Metabolic parameters and methanogenesis in the rumen liquid in in vitro testing experimental diets supplemented with phytobiotics and CoCl2

Dietary bioactives that increase the efficiency of feed nutrient use can provide sustainable and safe livestock products. Some bioactives are modifiers of rumen function in ruminants. These compounds are mostly administered separately. This paper is the first to describe the metabolic changes during in vitro incubation of the Kazakh white-headed bull ruminal liquid (RL) with feed compositions (biosubstrates) containing phytopreparations and cobalt chloride. The most effective combinations and dosages of these additives are evaluated. It was found out that Artemisiae absinthil herba (2.0 g/kg DM) + CoCl2 (1.5 mg/kg DM) increases digestibility of feed dry matter (by 2.1 %), the activity of digestive enzymes and the concentration of metabolites in the RL while decreases methane production by 33.9 %. Salviae folia (1.6 g/kg DM) + CoCl2 (1.5 mg/kg DM) provide the maximum reduction in methane emissions (by 46.3 %). Plant preparations increase the activity of RL amylase 2.6-4.0-fold and RL proteases 3.6-fold compared to control. Our goal was to reveal the effect of herbal preparation and cobalt chloride combination on the metabolic changes assessed in RL by in vitro technique. The experiments were carried out in 2021 at the BST RAS (Orenburg). Rumen liquid (RL) was sampled from four Kazakh white-headed bulls ( Bos taurus taurus ) weighing 250-265 kg at the age of 9-10 months. The samples were collected 12 h after feeding, through a chronic rumen fistula. The control ration (variant I) was 70 % coarse feed (mixed meadow hay) and 30 % concentrated feed (crushed barley). Test rations II was added with CoCl2 (1.5 mg/kg DM; OOO NPK Ascont+, Russia), III with Salviae folia (1.6 g/kg DM), IV with Artemisiae absinthil herba (2.0 g/kg DM), V with Salviae folia (1.6 g/kg DM) + CoCl2 (1.5 mg/kg DM), and VI with Artemisiae absinthil herba (2.0 g/kg DM) + CoCl2 (1.5 mg/kg DM). Each RL sample was tested 4-fold ( n = 16). Feed samples weighing 500 mg in polyamide bags were incubated for 48 h at 39.5 °C in a mixture of buffer solution with RL. At the end of incubation, the samples were rinsed and dried at 60 °C to a constant mass. The coefficient of digestibility in vitro of dry matter was calculated. Air samples were taken separately from each container to determine the methane content by gas chromatography (a Crystallux-2000M device, OOO NPF Meta-chrome, Russia). The amount of volatile fatty acids (VFA) in the RL was determined by gas chromatography with flame ionization detection (a gas Crystallux-4000M chromatograph). The concentration of various forms of nitrogen was determined by the Kjeldahl method (the Millab company equipment, Italy). Amylase activity was measured by Smith-Roy method modified by Anosone for high activity enzymes in the pancreatic juice. Proteolytic activity was assessed colorimetrically (λ = 450 nm) by destruction of Hammarsten Grade casein. The dry matter of biosubstrates was determined by drying to a constant mass at 60 °C. It was found that Salviae folia and Artemisiae absinthil herba shifted the fermentation during incubation towards propionate and butyrate. A. absinthil herba increased the intensity of nitrogen metabolism in RL during incubation, while total nitrogen content increased by 11.6 %, non-protein nitrogen by 144.3 %, ammonia by 71.4 %, and urea by 31,7 % (p function show_eabstract() { $('#eabstract1').hide(); $('#eabstract2').show(); $('#eabstract_expand').hide(); }