Effect of the dietary supplementation with sunflower oil-enriched bromoform from Asparagopsis taxiformis on lambs' growth, health, and ruminal methane production.

The red seaweed Asparagopsis taxiformis has a potent antimethanogenic effect, which has been proven both in vitro and in vivo. Vegetable oil immersions of this seaweed (hereafter Bromoil) help stabilise the bromoform (CHBr) responsible for its antimethanogenic effect. We evaluate the effects of increasing the levels of CHBr in lamb diets on growth performance, methane (CH) production, animal health and meat quality. Twenty-four Merino Branco ram lambs were fed a ground complete compound feed, supplemented with 50 mL/kg DM of sunflower oil with different CHBr content. The treatments were defined by the CHBr doses in the oil: 0 mg (control - B0), 15 mg (B15), 30 mg (B30) and 45 mg (B45) of CHBr per kg of feed DM. The feed was prepared daily by mixing Bromoil with the compound feed. At the end of the experiment, the lambs were sacrificed, the ruminal content was collected for in vitro fermentation to evaluate CH production and organic matter (OM) degradability, and the rumen mucosa was sampled for histological examination. Meat samples were collected for chemical composition and CHBr analysis. The half-life of CHBr in the air-exposed feed was 3.98 h making it very difficult to establish the practiced level of CHBr supplementation. Lambs-fed treatments B30 and B45 decreased DM intake by up to 28%. Average daily gain was also reduced due to CHBr supplementation, with B45 showing results 40% lower than B0. DM feed conversion ratio was similar for all treatments. The degradability of OM, the volume of total gas and of gas without CH were unaffected by the experimental treatments, evaluated by the in vitro method. However, the volume of CH decreased by up to 75% for treatments above 30 mg/kg DM, while the yield of CH/g OM degraded was reduced by up to 78% with treatments above 30 mg/kg DM. Meat chemical composition was not affected by Bromoil supplementation and no traces of CHBr were found in meat samples. During this experiment, the animals presented normal health and behaviour. However, postslaughter examination of the rumen showed distinct lesions on the ventral region of the rumen mucosa of animals supplemented with Bromoil. These lesions were more severe in the animals receiving treatments B30 and B45. This research determined that although concentrations of CHBr in the diet above 30 mg/kg DM helped to reduce CH emissions, it negatively affected the performance and rumen wall.