Variations in the sulphur content of wool from Merino sheep on two semi-arid grasslands

Abstract

Seasonal variations in sulphur content and growth rate of wool were measured at intervals of 6 weeks over a period of 1 year on two groups, each of six Merino wethers, which grazed on two semi-arid grasslands. Each group consisted of three high-producers and three low-producers, selected on the basis of wool growth rate. There were substantial seasonal variations in sulphur content, which followed very closely the seasonal pattern of wool growth. Mean sulphur contents on the two grasslands ranged from 3.25 and 3.32% during December–April, to 3.67 and 3.79% respectively during July-October. Seasonal variations in sulphur content and growth rate of wool were related to the amount of edible forage available, and it was concluded that these seasonal variations were due mainly to variable nutrition. The range of sulphur contents was 2.93 to 3.92%, owing to seasonal nutritional variations and differences between sheep; annual mean sulphur contents of wool from individual sheep ranged from 3.22 to 3.84%. The annual mean sulphur content of the wool from high-producers (3.39%) was lower than that of wool from low-producers (3.66%). The seasonal variation in sulphur content also appeared to be greater in wool from high-producers than in wool from low-producers.

Variation in the Sulphur Content of Wool of Merino Sheep Associated with Genetic Differences in Wool-Producing Capacity

“…They were significantly different from each other when tested by means of a z-transformation (Fisher 1954). The within-group relationship for the low group is similar to that observed by other workers (Reis 1965;Reis and Williams 1965;Gillespie and Reis 1966), but this is not so for the high group.…”

“…Other workers (Reis 1965;Reis and Williams 1965;Gillespie and Reis 1966) have reported differences between high and low producers within flocks, but the differences reported by them are phenotypic and the relative importance of the genetic and environmental components cannot be estimated. Our work has been reported as it clearly demonstrates variation in wool sulphur content associated with genetic variation in wool-producing capacity.…”

“…Variation in the sulphur content of wool from grazing sheep has also been reported by Ross (1961Ross ( , 1964 who suggested that there was an inverse relationship between rate of wool growth and its sulphur content. The sheep observed by Ross were Romney ewes and Reis and Williams (1965) have cast some doubt on the relationship suggested by Ross on the grounds that the seasonal variation in wool growth may have been affected by factors other than nutrition.…”

“…Copper deficiency has been shown to reduce sulphur content (Marston 1946), while the administration of sulphur-containing amino acids or casein directly into the abomasum has been shown to increase substantially both the sulphur content of wool and the rate of wool growth (Reis and Schinckel1961, 1963, 1964. Variation in the nutritional status of both pen-fed (Reis 1965) and grazing (Reis and Williams 1965) sheep, associated with variation in either the amount or the composition of the diet, has also been shown to influence sulphur content; wool growth and sulphur content have both increased as nutrition has been improved, and vice versa. Variation in the sulphur content of wool from grazing sheep has also been reported by Ross (1961Ross ( , 1964 who suggested that there was an inverse relationship between rate of wool growth and its sulphur content.…”

“…In the reports of Reis (1965), Reis and Williams (1965), and Gillespie and Reis (1966), there is an indication that some of the between-animal variation may be associated with differences in wool-producing capacity, higher wool producers tending to grow wool of a lower sulphur content. In these experiments, however, numbers of animals were small, and the differences in wool-producing capacity are phenotypic and would have been partly genetic and partly environmental in origin.…”