BOTANICAL COMPOSITION AND NUTRIENT CONTENT OF DIETS SELECTED BY GOATS GRAZING ON DESERT GRASSLAND IN NORTHERN MEXICO

The diets selected by esophageal-fistulated indigenous goats grazing on desert grassland in northern Mexico were characterized throughout the year, in terms of botanical composition, nutrient content and preference indices. Browse (primarily Parthenium incanun, Agave lechuguilla, Buddleja scordioides, and Atriplex canescens), constituted over 80% of the goats' diet throughout the year except 57% during the rainy season in April. Grasses made up less than 10% of the diet for most of the year except during the dry period in October. Bouteloua karwinskii was the grass most utilized. Sphaeralcea angustifolia was the most important forb in goats diet (23% of the diet in April). Goats showed the highest preference for A. canescens, B. scordioides, and S. angustifolia. Nutritional adequacy of forage for the greater part of the year was poor. Goats were not able to attain the NRC recommended total consumption of protein for pregnancy and lactation (levels of protein ranged from 7.1 to 12.1%). Phosphorus and energy intake were estimated to be inadequate always, even for maintenance. Despite these constraints, goats productivity in the area is acceptable. Perhaps indigenous goats have lower nutrient requirements than those given by NRC.