D. P. Morgavi

Effects of an exogenous enzyme preparation on microbial protein synthesis, enzyme activity and attachment to feed in the Rumen Simulation Technique (Rusitec).

The effects of an exogenous enzyme preparation, the application method and feed type on ruminal fermentation and microbial protein synthesis were investigated using the rumen simulation technique (Rusitec). Steam-rolled barley grain and chopped alfalfa hay were sprayed with water (control, C), an enzyme preparation with a predominant xylanase activity (EF), or autoclaved enzyme (AEF) 24 h prior to feeding, or the enzyme was supplied in the buffer infused into the Rusitec (EI). Microbial N incorporation was measured using (15NH4)2SO4 in the buffer. Spent feed bags were pummelled mechanically in buffer to segregate the feed particle-associated (FPA) and feed particle-bound (FPB) bacterial fractions. Enzymes applied to feed reduced neutral-detergent fibre content, and increased the concentration of reducing sugars in barley grain, but not alfalfa hay. Ruminal cellulolytic bacteria were more numerous with EF than with C. Disappearance of DM from barley grain was higher with EF than with C, but alfalfa was unaffected by EF. Treatment EF increased incorporation of 15N into FPA and FPB fractions at 24 and 48 h. In contrast, AEF reduced the 24 h values, relative to C; AEF and C were similar at 48 h. Infused enzyme (EI) did not affect 15N incorporation. Xylanase activity in effluent was increased by EF and EI, compared to C, but not by AEF. Xylanase activity in FPA was higher at 48 h than at 24 h with all treatments; it was higher with EF than C at 24 and 48 h, but was not altered by AEF or EI. Applying enzymes onto feeds before feeding was more effective than dosing directly into the artificial rumen for increasing ruminal fibrolytic activity.

Mode of action of exogenous cell wall degrading enzymes for ruminants

Recent studies have shown that adding exogenous fibrolytic enzymes to ruminant diets can increase milk production of dairy cows and weight gain of growing beef cattle as a result of enhanced feed digestion. While much progress has been made in terms of advancing feed enzyme technology for ruminants, considerable research is still required to develop more effective enzyme products. The mode of action whereby exogenous enzymes improve digestion of plant cell wall is complex, and there is evidence for numerous potential modes of action suggesting they are interdependant. A mode of action that accounts for the most critical factors that explain the observed increases in feed digestion is presented. Adding exogenous enzymes to the diet increases the hydrolytic capacity of the rumen mainly due to increased bacterial attachment, stimulation of rumen microbial populations and synergistic effects with hydrolases of ruminal microorganisms. The net effect is increased enzymic activity within the rumen, which enhance...

A rationale for the development of feed enzyme products for ruminants

The use of exogenous cell wall degrading enzymes is an emerging technology that shows potential in terms of improving feed utilization by ruminants. This review discusses current information related to enzyme product formulation for ruminants, and addresses the conditions necessary to ensure effective and consistent in vivo results of providing feed enzymes to ruminants. Research has demonstrated that, in some cases, adding fibrolytic enzymes to dairy cow and feedlot cattle diets improves cell wall digestion and, consequently, weight gain or milk production are enhanced. However, considerable research is required to develop more effective enzyme products and to ensure consistency of responses in vivo. There is a need to identify the key enzyme activities involved in the positive responses observed in vivo and these enzyme activities should be assessed using a temperature and pH representative of the conditions in the rumen. However, to date, it has not been possible to accurately evaluate exogenous enzyme...

Inhibition of ruminant feed enzyme polysaccharidase activities by extracts from silages

Extracts from 14 barley silages inhibited endo-1, 4-β-xylanase and α-amylase activities of a ruminant feed enzyme additive from Trichoderma longibrachiatum by 23 to 50% but had little effect on cellulase activity. The inhibitory factor(s) were <10 kDa in size and were stable to autoclaving. These observations may explain why feed enzymes are generally less effective when applied to silages than when applied to dry feeds. Key words: Silage, fibrolytic enzymes, Trichoderma, xylanase, inhibitors

Enzymes as Direct-Feed Additives for Ruminants

Fibrolytic enzymes hold great potential to improve feed utilization and productivity in ruminants. In the past, it was believed that the endogenous activity against plant cell walls could not be augmented by supplementary exogenous enzymes. However, when diets of dairy and beef cattle are supplemented with commercial xylanases and cellulases, animal performance is significantly improved. The most likely site of action is the rumen rather than in the small intestine as is the case for poultry. Because of the complexity of the rumen environment, it has been difficult to identify the exact mode of action for this beneficial response. Since xylanases and cellulases are the main activities that occur in efficacious enzyme mixtures, it may be assumed that the enzymes are having a direct, additive effect on the hydrolysis of plant fiber in the rumen. However, evidence to date suggests that the benefits of exogenous enzymes is synergistic to ruminal endogenous enzymes. This synergy may explain why relatively small amounts of enzyme can have such large effects on animal productivity. Limitations to the exploitation of this technology are the development of an adequate screening system for new enzymes, and the identification of the specific enzyme activities that are critical for efficacy.