Fermentation of straw-based diets containing azolla (<italic>Azolla caroliniana</italic> Willd) using the Rumen simulation technique (Rusitec): Fid-Bau Portal

Fermentation of straw-based diets containing azolla (Azolla caroliniana Willd) using the Rumen simulation technique (Rusitec)

Jayasuriya, M.C.N. / Hamilton, R. / Uriyapongson, S. / Eskew, D.L.

Abstract

AbstractA series of experiments was conducted to evaluate the nutritive value of Azolla species (Azolla caroliniana) as a supplementaru source of dietary nitrogen for high fibre-based diets. Experiment 1 was aimed at estimating the solubility of nitrogen and degradability of Azolla protein in rumen fluid. Azolla appeared to be low in soluble nitrogen compared to wheat bran. Azolla protein also showed a low rumen degradability but the post-rumen solubility of the undergraded protein was inadequate to categorise it as an exceptionally useful rumen non-degradable protein source. The second and third experiments examined the effect of incorporating Azolla (with or without urea) as a supplementary source of nitrogen for straw-based diets on fermentation characteristics using an artificial rumen (Rusitec). Untreated straw and Azolla in the proportion of 13:2 (SA) gave the lowest digestibility while the highest digestibility was recorded with the diet containing urea-ammonia-treated straw supplemented with Azolla in the same ratio (TSA-1). The addition of 100 mg urea day⁻¹ to the same dietary combination of straw and Azolla (SAU-1) raised the dry-matter digestibility and estimated microbial dry-matter production by 45% and 60%, respectively. A further increase in supplementary urea to 500 mg day⁻¹ (SAU-2) had no effect on digestibility or the output of microbial matter. The estimated ATP yield was highest with TSA-1 diet and lowest with SA diet. The estimated efficiency of microbial synthesis expressed as the yield of microbial nitrogen/unit of dry matter digested was lowest for the diet SA and highest for the straw diet supplemented with 100 mg urea. The diets that contained wheat bran showed a relatively higher efficiency than the others. The results suggest that in general Azolla is not very promising as a ruminant feed supplement. However, it could be considered as a source of rumen non-degradable dietary nitrogen rather than one supplying fermentable nitrogen in the rumen. Addition of wheat brain increases the availability of readily-fermentable energy, and thereby the efficiency of microbial synthesis. Since Rusitec is only a screening device, the most promising dietary regimes should be further tested by animal experiments before recommendations are made for practical use in animal rations.