Feeding sunflower oil enriched with bromoform from Asparagopsis taxiformis impacts young bulls’ growth, health, enteric methane production and carbon footprint

Concerns regarding greenhouse gas emissions from the ruminant livestock sector led to research into different anti-methanogenic strategies. One of these strategies involves supplementing ruminant diets with Asparagopsis taxiformis, which produces anti-methanogenic halogenated compounds. The present study focused on the impact of supplementing A. taxiformis macerate with sunflower oil (Bromoil) on enteric methane emissions, whole-system carbon footprint, animal performance, and health. Sixteen Angus-cross young bulls fed a total mixed ration (TMR) diet, comprising haylage and concentrate (50:50 in DM) and 20 g of oil/kg of DM, were randomly assigned to one of three treatments varying in dietary bromoform (CHBr₃) concentration: B0 (0 mg/kg DM), B20 (20 mg/kg DM) and B30 (30 mg/kg DM). After a 17-day adaptation period to the diets and experimental conditions, the animals were fed ad libitum for 77 days. Methane emissions were measured using a GreenFeed unit. The animals were weighed every 14 days prior to feed distribution. Treatments were suspended 72 h before slaughter. Physical and chemical traits were evaluated in meat. The half-life of CHBr₃ in air-exposed diets was 3.18 h, and at 24 h, about 87% of the CHBr₃ had disappeared from the samples. Dry matter intake and feed conversion ratio were not affected by the treatments; however, average daily gain was reduced by 10% in B30 when compared to B0. Methane production per kg of BW gain was reduced by 33% in B20 and by 48% in B30, when compared to B0. The carbon footprint reported to BW gain can be reduced by up to 16 and 23% for B20 and B30, respectively, primarily due to the decrease in methane emissions. Carcass parameters, meat physical traits and fatty acid profile were not affected by the treatments, and no CHBr₃ residues were detected in meat and liver. However, residues of other products resulting from the breakdown of bromoform in the rumen were not tested. Examination of the rumen wall revealed lesions in animals across all treatment groups, including Control (B0), the cause of which was not conclusive. Bromoil from A. taxiformis was effective in reducing methane emissions from young bulls at doses between 20 and 30 mg CHBr₃/kg DM, without leaving traces of CHBr₃ in meat samples. However, to effectively reduce the carbon footprint during the fattening phase of young bulls, the reduction in methane emissions must be combined with improvements across the entire animal production chain, especially in manure management.