Supplementation effects on early weaned calves grazing cool- and warm-season grasses.

摘要

Early weaning of their calves increases the likelihood that first calf heifers will rebreed, but there is little information regarding pasture-based feeding programs for the weaned calf. Research was conducted in Gainesville, FL, to evaluate the effect of supplement rates on performance of early weaned (80 d of age) beef calves grazing annual ryegrass ( Lolium multiflorum)-rye (Secale cereale) mixtures from January to April (winter) and Tifton 85 bermudagrass (Cynodon sp.) from May to August (summer) 2003 and 2004. Three levels of supplement (10, 15, and 20 g kg-1 of calf liveweight) were evaluated in a completely randomized design with three replications. The supplement contained 147 and 700 g kg-1 of crude protein (CP) and total digestible nutrients, repectively. Pastures were rotationally stocked using a variable stocking rate in both seasons with 21- and 14-d regrowth periods for rye-ryegrass and Tifton 85 bermudagrass, respectively. Average daily gain increased linearly during the winter (0.74-0.89 kg) and summer (0.53-0.72 kg) as supplementation rate increased. There was a linear increase in live weight gain per hectare with increasing supplement rate during the winter (950-1320 kg) and summer (1100-1780 kg). In addition, two plot studies were conducted with the same species used in the grazing trials to evaluate the effect of N fertilization levels and forage regrowth interval on in situ CP fractionation of the forage. Treatments were the factorial combinations of three N rates (0, 40, and 80 kg ha-1) and two regrowth intervals, 3- and 6-wk (rye-ryegrass) and 2- and 4-wk (Tifton 85). Increasing N fertilization levels increased rye-ryegrass CP Fraction A (readily degradable) (410-590 g kg-1) and decreased linearly CP Fraction B (slowly degradable) (510-360 g kg-1) and Fraction C (undegradable) (74-48 g kg-1). On Tifton 85, increasing N fertilization increased linearly Fraction B (330-455 g kg -1) and decreased linearly Fraction C (283-208 g kg-1). In addition, greater proportions of fraction C were observed in forage of 4-wk (280 g kg-1) than 2-wk maturity (200 g kg-1). Results of these studies indicate that pasture-based feeding systems with modest levels of supplementation (10-15 g kg-1 of liveweight) are practical options for raising early weaned calves in Florida.