INFLUENCE OF NATIVE SHRUBS ACACIA-RIGIDULA, CERCIDIUM-MACRUM AND ACACIA-FARNESIANA ON DIGESTIBILITY AND NITROGEN-UTILIZATION BY SHEEP

Leaves from the shrubs blackbrush acacia (Acacia rigidula), pale verde (Cercidium macrum), and huisache (Acacia farnesiana) were evaluated a s protein supplements in low-quality buffelgrass (Cenchrus ciliaris) s traw-based diets for sheep using in vivo (Trial 1) and in situ (Trial 2) digestibility trials. Leaves were collected in Marin, Nuevo Leon, M exico. In Trial 1, the four diets that contained approximately 1.5% N consisted of: (1) control-26% alfalfa hay plus 74% buffelgrass straw ( BS); (2) 30% blackbrush acacia plus 70% BS; (3) 16% pale verde plus 84 % BS; and (4) 21% huisache plus 79% BS. Twelve sheep (Pelibuey x Rambo uillet, average 37.5 kg BW) were fed the four diets (three sheep per d iet) in two equal portions daily (0800 and 1600) in addition to approx imately 400 g of a sorghum grain-based supplement (11%, CP) at 0800 h. In Trial 2 the rate and extent of dry matter (DM) and N loss from nyl on bags for alfalfa hay, blackbrush acacia, pale verde, and huisache w as evaluated using four ruminally cannulated sheep in a 4 x 4 Latin sq uare experiment. In Trial 1, nutrient digestibilities were low in shee p fed the blackbrush diet compared with the other three diets. Moreove r, sheep fed the blackbrush diet retained less N than sheep fed the ot her diets. Results of Trial 2 indicated large differences in the rumin al degradability among the four species. Alfalfa hay, pale verde and h uisache exhibited rapid rumen digestibility of DM and CP compared with blackbrush. Tannins from blackbrush may have negative effects on N an d fiber digestibility and N retention by sheep. However, low tannin sh rubs such as pale verde and huisache consumed at low levels, influence d nutrient digestibility and N retention of sheep in a manner similar to alfalfa hay. (C) 1998 Elsevier Science B.V.