Lactational performance effects of 3-nitrooxypropanol supplementation to dairy cows: A meta-regression.

Bovaer or 3-Nitrooxypropanol (3-NOP) is an anti-methanogenic feed additive that inhibits a key enzyme involved in the last step of methane (CH4) production by the rumen methane-producing organisms. Recent comprehensive meta-analyses have reported up to 33% reduction in daily CH4 emission, CH4 yield (on a DMI basis), and CH4 intensity (on a milk yield [MY] or ECM basis) by the feed additive in dairy cattle. There are however variable results, and these differences in production responses may be partially explained by dose, dietary nutrient composition, and supplementation length. However, the effects of these interactions on the lactation performance of dairy cows have not been reported in the most recent and comprehensive 3-NOP meta-analyses.

Producers are more likely to adopt CH4-mitigating strategies if they enhance animal performance or provide production co-benefits. The US Food and Drug Administration has recently determined that the agency has no questions or public health concerns about 3-NOP feeding to dairy cattle. Thus, it is important to determine whether 3-NOP supplementation affects feed intake, milk production and efficiency, and milk composition in dairy cattle, as the industry strives to find feasible ways of using anti-methanogenic feed additives for diet supplementation. Thus, the objective of the authors cited was to determine the effects of 3-NOP supplementation on intake, milk production, milk composition, and ruminal fermentation of dairy cows using a meta-analytical approach. Additionally, the aim was to investigate if dose, dietary nutrient composition, and supplementation length were associated with the potential effects of 3-NOP on lactation performance and milk fat concentration.

A meta-regression was conducted to determine the production effects of 3-NOP and investigate their associations with dose, dietary nutrient composition, and supplementation length in the dairy cows. Response variables were DMI, milk yield (MY), ECM yield, ECM feed efficiency, BW, BW change, and concentrations of milk fat, true protein, lactose, and MUN.

Compared with control, supplementation of 3-NOP decreased DMI and MY by 0.80 ± 0.149 and 0.98 ± 0.250 kg per day, respectively, but only numerically decreased ECM by 0.50 ± 0.298 kg per day. Consequently, feed efficiency was increased by 0.05 ± 0.012 kg ECM per kg DMI with 3-NOP supplementation. Body weight and BW change were not affected by 3-NOP supplementation. Milk fat, true protein, and MUN concentrations were increased by 0.09 ± 0.028%, 0.02 ± 0.006%, and 0.59 ± 0.106 mg per desilitre, respectively. Increasing 3-NOP dose further decreased DMI and increased milk fat and MUN concentrations. Increasing dietary NDF and forage-to-concentrate ratio, lessened the negative effect of 3-NOP on DMI and MY, respectively, and decreased its effect on milk fat and MUN. Similarly, increasing dietary CP lessened the negative effect of 3-NOP on DMI and decreased its effect on MUN.  Supplementation of 3-NOP tended to increase rumen pH and decreased NH3 concentration. Concentrations of total VFA, acetate, and the acetate-to-propionate ratio were decreased, whereas the concentration of propionate was increased, and that of butyrate only numerically.

Conclusions: Overall, 3-NOP supplementation of dairy cow diets decreased DMI and MY but did not affect ECM because of increased milk fat and true protein contents. Increased milk fat and MUN responses can be explained by shifted ruminal fermentation, and the increased milk true protein response may be explained by increased rumen propionate molar proportion by 3-NOP supplementation.