Rumen microbial population
Table 4 illustrates data on rumen microbes affected by ELM supplementation using direct count and roll tube technique. The present results show that total viable bacterial and fungal zoospores count were not changed in the supplemented diets. In contrast, proteolytic bacteria and protozoa were decreased in the ELM supplementation groups as compared with the control group. Several authors have suggested certain effects of EO compounds on specific bacteria populations. However, such effects of EO compounds on ruminal microbial populations are inconclusive (Wallace et al., 2008). For instance, Newbold et al. (2004) reported that ruminal protozoa counts were not affected when sheep and dairy cows were fed with 110 and 750 mg/d of a mixture of EO, respectively. Moreover, supplementation of dairy cows diets with 0.5 g of cinnamaldehyde per liter of rumen fluid had also no effect on the number of ciliate protozoa (Fraser et al., 2007). In contrast, Ando et al. (2003) observed that total number of protozoa was decreased when dairy steers were fed 200 g/d of peppermint.