EVALUATION OF BRASSICAS IN GRAZING SYSTEMS FOR SHEEP .2. BLOOD COMPOSITION AND NUTRIENT STATUS

Blood composition of lambs grazing Brassicas and stockpiled grass or g rass-clover pastures in the fall of 4 yr was monitored to assess possi ble effects of plant metabolites (e.g., glucosinolates, S-methyl cyste ine sulfoxide) on health and performance. Serum thyroxine (T-4) concen trations in lambs grazing Brassicas decreased upon initiation of grazi ng, with a subsequent recovery, and concentrations were increased by o ral dosing with I or I + CuO. Serum triidothyronine (T-3) increased gr adually with time and did not differ between lambs on Brassicas and on pasture at most time periods. In Exp, 3 and 4, T-4 levels were lower in lambs grazing Tyfon chinese cabbage hybrid (Brassica rapa L. x B. p ekinensis [Lour.] Rupr.) than in lambs on Forage Star hybrid turnip (B . rapa L.) Heinz body formation increased rapidly in lambs on Brassica s, with small decreases in packed cell volume (PCV); dosing with I + C uO reduced Heinz bodies in lambs on Tyfon and turnip pastures. In exp. 2, I + CuO treatment increased liver Cu concentrations but had no eff ect on serum Cu. Serum cholesterol and urea N concentrations declined rapidly in lambs on Brassicas, with little change in lambs on stockpil ed pastures. Decreases in serum triglycerides, and an increase in gluc ose concentration, were noted in Exp. 3 and 4 in lambs grazing Tyfon a nd Forage Star turnip. Although a number of differences related to pla nt composition were noted in blood lambs grazing Brassica forages rela tive to stockpiled pastures, the changes did not seem sufficiently sev ere to affect animal performance.