The role of feed supplements in improving intake and utilisation of low quality roughage in ruminants

Abstract

The studies in this thesis were undertaken to investigate ways to improve the value of roughages and byproducts as feeds for ruminants through supplementation. Low quality basal roughages are high in fibre, low in N and other minerals; as a result their comminution rate in the rumen (and clearance rate) is generally low, leading to low intake. Moreover, their digestion in the gut often results in absorption of digestion products that are imbalanced in protein to energy (PIE), and also in glucogenic to acetogenic substrates. The imbalance in nutrients leads to inefficiency in the utilisation of the absorbed nutrients, often manifesting as high heat increment and generally low voluntary intake (MacRae and Lobley 1982; MacRae et al. 1987). This problem is further compounded by the high ambient temperature in the tropics where most of the ruminant livestock subsisting on crop residues are raised, which makes dissipation of heat very difficult (Preston and Leng 1987; Leng 1990). Animals in the tropical environments therefore respond to low digestibility feeds by reducing feed intake which leads to lower animal productivity (Preston and Leng 1987). This study investigated how strategic supplementation with rumen degradable nutrients and by-pass nutrients in animals fed low quality roughage basal diets may be used to stimulate an efficient rumen fermentation (and intestinal digestion). It was hypothesized that this is likely to result in the absorption of balanced nutrients (PIE and glucogeniclacetogenic ratio) from the gut, and therefore enhance efficiency in nutrient metabolism in the body tissues, resulting in improved animal productivity (Leng 1990). The broad objective of the present study was to investigate the role of dietary N, protein and energy supplementation and ammoniation with urea in stimulating higher rumen fermentation, with a view of providing the small intestines with a better balance of protein and energy substrates (P: E), as well as of glucogenic to acetogenic substrates for digestion and absorption. It was hypothesized that when the body tissues are provided with balanced nutrients, this would lead to more efficient utilisation of those nutrients, lower heat production, and therefore higher animal productivity.