Carotenoid and retinol concentrations were determined in various tissues of sheep, goats and cattle, ruminants known to have widely different levels of pigmentation of their adipose tissues. An objective assessment of fat colour confirmed the whiteness of sheep and goat fat compared with that of cattle. No G-carotene was detected in the serum or fat of sheep and goats, but it was the predominant carotenoid present in the serum and fat of cattle. The major pigment present in serum and fat of sheep and goat was lutein, although its concentration was only 5-10% of that found in cattle. G-carotene was present in the liver of all three species with the highest concentration in cattle. Although lutein was the only carotenoid found in the serum and fat of sheep and goats, it could not be detected in their livers. The concentrations of retinol in serum and fat were similar for each species, but the liver of sheep had about three times the retinol concentration of the liver of goats and cattle. The transport of carotenoids in plasma was investigated. In sheep and goats, the pigments were associated mainly with very low density lipoprotein (VLDL) and low density lipoprotein (LDL), whereas in cattle, high density lipoprotein (HDL) was the major lipoprotein fraction involved.

Seventeen Brahman steers were removed from pasture and fed a high grain diet for 8 weeks prior to slaughter. Carotenoid concentrations were determined in samples of serum and subcutaneous fat obtained either from live animals or at slaughter. At slaughter carcass fat colour was assessed according to AUS-MEAT specification. The concentrations of G-carotene in the serum of these animals fell rapidly (over 60%, P lt; 0.001) in the first 2 weeks on the grain diet and then plateaued. There was no change in either the concentrations of carotenoids in subcutaneous fat or in fat colour of these cattle during the whole period of grain feeding. The overall average liveweight gain was 0.59 kg/day. Failure to observe changes in concentrations of carotenoids was unexpected, and may be partly due to the fact that these cattle did not settle to the trial conditions in the feedlot, as indicated by the significantly higher cortisol concentration in their serum compared with the initial slaughter group. The implications of the outcome of this study are discussed.