Introduction

The main condition for increasing animal productivity is to provide them with the right amount of feed to meet their nutrient and mineral requirements (Gull & Kausar, 2019; Pham et al., 2020). However, most feeds are deficient in some nutrients, particularly manganese, and excessive in others. Due to insufficient content of minerals in feed and disturbance of their proportions, their digestibility and assimilation of nutrients in feed is often reduced. This, in turn, leads to a decrease in productivity and reproductive ability of animals and the occurrence of various diseases associated with mineral deficiency (Lapshin, 1979; Kwiatkowski & Sldonskl, 1987; Mungin, 2009; Mohammed & Razzaque, 2016; Uslu et al., 2017; Mandzhiev & Gayirbegov, 2019).

Despite the detailed study of manganese metabolism in the organism of ewes, the issues of rationing this element in diets of fat-tailed ewes depending on their physiological condition and zonal features of their breeding remain insufficiently studied.

The manganese norms recommended in 2003 by the Russian Academy of Agricultural Sciences for fat-tailed ewes do not consider the peculiarities of this direction of production and are the same as those for wool and wool-meat sheep (Kalashnikov et al., 2003). In this regard, the objective of the study was to scientifically justify the optimization of manganese in diets of single fat-tailed ewes in dry climatic conditions of their breeding. To achieve this goal, using the factorial method of research, the following tasks were solved:

• To determine the content of manganese in organs, tissues, and gastrointestinal tract of ewes during the non-dairy period and the degree of manganese assimilation from diets
• To calculate the daily requirement and rate of manganese for single ewes

Materials and Methods

Physiological studies were conducted in the production conditions of the farm "Budda" of the Republic of Kalmykia on Kalmyk fat-tailed ewes after weaning and before mating, 3 animals of each period with an average live weight of 55-57 kg. During the experiment, the animals were kept in individual cages and fed according to the recommended RAAS norms (Kalashnikov et al., 2003), about the chemical composition of the local feed.

The diets of the ewes during the period of failed impregnation included: grass from mixed grass pasture ― 3.5 kg, alfalfa hay ― 0.3 kg, barley sod ― 0.1 kg, table salt ― 11 g, and sulphuric manganese ― 58 mg. It contained manganese according to the norm of the Russian Academy of Agricultural Sciences (2003), in the amount of 65 mg.

To study the level of absorption of manganese from diets, to find out the real daily requirement of ewes in this element, and to establish its rates in diets, physiological (balance) experiments were conducted on single ewes after weaning and on single ewes before they were mated. On the day of the end of each balance experiment, to study the manganese content in organs, tissues, and the whole organism, three ewes of similar weight in every single period were slaughtered. The weight of the organs, tissues, and contents of the digestive tract of each ewe was determined. Three samples of each organ and tissue of sheep were taken to determine the concentration of manganese using an atomic absorption spectrophotometer (Getachew et al., 2017; Abdoli et al., 2018; Mirzaei-Alamouti et al., 2018; Mandzhiev et al., 2019).

To calculate the manganese requirement of ewes, we used the factorial method of research, which, according to data (Georgievskii et al., 1979; Kalnitskii et al., 1988; Gromova & Kuznetsov, 2003; Chalmeh et al., 2020), is the most reliable and accurate.

As this method provides, we determined the total content of manganese in the body of ewes, then determined the amount of this element that is deposited in the body during the non-dairy period and per day. Endogenous losses of manganese with urine were determined by the direct method, and with feces by calculation, using data (Georgievskii et al., 1979) obtained based on the generalization of literature data and results of own experiments carried out by radioisotope studies.

Received daily accumulation of manganese in ewes and endogenous losses of this element with feces and urine were summarized and, thus, the true daily requirement of the studied element was established.

Based on the results of balance experiments, considering endogenous losses in feces, the true digestibility of manganese from diets was calculated using the following formula:

where: R ― actual digestibility, %;

I ― intake of the element in the diet, g;

Ex ― excretion of the element in feces, g;

E ― endogenous losses in feces, g.

The determined total actual requirement was divided by the percentage of actual digestion and the result was the amount of the element that should be contained in the diet.

The digital material obtained from all the studies was processed on a computer using the program "Statistics". The results were studied and compared by the group method. The difference in the average indices between the groups was considered reliable at the level of probability (p=0.05), determined using Student's t-test according to E.K. Merkureva (Merkureva, 1970).

Results and Discussion

A study showed that, as a biologically active element, manganese is present in all tissues of ewes but distributed unevenly among them (Table 1). For example, in single ewes, the highest concentration of manganese was concentrated in the brain. In ewes after weaning their lambs, the concentration was 258.44 mg/kg, but in ewes before mating, it increased by 1.4 times to 362.14 mg/kg.

A relatively high concentration of manganese is observed in the tongue, which is also subject to large variations depending on the period of failed impregnation of the ewes and the content of their ration. During the non-dairy period of ewes, the concentration of the element in the tongue increased from 189.61 to 293.07 mg/kg, and its total amount from 18.0 to 27.0 mg, or 1.5 times.

From the fatty tissues, the internal fat and tail fat are slightly inferior to the circumrenal fat in terms of the concentration of this element. Due to the increase in the concentration of the element, the total amount of the element in the inner fat increased from 8.0 to 13 mg or 1.6 times, in the fatty fat from 23.0 to 26.0 mg or 1.13 times, and in the circumrenal fat from 5.0 to 9.0 mg or 1.8 times.

Among all tissues, blood had the lowest concentration of manganese. In single ewes, it contained 12.17-17.28 mg/kg of the element. A high concentration of manganese was also found in bone tissue, which contained 55.90 to 95.36 mg/kg in the case of single ewes. As for muscle tissue, manganese concentration in it was 2.5-2.6 times lower in non-dairy ewes than in bone tissue. As the concentration of the element increases, so does the total amount in bone tissue, from 362 to 657.0 mg.

The main organ depositing manganese is the liver, which has the highest concentration of this element (355.92-651.43 mg/kg), then, with decreasing concentration of this element, the internal organs of single fat-tailed ewes are in the following order: spleen (120.09-247.39 mg/kg), kidneys (83.0-107.2 mg/kg), heart (76.66-87.96 mg/kg), lungs (20.42-24.48 mg/kg). The total amount of manganese in the heart and lungs increased by 1.3 times, in the liver ― by 1.8 times, in kidneys ― by 1.4 times, in the spleen ― by 2.4 times (Table 1).

Since the places of absorption and excretion and the intensity of absorption of minerals in different parts of the gastrointestinal tract of ruminants are not the same, it was interesting to study the accumulation of this element in them.

The conducted analyses of gastrointestinal tract samples of single ewes showed that the highest concentration of manganese was observed in the walls of the omasum (260.78-547.898 mg/kg) and small intestine (62.49-243.25 mg/kg). The remaining parts, in descending order of this element, were as follows: large intestine ― rumen ― reticulum ― rennet. It should be noted that the concentration of manganese increased in all parts of the digestive tract of single ewes by the end of the period under study: in the rumen by 3.3% (p>0.05), in the reticulum and omasum by 2.1 times (p<0.05), in the rennet by 1.3 times (p<0.05), in the small intestine by 3.9 times (p<0.001), and in the large intestine by 1.2 times (p<0.001. All these testify that the metabolism of manganese in digestive organs of single ewes of meat production type becomes more intensive to the mating period. The total content of manganese in an alimentary tract wall of single ewes by the end of the period of observation gradually increases and reaches its maximum in the small intestine (304 mg), followed by the large intestine (178 mg), omasum (104 mg), rumen (84 mg), rennet (17.2 mg), and reticulum (12 mg).

During the absorption and redistribution of manganese in the body of single ewes, the chymus of the gastrointestinal tract departments are also of particular importance. Studies showed an uneven distribution of this element in the contents of the digestive tract.

In single fat-tailed ewes, the chymus of the omasum and the small and large intestine are more saturated with this element.

The absolute content of this element in the rumen and reticulum contents increased by 1.9 times (p < 0.001), in the scut 2.9 times (p < 0.001), in the omasum by 7.6% (p> 0.05), in the small intestine by 1.8 times, and in the large intestine by 3.1 times (p < 0.001) during the studied period.

In general, the total amount of this element in single ewes increased from 2,273.2 mg to 4,657.3 mg.

Table 1. The Manganese Content in the Tissues and Organs of Single Ewes