Abstract
Backfat depths, marbling scores, and concentrations of plasma insulin, cortisol, triiodothyronine (T3), and thyroxine (T4) were determined in 394 calves with and without Wagyu genetics. Hormone concentrations were determined three to five times for hormones between weaning and slaughter. Calves were weighed and backfat was ultrasonically determined at 28-d intervals, and assigned for slaughter when ultrasonic backfat depths approached 12 mm. Heifers weighed less (P < 0.001) and had more backfat (P < 0.05) and more marbling (P < 0.05) than steers at slaughter. Breed influenced slaughter weight (P < 0.001) and average backfat depth (P < 0. 001), with Wagyu/Angus and Wagyu/Hereford crosses and Angus purebreds generally having greater backfat depths and lower slaughter weights than other crosses and purebreds. Marbling scores were not affected by breed (P > 0.1), although Wagyu crosses had more marbling (P < 0.05) compared with purebreds when variability in marbling due to differences in backfat depth was removed. Plasma cortisol, T3 and T4 were affected by calf breed, although there were no clear patterns for groups of breeds or breed crosses. There was a slight trend (P < 0.2) towards higher insulin levels and lower cortisol, T3 and T4 levels in some groups of calves with more backfat. Higher mean levels (P < 0.05) of T3 and T4 were found in all but one group of animals with more marbling. Thus, thyroid hormones may have a role to play in enhancing marbling in cattle. Key words: Wagyu cattle, marbling, backfat, insulin, cortisol, thyroid hormones
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