Diets varying in ratio of sweet sorghum silage to corn silage for lactating dairy cows: Feed intake, milk production, blood biochemistry, ruminal fermentation, and ruminal microbial community

摘要

The objective of this study was to investigate theeffects of partial substitution of corn silage (CS) withsweet sorghum silage (SS) in the diets of lactatingdairy cows on dry matter (DM) intake, milk yield andcomposition, blood biochemistry, and ruminal fermentationand microbial community. Thirty mid-lactationHolstein dairy cows [mean ± standard deviation; 639± 42.0 kg of body weight; 112 ± 24.0 d in milk (DIM)]were assigned to 3 groups (n = 10/treatment) by consideringparity, milk yield, and DIM. The cows were fedad libitum total mixed rations containing 55% forageand 45% concentrate, with only the proportion of CSand SS varying in 3 treatments (DM basis): SS0 (0%substitution of CS), 40% CS and 0% SS; SS25 (25%substitution of CS), 30% CS and 10% SS; and SS50(50% substitution of CS), 20% CS and 20% SS. Drymatter intake and milk protein concentration tended tolinearly decrease with increasing proportion of SS in thediet. Yields of milk (mean ± standard deviation, 30.9 ±1.12 kg/d), 4% fat-corrected milk (30.0 ± 0.81 kg/d),energy-corrected milk, milk protein, lactose, and totalsolids, concentrations of milk fat, lactose, somatic cellcounts, and milk efficiency did not differ among diets.The concentrations in blood of urea nitrogen, phosphorus,aspartate aminotransferase, and malondialdehydelinearly increased with increasing SS proportion. BloodIgA decreased with increasing SS substitution rate, butblood IgG and IgM were not different among diets. RuminalpH did not differ among diets, whereas ruminalNH3-N concentration quadratically changed such thatit was greater for SS50 than for SS0 and SS25. Molarproportions of propionate and acetate to propionateratio were less for SS25 than for SS0. Although the diversityand general ruminal microbial community structurewere not altered by partially replacing CS withSS, the relative abundances of predominant bacteriawere affected by diets at the phylum and genus levels.Firmicutes and Bacteroidetes were dominant phyla inthe ruminal bacterial community for all diets, and theirrelative abundance linearly decreased and increased,respectively, with increasing SS substitution rate. Prevotella_1 and Ruminococcaceae_NK4A214_group weredetected as the most and the second most abundantgenera, with their relative abundance linearly increasedand decreased, respectively, with increasing SS substitutionrate. The relative abundance of Fibrobacter linearlyincreased with increasing dietary SS proportion,with greater abundance observed for SS25 and SS50than for SS0. These results suggest that substitutionof CS with SS altered the relative abundances of somepredominant bacteria; however, these changes had littleeffect on ruminal fermentation and milk yield. Underthe current experimental conditions, substituting up to50% of CS with SS had no negative effects on milk yield,indicating that SS can partially replace CS in the dietsof high-producing lactating dairy cows without addingextra grain, when diets are fed for a short time. As theeffects of substituting CS with SS depend upon thechemical composition and digestibility of these silagesand the nutrient requirements of the cows, additionalgrain may be required in some cases to compensate forthe lower starch content of SS.