The response of pig erythrocytes to the technological stress, depending on gender

. The article considers the issues of the peculiarities of how the technological stress influences the indicators of red blood cells in pigs. Clinically healthy animals were selected at the stage of mobilization of the development of stress response according to the principle of pairs of analogues: group I - breeding boars, group II - breeding sows. The oxygen budget of the body, determined by the indicators of red blood cells, during the development of a stress reaction in breeding pigs of “mature age” is also determined by their gender. Boars had average values of erythrocytes and hemoglobin in reference values, but the degree of saturation of erythrocytes with hemoglobin was lower than normal and lower than that of sows. This may indicate that boars experience a greater shortage of oxygen supply to the tissues. Sows, in general, are more stress-resistent, as evidenced by the values of the ratio of lymphocytes and neutrophils, as well as their erythrocyte indicators. They differed from boars by a significantly lower level of erythrocytes and the reference level of hemoglobin in all examined individuals. In sows, the indicator of erythrocyte saturation with hemoglobin was significantly higher than in boars.


Introduction
Currently, it is known that modern technologies of breeding and keeping farm animals cause them a stressful state and can negatively affect many physiological functions and the quality of the products obtained [1][2][3][4][5].Among other farm animals, the technological stress affects pigs [6].
As a result of the intensive technology use for the livestock production, the effect on animals of various factors in nature and strength is often observed, leading to a mismatch of the "genotype × environment" interaction.In pig breeding, in recent years, the goal of breeding programs is to obtain and breed healthier and more efficient animals.This implies the development of an appropriate strategy for managing the interaction "genotype × environment" [7].
Since it is impossible to eliminate many of the technological and environmental stress factors, it is of paramount importance to search for mechanisms of their adverse combined effects on various life support systems, primarily on the blood system, in order to mitigate them.
The increased interest of researchers in the erythrocytes is due to their unique biochemical, biophysical and mechanical properties.It is widely known that erythrocytes are responsible for respiration and gas transport [8,9].In addition, these cells have specific structural features, can remain in the bloodstream for up to 120 days [10] and make up ~ 40-50% of the blood volume [11].
The environment can influence the morphology and functions of erythrocytes [12][13][14].The effect of the stress reaction on red blood cells, at present, is beyond doubt.These cells, according to some literature data, can act as indicators of physiological stress caused by environmental factors [15].According to the report of I. Martínez-Vieira with co-authors (2019) [16], the effect of stress influences leads to a decrease in the number of red blood cells and hemoglobin in the blood.At the same time, the resistance of erythrocytes to the action of stress factors in farm animals, according to some reports [17], has specific features.
In our work, we decided to trace the relationship of the indicators characterizing the course of the stress reaction with the indicators of red blood cells characterizing functional capacity at the level of the whole organism.We believe that in order to further improve the technological conditions for breeding and keeping pigs, to increase their adaptability, it is important to identify the basics of an intensive and constant response to risk factors caused by prolonged stress.Taking into account the known gender differences in indicators characterizing morphofunctional features of erythrocytes [11], the purpose of our work was determined.
The purpose of our study is to study the possibilities of pig blood erythrocytes' response to technological stress conditions depending on gender.

Materials and methods
Our research was carried out on the material obtained in the conditions of LLC "Breeding Plant 'Belovodsky'" (Lugansk region, Ukraine) on the purebred livestock of the main boars and sows of the Poltava meat breed.
The environmental conditions of the animals -feeding, keeping, carrying out veterinary measures -met the technological standards developed by the Institute of Pig Breeding and Agro-Industrial Production of the Ukrainian Academy of Agrarian Agricultural Sciences, taking into account age, body weight and physiological condition.The type of feeding is concentrated with the use of feed of own production.The keeping method is single-housed, free-range.
The technological factor was used as a stressor.During the experiment, the animals were subjected to planned (vaccination, drift, transfer to another room, weighing, hypokinetic stress with prolonged close confinement, etc.) and unplanned technological stresses (social factors, alterations of the developed feeding stereotype and switching to other diets, stresses arising under the influence of microclimate and climate factors (due to changes in weather conditions).
At the first stage, all the main boars and sows of the breeding herd of the farm were examined in order to determine the stage of development of the stress reaction.At the second stage, clinically healthy animals in the stage of mobilization of the development of a response to environmental factors were selected for the study on the principle of pairs of analogues: group I -breeding boars of the main herd (n=17), group IIbreeding sows of the main herd (n=3).
Blood sampling was carried out in the summer, in the morning, before feeding the animals, by puncture of the ear vein, in vacuum tubes.The following parameters were determined in the blood: the number of erythrocytes, hemoglobin, leukocytes, and the leukocyte blood picture (formula).The average content of hemoglobin in an erythrocyte was calculated [18].To characterize the stress stage, an integral hematological index of the ratio of lymphocytes and neutrophils was used [19], taking into account the blood profile in pigs.
The obtained data were processed by methods of variational statistics using the "Statistika-6" application software package with a probability of <0.05.The average value of the feature (M), the error of the average (mM), the reliability of the difference of the average values (p), the coefficient of variation (Cv) were calculated.

Results
The use of industrial production technology on the farm turned out to be stressimplementing for the pigs of the main herd of the Poltava meat breed, which was confirmed by the calculated ratio of lymphocytes and neutrophils characterizing the development of stress in this animal species.
According to the general assessment among the examined animals, all boars (100%) were in the state of the first stage of stress reaction development -"mobilization of response development".The majority of sows (56.5%) had the second stage of stress reaction development -"resistance stage", 30.4% had the third stage -"exhaustion stage" and only 13.1% of bala sows had the first stage of stress reaction development -"mobilization of response development".In the future, we evaluated the obtained morphofunctional parameters of erythrocytes of pigs at the same stage of stress reaction development, depending on gender.
The obtained data on the erythrocyte indices of the main boars and sows of the Poltava meat breed at the stage of mobilization of response development, triggered by the effects of technological stress, are shown in Table 1.We found that in the breeding pigs of the main Poltava meat breed herd, the totality of all the studied indicators of the erythrocyte blood pattern differed in uniformity because the obtained variation coefficients did not exceed 33%.
According to L. Massaccesi and co-authors (2020) [20], erythrocytes are deeply sensitive cells and important indicators of health.
According to the conducted analysis results, the established average number of red blood cells in the blood of all boars in the main herd was within the reference intervals specified in the literature.At the same time, the range of values in boars (Lim) in terms of the number of erythrocytes did not coincide with the specified reference intervals, i.e. in the herd of the main boars there were animals that, under the same conditions of feeding and maintenance, had an indicator inferior to or exceeding the literary values of the reference intervals for this type of animal.The variability of the value in boars was characterized by an average level of variation and was of the greatest importance among all the studied indicators of erythrocytes, which may indicate that these cells are more exposed to functional loads and are more widely involved in the adaptation of the body to these conditions.
The average values of the number of erythrocytes in sows were lower than the literary reference intervals and significantly inferior to boars by 15.2% (p≤0.05).They had an insignificant level of variability of this indicator and its smaller scope.
The indicator of the average amount of hemoglobin in all animals was within the limits of reference values and there were no significant gender differences in this indicator.However, in the examined boars, the range of values of the amount of hemoglobin forming the range of variability of the trait (Lim) did not fall within the values of the literary reference intervals, unlike sows.
It should be noted that the variability of the indicator of the amount of hemoglobin did not differ by much variation and was the smallest among all other studied indicators in all pigs.Despite this, it should be noted that according to this indicator, we also noted the greatest variability in boars, unlike sows.
The impact of stress factors, including technological ones, leads not only to a qualitative change in erythrocytes in the blood, but also affects the value of erythrocyte indices and their dynamics during the development of a stress reaction.
The degree of saturation of erythrocytes with hemoglobin in all examined pigs did not correspond to the value of the reference interval indicated in the literature.Only a small number of boars (based on the ranges of the range of variation) had this indicator corresponding to the lower limit of the interval.
Boars by the degree of saturation of erythrocytes with hemoglobin were significantly inferior to sows by 13.64% (p≤0.05), with an average level of variability.The level of variability of the indicator in sows was insignificant.

Discussion
Technological factors in the body of the main Poltava meat breed pigs caused the development of a stress reaction, which was confirmed by calculating the appropriate ratio of lymphocytes and neutrophils.However, sows are less sensitive to the effects of stress factors.All the examined boars of the herd were in the stage of mobilization of the development of a stress reaction.At the same time, most of the sows were at the stage of resistance, which may indicate that the body's defenses coped with the effects of the stress factor.
The oxygen budget of the body, determined by the indicators of red blood cells, during the development of a stress reaction in breeding pigs of "mature age" is also determined by their gender.At the same time, the level of its adaptive changes affects both quantitative (morphological) indicators and qualitative (functional) indicators of erythrocytes.
The erythrocytes in boars react differently in response to the action of stressors in the conditions of using industrial technology: both by increasing and decreasing the quantity.The main burden of providing the oxygen budget of the body under the action of stress factors in boars, in our opinion, is more significant and affects all indicators of red blood cells based on the analysis of the value of Cv.At the same time, the indicator of the amount of hemoglobin in the blood of individuals of this group is the most stable value.In the group of boars, according to all the studied indicators, there are animals whose indicators do not correspond to the reference intervals.
The calculation of the degree of saturation of erythrocytes with hemoglobin, in general, from the "normal" average values of erythrocytes and hemoglobin in the blood of boars, showed clear body tendencies in the conditions of stress reaction development to not yet obvious adverse shifts.
In sows, the stress reaction caused a decrease in the number of red blood cells.In these conditions, sows had, in general, better formed mechanisms of adequate response of adaptive potential.These mechanisms manifested themselves in maintaining the hemoglobin index in the blood at the level of literary reference intervals and a higher degree of saturation of erythrocytes with hemoglobin, despite their low values.At the same time, a decrease in the level of red blood cells did not lead to a decrease in the amount of hemoglobin.It should also be noted that these indicators do not have a stressful presence in the form of tension and instability, as evidenced by unidirectional changes in variability indicators.The lowest environmental load was experienced by the functional indicatorthe degree of saturation of erythrocytes with hemoglobin.
Probably, under the conditions of long-term stress factors, with the depletion of the population of erythrocytes in sows in peripheral blood, other adaptive response mechanisms, in particular, hemoglobin ones, came to the fore.

Conclusion
The effect of technological factors in pigs leads to the development of a stress reaction and causes changes in the erythrocyte link of the blood.At the same time, the sex of animals affects the provision of the oxygen budget of the body by changing the level and direction of adaptive reactions of erythrocytes.
In the conditions of modern pig breeding technologies, developed anti-stress measures to ensure a full oxygen budget in the body, taking into account the sex of the animals, may become prerequisites for a possible increase in the level of adaptability under the action of technological factors may be.

Table 1 .
Red blood indicators of main herd breeding pigs of the Poltava meat breed, which are in the stage of stress reaction development mobilization, (M±m).