Comparative assessment of natural feed additives for functional effects on the digestive processes in the rumen of sheep (Ovis aries)

Abstract

In ruminant husbandry, ergotropics, fungal cultures, modifiers, antioxidants, enzymes, and other feed additives with various biological properties help practitioners to create optimal conditions for ruminal microorganisms to grow and to digest various feed substrates of the diet. This paper first compares functional effects of bioactive natural substances (dihydroquercetin, organic iodine, micellar calcium, spirulina, and shungite) on the rumen digestion in Romanov sheep. The work aimed to investigate the peculiarities of the influence of natural feed additives different in their biological properties on fermentative and microbiological processes in the rumen of sheep. Dietary trials were performed in the conditions of the physiological yard, the Ernst Federal Science Center for Animal Husbandry, with Romanov sheep (Ovis aries). In 2014, 12 animals aged 4-5 months were assigned to four dietary treatments: a basal diet without supplementation (BD, the control animals), BD + shungite (0.3 % dry matter), BD + shungite (0.9 % dry matter), and BD + shungite (1.5 % dry matter). In 2018-2019, six fistulated sheep aged 2 years were fed according to two schemes. The first scheme of dietary treatment was as follows: BD for equalization, BD (control), dihydroquercetin (DHQ) (100 mg ∙ head-1∙ day-1) + organic iodine (OI) (1.05 mg ∙ head-1∙ day-1), BD for equalization, and DHQ (100 mg ∙ head-1∙ day-1), each period lasted 14 days. In the second scheme, micellar calcium (M-Ca) injected into the rumen through a fistula (50 µl ∙ head-1∙ day-1) was used instead of DHQ + OI, and spirulina (1,25 g ∙ head-1∙ day-1 -1 day-1, the dry powder mixed with 23.75 g filler) instead of DHQ. In all tests, at the end of each period, 3 hours after feeding, rumen contents were sampled to assess pH, redox potential (ROP), oxidization, total amount of volatile fatty acids (VFA), concentration of ammonia nitrogen, amylolytic activity, the biomass of ruminal protozoa and bacteria, and the microbial profiles. It was found that DHQ and spirulina have the most pronounced effect on ruminal pH, with a 12.7 and 9.5 % increase in the chyme pH, respectively. All dosages of shungite and M-Ca provide higher production of volatile fatty acids (VFA), the 20.6; 27.2 (р < 0.05), 22.8 and 6.6 % of the controls. DHQ + OI, DHQ and spirulina, in contrast, depress VFA production to 93.5, 81.2 and 81.8 % levels of the controls. The dietary additives, except for DHQ + OI, decrease the chyme level of ammonia, which was the greatest for DHQ and M-Ca, by 24.1 % at p < 0.01 and 26.3 %, respectively. Shungite also depresses the chyme ammonia concentration by 18.7 (p < 0.05), 14.9 (p < 0.05) and 9.4 % compared to the control. Dietary DHQ + OI, on the contrary, increases this indicator by 16.5 %. Dietary spirulina, M-Ca and DHQ + OI resulted in the 6.1, 1.7 and 1.1 % increase in the chyme amylolytic activity, respectively, the dietary shungite causes its significant decrease, by 16.8-19.9 %, while the influence of DHQ is the least with a 7.3 % decrease. It was shown that the rumen fermentation affects counts and species composition of the microbiota. The greatest increase in the chyme microbial biomass results from dietary shungite and depends on the mineral dosage. Dietary shungite increases the overall number of microorganisms 2 times (p < 0.01), by 47.4 % (p < 0.05) and 25.2 %, respectively, mainly due to infusoria, and changes the percentage ratio between infusoria and bacteria. DHQ + OI, DHQ and M-Ca also lead to an increase in the chyme microbial biomass but to a much lesser extent as compared to the shungite, i.e. to 14.6, 2.2 and 1.8 % of the control, respectively. Dietary spirulina depresses the total number of microorganisms by 14.3 %. The study traces a positive relationship between the effects of the studied natural feed additives on the rumen microbiocenosis and the ammonia/VFA ratio of, which can characterize the rate of feed conversion to microbial protein.