Perennial ryegrass for dairy cows: effects of cultivar on herbage intake during grazing

Keywords:Perennial ryegrass, Lolium perenne , sward morphology, sward cutting, n-alkanes, herbage intake, selection, preference.Perennial ryegrass ( Lolium perenne L.) is the most important species for feeding dairy cows. The majority of the farmers in the Netherlands graze their dairy cows during summer. During grazing, the limited herbage intake is the main limitation of the dairy cows' production. This study examined opportunities for grass breeders to influence the quality of perennial ryegrass cultivars to improve the herbage intake of dairy cows.Six cultivars of perennial ryegrass (Abergold, Respect, Agri, Herbie, Barezane,Barnhem) were intensively studied during two years (2000 and 2001) between June and September. There were differences between the cultivars for important characteristics influencing herbage intake, e.g. herbage yield, sward surface height and density. Furthermore, differences between cultivars were found for the proportions and the biomass of leaf, stem and pseudostem in the sward. The sward cutting and the n-alkanes technique, both methods to determine the herbage intake by grazing dairy cows, were compared with an average that was calculated from the milk production and the live weight of the dairy cows. The sward cutting technique gave very variable results that varied largely per cow and year, and did not match with the expected calculated intake. The n-alkanes method gave less variable results that were more related to the expected calculated intake values. Within the n-alkanes method, the ratio C 32 :C 33 gave the best results.The effects of perennial ryegrass cultivars on the intake of grazing dairy cows were examined. In 2002 and 2003, cows grazed each of the four cultivars during four 2-week periods. Herbage intake was estimated using the C 32 :C 33 -alkanes method. In 2002, a clear difference was found between the cultivars, but in the second year no differences were found. A higher herbage intake was related with a higher mass of herbage and green leaf, a higher sward surface height, a lower infestation rate of the crown rust fungi anda lowerlignin content in the herbage. The cultivars differed too little in the other quality parameters to induce effects in the cow. The aspects of selection and preference were examined in an experiment with the six earlier described cultivars. The experiment was conducted in three 4-day periods in spring, summer and autumn. Herbage intake was measured using the sward cutting method. The dairy cows very consistently preferred cultivars with a high water soluble carbohydrates concentration, a high digestibility, a low cell wall concentration and a low ash concentration. It was concluded that in the selection process the chemical quality of the herbage plays an important role.