The effects of method of pre-lamb shearing of ewes on production and physiological indicators of cold stress : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
This experiment was undertaken to compare the effects of two methods of pre-lamb shearing on physiological and production characteristics of ewes and their lambs with the objective of determining which method gives the greater advantages. In July, approximately 20-63 days before lambing, sixty Romney ewes were divided at random into two equal groups, one group was shorn with a conventional comb and the other using a cover comb. The former left wool 1-3 mm in length and the latter 6-13 mm of wool on the animal after shearing. The ewes were run together on a rye grass white clover pasture for a 67 day period after shearing. Climatic conditions were considered mild with average minimum temperature of 5.2 °C, and average maximum temperature of 13.4 °C, average wind speeds of 8.5 km/h, relative humidity 80.1 %, sunshine 4.7 h and 1.2 mm of rainfall over the 67 days period after shearing. Food intake, measured indirectly using controlled-release capsules containing chromium sesquioxide placed in the rumen, did not differ between the groups over a 21 day period after shearing. This was reflected in a lack of effect of treatment on the live weight of the ewes, birth weight of the lambs, growth rates of the lambs or wool growth of the ewes over the 67 day period. Ewes shorn by the conventional comb, however, were more severely stressed than the ewes shorn with the cover comb as indicated by the higher concentrations of non-esterified fatty acid (NEFA) and 3-hydroxybutyrate in the plasma of the former group on days 1 and 3 after shearing. Rectal temperature was a less sensitive measure than the concentrations of the metabolites and the difference between the groups in rectal temperature after shearing was not statistically significant. It was concluded that shearing with a cover comb reduces the cold stress on the ewe in comparison with the conventional method of shearing. Furthermore, it was suggested that under more severe climatic conditions than those experienced in the present experiment, that shearing with the cover comb might be expected to result in increased production.