The use of microbial additives in rations has become a common practice in ruminant’s nutrition. One of these additives are prebiotics based on yeast cultures. The main purpose on their use is to increase cattle performance and production from early stages. Their active principle is unclear, but some of their compounds are known to have an effect over performance and gut health by stimulating growth of specific bacteria in the gut. The objectives of this study were to evaluate the effect on the use of prebiotics based on yeast cultures of Saccharomyces cerevisiae fermentation products and Aspergillus oryzae fermentation extracts on gut permeability, hormone concentration, and growth. One hundred twenty heifers (40 per treatment) were randomly assigned to a Control (C), Saccharomyces cerevisiae fermentation products (SCFP) (1 g/head per day of prebiotic in milk + 0.7% of prebiotic in the solid feed), or Aspergillus oryzae fermentation extracts (AOFE) (3 g/head per day of prebiotic in milk) treatment. All calves were fed 2 L of colostrum during the first 4 feedings on the first 36 hours following birth. From the 5th feeding until the end of the trial all animals received 3 L of pasteurized milk twice a day. Animals had ad-libitum access to a started feed from day 3. Body weight was recorded at birth, and on days 14, 30, 45, and 60. Between the first 24-48 hours after birth a blood sample for assessment of Ig G was taken. Dry feed offered was measured daily and refusals twice a week to obtain an average DMI. Diarrhea events were recorded daily and fecal scores were classified by using a 4 point scale. Blood was sampled on days 7 and 14 for plasma glucose, NEFA, urea, insulin, and IL-1ß concentrations. Lactulose and D-mannitol were included in the morning feeding of day 14 and blood samples were taken an hour after feeding for assessment of intestinal permeability. At the same time, a different blood sample was taken for plasma GLP-2 concentration. Finally, on day 30, fecal samples were collected for measurements of Salmonella and E. coli concentration on feces. Data was analyzed as a randomized complete block design with repeated measurements on SAS. The model included the random effect of calves within block, and the fixed effect of treatment, time, and their interaction. Linear regressions were used to evaluate the effect of plasma GLP-2, IL-1ß, Ig G concentration and intake at day 14 on the sugars ratio (lactulose: D-mannitol); and DMI (average at day 14), sugars ratio, plasma insulin concentration, and serum Ig G were used to evaluate ADG (average at day 14). Pearson correlation procedures were used to evaluate the association between total intake at day 14, GLP-2, lactulose, D-mannitol concentrations, sugars ratio, and ADG at day 14. Plasma concentration of Ig G showed a correct passive transfer of immunity on all animals at the beginning of the trial. No treatment differences were found for body weight (BW) or dry matter intake (DMI) (P > 0.1). There was a time by treatment difference (P = 0.01) on ADG on day 45 where C animals had a greater ADG when compared with SCFP and AOFE. Diarrhea incidence did not change between treatments (P > 0.1) and Salmonella and E-coli were not found in feces. Results from the current study also showed non-significant differences between treatments (P > 0.1) for plasma GLP-2, glucose, insulin, or urea concentrations. There was a time by treatment tendency (P = 0.01) for NEFA concentrations which tended to be higher on day 7 for C and AOFE when compared with day 14. Results from plasma IL-1ß concentrations showed a treatment tendency (P = 0.06) due to differences between C and SCFP with a plasma IL-1ß concentration of 15.71 and 32.01 pg/mL, respectively. Neither plasma concentration of the sugar markers, nor their ratio, showed significant differences between treatment groups (P > 0.1). Correlation analysis showed that total intake at day 14 positively correlated with GLP-2 concentration, as well as with ADG. Plasma GLP-2 was negatively correlated with D-mannitol concentration and positively correlated to the sugars ratio (lactulose: D-mannitol ratio). Lactulose concentration was positively correlated with D-mannitol and the sugars ratio. Regression analysis showed a negative association between DMI at day 14 with sugars ratio. Plasma IL1-ß had a tendency to be positively associated to sugars ratio. There was a significant association of Ig G with sugars ratio. Finally, only DMI at day 14 had a positive effect on ADG at day 14.
In conclusion, under the current conditions, supplementation with prebiotics did not improve performance parameters. As a result, plasma GLP-2 concentration, intestinal permeability, and plasma metabolites did not differ after prebiotic supplementation. Because prebiotics have been shown to generate better responses under stress conditions, a different model using challenges like caloric stress, abrupt weaning, or pathogenic microorganisms could be implemented to evaluate potential differences between animals supplemented or not with these prebiotics.