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ABSTRACT A meta-regression was conducted to determine the production effects of 3-nitrooxypropanol (3-NOP) and investigate their associations with dose, dietary nutrient composition, and supplementation length in dairy cows. Forty treatment and control mean comparisons extracted from 21 studies conducted or published between 2014 to 2024 were used in the meta-regression. 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. Treatment and control mean differences (MD) as well as standardized MD were calculated and used for data presentation and statistical analysis, respectively. Dose (± SD; 77.0 ± 33.17 mg 3-NOP/kg DMI), forage-to-concentrate ratio (FC; 58.9 ± 8.83%, expressed as average ± SD% of forage in the diet), dietary concentrations of CP, ether extract, NDF, and starch (16.3 ± 1.84%, 4.3 ± 1.03%, 33.7 ± 4.40%, and 20.9 ± 3.97%, as average ± SD% of DM, respectively), supplementation length (days), and DIM and BW of the cows at the beginning of the study were used as continuous explanatory variables. Mixed-effects models were fitted using the robust variance estimation method. Full models containing uncorrelated explanatory variables (Pearson correlation 3 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 was numerically increased by 3-NOP supplementation. 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.
Martins et al. (Tue,) studied this question.