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

Two experiments were conducted to determine the rumen fluid disappearance r ates (kd) of beta-carotene, lutein, total carotene and total xanthophyll fr om lucerne (Medicago sativa) hay, in two ruminant species: Brahman steers ( fat-pigmenting) and Granadine goats (non-pigmenting). Within species, the i n vitro and the in situ methods were compared. The concentration of caroten oid compounds was determined by spectrophotometry and high performance liqu id chromatography. The in vitro disappearance trends were linear for all co mpounds (P < 0.01). beta-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 wer e quadratic (P < 0.01). Dry matter kd were 1.9 and 1.5% h(-1); cellular con tent, 2.0 and 2.3; beta-carotene, 2.5 and 1.2;lutein, 2.5 and 1.5;total car otene, 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 vi tro method in both species, can be related to the dry matter and cellular c ontent kd. These results suggest that carotenoids disappear probably by joi ning the cellular content and not by their direct destruction or by attack from the ruminal microorganisms, and the ruminal disappearance is independe nt of the species studied. (C) 1999 Society of Chemical Industry.