The effect of alternative grass species and nitrogen content of grass on the grazing preference of sheep for white clover : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

The proportion of white clover (Trifolium repens L.) in mixed pastures is often below 20%, which is perceived to be insufficient to maximise N fixation and animal performance. This study investigated whether alternative grass species reduce the preference of sheep for white clover relative to grass on experimental plots that were established in January 2007 at Lincoln University, Canterbury. The partial preference of sheep for white clover, offered in combination with diploid perennial ryegrass (Lolium perenne L.), tetraploid perennial ryegrass, timothy (Phleum pratense L.) and cocksfoot (Dactylis glomerata L.) was measured by visual observation and changes in pasture in three grazing tests. During the April preference test the paired plots (grass and clover) were grazed by three Coopworth ewe hoggets between 8.30 am and 3.30 pm. Compared with diploid perennial ryegrass (50.8% ), proportion of grazing time spent on clover was lower for tetraploid perennial ryegrass (34.6%) and higher for cocksfoot (77 .6% ). An hourly assessment of grazing time spent on clover found a consistent ranking of cocksfoot > timothy > diploid perennial ryegrass > tetraploid perennial ryegrass (most time spent on clover listed first). During the June preference test two ewe hoggets were grazed on each clover plots paired with grass plots which had received either 0 or 100 kg N/ha from 9 am to 1 pm. The N application increased the N concentration by about 1 % DM for all grass species which reduced the proportion of grazing time spent on clover and apparent dry matter intake by 23% and 31 % respectively. During the August trial an additional 50 kg N/ha was applied to the fertilised grass plots. The paired plots were then grazed by two ewe hoggets from 9 am to 1 pm. N increased sward height by up to 2.2 cm for all grass species. The increase in sward height and N content reduced the amount of time spent on clover and increased the time on grass. There was no significant difference in the height, mass or composition of the white clover plots in any of the preference tests. The general 70% partial preference for white clover when offered perennial ryegrass did not occur in this study but the preference ranking suggests that an alternative grass like tetraploid ryegrass which has a higher preference relative to diploid perennial ryegrass is a possible option to improve the clover content in mixed pastures.