Dairy cattle grazing preference among six cultivars of perennial ryegrass

Received for publication September 13, 2005. Six endophyte-free diploid perennial ryegrass (Lolium perenne L.) cultivars (Abergold, Respect, Agri, Herbie, Barezane, and Barnhem) were examined in an experiment to investigate the selection behavior of grazing Holstein Friesian cows in July and September 2003 and May 2004 and to identify factors related to preference. Three groups of dairy cows (Bos taurus) were allowed to select among these six cultivars that were sown in replicates in a randomized block design with 12 plots (36.7 by 2.0 m). Each experiment lasted 4 d, and every day cows were offered a new field with 12 plots. Herbage intake was measured using the sward-cutting method, measuring herbage yield before and after grazing. The Chesson¿Manly index was used to quantify cattle grazing preference. Dairy cows did select among the cultivars in every period. The pattern of selection was consistent over the three experiments, Abergold was selected most, and Agri and Respect were least selected (22 vs. 14%). In July 2003 and May 2004, cultivars differed in morphological characteristics, but this was not related with grazing preference. In all three experiments, distinct differences were found among cultivars in chemical composition [dry matter (DM), ash, neutral detergent fiber, and water soluble carbohydrates (WSC) concentration] and digestibility of organic matter, especially for WSC concentration, which, when averaged over experiments, ranged between 135 g kg¿1 DM (Barezane) and 165 g kg¿1 DM (Abergold). Dairy cows preferred the cultivars with low ash and fiber concentration and high WSC concentration and digestibility