Morphological characteristics of perennial ryegrass leaves that influence short-term intake in dairy cows

In sustainable agriculture, adaptation of swards to grazing is a major issue for breeding forage grass cultivars. Understanding the relationships between sward traits and animal production under grazing could help to identify criteria for selection. Intake is the major limiting factor for animal production under grazing. In this paper, short-term intake rate by grazing dairy cows (Bos taurus) is compared between eight diploid perennial ryegrass (Lolium perenne L.) populations. Four replicates per population were measured over four periods (April and May 2001, and April and October 2002) in two experiments per period, that is, intermediate- and late-maturity groups. For each period, sward structure was characterized by tiller density, leaf blade and sheath lengths, and green leaf and total dry matter (DM) yield, while nutritive value was characterized by in vitro dry matter digestibility (IVDMD), percent of DM, N, water-soluble carbohydrate (WSC), and neutral-detergent fiber (NDF) contents. For the late-maturity populations, the population with the shortest leaves had a lower fresh matter intake rate (10.5 kg h(-1)) than the three others (12, 12, and 11.6 kg h(-1), respectively). For the intermediate-maturity populations, differences in intake rates among populations were significant (P = 0.06) for all periods and were highly significant (P < 0.0004) in April 2002. In this period, 49% of the variation in fresh matter intake rate could be explained by blade length. In conclusion, differences in short-term intake rate between populations of diploid perennial ryegrass are highlighted. In both maturity groups, blade length appears to be an important factor explaining these differences.