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

Abstract

We reported recently that adding bakery by-products (BP) to the diets of dairy cows up to 30% improved performance and rumen pH, but caused major shifts in the nutrient profile and availability, likely modifying nutrient degradation patterns throughout the gastrointestinal tract. The aim of this study was to investigate the effects of the gradual replacement of cereals by BP on the apparent total-tract digestibility (ATTD), the fermentation patterns, and the microbial community in feces of dairy cows. Twenty-four mid-lactating Simmental cows (149 ± 22.3 days in milk, 756 ± 89.6 kg of initial body weight) were fed a total mixed ration ad libitum (fresh feed was offered twice per day) containing a 50:50 ratio of forage to concentrate (dry matter basis) throughout the experiment. The trial lasted 5 wk, whereby the first week was used for baseline measurements, in which all cows received the same diet, without BP. Cows were then randomly allocated into 3 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, volatile fatty acids (VFA), and 16S rRNA gene sequencing. The inclusion of BP resulted in an increase of ether extract and sugars, and a reduction of starch and neutral detergent fiber in the diet. Feeding BP linearly increased the ATTD of almost all nutrients resulting in up to 2 kg more digestible organic matter intake (DOMI). Increasing BP level up to 30% increased fecal total VFA concentration and decreased the pH. The proportion of butyrate in feces increased linearly, but the proportion of all other VFA was not affected by BP-feeding. The richness and diversity indices of the fecal microbiota linearly declined by the inclusion of BP. The cellulolytic phyla Fibrobacteres decreased, whereas amylolytic phyla, such as Proteobacteria, increased. Overall, re-sults showed that feeding BP linearly increased ATTD and DOMI, but impaired fecal microbial diversity and pH. In the interest of the optimization of BP inclusion in the dairy cows' feeding, a dietary level between 15 to 30% of BP might be a better compromise than 30% in terms of an enhanced DOMI and performance with still lowered risk of hindgut dysbiosis, but this will require further investigations.

Effect of inclusion of bakery by-products in the dairy cow's diet on milk fatty acid composition

“…Direct proof of the BP effect on ruminal microbiota in cows is currently not available, but a diet with 45% BP can impair ruminal fermentation and decrease microbial diversity as shown in vitro (Humer et al ., 2018). At the hindgut level, high BP inclusion could increase the odds for hindgut dysbiosis of animals (Kaltenegger et al ., 2021). Although 30% BP proved to be the most effective diet to enrich milk CLA, this high BP level might not be optimal for energy metabolism in mid-lactation cows (Kaltenegger et al ., 2020) and may negatively affect the microbiota.…”

“…The experimental design and feeding are reported in more detail in our companion studies (Kaltenegger et al, 2020(Kaltenegger et al, , 2021. The experimental procedures involving animal handling and treatment were approved by the institutional ethics committee of the University of Veterinary Medicine (Vetmeduni) Vienna and the national authority according to §26 of the Law for Animal Experiments, Tierversuchsgesetz 2012-TVG (GZ: 68.205/80-V/ 3b/2018).…”

“…The contribution of feeding BP to the nutritional quality of milk fat, however, has not been studied. As an extension of the previous research with BP (Kaltenegger et al ., 2020, 2021), the present study investigated whether different inclusion levels of BP also modify the fatty acid composition of the milk fat. A further aim was to assess the effect of the feeding period on the milk fatty acid composition, as well as potential interactions between diet and feeding period.…”

Considerations and best practices in animal science 16S ribosomal RNA gene sequencing microbiome studies

“…Yet, while colorectal or fecal samples are often considered as a proxy for rumen microbial activity, this may be of concern depending on the objective of the study. Using fecal samples maybe warranted if examining factors such as nutrient degradability ( Kaltenegger et al, 2021 ), the impact of a nutritional supplement or diet on fecal pathogen shedding ( Jacob et al, 2009 ), or as an indicator of ruminal acidotic status ( Plaizier et al, 2017 ; Neubauer et al, 2020 ). However, the rumen microbiome is quite distinct from the lower GIT, and fecal sampling should not typically be considered as a proxy for the ruminal microbiome in many cases.…”

Feeding Bakery Former Foodstuffs and Wheat Distiller’s as Partial Replacement for Corn and Soybean Enhances the Environmental Sustainability and Circularity of Beef Cattle Farming

“…Furthermore, these feeds contain less fiber than native cereal grains [30]. Conversely, production performance, digestibility, and rumen health were enhanced in scientific studies carried out on dairy cows and sheep fed with BFF [26,31,32].…”