Dose-dependent effects of the Asparagopsis taxiformis variety Brominata on enteric methane emissions of dairy cows

Abstract

The study objective was to assess the methane (CH4)-mitigating potential (CH4-MP) of an Asparagopsis taxiformis variety (Brominata; Blue Ocean Barns) and evaluate its effects on cow health when fed at increasing dietary inclusion rates (IR) in dairy cows. This paper reports data on the CH4-MP and production performance. In this study, 48 late-lactation cows (mean DIM = 386) blocked by parity were assigned randomly to receive 1 of 4 freeze-dried and pelletized Brominata IR treatments: 0% (CTL), 0.30% (standard IR [SIR]), 0.45% (SIR1.5), and 0.60% of DM (SIR2.0), with mean bromoform concentrations of 0, 17.4, 26.1, and 34.8 mg/kg of DM, respectively. The study consisted of a 10-d baseline measurement period (P1), a 4-wk IR ramp-up phase (P2), and a subsequent 9-wk response measurement period (P3). The pelletized Brominata was mixed uniformly into the TMR delivered daily to individual cows. The CH4 emissions were measured daily using the GreenFeed system (C-Lock Inc., Rapid City, SD). Milk composition, BW, and body condition scores were recorded once every 2 wk. The feces samples were collected directly from the rectum every 8 h over 2 consecutive days during the last week of P3 to determine the apparent total-tract digestibility of nutrients. Orts were examined periodically during P3 to assess pellet refusals. Treatment effects were analyzed using the MIXED procedure of SAS with the REPEATED option. The model included fixed effects of IR, time (in weeks), the treatment × time interaction, parity, the covariate effect of P1 measurements, and the random effect of cow. The DMI decreased linearly with increasing IR. The DMI decreases of SIR1.5 (32.4%) and SIR2.0 (46.5%) were sustained throughout P3, whereas that of SIR became negligible after the fourth week of P3. The pellet refusals revealed sorting against Brominata pellets, resulting in 37% to 43% lower Brominata concentrations in ingested DM compared with the treatment IR. The mean CH4 production decreased by 50%, 70%, and 77%, and CH4 yield decreased by 41%, 56%, and 59% compared with the CTL in response to SIR, SIR1.5, and SIR2.0, respectively. The CH4 yield reduction of SIR gradually decreased from the second week of P3 onward and became negligible in the last week, whereas SIR1.5 and SIR2.0 sustained it at 66% until the sixth week and then experienced a reduction to 36%. Consistently, the bromoform concentration (mg/g) in freeze-dried Brominata declined during P3, reaching a 23% reduction by the final 2 wk, primarily due to variability among harvested batches. Milk yield, milk component yields, and milk fat content decreased linearly with increasing Brominata IR. Compared with CTL, only SIR2 decreased those responses, except for milk fat yield, which was also decreased by SIR1.5. The nutrient digestibility had cubic relationships with IR, such that the DM, OM, and CP digestibility of SIR1.5 was lower than that of SIR but similar to that of CTL and SIR2.0. The results demonstrate that Brominata is highly effective in reducing enteric CH4 emissions of dairy cows. However, it is crucial to address palatability concerns and managing variability in bromoform concentration to sustain this efficacy under current feeding conditions in late lactation and possibly in other lactation stages.