Climatic adaptation in recently shorn merino sheep

Abstract

ABSTRACT.-Heart rates, respiratory rates, body temperatures, ad libitum 'day'and 'night' food consumption and body weight changes have been examined in 15 mature Merino wethers shorn in moderate environmental conditions. All sheep showed a depression in food consumption for two days after shearing. Sheep that gained weight during the next three weeks then increased their food consumption at night by approximately 30% although the average daily consumption was only increased by 5%. Sheep that lost weight showed a depressed food consumption throughout the three week period after shearing. Marked increases in the temperature difference between ear skin and air as well as thermal tachypnoea during the warmest period of the day were recorded in all sheep 14-16 days after shearing. This indicated that the critical temperature for all sheep had decreased by about 10oc. These signs of acclimatisation appeared at similar times in all sheep, suggesting that increased resistance to body cooling developed at similar rates in weight gain and weight loss sheep and independent of the origin of body heat production. The results of the investigations are discussed in relation to the concept that the initial response to cold stress includes a depression in food intake and that the duration of this depression is a function of the cold stimulus and the strain it induces in the sheep.

A note on the effect of autumn shearing on performance of fattening lambs

“…The increased food intake due to shearing, observed in the present experiment, is in agreement with results reported by others (Wodzicka-Tomaszewska, 1964;Ternouth and Beattie, 1970;Donnelly et al, 1974). Table 1 shows that the largest increases in food intake occurred during weeks 3 to 4 and 5 to 6 following shearing.…”

Shearing at the end of summer affects body temperature of free-living Angora goats (Capra aegagrus) more than does shearing at the end of winter

“…Similar results were found for sheep in cold weather, in that daily movement patterns remained unaltered or even decreased after shearing (Webster and Lynch, 1966). These results are likely to correspond to the depression in food consumption reported for newly shorn sheep exposed to extreme cold (Webster and Lynch, 1966;Panaretto and Vickery, 1971;Donnelly et al, 1974), which is proposed to be a consequence of acute cold stress (Sykes and Slee, 1969b). The reduction in food intake coupled with the increased metabolic Hetem, de Witt, Fick, Fuller, Kerley, Maloney, Meyer and Mitchell costs of thermoregulation may place the animals into negative energy balance, putting Angora goats at a greater risk of lethal hypothermia (McGregor and Butler, 2008b).…”

“…Vasoconstriction leads to a reduction in heat delivery to the skin, so that, when ambient temperature is below core temperature, a low skin surface temperature would reduce the outer temperature gradient and consequently slow the sensible heat dissipation from the goat's body (Bianca and Kunz, 1978). As with our goats, skin temperature was lower in shorn than in unshorn sheep, particularly when the sheep were exposed to cold environmental conditions (Slee, 1966;Webster and Lynch, 1966;Phillips and Raghavan, 1970;Donnelly et al, 1974;Glass and Jacob, 1992).…”

“…Compared to Merino sheep, the fleece of Angora goats is more lustrous (Cena and Monteith, 1975), has a lower grease content, a lower fiber density per unit area of skin and a lower thermal insulation, thus allowing greater penetration of air and wetting of the skin (McGregor, 1985 and2001). Such differences may explain why sheep remain susceptible to death for 2 weeks following shearing (Panaretto, 1967;Hutchinson, 1968;Donnelly et al, 1974), compared to nearly 6 weeks for Angora goats. Indeed, when exposed to the same environmental conditions, the risk of hypothermia and mortality following shearing was higher for Angora goats than for Merino sheep (McGregor and Butler, 2008b).…”

The effect of shearing in a hot environment on some welfare indicators in Awassi lambs

“…Lambs in shorn group were sheared at the beginning of the experiment. Wool growth varies by breed but at an average of 0.07-0.17 cm daily growth has been reported by Donnelly et al (1974). At this rate of wool growth, shorn lambs in this study would have had 0.4-0.66 cm wool coverage during the experiment where the wool coverage of unshorn lambs was 10-12 cm during the experiment.…”