Effect of Chemical Quality of Grass Silage on Utilization of Nitrogen in Sheep

Abstract

A first growth cutting of orchardgrass/Ladino clover mixture was stored as (1) silage from wilted, chopped forage, (2) silage from unwilted, chopped forage, (3) silage from direct cut untreated forage, and (4) field-cured hay. After a storage period of approximately four months, the forages were subjected to the determination of the chemical quality and nitrogen distribution, and were fed to four sheep (including two which were rumen-fistulated) to study the effect of chemical quality and the nitrogen distribution of forage on utilization of nitrogen. The results of the determination of pH value and the amounts of organic acids revealed that the quality of the silage was improved apparently by wilting and chopping at the time of ensiling. Wilted-chopped silage ranked first in quality, unwilted-chopped silage ranked second, and untreated silage last. Although a decrease in protein nitrogen followed by an increase in water-soluble nitrogen was observed irrespective of the quality of silage, there was a definite tendency' for the percentage of ammoniacal nitrogen to decrease in wilted-chopped silage and unwilted-chopped silage as compared with untreated silage. There were significant differences in nitrogen retention between the four forage treatments, being highest in the field-cured hay, followed by wilted-chopped silage and unwilted-chopped silage, and least in untreated silage. Rumen-ammonia concentration during the first four hours after feeding appeared to be higher in the untreated silage than in the other two silages. In contrast with the silages, only a slight increase in this measurement was observed in the field-cured hay. It is uggested that the increase in non-protein nitrogen in silage, especially ammoniacal nitrogen accompanied by a deterioration in quality of silage, is principally related to lower efficiency of nitrogen utilization in silage-fed ruminants.