A mathematical model used to describe animal performance on kikuyu and Coastcross II pastures.

Abstract

Data collected from a controlled grazing trial, in which the quality and quantity of kikuyu (Pennisetum clandestinum) and Coastcross II (Cynodon hybrid) pastures fertilized at 2 nitrogen levels (150 and 300 kg N/ha/a) and stocked at 3 stocking rates (8.05, 10, 74 and 13, 42 steers/ha) were related to animal performance. The individual variables significantly describing ADG were stocking rate (R 2 = 0, 86) and disc height (R 2 = 0, 70) (P < 0, 01). The quality variables, however, were less successful in describing ADG (percentage: crude fibre (R 2 = 0, 47), calcium (R 2 = 0, 63) and the Ca:P ratio (R 2 = 0, 49). When all the variables monitored were analysed using the multiple regression technique, ADG was found to be a function of the number of days spent on the pasture, stocking rate, nitrogen level, nitrogen/pasture type interaction, animal liveweigth, disc height lagged and the disc height lagged/pasture type interaction. The variance accounted for by this function was 90, 3%. However, the use of this function to predict ADG from an independent data set proved disappointing (R 2 = 0, 67) due to a difference in the regression coefficients between the response functions describing the test and trial data. The results indicated that herbage quantity plays a more dominant role in the description of ADG than herbage quality and until seasonal effects on herbage quantity can be adequately described, the prediction of animal performance from kikuyu and Coastcross II remains an illusive issue.

Keywords: adg; animal performance; coastcross ii; crude fibre; cynodon; grazing; herbage; kikuyu; natal; nitrogen levels; pasture quality; pennisetum clandestinum; south africa; stocking rate; stocking rates