Effects of vegetable oils on feed intake, nutrient digestibility, ruminal parameters, lactation performance, and milk fatty acid composition in cattle: A meta-analysis

Abstract

Vegetable oil, a widely used energy source, is frequently added to livestock and poultry feed to enhance energy density. However, its effects on cattle production have been inconsistent across various studies. Therefore, this study aimed to evaluate the impact of vegetable oils on cattle traits using meta-analysis and sub-group analysis, quantify these effects through meta-regression, and develop dosage-response models linking cattle traits to vegetable oil supplementation. Data from 146 articles were included in this study following strict selection criteria. The results showed that vegetable oils reduced TDMI by 0.649 kg/d, OM intake by 0.748 kg DM/d, CP intake by 0.176 kg DM/d, NDF intake by 0.272 kg DM/d, DM digestibility by 1.091 %, NDF digestibility by 1.619 %, total VFAs by 3.864 mmol/L, the concentration of N-NH₃ by 0.734 mg/100 mL, acetate by 1.080 mol/100 mol, butyrate by 0.397 mol/100 mol, acetate/propionate by 0.277, milk protein concentration by 0.042 %, milk fat concentration by 0.365 %, fat yield by 88.961 g/d, and the concentrations of C4:0, C6:0, C8:0, C10:0, C12:0, C14:0, C14:1, C15:0, C16:0, C16:1, C17:0, and C18:3 in milk. They also increased in EE intake by 0.303 kg DM/d, CP digestibility by 1.379 %, EE digestibility by 8.011 %, rumen pH by 0.039, propionate concentration by 1.248 mol/100 mol, milk yield by 0.413 kg/d, lactose yield by 24.329 g/d, and the concentrations of C18:0, C18:1, C18:2 and C20:0. Sub-group analysis of cattle categories revealed that vegetable oil supplementing in lactating cattle diets resulted in increases in body weight by 9.384 kg, CP digestibility by 0.850 %, and ruminal pH by 0.036. However, vegetable oils supplementing in non-lactating cattle diets led to an increase in isovalerate concentration by 0.051 mol/100 mol and decreases in N-NH₃ concentration by 1.469 mg/100 mL and digestibility of DM, OM, and NDF by 2.292 %, 1.964 %, and 3.406 %, respectively. The regression analysis indicated the linear or quadratic response of cattle traits to the supplemental amount of vegetable oils. Total dry matter intake, OM intake, total VFAs, acetate, butyrate, milk protein, milk fat, and fat yield exhibited quadratic relationships with the dosage of some kinds of vegetable oils. Additionally, several traits had linear relationships with some vegetable oils. For instance, a 1 % increase of linseed oil resulted in a 0.120 kg/d decrease in CP intake; a 1 % increase of soybean oil led to a 0.133 kg/d decrease in NDF intake; a 1 % increase in safflower oil led to a 0.145 % decrease in milk fat; a 1 % increase of safflower oil resulted in a 61.050 g/d decrease in fat yield. In summary, supplemental vegetable oils can significantly alter intake and growth, rumen fermentation, nutrient digestibility, lactation performance, and milk fatty acid composition in cattle. However, the magnitude of these effects depends on cattle categories, the type of vegetable oils, and the supplemental amount. These findings offer crucial information for refining feed strategies to improve cattle performance and milk quality.