Effect of Myiasis and Acute Restraint Stress on Plasma Levels of Immunoreactive , ß-Endorphin, Adrenocorticotrophin (ACTH) and Cortisol in the Sheep

Abstract

Cutaneous myiasis in sheep arising from the activity of Lucilia cuprina larvae can result in significant physiological changes in susceptible animals. The stress imposed on the pituitary-adrenal axis of the sheep in response to myiasis and acute restraint is the subject of this investigation. Merino wethers were exposed to handling restraint, and blood sampling, during examination for blowfly strike; where necessary, they were treated for cutaneous myiasis. Significant changes in the plasma concentrations of immunoreactive J3-endorphin (J3-EP), ACTH and cortisol were found in sheep with extensive myiasis, as compared with unstruck sheep or those with only localized myiasis. In five susceptible sheep with extensive cutaneous myiasis, mean plasma levels of J3-EP, ACTH and cortisol were 307 ± 71 pg ml-1, 953 ± 58 pg ml-1 and 232 ± 46 nmoll-1 respectively, compared with 818 ± 89 pg ml-1, 641 ± 41 pg ml-1 and 107 ± 17 nmol I-I in six unstruck sheep handled similarly. Whereas significant increases in plasma ACTH and cortisol can result from pituitary-adrenal responses to acute emotional or surgical stress, and are usually accompanied by a concomitant release of J3-EP from the pituitary, the present findings indicate a marked reduction in J3-EP levels and a significant increase in ACTH and cortisol in sheep following blowfly strike and acute handling restraint. This result suggests that cutaneous myiasis in susceptible sheep can alter the pituitaryadrenal response to acute restraint stress, and this could occur either by an alteration of precursor processing in the pituitary or by the selective release of ACTH.

Effects of Dystocia, Retained Placenta and Body Condition on Plasma .BETA.-Endorphin Profile in Periparturient Dairy Cows.

“…This result is comparable to the findings in sheep in which there were the different responses of plasma β-EP and cortisol to a change of environment [25]. It was reported that in response to acute stress, plasma β-EP, ACTH and cortisol levels in sheep increased and then β-EP declined while ACTH and cortisol levels remained elevated [26]. The different profiles of β-EP and cortisol may be related to the half-life of plasma degradation of these two hormones.…”

On-farm factors affecting physical quality of Merino wool. 1. Nutrition, reproduction, health and management

“…Most information demonstrates that wool from flystruck areas has lower SS than wool from adjacent non struck areas (Butcher et al, 1984), although variation between samples was considerable. It is likely that stress plays a role in causing 'tender fleeces' of struck sheep, with high ACTH and cortisol levels found in sheep suffering from blowfly strike (Shutt et al, 1988) and other studies demonstrating administration of these hormones can cause a 'break in the fleece' (Lindner and Ferguson, 1956;Chapman and Bassett, 1970;Thwaites, 1972). For affected animals some wool is lost if the infected areas are shorn.…”

Seasonal Patterns of Melatonin, Cortisol, and Progesterone Secretion in Female Lambs Raised Beneath a 500-kV Transmission Line

“…For example, Shutt et al (1987) reported significant increases in serum cortisol in lambs following various surgical procedures. Other studies of sheep found increases in cortisol due to fly bites and handling by humans (Shutt et al, 1988) and after yarding and vehicular transport (Fell et al, 1985).…”