Grazing behavior of steers on different annual ryegrass and white clover forage systems.

摘要

Studying grazing behavior of ruminants may help increase the understanding of the use of forage systems of varying forage types and composition. This study was conducted during 2008 at Raymond, MS, to evaluate grazing time by ruminants on various forage systems to examine any relationship with pasture composition and stocking rate (SR). Annual ryegrass (Lolium multiflorum Lam. 'Marshall') and white clover (Trifolium repens L. 'Durana') were used to create forage system treatments of either monoculture grass (MG) or monoculture legume (ML), a binary mixture of grass and legume (MIX), or a spatial system of adjacent grass and legume monocultures in a 50:50 land area ratio within the same paddock (SS). Two levels of SR (3 or 6 steers [Bos taurus] ha-1) were imposed on each of the four forage systems to give a 4x2 factorial arrangement of treatments with two replicate paddocks of each treatment combination in a completely randomized design experiment. Two Angus crossbred yearling beef steers (236+or-24 kg initial body weight [BW]) were randomly assigned to each of the 16 paddocks. Time spent grazing per animal on continuously stocked pastures was recorded for 10 d selected randomly during the months of April and May, with each day of observation lasting for 14 h (0615 to 2015 h). Forage system had an effect (P<0.001) on time spent grazing daily. Animals grazing MG and MIX spent similar time grazing (mean=442 min per animal), which was greater than daily grazing time on SS (380 min per animal). Grazing time was least on ML (341 min per animal). Also, SR had an effect (P<0.001) on daily grazing time. Animals on high SR (431 min per animal) spent greater time grazing than those on low SR (371 min per animal). There was no difference in time spent grazing on each component of the adjacent monocultures of grass and legume within the SS (P=0.23; 197 [the monoculture legume component of a SS] vs. 182 min per animal [monoculture grass component of a SS]). Less grazing time by animal on SS than MG and MIX may have implications for performance of animals grazing such a system because of expected lesser energy expenditure for grazing.