Evaluation of Brassicas in grazing systems for sheep: II. Blood composition and nutrient status

Blood composition of lambs grazing Brassicas and stockpiled grass or grass-clover pastures in the fall of 4 yr was monitored to assess possible effects of plant metabolites (e.g., glucosinolates, S-methyl cysteine sulfoxide) on health and performance. Serum thyroxine (T4) concentrations in lambs grazing Brassicas decreased upon initiation of grazing, with a subsequent recovery, and concentrations were increased by oral dosing with I or I+CuO. Serum triiodothyronine (T3) increased gradually with time and did not differ between lambs on Brassicas and on pasture at most time periods. In Exp. 3 and 4, T4 levels were lower in lambs grazing Tyfon chinese cabbage hybrid (Brassica rapa L. x B. pekinensis [Lour.] Rupr.) than in lambs on Forage Star hybrid turnip (B. rapa L.). Heinz body formation increased rapidly in lambs on Brassicas, with small decreases in packed cell volume (PCV); dosing with I+CuO reduced Heinz bodies in lambs on Tyfon and turnip pastures. In Exp. 2, I+CuO treatment increased liver Cu concentrations but had no effect on serum Cu. Serum cholesterol and urea N concentrations declined rapidly in lambs on Brassicas, with little change in lambs on stockpiled pastures. Decreases in serum triglycerides, and an increase in glucose concentration, were noted in Exp. 3 and 4 in lambs grazing Tyfon and Forage Star turnip. Although a number of differences related to plant composition were noted in blood of lambs grazing Brassica forages relative to stockpiled pastures, the changes did not seem sufficiently severe to affect animal performance.