Efficiency of conversion of food to wool at two nutritional levels by three merino strains

Abstract

Efficiency of conversion of fodder to wool in a fine-wool (F), a medium-wool (B), and a strong-wool (S) strain of Merino was estimated by measuring individual fodder consumption and wool production of nine wethers of each strain in two periods, each of 16 weeks. In the first period lucerne chaff and wheat were fed in a 7.2/1 ratio (dry basis) at a maintenance level. In the second, lucerne chaff and wheat were fed in a 2.8/1 ratio at approximately 1.4 times maintenance level. The efficiencies of the strains in the two periods in terms of pounds of oven-dry wool produced per 100 therms of net energy consumed were: Strain Maintenance Maintenance x 1.4 F 1.76 1.52 B 2.03 1.82 S 2.19 1.90 The overall strain differences F v. B and F v. S were significant (P < 0.001) but the remaining difference was not significant. Interactions of strains and nutritional levels were not significant. Individual sheep within strains tended to remain in a similar order of efficiency from one nutritional level to the other, the within-strain correlation between levels being estimated as 0.89. The results suggest that selection of strains and to a lesser extent of individuals on the basis of efficiency will not be seriously affected by the energy level at which efficiency is measured. In a digestion experiment involving all 27 animals of the efficiency experiments, each fed at its maintenance ration, differences between strains in digestibility of organic matter and of protein were extremely small and were non-significant. It is concluded that strain differences in efficiency depend largely on differences in utilization.