Diet Quality and Performance of Heifers in the Subtropics

The effects of continuous vs. rotational stocking of bahiagrass ( Paspalum notatum Flugge), previous winter nutritional regimen {corn ( Zea mays L.) + soybean [ Glycine max (L.) Merr.] meal (CS) vs. soybean meal (SBM)}, and breed [Angus, Hereford, and Senepol ( Bos taurus ) and Brahman ( B. indicus )] were determined in 1990 to 1992. Forage mass [kg ha −1 dry matter (DM)], forage nutritive value [crude protein (CP) and in vitro organic matter digestibility (IVOMD)], average daily gain (ADG), body weight (BW), body condition score (BCS), and plasma urea N (PUN) and glucose (PGLU) were measured. There was a consistent carryover effect ( P < 0.05) of winter supplementation for initial BW and BCS, with CS > SBM while for PUN, SBM > CS. Breed affected most animal variables, with the general ranking of Angus ≤ Hereford ≤ Brahman and Senepol. Forage mass varied from an average of 1000 kg ha −1 in 1990 to 2000 kg ha −1 in 1992 because of rainfall distribution. Grazing treatment did not affect forage DM, CP, or IVOMD, but heifers that were continuously grazed had higher ( P = 0.0001) PUN levels than heifers that were rotationally grazed. Only during 1990, when dry weather restricted forage growth, did this translate into a trend for improved ADG and final BW. Because grazing management did not affect heifer performance in most years, the effects noted in this study resulted from: (i) the change in forage nutritive value during the grazing season; (ii) the carryover effect of previous winter supplementation; and (iii) breed differences, particularly temperate vs. tropical breeds.