Effects of the macroalga Laurencia snackeyi on enteric methane emission and lactational performance in dairy cows

This study investigated the effects of dietary supplementation with a red macroalga, identified as Laurencia snackeyi (LS), on lactational performance and enteric gas emission in lactating dairy cows. In preliminary in vitro experiments, LS decreased CH₄ production up to 97% dependent on dose. In the current in vivo experiment, 8 Holstein cows (2 primiparous and 6 multiparous) averaging (±SD) 79 ± 11 DIM and 48 ± 5.6 kg/d milk yield (MY) were enrolled in a crossover design experiment with two 28-d periods with a 10-d washout period between the experimental periods. Treatments were the control (basal diet) or basal diet + 1.5% LS (diet DM basis). Dry matter intake and MY data were collected daily, and milk composition samples were collected 4 times during the final week of each period. Ruminal contents were sampled via ororuminal tubing at 4 h after feeding on 2 consecutive days in the final week of each period. Spot fecal and urine samples were collected across 8 time points during the final week of each period for determination of nutrient digestibility and N utilization. Blood samples were collected at 4 time points for quantification of blood cell counts. Enteric CH₄ emission was measured using the GreenFeed system (C-Lock Inc.) during the final week of each period. Dry matter intake was decreased 12% by LS compared with control. Milk composition was largely unaffected, except tendencies for decreased milk true protein and lactose yields (7% for both) in cows fed LS. Milk bromide concentration increased 4.6-fold with LS supplementation relative to control, and iodine concentration was decreased by 11%. Daily CH₄ production, yield (CH₄ g/kg DMI), and intensity (CH₄ g/kg ECM) were decreased by LS compared with control by 37, 26, and 27%, respectively. Conversely, daily H₂ emission was increased 2.2-fold by LS. The concentration of total VFA was unaffected by treatment, but molar proportions of valerate and butyrate increased by 18% and tended to increase by 13%, respectively, in cows fed LS. Apparent total-tract digestibility was unaffected, except for a tendency for LS to increase ADF and starch digestibility. As a percentage of N intake, LS increased fecal N excretion and tended to increase milk N secretion. As a proportion of total white blood cells, lymphocytes were decreased by 7% and eosinophils increased 51% by LS. In conclusion, despite the decrease in DMI, LS can be an effective enteric CH₄ inhibitor, at least during short-term supplementation. Long-term efficacy and impacts on animal health and performance need to be investigated. Additionally, the inhibitory mechanism of LS on methanogenesis remains to be identified.