Microbial inoculum composition and pre-weaned dairy calf age alter the developing rumen microbial environment

Authors: CERSOSIMO, LAURA - University Of Florida; Radloff, Wendy; Zanton, Geoffrey

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2019
Publication Date: 7/23/2019
Citation: Cersosimo, L.M., Radloff, W.J., Zanton, G.I. 2019. Microbial inoculum composition and pre-weaned dairy calf age alter the developing rumen microbial environment. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2019.01651.
DOI: https://doi.org/10.3389/fmicb.2019.01651

Interpretive Summary: Dairy cattle require a diverse community of ruminal microorganisms (bacteria, fungi, protozoa) to convert plant polysaccharides to the energy substrates for growth and milk production. The rumen of a newborn dairy calf is non-functional and sterile. The rumen microbial community continues to change as calves are transitioned from milk to solid feed (e.g., starter pellets and forage) with eventual establishment of a mature ruminal microbial community. This research evaluated the effects of inoculating the rumen of newborn dairy calves with bacteria-enriched or protozoa-enriched inoculum taken from adult dairy cows. The administration of ruminal inocula did not alter calf health or growth. Fermentation by-products were altered by microbial inoculum type despite no changes in microbial diversity and few differences in bacterial taxa. While some transient effects were observed, there were no sustained effects of inoculating with bacteria- or protozoa-enriched inoculum in this study.

Technical Abstract: The objective of this experiment was to determine if microbial inoculum composition alters the rumen microbial ecology and performance of pre-weaned dairy calves. Twenty Holstein bull calves were removed from their dam at birth, fed 3.8 L colostrum within 1-4 hours after birth, and housed individually. Calves were fed pasteurized milk 3x/d and offered a texturized calf starter ad libitum at 6d of age. A randomized complete block design with repeated measures and a 2 x 2 factorial arrangement of treatments was used to evaluate responses. Treatments were administered by stomach intubation and included: 50 mL autoclaved rumen fluid (RF), 50 mL bacterial-enriched RF (BE), 50 mL protozoal-enriched RF (PE); or 50 mL of each BE and PE inoculum. A rumen content composite was collected from 4 rumen fistulated, lactating Holstein cows. BE inocula were microscopically confirmed to be free of ciliate protozoa before inoculation, while PE contained 2.9±2.2 x 105 protozoa/mL. RF was collected from the calves and inocula were administered once/week at 3-6 weeks of age by stomach intubation. pH and total volatile fatty acid concentration of the PE inocula were greater than BE inocula (P<0.001). PE inoculum (3.7±0.5 mM) had lower NH3 concentrations than BE inoculum (6.8 mM). The bacterial community structure and composition differed by inocula type (P<0.01). Animal performance was not altered by inocula type. All calves were microscopically free of rumen ciliates at 3 weeks of age and calves that did not receive PE remained ciliate-free. Ciliate protozoa were observed in RF from 6, 8, and 6 PE calves (n=10) at week 4, 5, and 6, respectively. Ruminal NH3 was lower in PE calves (3.3 vs 6.8±1.0 mM), while ruminal butyrate molar percent was greater in BE calves (10.8 vs 8.3±0.8). Rumen bacterial diversity measures did not differ by treatment. Individual calf bacterial communities from treated calves became temporarily similar to the inocula, but these communities diverged from the inocula prior to the last inoculation. This study provides new information about two types of rumen-derived inocula and insight into the challenges of directing the rumen microbial environment in the pre-weaned calf.