In vitro and in situ disappearance of β-carotene and lutein from lucerne (Medicago sativa) hay in bovine and caprine ruminal fluids

Two experiments were conducted to determine the rumen fluid disappearance rates (kd) of β-carotene, lutein, total carotene and total xanthophyll from lucerne (Medicago sativa) hay, in two ruminant species: Brahman steers (fat-pigmenting) and Granadine goats (non-pigmenting). Within species, the in vitro and the in situ methods were compared. The concentration of carotenoid compounds was determined by spectrophotometry and high performance liquid chromatography. The in vitro disappearance trends were linear for all compounds (P < 0.01). β-carotene kd were 0.13 and 0.37; lutein, 0.20 and 0.25; total carotene, 0.20 and 0.62 and total xanthophyll, 0.30 and 0.77 h^-1 for steers and goats, respectively. The in situ disappearance trends were quadratic (P < 0.01). Dry matter kd were 1.9 and 1.5% h^-1; cellular content, 2.0 and 2.3; β-carotene, 2.5 and 1.2; lutein, 2.5 and 1.5; total carotene, 2.2 and 1.0 and total xanthophyll, 2.1 and 1.1% h^-1 for steers and goats, respectively. The large disappearance rates of carotenoids observed in the in situ method vs the virtual absence of disappearance in the in vitro method in both species, can be related tO the dry matter and cellular content kd. These results suggest that carotenoids disappear probably by joining the cellular content and not by their direct destruction or by attack from the ruminal microorganisms, and the ruminal disappearance is independent of the species studied.