Serum Cortisol Concentration in Different Sex-Types and Slaughter Weights, and its Relationship with Meat Quality and Intramuscular Fatty Acid Profile

N.J. Okeudo and B.W. Moss

A group of 84 crossbred lambs comprising 21 lambs for each of 4 sex-types (entire ram, vasectomized ram, castrate and ewe) were subdivided within each sex-type into 7 slaughter weights (32, 36, 40, 44, 48, 52, 56 kg). There were 3 lambs per slaughter weight. Lambs were born in the latter part of spring and were out on pasture with their dams, but were housed by September and fed a concentrate diet and hay. Lambs were slaughtered in a nearly abattoir and blood samples were collected for cortisol determination. Meat quality and fatty acid profile were assessed using the 6th-12th rib section of the Longissimus dorsi muscle. The mean serum cortisol concentrations ranged from 103.3-117.7 nMol L^-1 and differences due to sex - type were not significant (P>0.05). However, serum cortisol concentration was positively correlated with slaughter weight (r = 0.34, P<0.01) and age (r = 0.43, P<0.001). Whereas serum cortisol level was negatively correlated with initial pH and positively correlated with intramuscular fat in castrates (P<0.05), the same correlations in other sex-types were not significant (P>0.05). Cortisol level was negatively correlated with cooking loss in all sex-types (P < 0.01) and also significantly related to fatty acid profile (P<0.05).