Adaptive responses of cattle digestive system as influenced by dietary ultrafine iron particles combined with fat diets

Fats are a concentrated source of energy; the fatty components in the diets of farm animals are economically feasible and efficient. The fatty supplements in the diet of cattle improves the palatability of the diets and reduces the rate of feed passage through the gastrointestinal tract, which increases the availability of nutrients and increases livestock productivity. However, some papers indicate a decrease in the digestibility of nutrients in the presence of dietary fat. To increase the availability of nutrients in rations, it is necessary to use additional components in the feed, in particular, ultrafine particles. They, unlike their counterparts in micro- and macro-form, have higher physical activity, chemical neutrality, and high bioavailability ensured by an increased surface area. The limited practical use of ultrafine particles (UFP) in animal husbandry is due to insufficient knowledge about their biological effects on metabolism. Here, for the first time, we evaluated the effect of an ultrafine iron preparation on pancreatic secretion, enzymatic activity of pancreatic juice, morphological and biochemical parameters of blood, and digestibility of feed enriched with sunflower and soybean oils. The aim of our research was to characterize ultrafine iron particles as modulators of metabolic activity when using vegetable fats in the diet of ruminants. The experiments were carried out on Kazakh white-headed calves aged 8 months with an average weight of 120-130 kg (a vivarium of Federal Research Centre of Biological Systems and Agrotechnologies RAS, October 2019-October 2020). A Latin square 4×4 design was applied in five replicates. Control group were fed a standard balanced basal diet (BD), group I - BD supplemented with UFP Fe, group II - BD added with sunflower oil, group III - BD added with sunflower oil + UFP Fe, group IV - BD added with soybean oil, and group V - BD added with soybean oil + UFP Fe. Oils replaced 3 % dry matter of feed concentrates. To produce UDP Fe, we used electric explosion of a conductor in an argon atmosphere (Advanced Powder Technologies, Tomsk). UFPs Fe (d = 90 nm, Z-potential 7.7±0.5 mV) are 99.8 % Fe. Before use, ultrafine iron particles were dispersed in a physiological solution using UZDN-2T (NPP Akadempribor, Russia) (35 kHz, 300 W, 10 μA, 30 min) and added at a dosage of 2.2 mg per animal. To study the exocrine function of the pancreas, a duodenal anastomosis surgery technique was performed. Pancreatic juice and chyme samples were collected over 8 hours with a 60 min interval. The activity of amylase, proteases, and lipase was measured. The blood NO metabolites and trypsin activity were measured. Feed digestibility was assessed on day 7 in balance experiments based on the amount of the consumed feed, uneaten feed and excreted feces. The digestibility coefficient (DC) was calculated as the ratio of the digested nutrients to those entered the body. Dry matter, crude protein, fat and ash contents were measured. Blood for quantitative analysis of the morphological and biochemical parameters was sampled in the morning on an empty stomach on day 7 of the experiment. The research data indicate that dietary UFP Fe with the fat diets contributed to a significant (p ≤ 0.05) increase in the digestibility of crude fat, organic matter and nitrogen-free extractive substances, while the digestibility of crude fiber and crude protein decreased. Enrichment with UFP Fe and fatty ingredients had a stimulating effect on pancreatic secretion, leading to an increased amount of pancreatic juice. The UFP Fe selectively changed the activity of the digestive pancreatic enzymes. UFP Fe added to BD, increased the activity of lipase by 35.7 %, intestinal proteases by 43.1 % while the amylolytic activity decreased by 28.8 %. Dietary UFP Fe combined with sunflower and soybean oils reduced the enzymatic activity of the pancreas compared to the control: in group III, the activity of lipase and intestinal proteases increased by 12.1 and 16.7%, respectively (p ≤ 0.05), in group V - by 133.2 and 38.4 %, respectively (p ≤ 0.05). The BD supplementation with fatty ingredients, alone and in combination with UFP Fe, increased the level of NO-metabolites in all experimental groups compared to the control. When replacing BD with fat diets, the trypsin activity increased in group II by 106.6% (p ≤ 0.05), in group IV by 130.9 % (p ≤ 0.05). Added UFP Fe reduced the trypsin activity. Morphological analysis revealed a statistically significant (p ≤ 0.05) increase in the hemoglobin content in calves of the experimental groups, in group I by 9.7 %, in group II by 31.2%, in group III by 41.9 %, in IV by 28.0 %, in V by 30.1 %.