Abstract
The cell wall of animal feed grains contain a high proportion of xylan. Monogastric farm animals lack xylan-hydrolyzing enzymes in their gastro-intestinal tract. The indigestible dietary xylan impairs normal digestive function of single-stomached livestock by preventing efficient breakdown and assimilation of feed nutrients. The digestive capability of simple-stomached animals could be improved by providing them with a foreign xylanase gene for secretion of the enzyme into their digestive tract. In this study, we produced transgenic mice carrying an Aspergillus niger xylanse gene controlled by a salivary gland-specific regulatory element. The fungal xylanase is expressed specifically in the submandibular gland and secreted in the saliva of transgenic mice. The xylanase concentration in the saliva of transgenic mice reached 0.29 ± 0.03 U/ml. Digestibility of nutrients tends to increase in transgenic mice, although it does not differ significantly from that in wild-type controls. To our knowledge, this is the first demonstration of the production of fungal xylanase in the saliva of simple-stomached animals. Results from the present study encourage further investigation of employing transgenic technology to enhance the digestive capability of monogastric agriculture animals by introducing enzyme able to degrade dietary xylan into the digestive tract. Key words : Transgenic mice, xylanase, digestibility, saliva.
Highlights
Xylan is a major structural polysaccharide in plant cell wall (Collins et al 2005)
Using transgenic mice as models, we demonstrated that the fungal xylanase can be expressed in a salivary gland and secreted into the saliva
The transgenic mice producing salivary xylanase only showed a trend of increase, but not a statistically significant improvement, in feed digestibility
Summary
Xylan is a major structural polysaccharide in plant cell wall (Collins et al 2005). Animal feed cereals, including barley, wheat, rye and oats that contain high xylan. Indigestible feed xylan forms viscous gels together with other grain nonstarch polysaccharides in the gastro-intestinal tract inhibiting the breakdown and absorption of feed nutrients (Kim et al, 2005; McNab and Smithard, 1992). The presence of xylan in feed grains can markedly reduce feed digestibility and increase environmental pollution with excessive excretion of unabsorbed nutrients. Supplementation of cereal-based animal feed with xylanase has been shown to improve nutrient digestibility of monogastric animals by enhancing the hydrolysis of anti-nutritional dietary xylan (Esmaeilipour et al, 2011; He et al, 2010; Kim et al, 2008; Nortey et al, 2007; Pirgozliev et al, 2010). Many animal feeds during the production process are subjected to heat treatments which usually cause loss of enzyme activity (Walsh et al, 1993)
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