Chemical composition and nutritive value to sheep of untreated and oven-ammoniated ryegrass hays prepared from crops of differing maturities

Abstract

This work examines changes in the chemical composition and nutritive value to sheep of perennial ryegrass hays, prepared at 3 stages of plant development and subjected to thermoammoniation. Ammoniation lowered the content of water-soluble carbohydrate (WSC) and cellulase-undegradable cell walls in hay dry matter, but raised the concentrations of total nitrogen, neutral detergent insoluble nitrogen, acid detergent insoluble nitrogen (ADIN), hot-water insoluble nitrogen, soluble non-ammonia nitrogen (SNAN), 4-methylimidazole and lysinoalanine (LAL). Except for ADIN and LAL, the responses for nitrogenous fractions were most pronounced with the youngest hay and least with the mature hay. Significant relationships were found between the increases in SNAN and losses of WSC and between the increases in organic matter digestibility in vitro (OMD (vt)) and the modification or release of cell-wall ferulic acid. For sheep given untreated hays, decreases in intake of digestible organic matter (DOMI) and nitrogen, organic matter digestibility in vivo (OMD (vv)) and nitrogen retention (NR) were associated with advancing hay maturity. However, ammoniation produced different animal responses as the crop matured. With the mature hay it raised the nutritive value to that of untreated medium quality hay. In contrast, with the youngest hay appetite was reduced, despite improvements in OMD (vt). Individual sheep on each of the ammoniated younger hays displayed symptoms of toxicity and neurological disturbance. Possible causes of the toxicity are discussed. It is concluded that while the mature hay (with a high proportion of stem and low content of WSC) benefitted from treatment, the younger hays were damaged. Therefore, ammoniation should not be applied to leafy hays in high-temperature situations.