Evaluation of sun-dried Opuntia ficus-indica var. Algerian cladodes in sheep diets

English: The effect of incremental inclusion levels (0, 12, 24 and 36%) of dried and coarsely ground Opuntia cladode material in balanced diets to substitute some of the luceme was investigated with regard to the digestibility of the diets, as well as the effects of the Opuntia cladodes on rumen variables (pH, ammonia levels and volatile fatty acid concentration). The digestibility trial was conducted over a period of 19 days with 24 young Dorper wethers; divided in four treatment groups (TO, Tl2, T24 and T36) each receiving a different inclusion level of Opuntia cladodes. Feed grade urea was included in diets containing Opuntia cladodes to compensate for the lower crude protein (CP) content of the Opuntia cladodes. Water consumption, food intake and digestibility of the diets were measured. The inclusion of incremental levels of Opuntia cladodes caused a decrease in organic matter (OM), acid-detergent fibre (ADF), neutral-detergent fibre (NDF) and gross energy (GE), while the ether extract (EE) content increased. The water intake of the wethers increased significantly (P<0.05) with the increased Opuntia cladode content of the diets while urine excretion remained the same. The level of food intake as well as the faeces dry matter (DM) excreted remained the same for all diets but the DM content of the faeces decreased with the higher Opuntia cladode inclusion levels. This is ascribed to the mucilage content of the Opuntia cladodes. The incremental inclusion levels of Opuntia cladodes caused an increase in apparent DM digestibility coefficient (from 0.673 for diet TO to 0. 716 for diet T36) suggesting that the Opuntia cladodes are highly digestible. Due to the low OM content of the Opuntia cladodes there was a decrease in the digestible energy (DE) content from diet TO (17.253 MJ/kg) to diet T36 (12.689 MJ/kg). In spite of these results there appeared to be no discemable difference in overall performance of the sheep on the various diets. The rumen fermentation was studied with 4 rumen cannulated Dorper wethers in a trial with a crossover design during four successive 14-day periods. The incremental inclusion levels of Opuntia cladodes in the diets had no significant (P<0.05) influence on the rumen ammonia (NH3) concentration. The rumen NH3 concentration was consistently between 9.4 mg NH3/IOO ml rumen fluid and 58.5 mg NH3/lOO ml rumen fluid, with a peak at 2 hours postfeeding. The inclusion of Opuntia cladodes in the diets also had no effect on the rumen pH. The rumen pH consistently ranged between 6.3 and 7.2. The inclusion level of Opuntia cladodes also had no significant (P<0.05) effect on the rumen volatile fatty acids (VF A) concentration or the proportions of the acetate, propionate or butyrate in the total VF A pool in the rumen. There was also now significant (P<0.05) difference in the in sacco DM disappearance in the rumen, again suggesting no effect on the microbial activity in the rumen. The use of dried and coarsely ground Opuntia cladodes in balanced diets for sheep as partial substitution for coarsely ground luceme hay to an inclusion level of 36% in the diet is, therefore, a viable option and can decrease the cost of sheep diets. In practical terms the greatest challenge to overcome will be the successful drying of large quantities of Opuntia cladodes, thus enabling farmers to transport it over longer distances from the production areas to where it can be used as livestock feed. This study offer some suggestions about cutting and drying of the Opuntia cladodes but further research is required to determine what possible influence the processing and drying of the cladodes in the sun may possibly has on its nutritional value. More research is required on the role and especially the effects of mucilage on the digestive processes in ruminant feeds.