Tethering meat goats grazing forage of high nutritive value and moderate to high mass

A. K. Patra, R. Puchala, G. Detweiler, L. J. Dawson, G. Animut, T. Sahlu, and A. L. Goetsch

Journal of Animal Science 84(Supplement 1):27. 2006

Yearling Boer x Spanish goats (24) were used in a crossover design to determine effects of tethering on forage selection, intake, and digestibility, grazing behavior, and energy expenditure (EE) with forage of high nutritive value and moderate to high mass. Four 0.72-ha pastures of wheat (Triticum aestivum) and berseem clover (Trifolium alexandrium) were grazed in April to May. Each pasture hosted six animals, three with free movement and three attached to a 3 m tether for access to a circular area of 28.3 m2. One animal of each treatment and pasture was used to determine forage selection, fecal output, or grazing behavior and EE. Measures were in the second week of 2-wk periods. Mass of forage DM before grazing in Tethered areas averaged 2,649 and 2,981 kg/ha in periods 1 and 2, respectively. The CP concentration in ingesta was greater ((P < 0.05) 23.1 and 20.3%; SE = 0.82) for Free vs Tethered animals. The level of NDF (54.0 and 55.9%; SE = 1.66) and in vitro true DM digestion (75.7 and 76.5%; SE = 1.20) were similar between treatments. Metabolizable energy intake was greater (P < 0.05) for Free vs Tethered animals (12.7 and 10.4 MJ/d; SE = 0.89). There were small treatment differences (P < 0.05) in in vivo apparent digestiiblity of OM (71.7 and 72.3.4%; SE = 0.24) and NDF (63.3 and 65.2% for Free and Tethered, respectively; SE = 0.92). There were no treatment effects on time spent ruminating, idle, or eating (405 and 366 min/d for Free and Tethered, respectively; SE = 42.5). Energy expenditure was considerably greater (P < 0.05) for Free vs Tethered animals (633 and 512 kJ/kg BW0.75, respectively; SE = 27.4). In conclusion, differences in EE between goats freely grazing and tethered may not be solely attributable to ME intake, distance traveled, and(or) grazing time. Tethering as a model for free movement may offer a reasonable means of studying some aspects of grazing such as ingesta composition but appears inappropriate for others, including EE and efficiency of energy metabolism.