The effects of hay maturity and forage to concentrate ratio on digestion kinetics in goats

Abstract

The effects of addition of a sorghum grain-based mixture on the digestion of mature and immature hays were evaluated on four female goats, fitted with ruminal and duodenal cannulae. The goats were fed four diets, consisting of immature alfalfa-grass hay, mature alfalfa-grass hay, and a 1:1 mixture of a grain sorghum and soybean meal with mature or immature hay. Ruminal pH was lower ( p<0.05) in the grain-hay diets than in the hay diets, but did not differ between immature and mature hay diets. Ruminal ( p=0.12) and total tract dry matter (DM) and starch digestibilities were higher ( p<0.05) in the immature than mature hay-based diets. Grain sorghum addition did not affect the amount or proportion of DM digested in the rumen. The NDF digestibility coefficient in the rumen did not differ between diets containing 0% or 50% grain. The ADF digestibility coefficient was not affected by grain. Digestibility coefficients of DM and starch in the total tract were increased ( p<0.01) by incorporation of sorghum grain to the hay diets. Total VFA concentrations were greater ( p<0.05) in diets containing immature hay than mature hay. Hay maturity did not affect molar proportions of ruminal acetic, propionic or butyric acids. Grain sorghum addition decreased the molar proportions of acetic and propionic acids ( p<0.01) but increased butyric acid ( p<0.01). The acetate:propionate ratio was greater ( p<0.05) in goats fed hay-grain than hay diets at 0 and 2 h after feeding. Grain addition to the hay diets increased ruminal ammonia concentration at feeding ( p<0.05). Neither maturity nor grain addition affected duodenal flow of ammonia, bacterial, undegraded fed-N or microbial efficiency. It was concluded that supplementation with as much as 50% grain sorghum to an alfalfa-grass hay did not negatively affect fiber digestion.