Effect of nitrogen fertiliser on the protein quality of wheat for ruminants

Abstract

Seventy-four samples of wheat grain (c.v. Mercia) grown under a variety of different fertiliser nitrogen (N) regimes were milled through a 3mm screen. The rumen degradation characteristics of N were estimated using the nylon bag technique and N solubility in water was estimated in the laboratory. The values determined from the nylon bag technique for the immediately rumen soluble ('a') fraction (16.9 ñ 3.81%) and the rate ('c') of N degradation (0.128 ñ 0.0178 h-l) were both considerably lower than in previous reports in the literature. The N content of the grain exhibited a strong curvilinear relationship with the total N applied as fertiliser. Increasing fertiliser N and the resulting increase in grain N contents reduced and increased (P<0.01) the immediately rumen soluble ('a') anda insoluble but degradable N ('b') fractions respectively, although the relationships only accounted for about 10% of the variance. For both statistical and theoretical reasons these relationships may not be applicable to other samples of wheat. The work also showed that the water soluble N fraction as measured in the laboratory (8.3 ñ 1.84%) was on average only about 0.4 of the nylon bag zero hour loss (21.2 ñ 4.49%) and about 0.5 of the fitted 'a' value (16.9 ñ 3.81%). This suggests that the nylon bag technique can seriously overestimate the immediately soluble N fraction of wheat and probably other cereal grains.