The effect of water soluble carbohydrate concentration of ryegrass on the partial preference of sheep for clover : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

A preference feeding trial comparing perennial ryegrass cultivars and white clover monocultures was carried out to determine whether ploidy or water soluble carbohydrate (WSC) content would influence the partial preference for clover and ryegrass. Six mixed age Coopworth ewes were housed in individual pens and once a day were offered swardlet monocultures of white clover adjacent to one of three ryegrass cultivars. The ryegrass cultivars were 'Aberdart' (high sugar), 'Bealey' (tetraploid) and 'Bronsyn' (diploid). Before the preference test, one swardlet of each grass cultivar was shaded to prevent the accumulation of sugars over the day and a second swardlet of each cultivar was left unshaded as a means of further testing the effect of WSC on partial preference. WSC concentration did not differ between ryegrass cultivars. But the WSC of shaded grasses was lower (21.0%) than that of unshaded grasses (23.0%) (P=0.06). Shading significantly increased neutral detergent fibre (NDF) from 42.2% to 43.9% (P<0.01) in nonshaded and shaded grass respectively indicating a shift in the proportion of non-structural to structural carbohydrates due to shading. Partial preference for clover was increased with the high NDF and low WSC concentration of the shaded grass. The total number of bites from clover swardlets fed adjacent to shaded grass swardlets was 21 % greater (P=0.03) than when fed adjacent to non-shaded grass swardlets. Sheep took 44% of their bites from clover swardlets that were fed adjacent to non-shaded grasses and the percentage of bites from clover was significantly (P=0.03) higher at 55% when clover swardlets were paired with shaded grasses. There were no significant effects of ryegrass cul ti var on any aspect of the preference tests. The partial preference for clover does change with the variation in the WSC concentration of ryegrass as indicated by the shaded - non-shaded comparison. However differences in WSC content between ryegrass cultivars was not high enough in these trials to affect the partial preference for clover.