|Jung g a,|
|Pushkin r t,|
|Reid r l,|
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/10/1994
Publication Date: N/A
Citation: Interpretive Summary: Variability in performance of sheep and cattle grazing Brassicas in different countries has been attributed to metabolic inhibitors (e.g., glucosinolates, S-methyl cysteine sulfoxide), copper deficiency, lack of fiber or climatic conditions. Some of these possibilities were examined by blood and tissue analysis of lambs in the Brassica trials described in paper 1. Changes in some blood constituents, such as serum thyroid hormones (T3, T4), Heinz bodies, packed cell volume, were fairly consistent between years and reflected the presence of glucosinolates and SMCO in the Brassicas. Other changes were unexpected. There was a consistent depression in serum cholesterol (and triglycerides in later trials) and values were considerably below the normal concentrations observed in sheep. Concentrations of blood glucose and urea N also varied between pasture treatments and with duration of grazing. In one year, dosing with supplementary iodine and copper had no effect on serum copper levels but increased liver storage of copper. None of the blood changes observed provided much evidence for a strong effect of plant inhibitors on metabolism or on growth responses of grazing lambs.
Technical Abstract: 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 (glucosinolates, S-methyl cysteine sulfoxide) on health and performance. Serum thyroxine (T4) concentrations in lambs grazing Brassicas decreased initially after initiation of grazing, with a subsequent recovery, and concentrations were increased by oral dosing with I or I + CuO. Serum 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. perkinensis (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 on Brassicas, with little change 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. While 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.