The influence of the chemical composition of the diet on liveweight change in sheep

Abstract

An incomplete block design balanced for residual effects, with an extra period, was used to investigate the effect of seven diets, differing widely in their chemical composition, on the nutritional requirement for the maintenance of liveweight in individually penned sheep.

The mean liveweight changes for all diets at the chosen level of feeding were negative although all but one of the diets produced mean positive nitrogen balances.

Slightly more than 96% of the variation in liveweight change due to diets could be accounted for by the following regression:

Y = a + bX₁ + cX₂ + dX₃ + eX₄

where Y is the liveweight change (g/day), X₁ the dry matter intake (g/day), X₂ the initial liveweight (kg), X₃ the metabolizable energy plus methane intake (kcal/day), and X₄ the nitrogen balance (g/day).

X₁ alone accounted for approximately 75% of the variability.

The effect of X₃, once X₄ had been accounted for, was extremely small under these nutritional conditions.

After covariance adjustments for dry matter intake and initial liveweight to the seven dietary means, a regression was fitted for adjusted liveweight change on nitrogen balance. This equation had the form:

Y_A = a + bX₄+ cX₄²

Nitrogen balance is closely related to nitrogen intake ( = dry matter intake x percentage nitrogen). At constant dry matter intake, the above equation can be written in terms of percentage crude protein (N x 6.25) in the diet.

The possible reasons are discussed for the small effect of metabolizable energy intake on liveweight change once the dry matter intake is held constant.