Initial BW was not significant as a covariate. Final BW, ADG, daily intake and feed conversion were not affected (P>0.10, Table 2) by dietary inclusion of the herbal mixture. The pH showed a quadratic response (P<0.10), increasing with the intermediate concentrations. However, statistical differences were observed in the ruminal volatile fatty acids (VFA s). The acetate increased (linear and quadratic effect P<0.05) and propionate reduced (quadratic effect; P<0.05). Butyric acid and total VFA s were not affected by the inclusion of the herbal mixture (P>0.05).
The lack of response in this experiment contrasts with previous reports where the animals responded under stress conditions.
Misra and Agrawala (2005), who evaluated the same phytobiotic as support for the treatment of metabolic problems in ruminants, found positive responses and found that the variation in feed consumption between days decreased. Polyherbal products, due to the content of their metabolites, are sometimes used for their antibiotics, immunomodulators and immunostimulants, growth promoters, methane reducers and anthelmintic properties
(Lillehoj et al., 2018). The terpenes, phenols, polyphenols, carotenoids, oligosaccharides and vitamins from plant species can act as growth promoters
(Cardinali et al., 2015; Dalle Zotte et al., 2016) and effects depend on the metabolite and its mechanism of action. Additionally, the addition of herbs, species and bioactive compounds have beneficial effects in feed formulated for ruminants on the antimicrobial and immune properties (
Greathead, 2003;
Cardozo et al., 2006; Patra et al., 2012; Oh and Hristov, 2016). Research evaluating the dietary inclusion of a polyherbal formula in lambs reported that feed intake, daily weight gain and final weight increased due to secondary plant metabolites
(Mejia-Delgadillo et al., 2021). The inclusion of herbs and plants in the rations for lambs can increase the digestibility of DM and the daily gain due to the fermentative changes that their compounds can cause in their ruminal microbiota; thus, improving daily weight gain
(Wanapat et al., 2012; Celia et al., 2016).
The response in ruminal pH will depend on the type of plant and dose, therefore, results from other herbs can not be compared directly.
Rao et al., (2016) found a constant decrease in the pH in the rumen fluid as the inclusion of
Azadirachta indica increased, which contrasts with what is observed here. Tannins in plants can affect ruminal biohydrogenation
(Khiaosa-Ard et al., 2009) and tannins and phenols can affect the rumen protozoa
(Bhatta et al., 2012), which could modify starch digestion and indirectly change rumen pH (
Ortega and Mendoza, 2003).
Changes in VFA s will depend on the effects of herbs on the populations of bacteria and protozoa. Previous
in vitro evaluations of the same polyherbal mixture showed increases in the production of acetic and propionic acids
(Sardar et al., 1997); however, this showed increments in acetic and a reduction in the propionic proportion, which is energetically undesirable and explains the lack of response in daily gain. Phytobiotic compounds could improve ruminal microbiota by functioning as antimicrobials and/or growth promoters. Some tannins can alter the bacterial balance by affecting hydrogen cycles through the inhibition of oxidative phosphorylation in bacterial mitochondria, altering the hydrogen bonds or chelating mineral ions essential for bacterial metabolism (
Scalbert, 1991).
Although benefits are expected from herbals, they are not always observed.
Wanapat et al., (2008) evaluated the inclusion of
Allium sativum in the rations for ruminates, finding increases in propionic acid, decreases in the acetic-propionic ratio and degradation of ruminal nitrogen, associated with reduced rumen protozoa. Changes in rumen protozoa have been related to improvement in ruminal parameters
(Wanapat et al., 2012). The changes detected in acetate and propionate do not lead to a possible reduction of methane, although this mixture contains plants that have been evaluated
in vitro and have decreased methanogenesis
(Gupta et al., 2017) but
in vitro protozoa do not survive.
Chebulic myrobalan has been evaluated in an
in vitro fermentation and has been reported to influence the decrease in methane production
(Heidarian-Miri et al., 2013). Terminalia bellirica was controlled in
in vitro fermentations to measure its methane inhibitory capacity, discovering that it has a large number of tannins and concluding that these could act directly on the arches without altering the rumen protozoa
(Bhatta et al., 2012).
One of the main plants of this mixture is
Azadirachta indica, which is present in other polyherbals (
Martínez-Aispuro et al., 2019;
Razo-Ortíz et al., 2020).
Azadirachta indica is one of the most studied plants for its metabolites and the major components are terpenes and limonoids with a demonstrated antimicrobial activity and has been used in ethnoveterinary treatments in different species; in ruminants for udder infections and foot root and lice
(Ogbuewu et al., 2011). The higher acetate concentration and the higher pH with herbs could be indicators of a higher cellulolytic digestion, but this was not manifested in lambs’ performance as observed in other feed additives which contain
Azadirachta indica (
Martínez-Aispuro et al., 2019;
Razo-Ortíz et al., 2020). This means that the formulas and their proportions can result in combinations that may or may not be successful.
