Humic substances isolated from clay soil may improve the ruminal fermentation, milk yield, and fatty acid profile: A novel approach in dairy cows

The objective of this study was to examine the effect of clay derived-humic substances (CD-HS) on nutrient intakes, digestibility coefficients, rumen fermentation, milk yield, and milk components in Holstein-Friesian dairy cows. The experiment was designed as a 3 × 3 Latin square design using 12 dairy cows, which are allotted to basal diet without humic substance (Control), with CD-HS at 5 g/kg diet (CD-HS5), and 10 g/kg diet (CD-HS10). The experiment was conducted in 3 periods and each period consisted of 21 days with 14 days of adaptation and 7 days collection period. The humic substance supplementation did not affect the nutrient intakes and digestibility coefficients, except for crude protein, which showed a linear (P <0.01) increase. The ruminal pH was similar between the treatments, but the NH3-N content and protozoal population were decreased quadratically (P < 0.01) with CD-HS supplementation. Although the experimental diets did not affect the butyrate proportion, they caused a quadratic increase in total volatile fatty acids and the proportions of acetate and propionate contents. The CD-HS diets caused a linear increase (P < 0.05) in blood glucose and a decrease in cholesterol and blood urea nitrogen concentration. The diets did not affect (P> 0.05) the milk components, but they caused a linear increase (P < 0.05) on milk yield. Among the total fatty acids of milk, the levels of C18:0 and C24:0 and thrombogenicity index were decreased while increasing the C18:2 isomers (t9t12-C18:2 and C9,C12-C18:2) and polyunsaturated fatty acid contents. It was concluded that the clay derived-humic substances at 5 g/kg diet could cause desirable effects on nutrient intake, rumen fermentation profile, biochemical parameters, milk yield, and fatty acid profile.