FORAGE UTILIZATION FROM NATIVE SHRUBS ACACIA-RIGIDULA AND ACACIA-FARNESIANA BY GOATS AND SHEEP

Two trials, (in vivo and in situ) were conducted to evaluate the influ ence of shrub leaves on digestion and N retention by goats and ruminal digestion by sheep. In trial one, 12 male castrated Spanish goats (32 .5 +/- 2.1 kg LW) were housed in metabolism stalls and randomly assign ed to three diets (four goats per treatment): (1) 23% alfalfa hay (Med icago sativa) plus bean straw (Phaseolus vulgaris); (2) 25% blackbrush acacia (Acacia rigidula) plus 75% bean straw and (3) 20% huisache (Ac acia farnesiana) plus 80% bean straw. Nutrient intake of goats was sim ilar (P > 0.05) among diets. Digestibility of DM was similar (P > 0.05 ) among goats; however, CP digestibility was higher (P < 0.05) for goa ts fed alfalfa hay and huisache diets than those fed blackbrush acacia diet. The cell wall and its fractions were digested more efficiently (P < 0.05) by goats fed alfalfa hay compared with the blackbrush acaci a or huisache diets, but cellular content of forages was digested simi larly (P > 0.05). In addition, goats retained similar amount of N (P > 0.05) among diets. Leaves from the shrubs were digested poorly in the rumen of sheep, compared with the alfalfa hay. Tannins in shrubs may have adverse influence in situ on digestibility of CP and NDF. Moreove r, condensed tannins may have reduced goat digestion of CP and NDF and its fractions. However, native shrubs may have potential as an econom ical supplementary feed for goats because N utilization and DM intake levels were similar for goats given alfalfa hay and native shrub diets . (C) 1997 Elsevier Science B.V.