• Stocking rate effects on goats: A research observation

      Mellado, Miguel; Valdez, Raul; Lara, Laura M.; Lopez, Ramiro (Society for Range Management, 2003-03-01)
      Knowledge on the ecological effects of goat grazing on arid rangeland is far from complete, and specifically there is little scientific information on effects of heavy goat grazing on arid ecosystems. One objective of this study was to determine botanical composition of dairy-type goat diets on heavily (1.5 ha per goat) and lightly (15 ha per goat) grazed Chihuahuan desert range by fecal microhistological analysis. A second objective was to determine whether vegetation cover, some blood metabolites and mineral levels, as well as fertility of goats were sensitive to high grazing pressure. The lightly grazed site had more (P < 0.05) total foliage cover (38.6 vs 30.4%) than the overstocked pasture. Total shrubs in diets of goats was greater (86.4 vs 72.4 in the late-dry period, 78.6 vs 42.1 in late-wet period; P < 0.05) on the heavily stocked pasture than the lightly stocked pasture. Forbs in the diets were lower (P < 0.10) in the late-dry (11.4 vs 21.5%), early-wet (55.4 vs 64.0%) and late-wet period (15.0 vs 45.8%) on the heavily stocked pasture than the lightly stocked pasture. Substantially lower (P < 0.01) serum glucose, urea nitrogen, Zn and Mg concentration at the onset of the breeding period in goats on the heavily stocked pasture, compared to goats on the lightly grazed pasture resulted in a higher (P < 0.01) abortion rate (22 vs 12%) and consequently a lower (P < 0.05) kidding rate (42 vs 55%). We concluded that overstocking with goats greatly reduced shrub and grass cover. Also, decades of continuously high grazing pressure has forced goats to alter diet selection pattern by consuming more resinous, toxic, and coarse species. This switch was associated with a lower nutritional status, a negative daily weight gain, lower body condition score in the late-wet period, and lower fertility on heavily grazed range.