Relationships Among Protein Supplementation, Selected Blood Constituents, and Performance of Grazing Steer

Abstract

Beef steers grazing tobosagrass (Hilaria mutica [Buckl.] Benth.) range in western Texas were allocated to 3 groups (10 head/group) and fed either 0.00, 0.75, or 1.50 lb/hd/day of cottonseed meal each year of a 2-year study. Steer weights and samples of blood were collected at 21-day intervals beginning in April and ending in July to evaluate relationships among plane of nutrition, average daily gain (ADG), and selected blood components. Plasma was analyzed for glucose (GLU), non-esterified fatty acids (NEFA), thyroxine (T4), and triiodothyronine (T3). No consistent relationships were observed between supplement level and blood constituents. Serum GLU, T3, and T4 generally declined through each season as forage quality declined but did not closely reflect changes in daily gain of steers (r = 0.04, -0.05, -0.01, respectively). Environmental factors may have had a greater effect on daily gain than diet quality and, therefore, precluded the development of any useful relationships among blood components and AOG.