Abstract
Oregano essential oil (OEO), which has antimicrobial properties, may be used for altering the ruminal pH and microbial populations of sheep, as observed by the altered volatile fatty acid patterns. To further elucidate the effects of OEO on ruminal pH and microbial populations of sheep, 3 German merino sheep × local sheep crossbred rams with permanent ruminal fistulas were randomly assigned to a 3 × 3 Latin square design with 12-d periods. The treatments were as follows: control (CON); OEO4: OEO supplied at 4 g•d-1; and OEO7: OEO supplied at 7 g•d-1. Starting on day 11, rumen fluid was collected at 0 h, and at 4, 8, 12, 24 and 48 h after supplying OEO, and then pH values of rumen fluid were immediately measured. The abundance of microbial populations was determined by using qPCR. The ruminal pH values were similar among the sheep from all treatments. The abundance of ruminal fungi was higher for the sheep supplied OEO7 compared with the sheep supplied CON and OEO4, especially at 4 and 12 h. The abundance of ruminal protozoa decreased with supplied OEO, indicating that OEO could inhibit the protozoa. The abundance of the total ruminal bacteria was similar for the sheep from all treatments, but R. flavefaciens, R. albus and F. succinogenes increased in the sheep supplied OEO4 compared with those in the sheep supplied CON, however, the sheep supplied OEO7 had higher abundances of R. flavefaciens than the sheep supplied CON. These results demonstrated that supplying OEO to sheep did not affect the ruminal pH but could shift the rumen microbial population to one with less protozoa. Supplying OEO can preferentially enhance the growth of certain rumen microbial populations, but the shifts were influenced by the supply rate. Therefore, supplying low amount (i.e. 4 g•d-1) of OEO could have positive effects on ruminal microbial populations, whereas supplying elevated doses of OEO could be detrimental to those same ruminal microbial populations.
Highlights
In recent decades, a large number of chemical additives have been used in ruminant production to modulate rumen fermentation and to improve growth and feed efficiency
In the present study, supplementing Oregano essential oil (OEO) to sheep resulted in no differences (P > 0.10) in the mean ruminal pH values compared with sheep supplied the CON ration (Table 3)
The abundance of F. succinogenes was opposite that of R. flavefaciens and R. albus for sheep supplied OEO4, as it first decreased (P < 0.05) and increased to a maximum at 8 h; it was the highest (P < 0.05) compared with that of sheep supplied CON and OEO7. These results indicated that the supplying rate of 4 gd-1 of OEO favored the growth of R. albus, R. flavefaciens, and F. succinogenes, while the supplying rate of 7 gd-1 could be detrimental to the growth of these microbes
Summary
A large number of chemical additives (antibiotics, ionophores, etc) have been used in ruminant production to modulate rumen fermentation and to improve growth and feed efficiency. A number of studies have been conducted to investigate natural alternatives (essential oils, tannins, saponins, etc) to the chemical feed additives in ruminant production. Among these natural alternatives, essential oils (EOs) have been demonstrated that could manipulate rumen fermentation [3, 4], alter bacterial growth and metabolism of several rumen bacteria [5, 6], and improve ruminant performance [4]. The objective of the present study was to evaluate the effects of OEO on the ruminal pH and microbiota using qPCR in further
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