Twenty Holstein cows, 12 primiparous and 8 multiparous, with (mean ± SD) 91 ± 19 d in milk and 595 ± 81 kg were used in replicated 4 × 4 Latin squares to compare the effects of feeding conventional dried distillers grains with solubles (DDGS) and reduced-fat DDGS (RFDDGS) in combination with rumen-inert fat (RIF) on milk production and rumen fermentation; one square contained rumen cannulated animals for rumen measurements. In each 21-d period, cows were randomly assigned to 1 of 4 dietary treatments (values on a dry matter basis): (1) control (CON) that contained 0% DDGS; (2) DG contained 30% DDGS; (3) RFDG contained 30% RFDDGS in substitution of DDGS; and (4) RFDG+RIF was similar to RFDG with the addition of 1.9% RIF. Unlike most practical diets in the dairy field, our diets had <22% forage neutral detergent fiber and >18.0% crude protein. Dry matter intake was similar across treatments with any form of DDGS averaging 26.0 ± 0.6 kg/d, whereas the CON diet resulted in less dry matter intake, 21.6 ± 0.6 kg/d. Milk yield tended to be 1.7 kg/d greater for diets with either type of DDGS. Concentration of milk protein was greatest for the DG and RFDG diets, intermediate for the RFDG+RIF diet, and least for the CON diet, namely 3.22, 3.21, 3.12, and 3.07 ± 0.05%. Reduced milk fat percentage and yield were observed when cows consumed the DG diet, 3.27 ± 0.10% and 1.11 ± 0.04 kg/d, respectively, whereas these responses were similar among CON, RFDG, and RFDG+RIF, which averaged 3.68 ± 0.10% and 1.22 ± 0.04 kg/d. The presence of trans-10,cis-12 conjugated linoleic acid was only detected in milk from cows consuming the DG diet; similarly, concentration and yield of trans-10 18:1 were greater for cows consuming this diet. Rumen ammonia was similar across treatments averaging 27.0 ± 2.1mg/dL. The CON and RFDG+RIF diets had similar mean pH, 6.1 ± 0.11, whereas DG and RFDG resulted in lower pH averaging 5.79 ± 0.11. No effect on total concentration of volatile fatty acids was observed; the overall mean was 121 ± 4.11 mM; molar proportion of acetate was affected by treatment resulting in 67.3, 63.2, 61.4, and 60.9 ± 0.93 mol/100 mol for CON, RFDG+RIF, RFDG, and DG, respectively. Results from DNA sequencing showed that rumen bacterial community structure was relatively stable with minor changes at the family and genus levels; these changes may be associated with low starch diets, and hence reduced amylolytic bacteria populations. Feeding high proportions of RFDDGS resulted in greater dry matter intake with low risk for milk fat depression while supporting ruminal fermentation.

Aims: The effect of feeding dried distillers grains with solubles (DDGS) or reduced-fat DDGS (RFDG) on ruminal methanogenesis and the rumen bacterial community of dairy cattle was evaluated. Methods and Results: Treatments were CONT, a diet with no distillers grains; DG, inclusion of 20% DDGS; rfDG, inclusion of 20% RFDG; and MIX, inclusion of 10% DDGS and 10% RFDG. Methane emission was measured; rumen bacterial community was evaluated by sequencing the V4 region of the 16S rRNA gene. Total methane production remained unaffected. However, feeding distillers grains tended to reduce methanogenesis per unit of feed intake, decreased the abundance of the phylum Bacteroidetes and tended to increase Firmicutes. The abundance of Prevotellaceae positively correlated with feed intake; methane emission was positively correlated with the abundance of Prevotellaceae and was negatively correlated with the abundance of Succinivibrionaceae. Conclusions: DDGS or RFDG may reduce methanogenesis per unit of feed intake; shifts in the abundance of predominant ruminal bacterial families may influence methane formation, likely because of their role on hydrogen liberation and utilization pathways. Significance and Impact of the Study: Replacing corn and soybean meal with DDGS or RFDG in dairy rations may reduce the proportion of dietary energy wasted as methane, without detrimental effects on the overall bacterial population.

Four multiparous, lactating Holstein cows (average DIM 169.5 ± 20.5 d), fitted with ruminal and duodenal cannulas, were used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments to investigate the effects of 2-hydroxy-4-methylthio-butanoic acid (HM-TBA) when fed with diets differing in metabolizable protein (MP) supply and equal levels of crude protein on milk production and composition, rumen microbial activity, duodenal protein flow, and rumen bacterial community composition in vivo and in vitro. Experimental periods were 28 d in length. Cows were housed in individual tie stalls and were randomly assigned to 4 dietary treatments: low MP or high MP, supplemented with or without 25 g of HMTBA, which was top-dressed once daily at 0930 h. No interactions were observed between HMTBA and level of dietary MP, with the exception of ruminal acetate-to-propionate ratio. Milk yield was not affected by treatment and averaged 23.8 ± 2.06 kg/d. There was a tendency for increased milk protein percent in cows receiving low MP diets, averaging 3.30 ± 0.09% and 3.21 ± 0.09% for low MP and high MP, respectively. The total-tract apparent digestibility of organic matter, neutral detergent fiber, and nitrogen were greater in cows consuming the low MP diet. Rumen pH was lower in cows consuming high MP diets as well as in those consuming HMTBA. Rumen ammonia concentrations tended to be greater in cows consuming HMTBA, and volatile fatty acid concentrations were greater in cows consuming HMTBA. Duodenal dry matter flow, nitrogen flow, and microbial nitrogen flow did not differ between treatments. The bacterial community structure of cows receiving HMTBA was not affected at the phylum level. The relative abundance of bacterial phyla in vivo differed when compared with in vitro conditions for Firmicutes, Bacteroidetes, Proteobacteria, TM7, Tenericutes, Spirochaetes, SR1, and Verrucomicrobia.

Graphical Abstract Summary: In recent years, the dairy industry has been shifting toward the utilization of automated milking systems. As such, pelleted feeds are often used to incentivize cows to enter the milking box; however, data comparing different pelleting strategies are currently limited. The current experiment examined different pelleting formulation on feed preference of lactating Jersey cattle. Four pelleting formulations were compared in the taste preference experiment, including a pellet containing ingredients commonly found in dairy concentrate mixes (CMIX), a dry corn gluten feed (CGF) pellet, a pellet containing ingredients previously described to be palatable with oregano leaf (FLVR), and a high-energy pellet (ENG). Cow preference ranking from greatest to least preferred were CGF, FLVR, CMIX, and ENG pellet. Based upon Placket-Luce analysis, we conclude cows choose CGF pellets 78% of the time. These results suggest that animals prefer CGF pellets relative to those pellets containing what are often considered highly palatable ingredients, and exhibited lowered preference for pellets containing higher concentrations of starch.