Effect of shearing on water turnover and thermobiological variables in German Blackhead mutton sheep

Abstract

Current equations for estimating water requirements in sheep do not differentiate between shorn and unshorn sheep. Furthermore, the effect of shearing on thermoregulative responses in sheep has not been adequately studied under temperate environmental conditions. Therefore, the present study was conducted to investigate the effect of wool coverage on water turnover in relation to thermoregulation in sheep by using the deuterium dilution technique to predict total water intake before and after shearing. Physiological responses, such as water turnover, surface temperature, and rectal temperature, as well as drinking behavior of sheep were also evaluated. Fourteen nonlactating German Blackhead mutton ewes were randomly allocated into 2 groups: a control group (n = 7) that was already shorn, and a treatment group (n = 7) that was left unshorn (wool length: 10.6 ± 1.2 cm). Individual feed and water intakes were recorded throughout the experiment (d 1 to 71). Two weeks after measurements commenced (d 15), treatment sheep were shorn. Water intake was estimated twice for 2 consecutive weeks by using deuterium dilution techniques (d 1 to 15 and d 57 to 71). Ambient temperature (T(a)), relative humidity, and respiratory rate were measured daily, whereas BW, rectal and animal surface temperatures (using infrared thermography), and wool length were measured weekly. In the first 2 wk, when treatment sheep were unshorn, treatment and control ewes differed (P < 0.05) in DMI (52 ± 4 vs. 59 ± 4 g·kg(-0.75)·d(-1)), water intake (165 ± 17 vs. 134 ± 18 g·kg(-0.75)·d(-1)), respiratory rate (66 ± 5 vs. 31 ± 4 breath/min), rectal temperature (39.3 ± 0.2 vs. 38.8 ± 0.1°C), and surface temperatures (body side: 19.3 ± 0.3 vs. 24.5 ± 0.6°C; leg: 25.8 ± 2.4 vs. 27.4 ± 1.6°C). However, after shearing, these differences partly disappeared. The same trend in water intake between groups was confirmed using the isotope dilution technique. We found a significant relationship between T(a) and water intake, respiratory rate, and body surface temperatures. Even under temperate conditions (T(a) < 28°C), shearing significantly reduced core body temperature, water intake, and respiratory rate in German Blackhead mutton sheep, thus indicating heat stress in fleeced animals, which should be considered when determining the optimal shearing time in sheep as well as when estimating water requirements.