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The effect of soybean meal (SBM) replacement with fermented SBM (FSBM) on ruminal fermentation and bacterial abundance in Holstein calves was investigated in this study. Thirty nine calves were randomized to: (1) control: 27% SBM + 0% FSBM (FSBM0, n = 13); (2) 18% SBM + 9% FSBM (FSBM9, n = 13); and (3) 13.5% SBM + 13.5% FSBM (FSBM13, n = 13). SBM contained a greater amount of large peptides containing 3 to 10 amino acids (AAs), while FSBM had a greater amount of ammonia nitrogen (NH 3-N), free AAs, and small peptides containing 2 to 3 AAs. The calves fed FSBM13 had the lowest acetic acid, NH 3-N, and the ratio of acetate to propionate, with the greatest concentration of caproic acid, valeric acid and isovaleric acid in ruminal fluid. Compared to those fed FSBM9 or FSBM13, the calves fed FSBM0 had the greatest proportion of Butyrivibrio fibrisolvens and Ruminococcus albus in rumen fluid. However, the ruminal abundance of Prevotella ruminicola in calves fed FSBM13 was greater than in calves fed FSBM0. Network analysis showed that the abundance of the Ruminococcus albus was associated with large peptides, and butyric acid was correlated with small peptide. Taken together, our findings suggest that FSBM may have the potential to boost calf performance by changing the fermentation products and the relative abundance of some members of the bacterial community in the rumen. The calf starts its life with a physically and metabolically undeveloped rumen. Calves generally experience significant changes not only in the development of their rumen, but also in the rumen bacterial composition and community 1. This, in turn, enables calves to digest dry feeds for their growth needs, impacting productivity and future milk production capacity 1,2. Fibrolytic bacteria are important for the rapid anatomical and physiological growth of rumen, as the newborn calf moves from a liquid diet (i.e., milk) to a solid diet, such as grass and hay 3. Rumen microbes are classified into various functional groups, for example cellulolytic, amylolytic and proteolytic bacteria species 4. These organisms metabolize feed components and other microbial products 5. The rumen microbial community and the functional development of the stomach are affected by diets 4. For example, when forages are fed to ruminants, Bacteroidales and Ruminococcaceae become dominant 4. On the other hand, it is known that animals fed high-concentrate diets have more Prevotella and Succinivibrionaceae in their rumen fluid 4,6-8. Therefore, diets fed to animals can alter the relative abundance of bacteria and the profile of volatile fatty acids (VFAs) in the rumen 1,4. This, in turn, affects the evolution of the early ruminal development and microbiota 9 .

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Determining the best level of forage inclusion in diets for optimal performance of weaned calves will benefit the dairy industry greatly. This study evaluated the effect of feeding different forage to concentrate ratios on performance, behaviour, and metabolic responses of Holstein weaned calves. Forty-five Holstein female calves (70 d of age and 71.7 ± 4.4 kg body weight at trial initiation) were balanced for birth BW and randomly assigned to 1 of 3 treatments: (1) forage-to-concentrate ratio of 50:50, (2) forage-to-concentrate ratio of 35:65 and (3) forage-to-concentrate ratio of 20:80. Alfalfa hay was the sole dietary forage source. Calves were kept in individual pens until 120 d of age. Decreasing dietary forage concentration linearly increased dry matter and energy intake, and average daily gain. Body weight at d 95 and 120 linearly increased as alfalfa hay was replaced with concentrate. Ruminal pH at d 120 of age linearly decreased with greater inclusion of concentrate. Final heart girth, withers height and hip height linearly increased and final hip width tended to increase as concentrate was substituted for alfalfa hay. Plasma glucose concentration at d 95 of age linearly increased with greater concentrate levels, but the opposite was observed for b-hydroxybutyrate concentration. Increasing concentrate increased lying behaviour linearly, but decreased rumination behaviour. The results of this study indicated that feeding diets with a 20:80 forage to concentrate ratio enhanced feed intake, growth performance, and some skeletal growth parameters in the post-weaning period and increased lying behaviour and decreased rumination behaviour. HIGHLIGHTSDetermining the best level of forage inclusion in diets for optimal performance of weaned calves will benefit the dairy industry greatly. Decreasing dietary forage concentration linearly increased dry matter intake, body weight and withers height. Feeding diets with a 20:80 forage to concentrate ratio enhanced performance in the postweaning period of dairy calves.

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Steam-flaked corn (SFC) and ground corn (GC) of different particle sizes were evaluated for their effects on dry matter intake (DMI), milk yield and components, chewing activity, ration sorting, ruminal fermentation, and digestibility in lactating dairy cows. Eight multiparous Holstein cows in mid-lactation (46.6 ± 3.5 kg/d milk production and 101 ± 10 d in milk) were used in a double 4 × 4 Latin square design with 21-d periods. Cows were fed diets (dry matter basis) containing 36.2% forage (alfalfa hay and corn silage), 37.4% corn grain, and 26.4% other ingredients. The corn grain was ground (coarse: 1.08 mm; medium: 0.84 mm; and fine: 0.73 mm) or steam-flaked (SFC; density = 0.40 kg/L). The dry matter proportion retained on an 8-mm sieve was greater for the SFC diet than for the GC diets. There were no treatment effects on DMI, milk yield, fat-corrected milk, energy-corrected milk, fat or lactose yield, protein or lactose content, or milk urea nitrogen concentration. However, digestibility of dry matter and organic matter were greater for fine GC and SFC than the other diets. In addition, cows fed SFC had lower total-tract starch digestibility than cows fed GC diets. Cows fed SFC tended to have lower propionate proportion (22.8 vs. 27.1 mM) and total volatile fatty acid concentration (88.6 vs. 99.8 mM) in ruminal fluid than those fed GC diets. Acetate and butyrate concentration, acetate to propionate ratio, and ruminal concentration of ammonia-nitrogen were not affected by treatments. Ruminal pH (6.46 vs. 6.01) as well as milk fat content (2.75 vs. 2.59%) and efficiencies (fatcorrected milk/DMI and energy-corrected milk/DMI) were greater for SFC than GC, regardless of its particle size. Milk fat content tended to increase linearly with increasing particle size of GC. Eating activity (min/d) tended to be less for SFC compared with GC, but rumination activity (min/d) and total chewing activity (min/d) were not affected by processing or particle size. The results of study indicate that, compared with GC, steam flaking of corn with 400 g/L density increased milk fat content and efficiency of high-producing dairy cows without any negative effect on milk yield. For GC, milk fat content tended to linearly increase and starch digestibility decreased linearly with increasing particle size.

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