Effect of protein supplementation on forage intake and nitrogen balance of lambs fed freshly harvested wheat forage.

Wether lambs (mean BW = 32 kg) fed wheat forage freshly harvested daily (Exp. 1, n = 28; Exp. 2, n = 25) were used to evaluate the effects of supplemental energy and protein on forage intake, diet digestibility, and N retention. Experiment 1 was conducted in the winter of 1988 and the four treatments were 1) CONTROL, no supplement; 2) ENERGY, low-protein corn-based supplement; 3) CSM, 22% CP supplement with cottonseed meal; and 4) CGM, 22% CP supplement with corn gluten meal. Experiment 2 was conducted in the spring of 1989, and the five treatments were 1) CONTROL; 2) ENERGY; 3) CSM, 23% CP with cottonseed meal; 4) FTM, 25% CP supplement with feather meal and corn gluten meal; and 5) BM, 25% CP supplement with blood meal and corn gluten meal. All supplements were isoenergetic and composed 22 and 24% of total DMI in Exp. 1 and 2, respectively. In Exp. 1, forage intake was not affected but total and digestible DMI were increased (P < .01) by energy and protein supplementation. Protein supplements did not (P > .10) increase total and digestible DMI compared to ENERGY supplementation but tended (P < .10) to increase N retention (g/d). In Exp. 2, digestible DMI and N retention did not differ among the five treatments. Results suggest that lambs consuming wheat forage in the vegetative stage (Exp. 1) will have greater digestible DMI if supplemental energy or protein is provided. When more mature wheat forage was fed (Exp. 2), energy seemed to limit animal performance.