Use of Self‐Limiting Fishmeal and Corn Supplements for Calves Grazing Rye‐Ryegrass Pastures

Young, growing calves (Bos taurus × Bos indicus) grazing annual small grain‐ryegrass (Lolium multiflorum Lam.) pasture typically gain weight below their maximum genetic capability. Two trials were conducted to determine the influence of self‐limiting protein and energy supplements on performance of Simmental crossbred calves grazing ‘Elbon’ rye (Secale cereale L.)‐‘Marshall’ ryegrass pasture. Pastures were located on an upland, well‐drained Darco soil (loamy, siliceous, thermic Grossarenic Paleudult). In Trial 1,40 ½ Simmental × ¼ Hereford × ¼ Brahman calves (20 steers and 20 heifers) were allotted by weight (670 lb) and visual condition score to either rye‐ryegrass pasture with free‐choice mineral (PAS); PAS plus a fishmeal supplement (FML); PAS plus a corn (Zea mays L.) supplement (CRN); or PAS plus a corn supplement containing rumen‐stable lysine and methionine (CAA). In Trial 2,30 calves of the same breed composition were allotted (600 lb) to three of the same four treatments as in Trial 1 except that the CAA treatment was excluded. Two replicate pastures of each treatment were used in both Trial 1 and Trial 2. Experimental durations of Trial 1 and 2 were 90 d and 102 d, respectively. In Trial 1, average daily gain (lb/d) for calves that received CRN (3.47) and CAA (3.26) was higher (P < 0.01) than for calves on PAS (2.21) or FML (2.62). In Trial 2, the average daily gain of calves assigned to CRN (2.77) was greater than calves assigned to either FML (2.53) or PAS (2.40 lb/d). Animal data from both trials suggested that CRN and FML supplements were converted to additional gain at 2.2:1. Supplement conversion to extra gain at a 2.2:1 ratio suggested that forage intake and/or use may have been increased. Supplemental energy also may have provided a source of rapidly fermentable energy which was well synchronized with NH3 and peptide production from forage protein degradation; which, in turn, may have resulted in a greater synthesis of microbial protein.