Biotechnology of regulation of reproductive functions of Bos primigenius taurus

. Since cattle are biologically capable of giving birth to only one calf per year, they are considered a single-fruited animal species. One of the cardinal methods of solving the problem of accelerated reproduction of livestock is biotechnological regulation of reproductive function in cows and synchronisation of their sexual activity. The aim of the study is to investigate the peculiarities of the reproductive function


INTRODUCTION
Modern livestock farming, including cattle breeding, requires intensive reproduction, which is impossible without stimulating and synchronising the sexual function of heifers and cows for the full operation of the industry, i.e. obtaining one calf per year and planned predictable artificial insemination.Therefore, improving methods to maximise the reproductive potential of females requires a comprehensive understanding of the processes that control follicle development (Melnik et al., 2022).
Various strategies and biotechnological techniques are used to achieve optimal reproductive function or reproductive health management.Although exogenous agonists of human chorionic gonadotropin (HCG) and gonadotropin-releasing hormone (GnRH) (A) are commonly used to trigger ovulation during estrous cycle synchronisation, little is known about their effects on the ovarian follicle (Ziecik et al., 2021).
According to A. Abbara et al. (2018a), even an accurate estrus timing does not compensate for the variability of the interval between its onset and the actual time of ovulation.Hormonal treatment has been used by the authors in various studies to control the reproductive functions of cows and heifers, which allows overcoming this problem and synchronising ovulation.Follicle recruitment and atresia are important processes associated with the rate of ovulation in cattle.Follicle-stimulating hormone (FSH) regulates the distribution, differentiation and steroidogenic function of granulosa cells and thus has a significant impact on follicle growth and development.Although local factors such as growth factors and steroid hormones can regulate follicular development by controlling gonadotropin receptor expression or modulating other related processes, the dominant role of FSH cannot be ignored (Abbara et al., 2018b).
According to M. Besbaci et al. (2020), one of the strategies to improve bovine fertility is the administration of GnRH or hCG during the luteal phase, which increases progesterone (P4) secretion and slows luteolysis.P4 insufficiency is associated with a decrease in the number of pregnancies per AI (P/AI), abnormally early embryo development, and reduced maternal pregnancy recognition signalling.The authors also found that by inducing luteolysis in cows with PG F 2α -sensitive CL and subsequent treatment with exogenous P4 at subluteal concentrations, treatments 2 and 3 induced follicular persistence in a large proportion of cyclical cows.
Programmes for hormonal control of the estrous cycle of cattle were used by R.C. Bonacker et al. (2020) for the widespread use of reproductive technologies such as fixed-time artificial insemination (FTAI) in beef and dairy cattle.For example, scientists demonstrate an approach to stimulating follicular maturity by administering PG F 2α and treating with a CIDR insert for seven days before GnRH administration.Similar studies were conducted by E.M. Cabrera et al. (2021).Holstein cows during lactation were subjected to a double diagnosis (DO) procedure for the first artificial insemination (TAI) after an independence period of 73 days.The researchers concluded that administration of a dose of hCG ≥ 2000 IU induced a greater ovulatory response in lactating Holstein cows than 100 µg GnRH or 1000 IU hCG and resulted in the greatest quantitative increase in plasma P4 concentration between 7 and 14 days.
Therefore, the purpose of the research was to use biotechnological methods to regulate the reproductive function of Bos primigenius taurus females using new generation hormonal drugs, which will have a positive impact on reproduction management in lactating dairy cows and will allow artificial insemination at a certain time of ovulation and eliminate the need to detect estrus.

LITERATURE REVIEW
The difficult economic and social situation in the livestock sector poses great challenges for agricultural workers to further ensure a sustainable increase in livestock production (Gonchar & Sotnichenko, 2015;Pidpala et al., 2018).One of the aspects of such tasks is the use of biotechnological solutions to increase the reproductive capacity of animals (Bezuhlyi, 2002;Kamenska, 2013;Kruglyak, 2016).
According to M.P. Zhuravel & M.V. Davydenko (2005), in order to obtain calves from cows every 10.5 months and thus have a yield of 110-115 calves per 100 cows, it is necessary to use the potential fertility of animals wisely -with the use of biotechnological solutionsto ensure high organisation of their reproduction.Such use of prophylactic drugs will help to synchronise the heifers' sexual desire and increase their fertility during insemination.And the organisation of cattle reproduction and the proposed biotechnological ways to improve artificial insemination of the red steppe breed breeding stock will significantly improve their reproductive status, which will increase the overall economic efficiency of the industry Keywords: prostaglandins; sexual desire; service period; insemination index; dry period; artificial insemination intensification of reproduction allows to increase calf yield by at least 10-15%, increase milk productivity of each cow by an average of 250-300 kg of milk per year, and extend the life of animals, which is confirmed by a number of scientists (Ponomarenko, 2005;Ugnivenko & Demchuk, 2018;Fedorovych, 2019).
According to I.V. Ponomarenko (2005), the constant growth of livestock and animal productivity is closely related to the state of the reproductive function of the breeding stock.The presence of pathological processes both in the reproductive apparatus and in the whole organism complicates the fertilisation processes, leads to changes in the reproductive function of animals, an increase in infertility, and the percentage of infertile cows in the structure of the animal herd, which reduces the level of profitability of milk production, increases milk production costs, and increases its cost (Ostashko, 1995; Zvierieva et al., 2001).
According to V.F.Stakhovsky (2009) and O.V. Kruglyak (2016), the main task in cow reproduction is to intensify the reproductive function of cows, including biotechnological solutions, prevention and elimination of infertility.Improvement of breeding decisions in the use of biotechnological products is also reflected in the studies of V.M. Chukhriy et al. (1998), V.M. Nadtochiy et al. (2011), G.P. Gryshchuk (2012).At the same time, the use of artificial insemination of the breeding stock of cows is proposed by V.V. Vechorka (2010).
To intensify and restore the reproductive function of cows, a variety of methods and means are successfully used in practice (Bushtruk, 1998;Pabat & Vinnychuk, 2001;Guntik, 2003).And, as a number of scientists point out, stimulation and synchronisation of reproductive function is one of the links in the complex system of prevention and elimination of infertility and increase of reproductive function of cows (Yablonskyi, 1995; Yablonskyi et al., 2011;Bobryk, 2020).
The use of biotechnological techniques in synchronising estrus in cows has been reported by a number of American scientists.For example, J.R. Pursley et al. (1995) reported synchronisation of ovulation time in cattle using GnRH and PG F 2α .Lactating dairy cows aged 36 to 280 days after calving and young heifers aged 14 to 16 months were injected intramuscularly with 100 µg of GnRH at a random stage of the estrous cycle.Seven days later, cattle received PG F 2α for corpus luteum (CL) regression.Lactating cows and heifers received a second injection of 100 µg GnRH 48 and 24 hours later, respectively.The lactating cows were artificially inseminated 24 hours after the second GnRH injection.All cows and heifers ovulated with a newly formed dominant follicle between 24 and 32 hours after the second GnRH injection.Ten of the 20 cows were ready for timely artificial insemination.Therefore, the studies confirmed a great impact on reproduction management in lactating dairy cows and allow artificial insemination at a certain time of ovulation and eliminate the need to detect estrus.
Thus, timely detection of cows in heat, regulation of estrus with biotechnological products and elimination of negative factors affecting cow fertility will help develop appropriate measures to improve the reproductive capacity of dairy cows, increase the frequency of pregnancy during the first artificial insemination and, as a result, determine the economic efficiency of the industry.

MATERIALS AND METHODS
The research was conducted in the period from 2018 to 2020 in the conditions of the Additional Liability Company (ALC) Pivdennyi Kolos of the Novo Odesa district of the Mykolaiv region on cows of the red steppe breed in compliance with the technological standards of use and maintenance of farm animals (Ostashko, 1995;Bezuhlyi, 2002;Zhuravel & Davydenko, 2005).Also, all ethical standards of animal treatment were observed in accordance with the Code of practice... (2014) and Law of Ukraine No. 3447-IV (2006).The development of the livestock industry was analysed according to the documentation of zooveterinary and breeding records.The results of obstetric and gynaecological examination of 195 cows were used in the work.An analysis of the reasons for the shortfall in calf production in 2018-2020 was carried out in accordance with the Order of the Ministry of Agrarian Policy of Ukraine No. 230 (2001).The research used a technician's calendar and a stand for the physiological state of cow reproduction on the farm.During artificial insemination of cows and heifers, the rectocervical method of sperm injection into the genital tract at the animal housing facilities and in the artificial insemination arena was used, which is in accordance with Order of the Ministry of Agrarian Policy of Ukraine No. 230 (2001).
Semen was used in uncoated granules and paiets, stored at -196 0 C in liquid nitrogen and delivered from the private enterprise Genetics and Selection (Kyiv).The reproductive function of cows was studied according to the following traits and indicators: postpartum period; fertility from the 1 st insemination; calving to conception interval (CCI), insemination index.To study the effectiveness of insemination of cows depending on the period after calving (index period), all cows were divided into 4 groups with different terms of coming into heat and insemination according to the insemination period after calving: Group I -up to 30 days; Group II -31-60 days; Group III -61-90 days; Group IV -91 days and more.
To study the effect of reproductive capacity on cow milk production, 53 cows were selected, and four groups were formed according to the year of birth and the serial number of their lactation in 2018, 2019 and 2020.For each animal in these groups, as well as for the whole farm, the following milk yield traits were determined and analysed: milk days, lactation yield, average daily yield, fat content and amount of milk fat.The cows were also studied for signs of reproductive capacity: the number of dry days, the yield and sex of the offspring, and the duration of the calving to conception interval (CCI).
In the production environment of Pivdennyi Kolos, the sexual activity is determined visually by the "immobility reflex" when observing animals in the herd during a walk and before morning and evening milking.Determine the sexual activity at least three times during the daylight hours: at 6-9 am, 2-3 pm and 5-7 pm.When the "immobility reflex" is established, animals are separated from the herd to special places for standing, where they are kept before insemination and afterwards until the signs of sexual desire cease.
The biometric analysis of the data was carried out in accordance with accepted methods of analysis (Povod et al., 2015).The correlation analysis of the relationship between the milk production of cows of different groups and their reproductive capacity was carried out by the following characteristics: "dry days ↔ milk yield", "milk yield (lactation) ↔ calf yield", "average daily milk yield ↔ calf yield", "calving to conception interval ↔ calf yield", "calving to conception interval ↔ milk yield", "milk yield for I-VI lactation ↔ calf yield", using the formula: where r -the correlation coefficient, x -the first of the indicators between which the correlation is determined, y -the second of the indicators.For the calculation, computer equipment with the Microsoft Excel application was used.
To study the issue of regulation and synchronisation of sexual desire of repair heifers using an analogue of prastaglandin F 2α -Estrophan and its use in combination with the drugs Tetravit and Catozal, three groups of 18 heifers were formed; after their treatment with the drugs, insemination was carried out.During the study of the effect of live weight of repair heifers on their fertility, seven groups were formed by weight categories, and to study the effect of the age of first insemination on fertility, five groups were formed, after insemination, the results of fertilisation from the first insemination were calculated.The comparative evaluation of animals of different groups in terms of the development of the trait under analysis was carried out by determining the absolute difference (d) between the mean values and their errors (S d ), and the level of probability of this difference (p) was determined by the standard values of the Student's t-test (Kravchenko, 1973).On the basis of the research and the results obtained, the relevant conclusions are drawn and specific proposals for production are provided.

RESULTS AND DISCUSSION
Stable reproduction is a prerequisite for ensuring the efficiency of cattle breeding.Milk production depends on this to the greatest extent, as lactation activity is inextricably linked to the full functioning of the reproductive function and the production of offspring (Motta et al., 2020).The distinctive features of red steppe cattle are their strong constitution, satisfactory milk production, good fattening and meat qualities, and high adaptability to harsh natural and climatic conditions.At the same time, the animals are highly resistant to leukaemia, tuberculosis and limb diseases.Deviations in reproductive function in red steppe animals are somewhat less common than in black-and-white cattle.However, under conditions of industrial technology, they often have problems with reproduction.Due to the disturbance of the hormonal balance of the body and, above all, the gonadotropic function of the pituitary gland, the susceptibility to functional disorders of the reproductive organs increases (Fricke & Wiltbank, 1999).
An analysis of the state of reproduction of the cow population is given in Table 1, which shows that over the years studied, there has been an increase in the number of cows.Thus, in 2018 there were 175 cows, in 2019 there were 185 cows, and in 2020 there were 195 cows.Every year, 96-98% of them are inseminated, but the yield of calves is not stable and was 89 calves per 100 cows in 2018, 91 calves in 2019, and 90 calves in 2020, respectively.In this regard, the reasons for the shortfall in calf yield over the past three years were investigated.

Source: authors' own development
The research revealed that 80 calves were lost in just three years.The main reason for this in 2018-2020 was the death of 31 cows, and the second reason for culling was cow fatness or the extension of the calving to conception interval -23 cows.In addition, eight pregnant cows were culled for various reasons: disease, injury, forced slaughter, etc.An important role in the prevention of postpartum diseases and infertility is played by obstetric and gynaecological examination, a set of diagnostic, preventive and therapeutic measures aimed at ensuring the normal course of pregnancy, childbirth and the postpartum period in cows, and preserving the viability of the young animals born to them.K. Moore & W.W. Thatcher (2006) in their research came to a similar conclusion, namely, that existing intensive commercial systems for keeping lactating dairy cows require careful management of breeding, treatment and preventive measures even before the introduction of follicular waves, CL regression and ovulation induction in programming, which will solve the problem of increasing the reproductive efficiency of high-yielding dairy cows.The analysis of Table 2 shows that the number of pregnant cows on the farm on the day of the inspection was 106 heads or 54%, which corresponds to the norm, while 15 heads or 7.7% of problem cows were identified, which is slightly below the norm and convincingly confirms the existence of an established obstetric and gynaecological examination and prevention and treatment of problem cows.

Table 2. The results of obstetric and gynaecological examination of cows in the conditions of Pivdennyi Kolos in June 2020
It is worth noting that at the time of the herd examination, there was an increase in the number of cows after insemination -48 heads, which is 24.6%, which can be considered conditionally pregnant, respectively, which will increase the percentage of pregnant cows in the farm.In the course of the research, it should be noted that the gynaecological examination of cows combines diagnostic, preventive and therapeutic measures, which, in turn, are aimed at timely detection of postpartum complications, infertility and restoration of reproductive capacity.
In their research, R.B. Walsh et al. (2007) also point out that there are many factors that affect the time to first ovulation and whether normal estrus and ovulation cycles will be maintained, including cow breed, parity, season, BCS (Body Condition Scoring), postpartum illness and different types of feeding.The authors' attention was focused on the link between postpartum negative energy balance and the restoration of cyclicity in dairy cows.Scientists emphasise the important link between perinatal health and reproductive function and performance.
Similar results were obtained by J. Denis-Robichaud et al. (2018).Prolonged postpartum anovulation is a problem because it is associated with increased time to first insemination and reduced risk of conception and usually affects 20% of cows in dairy herds and is caused by various gynaecological diseases.An analysis of the work of artificial insemination technicians in 2018-2020 found that 57-64% of cows and 64-70% of heifers conceive from the first insemination (Table 3).

Table 3. Performance of artificial insemination technicians in 2018-2020
Thus, it was found that thanks to these biotechnologies, 36 to 40 first-born calves per 100 cows are introduced into the main herd annually.At the time of the study, the farm used bull semen frozen in the form of open pellets or straws (paietas).The artificial insemination technician at the base farm also takes into account additional signs of the stage of sexual cycle excitation, which most often precede heat -general anxiety, desire for other animals, poor appetite and reduced milk production, back bending, increased reaction to his voice or the milker, rubbing of the tail root, traces of mucus on the tail and hind limbs, and the manifestation of a hugging reflex to other cows.In addition, the artificial insemination technician has rectal diagnostics of the degree of follicle maturation, accurately determines the time and frequency of insemination, the course of estrus and the duration of heat.
Thus, the main factors that ensure high fertility of animals with the rectocervical method of insemination are the massage of the genitals during their examination and insemination of the animal, which increases uterine motility, promotes the movement of sperm through the oviducts and accelerates ovulation.The Source: authors' own development use of disposable sterile plastic instruments allows insemination to be performed under aseptic conditions and requires little time for instrument processing.In addition, the deep insertion of sperm into the cervical canal prevents its backflow into the vagina, promotes faster sperm movement and maintains a high fertilisation rate.And examination of the internal genitalia before insemination makes it possible to monitor the development of follicles, identify sick animals and prescribe timely treatment.It is particularly important to note that this reproduction biotechnology allows for one-time insemination of cows and heifers in one heat, which increases the efficiency and economic feasibility of artificial insemination.
However, the analysis of herd reproduction that was carried out does not fully reveal the reasons for the decline in calf yield, so the impact of the period of time of arrival at the first heat after calving (independence period) on the effectiveness of insemination of cows, the impact of the number of inseminations (insemination index) on the reproductive capacity of cows was investigated, the analysis of which is presented in Table 4.
The calculated data indicate that the average independence period in cows was 54.1 ± 7.38 days, the lowest in group 1 -28.6 ± 2.14 days, the highest in group 4 -120.4± 16.31 days, respectively.Therefore, the calving to conception interval was the highest in the 4 th group of cows -118.2 ± 9.11 days, and the lowest in the 1 st group -65.1 ± 3.15 days, while the average calving to conception interval on the farm was 85.5 ± 6.17 days, which is slightly higher than optimal.
The fertility from the 1 st insemination averaged 60.7%, which is a normal indicator.The analysis shows that the highest insemination efficiency was after 61-90 days after calving and was 73.3%, respectively.In addition, there is a straightforward proportional relationship between the independence and calving to conception interval and the insemination index.Cows that were inseminated in the first month after childbirth had the lowest insemination index -1.6 ± 0.12 with a minimum independence period of 28.3 ± 2.15 days and a calving to conception interval of 65.1 ± 3, 15 days, and in cows inseminated after the 91 st day, the insemination index is the highest -3.2 ± 0.45 with a maximum independence period of 120.4 ± 16.31 and calving to conception interval of 118.2 ± 9.11 days.
In the scientific literature, there are ambiguous statements regarding cow fertility and how much it depends on the length of the calving to conception interval.Thus, F. López-Gatius (2012) points out that the reasons for the decline in fertility are multifactorial and cannot be attributed solely to increased milk production.In fact, by improving feeding and housing practices, individual milk production can be positively related to high fertility, but heat stress, the sire bull and the artificial insemination operator remain the main factors that negatively affect herd fertility.And the latter does not depend on the duration of the period from launch to calving.
At the same time, B. Tadesse et al. (2022) obtained the opposite results.Thus, the authors point out that 37% of cows that did not conceive during the first artificial insemination are associated with a large number of days of stall housing and with reproductive processing.At the same time, scientists link the length of the calving to conception interval to the season of the year.Based on the season of artificial insemination, a significant difference in insemination in winter and spring was found in 13% of animals.Cows that did not conceive during the first insemination but conceived during the 2 nd and 3 rd inseminations had an average interval between calving and insemination of 45.04 days longer than cows that were conceived during the first insemination.
On the farm, the artificial insemination technician practices a single insemination of cows during heat by establishing the optimal insemination time according to the degree of follicle maturation during rectal examination.However, it is necessary to take into account the survival rate of sperm in the genital tract, which is almost impossible.In this regard, according to the instruction Order of the Ministry of Agrarian Policy of Ukraine No. 230 (2001), it is recommended to inseminate twice in one heat with an interval of 12 hours.Thus, single insemination of cows in a farm may be one of the reasons for the decrease in cow fertility.Therefore, the effect of the number of inseminations on the reproductive capacity of cows was studied (Table 5).Thus, it was found that the insemination index -"1", the duration of the calving to conception interval is 74.3 ± 3.51 days and with its increase, an increase in the calving to conception interval is observed.And, in turn, cows that were not inseminated after the fifth or more inseminations had a calving to conception interval of 146.3 ± 21.31 days, respectively, i.e. these cows were problematic and were subject to rectal gynaecological examination, or treatment and stimulation, as well as culling for reproductive system problems.

Number of cows
The effectiveness of the use of artificial insemination and synchronisation of estrus is also indicated by M.F.Sá Filho et al. (2013).Thus, the authors note that the comparison of the reproductive efficiency of breeding programmes that used natural service (NS), artificial insemination after detection of estrus (ED) and timed artificial insemination (TAI).The researchers concluded that the inclusion of TAI programmes at an early stage of estrus increased the reproductive capacity of beef and dairy cows and reduced the number of artificial inseminations per cow, i.e. the insemination index was at an optimal level.C.M. Tippenhauer et al. (2021) indicate that the number of inseminations of cows is influenced not only by the period of insemination, but also by the type of semen.Specifically, when artificial insemination of cows was used between 1 and 18 hours after peak estrus activity, the effectiveness was highest regardless of the type of semen (fresh or frozen).Cows inseminated within six hours before the peak estrus activity with frozen semen had a higher insemination rate compared to cows inseminated with fresh semen and inseminated with 1-2 inseminations.Cows inseminated with fresh semen within five hours before peak activity had a higher efficiency compared to cows inseminated with frozen semen; they were inseminated with 2-3 inseminations.And cows inseminated with frozen semen in the period from 13 to 18 hours after peak activity had higher fertilisation efficiency compared to cows inseminated with fresh semen, and it took 3-4 insemination procedures to inseminate them.
During the experiment, the influence of reproductive capacity on the milk production of Red Steppe cows and the dynamics of this relationship depending on the calendar year was determined.The research has established (Table 6) that there is a negative correlation between the duration of the period from launch to calving and subsequent milk yield during the study period.

Source: authors' own development
The reason for this phenomenon is that early cow start-up leads to a shortfall in milk production.Then the duration of the period from launch to calving was brought to the optimum value of 45-60 days.There was some difference between years in this indicator: the lowest value of the negative correlation was in 2017, which, as previously established, was the most favourable for the animals on this farm.
When determining the relationship between milk yield per lactation and calf yield, a positive correlation was found.It was particularly high in 2019, due to high milk yields and a sufficient level of reproduction shown by the cows on the farm that year.It has been established that a higher number of offspring born helps to increase the milk production of cows, i.e. these two most indicative parameters have a mutual positive influence on each other, which is certainly effective for the operation of a dairy farm.
It is worth noting that a similar trend is observed when identifying the relationship between average daily milk yield in cows and calf yield: a positive correlation between these indicators with a similar trend, which confirms the above conclusion about the relationship between the number of calves and the amount of milk produced.There is a weak positive correlation between the length of the calving to conception interval and calf yield, which was only established in 2019; in all other years, the correlation was negative.This is due to the fact that a shorter calving to conception interval indicates a faster recovery of the cow after calving and her greater readiness for the next pregnancy.
In addition, the relationship between the duration of the period from launch to calving and milk yield in cows was investigated.Based on this, a negative correlation was found regardless of the year under study.This confirms the conclusion made earlier that reducing the period from launch to calving from an excessively long 82-90 days to an optimal 30-60 days is likely to increase the milk yield of the farm's cows.When studying the relationship between reproductive capacity and milk production of Red Steppe cows for a certain lactation, a mutual positive influence of these traits was established.The highest correlation coefficients were found between the traits "milk yield for the third lactation" and "calf yield" obtained from cows at this time.
Many hypotheses regarding the relationship between the level of milk production and the reproductive capacity of cows have been described by world scientists.For example, a number of scientists (Patton et al., 2007) do not link the level of cow milk yield with their fertility.The relationship between the components and indicators of energy balance (EB) in early lactation and fertility in Holstein cows was investigated.Milk production, dry matter intake (DMI), BCS, endocrine and metabolite data from 96 cows were analysed using multivariate logistic regression and survival analysis.Fertility variables studied included the interval to onset of luteal activity (C-LA), calving to conception interval (CCI) and conception to first insemination ratio (CON1).The average daily EB, milk protein content and DMI during the first 28 days of milk production were positively related to CON1.Cows with lower fatness (≤ 2.25) at first insemination had lower CON1.Positive associations were found between EV, milk protein content, DMI and the probability of a shorter interval to C-LA.Cows with higher DMI and more positive EB had an increased probability of a shorter CCI, while lower BCS supervision was associated with an increased probability of a longer CCI.Thus, milk yield was not associated with any of the fertility variables studied (Patton et al., 2007).R.L. Nebel & M.L. McGilliard (1993), on the contrary, indicate correlations between reproductive traits and milk yield, namely, higher milk yields are phenotypically and genetically associated with reduced reproductive capacity in lactating cows.D. Raboisson et al. (2014) found an average positive correlation between age and milk yield, and age and reproductive capacity.Thus, when analysing age-related changes in the reproductive capacity of cows, it was found that the duration of the calving to conception interval decreased with the age of the animals.The duration of the period between calvings was optimal on average for cows, while its reduction with age was observed.The authors noted that with increasing age of cows, the number of inseminations for fertilisation increased.Currently, in the field of cattle breeding, the developed promising methods of biotechnological regulation of sexual functions in animals through the use of synthetic analogues of prostaglandins F 2α are widely used.Data on the effect of various drugs to regulate and synchronise the sexual desire of replacement heifers are shown in Table 7.The experiments proved that the highest percentage of heifers coming into heat from the first treatment was observed in the group where the drug Catozal was used -44.4%, and the second group was the group that was injected with the hormonal drug Estrophan along with the vitamin Tetravit -38.9%.After 11 days, the heifers that did not come into heat were re-injected with the drugs and the following results were obtained: in both experimental groups, the same number of heifers came into heat -nine heads each, which is 50%.Females of the control group, where heifers were not administered any drugs at all, did not become pregnant, and two (11.1%)animals of the second experimental group did not become pregnant after the second treatment and one head did not become pregnant in the third experimental group, which is 5.6%, respectively.In the control group (no stimulants were used), 10 heifers conceived from the 1 st insemination, which is 55.5%, in the II experimental group, where Estrofan and Tetravit were used, 14 heifers conceived from the 1 st insemination, which is 77.8%, in the III experimental group, where Catozal was used, 16 heifers conceived from the 1 st insemination, which is 88.9%.

Source: authors' own development
Various hormonal preparations are widely used for the treatment, prevention and regulation and synchronisation of the reproductive function of cows in the world.The use of biological products after calving cows reduced the risk of uterine subinvolution, endometritis and mastitis and improved the reproductive performance of cows.It has been shown that after the use of Salus-PE, 100% of cows are inseminated, of which 60% are inseminated in the first heat and 40% in the second heat.The fertilisation index was 1.4 (Barkema et al., 2015).
A.W. Jonczyk et al. (2022) confirm the effectiveness of the method of intracellular administration of drugs/hormones, which can be a common tool for cattle reproduction.Arab scientists recommend the use of cloprostenol, which is an analogue of prostaglandin F2 (PG F2), but obtained synthetically, which acts as an agonist of the FP receptor and can cause luteolysis.Luteolysis is a key event in Ovsink's programmes for lactating dairy cows.The authors note that 20% of cows treated in the Presink/Ovsink programme experienced delayed or incomplete luteolysis with dinoprost tromethamine.Cows need to have complete luteolysis to have a chance of getting pregnant (Shahzad et al., 2023).
The next stage was to study the effect of treatment of repair heifers with biologically active preparations (Estrofan + Tetravit, Catozal) on their reproductive capacity after calving and milk production (Table 8).It was established that the use of Estrofan together with Tetravit and Catozal does not reduce the milk yield of first-born cows, since according to the results of control milk yields for the first month in this group, the average daily yield was 16.7 kg, for the second -18.1 kg and for the third -at the level of 17.9 kg.Further, analysing the service period for the first-born group, it was found that the minimum was 30 days, the maximum was 86 days, and the average for the group was almost 58 days, which is typical for this farm.Planned reproduction of cattle involves the regulation of the estrous cycle and the use of artificial insemination.Cycle control involves the administration of exogenous progesterone for 5-8 days in a controlled manner, which allows females to synchronise their ovulation (Helbling et al., 2018).Synchronisation of estrus using prostaglandin F 2α (PG F 2α ) and a combination of PG F 2α and gonadotropin-releasing hormone was also used in Indonesian research.The estrus response can be enhanced by providing PG F 2α and a combination of PG F 2α -GnRH to allow for precise timing of mating using artificial insemination.Therefore, scientists concluded that the use of PG F 2α was more effective for the duration and intensity of estrus, and the PG F 2α -GnRH combination was more effective for stimulating estrus (Astuti et al., 2020).
A. Ayad et al. (2015) in the research used norgestomethate Crestar on estrus synchronisation and reproductive function of dairy cows.Treatment with norgestomethate Crestar, which was carried out for 9-10 days, did not improve the reproductive performance of dairy cattle.Nevertheless, the authors point out that this hormonal protocol can be used to obtain high estrus rates in cows to correctly determine the time of insemination.In addition to the above studies, the influence of live weight of repair heifers on the results of artificial insemination was studied.For this purpose, seven groups of heifers were formed depending on their live weight at the first insemination (Table 9), using thawed semen from the red steppe bull Pilot 1069 by the rectocervical method.

Table 9. Influence of live weight of repair heifers on their fertilisation after artificial insemination
It was established that the first group of heifers had an average live weight of 271 ± 6.3 kg and 8 heads, or 47.1%, were fertilised from the first insemination in this group.The second group of heifers weighed 292 ± 4.7 kg, and 66.7% of this group were fertilised from the first insemination.The highest percentage of fertilisation -77.8 was in the fifth group of heifers with a live weight of 352 ± 7.7 kg, and further, with an increase in live weight, there is a decrease in the percentage of fertilisation from the first insemination, which in the group of heifers weighing 393 ± 5.2 was 66.7%.Since live weight does not sufficiently reflect the optimal time of insemination of heifers, therefore, in further experiments, the effect of the age of first insemination on their fertilisation was studied.For this purpose, heifers were selected and 5 age groups were formed (Table 10).Many global scientists have concluded that achieving pregnancy for lactating dairy cows in the range of every 365 days optimises profitability for most cows and depends on the length of the voluntary waiting period (VWP) and reducing the number and variation of days to conception after cows become eligible for pregnancy (Stevenson & Britt, 2017;Stangaferro et al., 2018;Fyl, 2020).Through the introduction of reproductive management programmes and technologies that better control artificial insemination rates and significantly increase pregnancies per artificial insemination (P/AI) for the first and subsequent artificial insemination operations.Therefore, combining an effective management programme with a service period that optimises the time to pregnancy during lactation can be a feasible strategy to increase herd profitability.The use of synchronisation programmes is a standard component of efficient cow management in dairy herds.Many of them are based on measures that allow for timed insemination (TAI) to avoid the practical difficulties associated with detecting cows in heat.Almost all of the measures involve injections of prostaglandin F 2α (PGF) and gonadotropin-releasing hormone (GnRH) at strategically timed intervals, which determines the economic efficiency of the industry as a whole.

CONCLUSIONS
The analysis of the reproduction status shows that there is an annual shortfall in calf production, and the main reasons are: cow retirement, as well as beef cows and cows with an extended calving to conception interval.It has been established that pregnant cows left the herd for various reasons, such as injuries, diseases of various types, forced slaughter, etc. Reducing the calving to conception interval will contribute to a higher calf yield in cows, which has a positive impact on milk production.At the same time, it should be borne in mind that the calving to conception interval can be reduced to a number that is not less than 30 days, i.e. the period required to prepare the cow's body for new insemination.
The calculations of the correlation coefficient between the main signs of reproductive capacity and milk production of Red Steppe cows allowed us to establish a mutual positive influence between them.The conclusion made earlier about the best functioning of all organs and systems of the cow's body during the third lactation was confirmed.It also confirms the statement about the plasticity of the cows' organism and their active response to the favourable conditions of a particular year by increasing productivity and fertility.It has been established that the use of prophylactic drugs contributes to the synchronisation of heifers' sexual desire and increases their fertility during insemination.The latter should be started when heifers reach a live weight of 314 ± 6.5 kg, which will allow to obtain fertilisation from the first insemination at the level of 73.7-77.8%,and an increase in heifer weight leads to obesity, and therefore reduces the percentage of fertilisation from the first insemination.The optimal age for artificial insemination of heifers is 17.5 ± 1.5 months, and an increase in the age of heifers leads to overgrazing and culling them from the farm.
To diagnose problem cows in terms of reproductive function, it is worthwhile to conduct an early check on the 25-30 th day of pregnancy in inseminated cows using ultrasound diagnostics.It is necessary to establish obstetric and gynaecological examination and treatment of problematic replacement heifers and cows, and it is advisable to use prostaglandin F 2α analogues in combination with vitamins or biologically active drugs to stimulate the sexual function of cows and heifers.The maximum number of Red Steppe heifers should be inseminated at the age of 16-18 months with a live weight of 314-360 kg to achieve a fertility rate of 75-77% from the first insemination.The prospect of further research on this topic may be the search for new insemination programmes that can increase the level of these two hormones during oestrus, which can help solve the problem of low fertility in lactating dairy cows.

Table 8 .
Influence of prophylactic drugs on reproductive capacity and milk production of repair heifers

Table 10 .
Influence of age at first insemination on fertility of replacement heifersAnalysis of the table data shows that in the first group of heifers the average age was 17.5 ± 1.5 months.It was established that during artificial insemination, 14 out of 18 heads were fertilised from the first insemination, which is 77.8%; this is the highest fertility rate from the first insemination.With increasing age of heifers, there is a decrease in fertility from the first insemination, which was the lowest -40% in heifers with an average age of 26.8 ± 2.7 months.