A comparative study of nutrients utilization, alkaline phosphatase activity and creatinine concentration in the serum of sheep and goats fed diets based on olive leaves.

The aim of this study was to compare, in goats and wethers, the nutritive utilization of diets including olive leaves (OL) and the possible detrimental effect of that by-product. Three different diets were studied: OL, OL plus polyethylene glycol (PEG) (OLP) and OL supplemented with barley [164 g/kg dry matter (DM)] and faba beans (59 g/kg DM) (OLSUP). Apparent digestibility of nutrients and energy and nitrogen balances were determined along with creatinine concentrations and alkaline phosphatase (ALP) activity in the serum. The apparent digestibility of OL was low and similar in goats and wethers (54.4% and 53.5%, 22.2% and 21.6% and, 47.7% and 46.6% for DM, crude protein and neutral detergent fibre in goats and wethers, respectively). The addition of PEG did not improve (p > 0.05) digestibility of OL, although a slightly beneficial effect on the digestion of structural carbohydrates was observed (up to 8.4% and 7.10% in goats and wethers, respectively). The supplementation of OL with barley and faba beans increased (p < 0.001) the apparent digestibility of nutrients and the energy value. The consumption of the OL led to high ALP activity in the serum. Despite the higher sensitivity of wethers to Cu levels, our results show a similar digestive use of OL by wethers and goats and suggest the need of further comparative investigations focusing on the effect of the presence of high Cu levels in the by-product on the animal health.