Lactation Holstein Dairy Cows (Report‪)‬

INTRODUCTION During early lactation, cows experience huge negative energy balance and insufficient dry matter intake (DMI) that may increase the incidence of energy-related metabolic disorders. As achieving maximum potential intake is difficult during this critical stage, a promising approach is to use additives that increase the digestibility of the diet, especially fiber fractions, and consequently increase energy and nutrient supply. Live yeasts are among those additives that have been shown to increase digestibility of fiber and CP (Erasmus et al., 1992; Wohlt et al., 1998) in some but not all (Arambel and Kent, 1990; Wohlt et al., 1991) studies. As an alternative, some forms of complex oligosaccharides including mannan-, galacto-, and fructo-oligosaccharides, which recently have been used as prebiotics in monogastric feeding regimens (Shafey et al., 2001; Yang et al., 2007), may also be examined in ruminant diets to test whether or not these compounds act as agents that selectively attach to bacteria and may thus ultimately modify ruminal metabolism. At the intestinal level, irreversible attachment of fructo- and mannan-oligosaccharides to pathogens, which thereby reduce the chance of pathogen attachment to intestinal mucosa, has been documented (Sohn et al., 2000). In sheep and cattle, galacto-oligosaccharides (GOS) have been used with the objective of reducing methanogenesis or improving nitrogen utilization efficiency through decreased urinary N excretion (Mwenya et al., 2004; Sar et al., 2004b; Mwenya et al., 2005b). Very limited data is available about the ruminal effects of oligosaccharides when they are supplemented to diets of dairy cows. Mwenya et al. (2005a) observed that GOS lowered ruminal pH, increased VFA concentrations and had minor effects on ruminal DM degradation profile and microbial nitrogen supply. However, information regarding the consequences of using selected oligosaccharides on performance is scarce. In terms of microbe-attaching properties and also as a nutrient source for some selected microorganisms, it seems limited studies have been conducted on ruminal effects of mannanoligosaccharides (MOS). We hypothesized that MOS may also modify ruminal fermentation by selective inhibition or stimulation of microbial activity, thus they may also have an influence on milk production or composition. Examining the feeding of a mixture of yeast and MOS in diets of lactating cows would be of interest because the stimulatory impact of SC (Chaucheyras-Durand et al., 2008) may interact with possible inhibitory effects of MOS, at least on certain ruminal populations, and would alter the net products of rumen metabolism.