Relationships of circulating cortisol levels with growth rate and meat tenderness of cattle and sheep

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Abstract
Plasma or serum levels of cortisol have been measured in cattle and sheep in four experiments and have been related to growth rates and meat tenderness. Significant treatment effects on cortisol levels included: (i) higher values in samples taken at slaughter from 30-month-old Angus steers (n = 30) than Hereford steers (n = 30) (P < 0.001); (ii) higher values in samples taken at slaughter from Cheviot sheep (n = 51) than Romney sheep (n = 48) (P < 0.02); (iii) higher values in jugular samples taken from a lighter group of lambs (n = 16) than a heavier group (n = 28) (P < 0.005); (iv) higher values following a period of stress induced by restraint for wether lambs (n = 23) than ram lambs (n = 21) (P < 0.02). Plasma cortisol levels in a group of 10 lambs sampled three times a week over a period of 11 weeks remained reasonably consistent for both stressed and unstressed animals. Relationships between cortisol levels and growth rate were significant for the cattle (r = -0.44**, n = 60), but were very low for all the groups of sheep. The relationships with meat tenderness (Warner-Bratzler shear) were significant only for cold-shortened samples of beef (r - 0.29*, n = 45).