Dietary preference of dairy cows for perennial ryegrass cultivars growing with and without white clover

Dietary preference of dairy cows for eight perennial ryegrass cultivars (AberMagic, Alto, Base, Bealey, Commando, Kamo, One50 and Prospect) growing with and without white clover was examined at two vegetative stages (May and October) and one reproductive stage (November). Groups of dairy cows (n = 8) were offered free choice among cultivars growing with or without white clover for 6 to 8 hours. Preference was defined as the relative decreasing rate in sward surface height. Preference was higher for the tetraploid cultivars, Base and Bealey and the high-sugar diploid cultivar, AberMagic (preference ranged from 1.02 to 1.45). Preference was negatively correlated with herbage mass (r = -0.179, P = 0.013), proportion of dead material (r = -0.301, P < 0.001) and neutral detergent fibre (r = -0.287, P < 0.001), and positively correlated with sward surface height (r = 0.386, P < 0.001), ryegrass lamina length (r = 0.233, P = 0.001), tiller mass (r = 0.338, P < 0.001), water-soluble carbohydrate concentration (r = 0.143, P = 0.049) and organic matter digestibility in dry matter (r = 0.312, P < 0.001). Although the proportion of white clover was low (< 7% DM) in all three experiments, the interactions between perennial ryegrass cultivar and the presence of white clover were significant (P = 0.004 at pre-heading stage, P = 0.046 at reproductive stage and P = 0.038 at post-heading stage), with differences among preference for perennial ryegrass cultivars reduced when white clover was presen