ABSTRACT
Most prediction equations of feedlot performance cover average daily gains (ADG) below 1.5 kg/d. The question is whether these equations would be accurate for higher ADG. Medium-to-large-framed weanling and yearling steer calves were fed individually using a transponder-electronic gate system in three feedlot trials and fed in groups in two trials. Average daily gain ranged from .9 to 2.1 kg. Steers were implanted, fed to the same degree of finish, and slaughtered to obtain dressing percentage and cold carcass weight. Initial carcass weights were estimated from initial slaughter groups. Dietary ME concentration (i.e., 10.5, 11.5, 12.0, and 12.5 MJ ME/kg of DM, where 1 Mcal = 4.184 MJ), initial weight, dry matter intake (DMI), and days fed could explain 57% of the variation in ADG. The partial contribution of DMI to the total variation was only 5.2%, confirming the low correlation between DMI and ADG in feedlot trials. The correlation between metabolizable energy intake (MEI) and MEI/ADG also was low, but 80% of the variation in MEI/ADG was accounted for by the variation in ADG. Intake patterns, regardless of dietary energy concentration, indicate that ADG increased with DMI only when ADG was below 1.5 kg/d. Therefore, current prediction equations apparently overpredict ME requirements for fast-growing feedlot steers. Optimal performance occurred at a ME concentration of 12.0 MJ/kg of DM rather than 12.5 MJ/kg of DM. Dressing percentage and carcass gain increased as dietary energy concentration and ADG increased, and current prediction equations should predict that of fast-growing feedlot steers equally well.
Subject(s)
Animal Feed/standards , Cattle/growth & development , Energy Metabolism/physiology , Animals , Body Composition/physiology , Cattle/physiology , Eating/physiology , Male , Models, Biological , Predictive Value of Tests , Random Allocation , South Africa , Weight Gain/physiologyABSTRACT
The influence of different breeds of sire and dam types on cow productivity in an arid, subtropical environment was studied. Cows with calves sired by Simmentaler, Hereford and Bonsmara bulls were more (P less than 0.05) productive than those with calves sired by Afrikaner bulls. Simmentaler sires were superior (P less than 0.05) to Bonsmara sires. Crossbred cows of predominant (greater than 50%) Bos taurus breeding were generally superior to crossbreds of predominant B. indicus breeding and purebreds. Crossbreeding systems to utilize breed effects to optimise cow productivity within environmental constraints are discussed.
Subject(s)
Cattle/physiology , Reproduction , Animals , Cattle/genetics , Climate , Crosses, Genetic , Female , Genotype , Inbreeding , Male , Pregnancy , Reproduction/genetics , South AfricaABSTRACT
Response of Dorper sheep to treatment with FSH and PMSG and fertilisation after natural service, natural service following application of PGF2 alpha-containing gel on the posterior os cervix and surgical insemination with fresh semen were evaluated. FSH gave a significantly (P greater than 0.05) better response than PMSG. No significant differences between the different methods of fertilisation were observed.
