Digestibility, nitrogen balance and weight gain in sheep fed with diets supplemented with different seaweeds

Three completely randomised design experiments examined the effects of the inclusion of three seaweed species (Ruppia sp., Ulva sp. or Chaetomorpha sp.) into the diet on digestibility and nitrogen balance in Barbarine sheep. Diets were composed of oat hay ad libitum supplemented with 600 g of concentrate. Seaweeds were incorporated into the concentrate at increasing levels (0, 200, 300 or 400 g seaweed kg(-1) concentrate, dry matter (DM) basis) in replacement of other ingredients. Feed intake and water consumption were increased (P < 0.01) linearly with Ruppia supplementation. As the proportion of Ruppia was increased in the diet, the digestibility of organic matter decreased linearly (P < 0.01) from 0.698 (no seaweed) to 0.642 (400 g seaweed kg(-1) concentrate). Increasing the level of inclusion of Chaetomorpha up to 300 g kg(-1) did not affect the intake of concentrate. Organic matter digestibility decreased linearly (P < 0.001) from 0.685 with the control diet to 0.622 with the diet containing 400 g Chaetomorpha kg(-1) concentrate. The level of inclusion of Ulva did not affect feed intake or water consumption, but decreased linearly (P > 0.001) organic matter digestibility from 0.637 with the control diet to 0.599 with the diet containing 400 g Ulva kg(-1) concentrate. In all the experiments, nitrogen balance was positive and there were no differences among levels of seaweed supplementation in N retention or daily weight gain. These results suggest that seaweeds such as Ruppia, Ulva or Chaetomorpha can be incorporated into sheep concentrates up to 30% (DM basis) without adverse effects on feed digestibility or growth performance.