Effects of dietary supplementation with linseed oil, Ascophyllum nodosum or treated A. nodosum on animal performance, gaseous emissions, ruminal fermentation and microbiota, and meat quality in growing dairy beef bulls

Abstract Oils high in polyunsaturated fatty acids (PUFA) and seaweeds containing phlorotannins have potential anti-methanogenic effects in ruminants. This study assessed the potential of dietary supplementation with linseed oil, Ascophyllum nodosum or treated A. nodosum in an intensive beef cattle feeding system on animal performance, gaseous emissions, ruminal fermentation and microbiota, and muscle fatty acid profiles. Seventy-two dairy-beef bulls (380 kg; 11 months of age) were randomly allocated to one of four dietary treatments (n = 18) for a 70-d period. The diet consisted of a 60:40 grass silage:concentrate ratio. Silage was offered daily (0900 h) and concentrates were offered twice daily (0800 h and 1500 h). Dietary treatments were incorporated into the concentrate portion of the diet as follows; 1) CON (no supplementation), 2) LSO (linseed oil), 3) SW (A. nodosum) and 4) EX (A. nodosum extract), included to target 0, 4, 2 and 2% of dry matter intake (DMI), respectively. The concentrates were formulated to be isonitrogenous across the four treatment groups. Total DMI (American Calan Inc., Northwood, NH), average daily gain (ADG), gain:feed and enteric emissions (GreenFeed; C-Lock Inc., Rapid City, SD) were measured for the 70-d supplementation period. Total DMI (P = 0.17), ADG (P = 0.28), gain:feed (P = 0.68) and total tract digestibility (P = 0.70) did not differ across treatments. Daily methane production (P < 0.001) for CON, LSO, SW and EX was 210, 170, 202 and 193 g/d, respectively, resulting in reductions of 19 and 8% for LSO and EX, respectively, relative to CON. Ruminal fermentation parameters show that LSO was the only dietary treatment to increase propionate (P = 0.09) and decrease butyrate (P = 0.04) concentrations relative to CON. Microbial analyses showed LSO supplementation increased and decreased relative abundances of fungal genera Buwchfawromyces and Piromyces, respectively, while altering relative abundances of the bacterial genera Muribaculaceae, Bacteroidales RF16 group and Bacterium F082. Additionally, LSO increased linolenic acid (P < 0.001) and n-3 PUFA (P < 0.001) concentration of the longissimus dorsi muscle compared to CON, SW and EX. In conclusion, LSO was the most effective dietary supplementation strategy compared to CON, EX and SW, whereby it reduced methane emissions, modified ruminal fermentation and microbial profiles, and enhanced beneficial muscle PUFA concentration, without impacting animal performance.