Forty-eight multiparous, medium-framed cows, calving between Jan. 02 and Mar. 05 were used in a 3 × 2 factorial experiment with three totally mixed ration (TMR) formulations and two levels of protein supplementation. The TMRs were formulated to contain 75, 50 or 25% silage (DM basis). The balance of the diet comprised barley, barley straw, soybean meal and urea, such that all TMRs were formulated to be isoenergetic and isonitrogenous. Supplemental protein was supplied as soybean meal at either 0 or 0.44 kg DM d-1. Diets were fed from Jan. 11 to turnout on May 26. Intake and performance were monitored during this period, and performance at pasture was recorded until weaning on Sep. 03. The only interactions between TMR and protein supplementation were a positive response to protein for DM intake (P < 0.05) at the 50% silage level and for blood urea N (P < 0.05) at the 25% silage level. Reducing the amount of silage in the TMR had no effects on calf performance or milk production, except that milk protein concentration was higher when the TMR contained 50% silage (quadratic effect; P < 0.04). However as the percentage of silage in the TMR declined, cows lost less body weight (linear effect; P < 0.001) and appeared to improve in condition. The interval between calving and conception increased linearly as the percentage of silage in the TMR declined (P < 0.05). Supplemental protein had no major effects on performance, but limited the loss of body condition during the feeding period (P < 0.03), although this was offset by increased loss of condition on pasture (P < 0.01). There were no effects of protein supplementation on calf performance or reproductive efficiency. It is concluded that silage can be successfully replaced with other ingredients in winter beef rations, provided the nutrient concentration is balanced. Supplemental protein had little effect on any parameters of performance. Key words: Beef cow, cow-calf, silage, straw, gains, weaning weight, reproduction
Influence of supplemental copper, manganese, and zinc source on reproduction, mineral status, and performance in a grazing beef cow-calf herd over a 2-year period
