Feeding dairy cows bakery by-products enhanced nutrient digestibility, but affected fecal microbial composition and pH in a dose-dependent manner

摘要

We reported recently that adding bakery by-products(BP) to the diets of dairy cows up to 30% improvedperformance and rumen pH, but caused major shiftsin the nutrient profile and availability, likely modifyingnutrient degradation patterns throughout the gastrointestinaltract. The aim of this study was to investigatethe effects of the gradual replacement of cereals by BPon the apparent total-tract digestibility (ATTD), thefermentation patterns, and the microbial communityin feces of dairy cows. Twenty-four mid-lactating Simmentalcows (149 ± 22.3 days in milk, 756 ± 89.6 kgof initial body weight) were fed a total mixed ration adlibitum (fresh feed was offered twice per day) containinga 50:50 ratio of forage to concentrate (dry matterbasis) throughout the experiment. The trial lasted 5wk, whereby the first week was used for baseline measurements,in which all cows received the same diet,without BP. Cows were then randomly allocated into3 groups differing in the BP content of diets (0% BP,15% BP, and 30% BP on a DM basis) and fed for 4 wk.Fecal samples were taken for analysis of pH, volatilefatty acids (VFA), and 16S rRNA gene sequencing. Theinclusion of BP resulted in an increase of ether extractand sugars, and a reduction of starch and neutral detergentfiber in the diet. Feeding BP linearly increasedthe ATTD of almost all nutrients resulting in up to 2kg more digestible organic matter intake (DOMI). IncreasingBP level up to 30% increased fecal total VFAconcentration and decreased the pH. The proportion ofbutyrate in feces increased linearly, but the proportionof all other VFA was not affected by BP-feeding. Therichness and diversity indices of the fecal microbiotalinearly declined by the inclusion of BP. The cellulolyticphyla Fibrobacteres decreased, whereas amylolyticphyla, such as Proteobacteria, increased. Overall, resultsshowed that feeding BP linearly increased ATTDand DOMI, but impaired fecal microbial diversity andpH. In the interest of the optimization of BP inclusionin the dairy cows’ feeding, a dietary level between 15 to30% of BP might be a better compromise than 30% interms of an enhanced DOMI and performance with stilllowered risk of hindgut dysbiosis, but this will requirefurther investigations.