Effects of ammoniation of wheat straw and supplementation with soybean meal or broiler litter on feed intake and digestion in yearling Spanish goat wethers

The quantity and quality of available feedstuffs are major factors influencing productivity of ruminants in many parts of the world, especially regions with high animal numbers. Ruminants in such areas depend largely on crop residues at least during the long dry periods of the year for maintenance as well as production of meat, milk, skin and fiber. However, animal performance with such feedstuffs can be poor due to low voluntary intake and digestibility, which result from low protein concentrations and high levels of indigestible or slowly degradable fiber. Various physical, chemical and biological treatments have been used to improve utilization of low quality forages such as crop residues. In parts of the world where small farms predominate, treatment with a urea solution followed by a period of storage under air-tight conditions may be more practical. Treatment of crop residues with urea has three primary interrelated benefits, namely increased nitrogen concentration, digestibility and feed intake. An alternative to treatment of crop residues to enhance utilization is supplementation, although quality, availability and cost of potential supplements can limit application. Broiler litter is a low-cost agricultural byproduct available in many areas of the world that has been used as a supplementary feedstuff for low and moderate quality forages. Therefore, objectives of this experiment were to determine effects on feed intake and digestion in yearling Spanish wethers of supplementation of wheat straw treated with urea for ammoniation or untreated with soybean meal or broiler litter. Eight yearling Spanish wethers were used, consuming basal diets of wheat straw treated (ammoniated) with urea (T) or untreated (U) supplemented with soybean meal or broiler litter. Supplements were C (ground corn-based and fed at 0.64% body weight, dry matter basis, S (C plus 0.25% body weight of soybean meal) and LL and HL (C plus 0.5 or 1.0% body weight of broiler litter, respectively). Addition of soybean meal or different levels of broiler litter a moderate level of a grain-based supplement increased digestible organic matter intake by yearling Spanish goat wethers consuming a basal wheat straw diet, with magnitudes of change not significantly affected by ammoniation of wheat straw and being greater for the high level of broiler litter compared with the lower level and with soybean meal. Presumably because of extensive nitrogen recycling, including nitrogen from mobilized tissue, which prevented impact on extent of wheat straw digestion,change in digestible organic matter intake appeared primarily because of additional digestible organic matter provided by soybean meal and broiler litter without substitution for wheat straw intake. However, with prolonged feeding of untreated crop residues, limited tissue nitrogen available for recycling might be conducive to impact of supplemental nitrogen on intake and ruminal digestion. Ammoniated crop residues and concentrate supplements high in ruminally degraded nitrogen can be employed together when high nutritional planes are desired, although supplements with a lower concentration of nitrogen might be more economical. A relatively high level of broiler litter to supplement untreated wheat straw, in addition to a moderate level of supplemental concentrate, may be necessary to achieve digestible organic matter intake comparable to that with ammoniated wheat straw and a moderate level of concentrate supplement.