Liquid feeding regime and plant extracts affect rumen fermentation and bacterial community in calves

Liquid feeding regime and nutrition of calves may produce long-term effect on growth, health, and milk production performance of the adults by influencing the establishment of ruminal microbiota. The objective of this thesis was to investigative the effect of early feeding regime and nutrition on rumen fermentation and bacterial community in calves, and then we follow calves for 6 or 9 months of age to detect any persistence of microbial programming effects. In experiment 1, fifty-four Holstein calves were randomly allocated to one of three treatments and fed pasteurized waste milk (WM), whole milk (M), or milk replacer (MR) during 7 to 63 days of age. Male calves were slaughtered at age 2 months to measure the organ development of forestomach. Female calves were followed for 6 months to determine body weight, blood indices, rumen fermentation, and ruminal bacterial community. The results indicated that the average daily gain was lower but the concentration of total volatile fatty acids was higher in calves fed MR at 2 months of age. This may induce a microbial programming effect at 6 months of age that the ruminal propionate molar proportion was lower, but the ruminal pH and acetate/propionate ratio were higher, for the MR group. Calves fed WM had lower starter intake, rumen weight, but higher concentration of isovalerate at 2 months of age. Meanwhile, the concentrations of serum growth hormone, insulin-like growth factor 1, and the growth hormone to insulin ratio were higher, but the levels of insulin and nonesterified fatty acids were lower, for the WM group, at 2 months of age. Calves fed WM had a different ruminal bacterial composition at age 2 months. No difference was observed in growth, blood indices, rumen fermentation and microbiota between WM and M at 6 months of age. In experiment 2, fifty-four female Holstein calves were randomly assigned to three treatments consisting of basal diet alone or supplemented with sanguinarine or resveratrol during 7 days to 6 months of age. Body weight was measured at the beginning of the experiment and 2 or 6 months of age. Ruminal liquids were sampled at 1, 2, 3, 4, 5, 6, and 9 months of age to monitor rumen fermentation parameters, and samples at 3 and 6 months of age were used to analyze the bacterial community by high-throughput sequencing. The copy number of Desulfovibrio and methanogenic archaea were quantified using droplet digital PCR. Supplementing the basal diet with plant extracts affected rumen fermentation parameters as well as the bacterial community. In addition, the Desulfovibrio population increased after addition of sanguinarine or resveratrol, whereas the methanogenic archaea population decreased after addition of resveratrol. However, no difference were observed in rumen fermentation parameters and bacteria community structure among treatments at 6 months of age. To sum up, liquid feeding regime and nutrition can affect rumen fermentation and bacterial community in calves. Calves fed WM had a different rumen fermentation and bacterial community at 2 months of age. However, this alteration can not persist to 6 months of age. Similarly, supplementation of sanguinarine or resveratrol to calves altered rumen fermentation parameters and microbiota during 3-5 months of age. But, no difference was detected at 6-9 months of age once the dietary treatment was ceased. It is noteworthy that calves fed MR had a higher concentration of TVFA in rumen, which might be a key factor that induced a more long-lasting effect on the rumen environment