Abstract
The development of the functional rumen in calves involves a complex interplay between the host and host-related microbiome. Attempts to modulate rumen microbial community establishment may therefore have an impact on weaning success, calf health, and animal performance later in life. In this experiment, we aimed to elucidate how rumen liquid inoculum from an adult cow, provided to calves during the pre-weaning period, influences the establishment of rumen bacterial, archaeal, fungal, and ciliate protozoan communities in monozygotic twin calves (n = 6 pairs). The calves were divided into treatment (T-group) and control (C-group) groups, where the T-group received fresh rumen liquid as an oral inoculum during a 2–8-week period. The C-group was not inoculated. The rumen microbial community composition was determined using bacterial and archaeal 16S ribosomal RNA (rRNA) gene, protozoal 18S rRNA gene, and fungal ITS1 region amplicon sequencing. Animal weight gain and feed intake were monitored throughout the experiment. The T-group tended to have a higher concentrate intake (Treatment: p < 0.08) and had a significantly higher weekly weight gain (Treatment: p < 0.05), but no significant difference in volatile fatty acid concentrations between the groups was observed. In the T-group, the inoculum stimulated the earlier establishment of mature rumen-related bacterial taxa, affecting significant differences between the groups until 6 weeks of age. The inoculum also increased the archaeal operational taxonomic unit (OTU) diversity (Treatment: p < 0.05) but did not affect the archaeal quantity. Archaeal communities differed significantly between groups until week 4 (p = 0.02). Due to the inoculum, ciliate protozoa were detected in the T-group in week 2, while the C-group remained defaunated until 6 weeks of age. In week 8, Eremoplastron dilobum was the dominant ciliate protozoa in the C-group and Isotricha sp. in the T-group, respectively. The Shannon diversity of rumen anaerobic fungi reduced with age (Week: p < 0.01), and community establishment was influenced by a change of diet and potential interaction with other rumen microorganisms. Our results indicate that an adult cow rumen liquid inoculum enhanced the maturation of bacterial and archaeal communities in pre-weaning calves’ rumen, whereas its effect on eukaryotic communities was less clear and requires further investigation.
Highlights
The microbial ecosystem inhabiting the rumen enables ruminants to utilize plant materials as feed
Methanogenic archaea start populating the rumen during the first days of life (Guzman et al, 2015; Friedman et al, 2017), while anaerobic fungi have been observed in the rumen at around 1 week after birth (Fonty et al, 1987)
No significant changes related to the initiation of inoculation were observed in the immunoglobulin G (IgG) levels in the the groups at birth (T-group) at the age of 2 weeks (Treatment: p > 0.05, Treatment × week 3 (Week): p > 0.05)
Summary
The microbial ecosystem inhabiting the rumen enables ruminants to utilize plant materials as feed. During the pre-ruminant phase (0–14 days), when calves are sustained on a liquid diet, the rumen function is still very low, as most of the liquid is digested by the enzymes in the abomasum and small intestine (Comline and Titchen, 1951; Ørskov et al, 1970; Baldwin et al, 2004) During this period, the rumen starts being populated by the aerobic and facultative anaerobic bacteria, gradually changing to obligate anaerobes (Jami et al, 2013; Rey et al, 2014). Methanogenic archaea start populating the rumen during the first days of life (Guzman et al, 2015; Friedman et al, 2017), while anaerobic fungi have been observed in the rumen at around 1 week after birth (Fonty et al, 1987)
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