Effective methods of horse reproduction in the production of mare’s milk

Métodos eficazes de reprodução equina na produção de leite de égua

Abstract

The research aims to study the dynamics of reproductive system pathologies in mares of Kazakh and Mugalzhar horse breeds and their impact on the reproductive traits of the breeding stock. The object of the research was horses of the Kazakh and Mugalzhar breeds. The formation of experimental groups was carried out using the pair-analog method. It was found that the frequency of detection of infertile mares is 13.8-25.0%. Subinvolution of the uterus from the total number of infertile mares is 8.3-10.7%, endometritis - 16.6-23.3%, atony and hypotonia of the uterus – 8.3-13.3%, ovarian diseases – 19.6-43.4%, other diseases – 10.0-39.4%. The pregnancy rate of mares of the Kazakh and Mugalzhar breeds was 78.8%. The frequency of abortions, weakly born, and stillborn foals was 2.8%. Successful foaling was 76.0%. It was established that successful foaling in mares under 5 years old is 65.6%, 6-9 years old - 79.5%, and 10 years and older - 74.6%. Pregnancy rates are lowest in mares under 5 years of age (74.4%), compared to 6-9 years of age (88.0%) and 10 years of age and older (82.0%). Milk productivity analysis of first-lactation mares revealed significantly higher yields on farms specializing in mare’s milk production, accompanied by slight improvements in fat and protein content. The findings highlight the strong influence of management practices, nutritional status, and timely reproductive monitoring on the reproductive success of local horse breeds.

Keywords:
productive horse breeding; mares; reproductive system; pathology; mating

Resumo

A pesquisa tem como objetivo estudar a dinâmica das patologias do sistema reprodutivo em éguas das raças cazaque e mugaljar e seu impacto nas características reprodutivas do plantel de cria. O objeto da pesquisa foram cavalos das raças cazaque e mugaljar. A formação dos grupos experimentais foi realizada utilizando o método de pares análogos. Constatou-se que a frequência de detecção de éguas inférteis é de 13,8-25,0%. A subinvolução do útero representa 8,3-10,7% do total de éguas inférteis, a endometrite – 16,6-23,3%, a atonia e hipotonia uterina – 8,3-13,3%, doenças dos ovários – 19,6-43,4%, e outras doenças – 10,0-39,4%. A taxa de prenhez das éguas das raças cazaque e mugaljar foi de 78,8%. A frequência de abortos, potros nascidos fracos e natimortos foi de 2,8%. Partos bem-sucedidos totalizaram 76,0%. Verificou-se que o índice de partos bem-sucedidos em éguas com menos de 5 anos é de 65,6%, entre 6 e 9 anos – 79,5%, e em éguas com 10 anos ou mais – 74,6%. As taxas de prenhez são menores em éguas com menos de 5 anos (74,4%), em comparação com aquelas de 6-9 anos (88,0%) e de 10 anos ou mais (82,0%). A análise da produtividade de leite de éguas na primeira lactação revelou produções significativamente maiores em fazendas especializadas na produção de leite de égua, acompanhadas de ligeiras melhorias no teor de gordura e proteína. Os resultados destacam a forte influência das práticas de manejo, do estado nutricional e do monitoramento reprodutivo oportuno sobre o sucesso reprodutivo das raças locais de cavalos.

Palavras-chave:
criação produtiva de cavalos; éguas; sistema reprodutivo; patologia; acasalamento

1. Introduction

Local horse breeds are of particular interest because they have been bred for centuries in purity without the addition of blood from factory breeds (Atroshchenko et al., 2023). When breeding local horse breeds, new approaches to breeding stock selection are necessary (Kvist et al., 2019). Preservation of local breeds of domestic animals is one of the important indicators of sustainable agricultural development in specific countries. This is especially true for local horse breeds in terms of lifestyle, expectations, requirements, and experience in selection and breeding work (Prišenk et al., 2022). With the diversity of horse breeds, genetic research methods are used to improve traditional breeding methods (Gupta et al., 2014; Sild et al., 2019; Ma et al., 2019; Koveshnikov et al., 2019). Monitoring of horses is necessary for identifying a suitable breed in the region of their breeding (Putnová and Štohl, 2021). Monitoring the development of foals by biometric parameters of the body and live weight allows for determining the breeding value of mares (Hunka et al., 2014; Pimentel et al., 2017). The qualitative composition of mare's milk is of interest for the good development of foals. Mare's milk is a valuable raw material due to its unique protein composition. Therefore, in breeding work with horses, it is necessary to pay attention to the study of the protein composition of mare's milk (Fotschki et al., 2020).

There is scientific evidence confirming the immunomodulatory properties of horse milk for foals in the first months of development (Fotschki et al., 2016). In the reproduction of horses of a limited gene pool of breeds, inbreeding must be avoided during selection and selection (Duncan et al., 1984). The consequences of poor breed management and inbreeding can range from a gradual decline in individual productivity to more serious problems with fertility and mortality (Dell et al., 2021).

Traditional methods of horse breeding are relevant. The effectiveness of using classical breeding methods depends on the approach used to evaluate horses for productivity and breeding value (Klecel and Martyniuk, 2021).

To Kazakhstan of particular interest is the Kazakh horse breed. The Kazakh horse is the oldest breed in Kazakhstan, the breeding culture of which is 10 thousand years old (Assanbayev et al., 2021). Given the deterioration of natural pastures, drought, and vegetation conditions, it is necessary to adjust the horse population, regardless of their genotype (Deshpande et al., 2019). Artificial selection in horse breeding increases the genetic diversity of breeds (Arnason, 2000).

Improving the productive qualities of horses to meet the needs of the population for food products is being done all over the world. There is a displacement of less competitive aboriginal breeds and populations of horses, which are characterized by slightly lower productivity but are well adapted to environmental conditions (Ilnytska et al., 2020).

The dairy industry is showing some interest in producing mare's milk on an industrial scale (Miraglia et al., 2020; Barłowska et al., 2023; Langlois, 2011).

Mare's milk has been consumed as food for hundreds of years in Central Asia and Eastern Europe. The range of food products made from natural mare's milk is expanding (Barłowska et al., 2023). Of particular interest are studies assessing the effects of machine and hand milking on the behavior, milk yield, and milk composition of mares. It has been established that machine milking of mares can improve the quality and gross milk yield of mare's milk. Machine milking of mares results in a higher fat content in milk (1.63%) than with hand milking (1.06%) (Caroprese et al., 2007). Breed influences the composition of mare's milk, especially the protein, fat, and lactose contents (Pieszka et al., 2011).

Local horse breeds are very hardy and well adapted to local environmental and climatic conditions. The study of genetic factors influencing the formation of adaptive traits in aboriginal breeds and the search for ways to preserve genetic diversity for effective reproduction of the population is a relevant area of ​​research in herd horse breeding (Atroshchenko et al., 2023).

In the Republic of Kazakhstan, the most numerous horse breed is the Kazakh breed with multiple intra-breed and zonal types. The extreme conditions of the sharply continental climate of Kazakhstan determine various approaches to conducting selection and breeding work regarding domestically bred horses of productive direction. The population's demand for food products of animal origin necessitates an increase in the number of cattle, camels, and horses. Horses of the Kazakh breed of the south-eastern zonal type have not been studied to date. There is no scientific data on the patterns of growth and development of young animals, the exterior of adult stock, the dynamics of dairy productivity of mares, etc. In domestic herd horse breeding in modern economic conditions, the urgent problem remains the increase in the level of reproduction of the breeding stock. Reproduction of breeding mares of high-value stud lines of horses is controlled by the ability to bring one foal annually.

The study of Kazakh horses is of scientific, theoretical, and practical interest in herd horse breeding in the Republic of Kazakhstan. In productive horse breeding in Kazakhstan, increasing the main parameters of reproduction of the breeding stock is a promising direction in the technology of the industry. This problem is relevant when keeping mares over 10 years old due to the increase in the frequency of age-related disorders of the fruit-bearing functions and the impossibility of regularly obtaining foals from them within the established technological timeframes. Therefore, it is recommended to prepare the mare for breeding using a feeding program that includes a sufficient amount of high-quality feed, balanced in nutrients.

For reproductive specialists, a more important aspect is the assessment of the mare's ability to conceive and bear a healthy foal. Weaning losses are mainly related to the technology of feeding and keeping suckling mares with foals and, except for milk production and the expression of maternal instinct, do not characterize their reproductive qualities. Therefore, the most informative in terms of reproduction will be the indicators of pregnancy and successful foaling, as well as the percentage of abortions, and weak and stillborn foals from the number of mares that have conceived, which we used for statistical processing of the collected material. The aim of the research. To study the dynamics of reproductive system pathologies in mares of Kazakh and Mugalzhar horse breeds and their impact on the reproductive traits of the breeding stock.

2. Materials and Methods

The object of research and development: horses of the productive direction of Kazakhstan selection: Kazakh breed from the south-eastern natural and climatic zone of Kazakhstan (farm “Ertai” of Zhualyn district, farm “Shau -shen” of Turar Ryskulov district, farm “Shili-Karyn” of Baizak district of Zhambyl region); Mugalzhar breed in the southern natural and climatic zone of Kazakhstan (farm “Senim” of Suzak district of Turkestan region).

The formation of experimental groups was performed using the pair-analog method (Baimukanov et al., 2024).

Signs of sexual arousal and estrus in mares were determined in the following ways:

1. Visual (observation of the mare's behavior). Mares show anxiety, make sounds, appetite, and milk yield decrease. At the beginning of sexual arousal, slightly whitish mucus flows from the genital slit, which becomes transparent by the middle of the estrus, and becomes cloudy and thickens at the end of the estrus. Mares show a search reaction to the male. Mares allow the stallion to jump and show a reflex of immobility;

2. Reflexological (using a stallion-tester). The mare shows interest in the stallion, approaches him, and allows the stallion or the tester to jump on her;

3. Vaginal (examination of the vagina and cervix using a vaginal speculum). Swelling of the labia, swelling, and redness of the vaginal mucosa are observed, the cervical canal is slightly open, and transparent viscous mucus flows out of it, which accumulates at the bottom of the vagina, and then is released from the genital slit;

4. Rectal (palpation of the follicle on the surface of the ovaries through the wall of the rectum). When gently pressing with a finger, fluctuation is felt on the surface of the ovary, and the walls of the follicle are gently pressed. The immature follicle protrudes slightly above the surface of the ovary and is dense to the touch;

5. Ultrasound (determining the degree of follicle development using an ultrasound scanner). Using an ultrasound scanning device, the degree of development of the preovulatory follicle is examined.

The efficiency of reproduction of the Kazakh horse population was determined by three main indicators: pregnancy rate of mares, successful foaling, and commercial yield of foals.

The pregnancy rate was calculated as the number of mares that became pregnant per 100 inseminated (fertilely covered) mares.

Successful foaling was determined by the number of successfully foaled mares (excluding abortions, stillborn, and weak-born foals) from the number of inseminated (fertilely covered) mares. This value is calculated from the number of fully pregnant mares.

The commercial yield of foals was determined by the number of live foals preserved until weaning (6 months) per 100 inseminated (fertilely covered) mares or by the number of live foals born (successful foaling). To calculate these indicators, data from the mating and foaling register for each farm were used, which indicated the number of mares admitted to mating, unbred, the number of abortions, stillborn and weak-born foals (died in the first 3 days after foaling) foals and the loss of foals before weaning.

Available information on all reproductive activity was collected for each mare. The phase and completeness of the mares' sexual cycle were determined using a stallion tester, as well as rectal, vaginal, and ultrasound examination methods, counting the beginning of the cycle from the moment of ovulation (day 0). The ultrasound examination was performed using ultrasound scanners EXAGO (France) and Mindrey DP50Vet (China).

Based on rectal, ultrasound, vaginal, cytological, and bacteriological examinations, the mares were divided into two groups: conditionally gynecologically healthy mares; and mares with signs of functional disorders of the genital tract. The signs of functional disorders of the genital tract included discharge/flushes from the vulva, hyperemic vaginal mucosa in diestrus, the presence of fluid in the uterine lumen during ultrasound, and repeated empty mares in previous years from mating with a stallion tested for fertility. By age, the mares were divided into three groups 1) under 5 years old; 2) from 6 to 9 years inclusive; and 3) 10 years and older.

The study material included summary records of mating and foaling of mares, ultrasound echograms of the uterus and ovaries of mares, samples of cervical and endometrial mucus and uterine smears/washings for cytological and bacteriological studies, and endometrial biopsy samples obtained from mares during estrus and diestrus. Cytological samples of mucus from the surface of the cervix and endometrium were obtained using Minitube instruments (Germany) or from the sedimentary layer of the washing fluid, then applied to a glass slide, dried in air, and stained with May Grunewald dye. Cytological smears were examined under immersion with a magnification of x1000. The number of normal epithelial cells and those with signs of degeneration, neutrophilic leukocytes (PMN cells), and lymphocytes was recorded on average in 6 fields of view (units of field of view).

Statistical processing of the research data was done according to the common method of statistical analysis using the Microsoft Excel program. The reliability of the difference between the average values of the characteristics was determined by the Student's t-test (Vishnevec et al., 2011).

Statistical data processing was performed using the biometric analysis method with the help of Microsoft Excel 2010, Statistica 10 (StatSoft, Inc., USA) programs with reliability assessment using Student’s t-test and Fisher’s criterion, factor analysis using the principal component method, at three levels of probability (*– P < 0.05; ** – P < 0.01; *** – P < 0.001).

Correlation relationships between indicators in groups were calculated using the rank correlation coefficient according to Spearman's method.

Milk yield accounting for first-foaling mares was carried out in the 3rd month of lactation (Baimukanov et al., 2021), followed by the calculation of the projected milk yield for 150 days of lactation. The obtained data were compared with the actual milk yield indicators for 150 days of lactation (Baimukanov et al., 2023).

Foals were weaned from mares upon reaching a live weight of 180 kg (Aubakirov et al., 2022, 2025).

Samples of mare’s milk were collected in accordance with GOST R 52973-2008 (Russia, 2009). The milk temperature was determined according to GOST 26754-85 (Russia, 1985), milk purity according to GOST 8218-56 (Russia, 1956), milk density according to GOST 3625-84 (Russia, 1984), moisture and total solids content according to GOST 3626-73 (Russia, 1973). The fat content in the milk was determined according to GOST 5867-69 (Russia, 1969), and the protein content according to GOST 25179-2014 (Russia, 2014) using the “Laktan 3” device (Russia).

3. Results

The occurrence and development of obstetric and gynecological diseases in mares are caused by: lack of proteins, carbohydrates, vitamins, minerals in the diet; feeding poor quality feed; lack or limitation of active exercise; shortened dry period; violation of machine milking technology; premature use of fillies before reaching physiological maturity and mares with low live weight for reproduction; keeping mares that have lost their economic value due to insufficient stocking of the herd with replacement young stock.

Examination of the breeding stock of Kazakh horses shows that obstetric and gynecological diseases are most widespread, where mares are fed without taking into account their physiological condition and the technology of keeping and using animals is violated. In such cases, 30-40% of mares and fillies have a protein-vitamin-mineral metabolism disorder during the winter-stall period. In such mares, labor is accompanied by weak contractions and pushing, there is a mass retention of the placenta, and subinvolution of the uterus, subsequently leading to various inflammatory processes of the uterus (Table 1).

Table 1
Pathology of the reproductive system in mares.

Indicators		Name of farms
		Ertai	Shau-shen	Shili-Karyn	Senim
Researched	animals	80	405	115	120
Infertile mares detected	animals	12	56	23	30
	%	15.0	13.8	20.0	25.0
Including:
Subinvolution of the uterus	animals	1	6	2	3
	%	8.3	10.7	8.8	10.0
Endometritis	animals	2	12	5	7
	%	16.6	21.4	21.8	23.3
Atony and hypotonia of the uterus	animals	1	5	3	4
	%	8.3	8.9	13.0	13.3
Ovarian diseases	animals	4	11	8	13
	%	33.4	19.6	34.7	43.4
Other diseases	animals	4	22	5	3
	%	33.4	39.4	21.7	10.0

The results of the study showed that on farms producing mare's milk (farm “Ertai” and farm “Shau-shen”) the frequency of reproductive system pathology (13.8-15.0%) is significantly lower compared to farms where milking mares for kumiss production is not practiced (20.0-25.0%) (farm “Shili-Karyn” and farm “Senim”).

The analysis of the indicators of mare reproduction revealed that the average numbers in the base farms have uniform dynamics in terms of the pregnancy rate of mares and the output of live foals (successful foaling). On average, they amounted to 76.2-78.9%, respectively, and had no reliable differences between the farms (Table 2).

Table 2
Reproduction indicators of breeding mares.

Name of the farm	Reproductive performance of mares
	In mating (fruit years)		Got pregnant	Abortions, w/b, s/b	Successful foaling
Ertai	n	65	52	2	50
	%	100	79.9 ± 1.0	3.1 ± 0.3	76.8 ± 1.2
Shau-shen	n	310	238	8	230
	%	100	76.8 ± 0.9	2.6 ± 0.4	76.2 ± 1.1
Shili-Karyn	n	102	83	3	80
	%	100	81.3 ± 1.2	2.9 ± 0.4	78.4 ± 1.2
Senim	n	90	74	3	71
	%	100	82.2 ± 1.1	3.3 ± 0.3	78.9 ± 1.1
Total	n	567	447	16	431
	%	100	78.8	2.8	76.0

• Note: w/b = weak-born foals; s/b = stillborn (from mares that have given birth).

In herd horse breeding, in breeding Kazakh and Mugalzhar horses, division by age is practiced: up to 5 years old, 6-9 years old, 10 years and older (Table 3).

Table 3
Reproduction indicators of breeding mares.

Age	Reproductive performance of mares
	In mating (fruit years)		Got pregnant	Abortions, w/b, s/b	Successful foaling
≤5 years	n	90	67	8	59
	%	100	74.4 ± 3.7	8.8 ± 4.3	65.6 ± 5.3
6-9 years	n	233	205	20	185
	%	100	88.0 ± 2.9	8.5 ± 1.7	79.5 ± 2.9
10 years and older	n	244	200	18	182
	%	100	82.0 ± 1.8	7.4 ± 1.8	74.6 ± 3.1

• Note: w/b = weak-born foals; s/b = stillborn (from mares that have given birth).

The conducted research has established that the most productive period for using mares of the productive direction is the age from 6 to 9 years, after which the reproduction rates begin to decrease. At the same time, high reproduction rates in mares are maintained under 12-13 years of age. After 13 years, it is recommended to cull older mares.

In addition, specialists are well aware that only mares that regularly produce foals remain in the broodstock until old age. Subfertile mares are usually sold or culled, and valuable mares are worked with more carefully and effectively, spending more attention, effort and money on them. Probably for this reason, the tendency for average reproduction rates in mares to decrease after 10 years was not reliably confirmed in our studies.

The effective period for fruitful insemination (natural mating) is the time interval between 13 and 20 hours after the first signs of estrus are detected. When mucus is secreted during estrus, the appropriate time for insemination is the period when the secreted mucus breaks off at the level of the hock. The most suitable mating option: mares that came into estrus in the morning are recommended to be mated in the evening, and individuals that came into estrus in the afternoon and evening are mated in the morning of the following day.

The reproductive traits of mares are poorly inherited. In addition, they are influenced by many other factors, such as feeding technology, the hormonal system and associated diseases, the level of milk production, the condition of each individual, the way pregnancy occurs, etc.

Reproduction of the existing horse population largely determines the productivity and economic efficiency of their breeding. Table 4 shows the parameters for managing the reproduction of the horse population. It has been established that for effective reproduction management in herd horse breeding, the recommended physiological recovery period for mares after foaling is 45-65 days. A fertile mating rate of more than 70% on days 60-95 is required in herd breeding. The insemination index should not exceed 3.0 doses, with variations ranging from 1.5 to 3.0 doses. When the insemination index exceeded 3.0, reproductive organ diseases were detected in the mares.

Table 4
Reproduction management of the existing horse population.

Controlled parameters	Optimal levels	Way to achieve
Age of first foaling	36-38 months	Proper feeding and maintenance of natural pastures
Duration of the sexual cycle	21 (18-23) days	-
Duration of the sexual cycle	48-288 h	-
Time of ovulation	24-48 h before the end of the hunt	-
The period between the first foaling and insemination (fertile mating)	45-65 days	Compliance with requirements that guarantee a normal gynecological condition
The interval between inseminations (fruitful matings)	0 days	Quality insemination (fruitful mating)
Service period	60-90 days	Balanced feeding, maintenance
Fruitful mating index	1.5-3.0 doses	Quality insemination
Interfertile period	375-465 days	Optimal management reproduction
Percentage of non-repeat insemination (fruitful mating) on day 60-95	More than 70%	Proper organization reproduction
Result of primary insemination (fertile mating)	More than 70%	Gynecological control functions of the animal
Percentage of foaling	More than 80%	Proper herd management

The pregnancy period in mares lasts 330-340 days. Factors such as the season, the sex of the foal, and the mare's feeding directly affect the variation in the period of fruiting. After this, foaling occurs, which in most mares occurs without complications and does not require human intervention during childbirth. However, there is a risk group. In mares in their first pregnancy, mares with a history of abortions, pathological births, endometritis, miscarriages, and whose previous foals suffered from congenital diseases, foaling is more difficult. Difficult foaling is caused by the fact that the foal's size exceeds the size of the pelvic passage. Sometimes there is an incorrect position of the fetus during childbirth. Abnormal foaling can last more than 6 h. In these cases, the intervention of a reproductive physician is required. Difficult foaling is one of the causes of death of newborn foals. Difficult foaling is usually caused by underfeeding and underdevelopment of mares, and in rare cases, overfeeding.

Treatment of mares with endometritis, the basis of which is local etiotropic therapy, should be complex. In mares with acute postpartum endometritis of bacterial-mycotic etiology, the following associations are often identified: Str. pyogenes + P. vulgaris + Candida albicans - 22.8%, Staph, aureus + E. coli + Candida albicans - 21.8%, Staph, aureus + P. mirabilis + Candida albicans - 20.0%, E. coli + P. mirabilis + Candida albicans - 11.4%, E. coli + P. vulgaris + Candida albicans + Aspergillus fumigatus - 8.5%, Staph, aureus + E. coli + Candida albicans + Aspergillus fumigatus −8.5%, Staph, aureus + P. mirabilis + E. coli + Candida albicans + Aspergillus fumigatus + mucor racemosus - 5.7% (Ganiev et al., 2024; Stepochkina et al., 2024).

In this regard, the principle of prescribing broad-spectrum antimicrobial drugs is relevant, since the economic damage from this disease leads to a shortage of milk, a shortage of foals, and early culling of highly productive animals.

In mares, a return to the normal estrus cycle is observed on the 60th day after foaling. A balanced diet promotes the consumption of a larger volume of feed, the production of a large amount of milk and guarantees the high reproductive capacity of the existing herd. Deterioration of the reproductive functions of mares occurs with infectious diseases, including postpartum (various forms of endometritis), lack of protein, energy, and mineral micro/macro elements in the diet.

A study was conducted on the milk productivity of first-foaling mares from the surveyed farms (n = 20) (Table 5). It was found that the highest average daily milk yield of first-lactation mares was observed in the “Ertai” farm (8.7 L), which significantly exceeded the indicators of the “Shili-Karyn” farm by 3.0 L (52.6%) and the “Senim” farm by 2.1 L (31.8%) (P ≤ 0.001). The actual milk yield over 150 days of lactation was also highest in the “Ertai” farm (1421.7 kg), whereas the lowest values were recorded in the “Shili-Karyn” farm (911.7 kg). Thus, the Kazakh breed mares from the “Ertai” farm demonstrated the highest milk productivity among the studied farms.

Table 5
Milk productivity of first-foaling mares (first lactation).

Name of the farm	Breed	Average daily commercial milk yield in the 3rd month of lactation, L.		Predicted commercial milk yield for 150 days of lactation, kg		Actual commercial milk yield for 150 days of lactation, kg
		X ± mx	Cv	X ± mx	Cv	X ± mx	Cv
Ertai	kazakh	8.7 ± 0.4	21.7	1305.5 ± 84.7	27.2	1421.7 ± 63.2	23.4
Shau-shen	kazakh	7.8 ± 0.3	18.2	1171.6 ± 69.1	22.4	1334.9 ± 91.4	21.7
Shili-Karyn	kazakh	5.7 ± 0.6	14.3	855.8 ± 53.6	19.9	911.7 ± 65.2	26.3
Senim	mugalzhar	6.6 ± 0.5	30.1	990.7 ± 78.3	37.1	1288.1 ± 111.5	19.6

• X ± mx: mean value; ±: standard error of the mean; Cv: coefficient of variation (%).

In this regard, the chemical composition of milk from first-foaling mares (n = 20) was examined (Table 6).

Table 6
Chemical composition of milk from first-foaling mares (first lactation).

Name of the farm	Breed	Fat, %		Protein, %		Lactose, %		Ash, %
		X ± mx	Cv	X ± mx	Cv	X ± mx	Cv	X ± mx	Cv
Ertai	kazakh	1.85 ± 0.05	11.6	2.31 ± 0.08	8.3	6.9 ± 0.74	0.8	0.91 ± 0.02	1.1
Shau-shen	kazakh	1.78 ± 0.04	12.3	2.28 ± 0.07	7.7	6.6 ± 0.78	0.6	0.89 ± 0.01	0.9
Shili-Karyn	kazakh	1.73 ± 0.05	9.9	2.19 ± 0.08	6.5	6.2 ± 0.91	0.5	0.87 ± 0.02	0.8
Senim	mugalzhar	1.74 ± 0.05	10.1	2.15 ± 0.08	7.4	6.3 ± 0.78	0.6	0.88 ± 0.01	0.8

• X ± mx: mean value; ±: standard error of the mean; Cv: coefficient of variation (%).

The chemical composition of milk in first-lactation mares was characterized by low inter-farm variability. The highest fat (1.85%) and protein (2.31%) contents were recorded in the “Ertai” farm, while the lowest values were observed in the “Shili-Karyn” and “Senim” farms. Lactose and ash levels remained stable across all farms. Overall, the milk composition corresponds to physiological norms and varies only slightly depending on the productivity level of the mares.

4. Discussion

The conducted research allowed to obtain important data on the state of reproductive health and efficiency of reproduction of mares of Kazakh and Mugalzhar breeds in the conditions of productive horse breeding in Kazakhstan. The obtained results require discussion in the context of modern scientific knowledge.

The detected infertility rate in the studied farms (13.8-25.0%) is within the limits described in the world literature for herds management of horses. However, it is interesting to note a significantly lower level of pathologies on farms specializing in mare milk production compared to farms not practicing milking.

This may be indirectly related to more intensive and controlled management on dairy farms, including regular veterinary check-ups, balanced feeding of dairy mares and, as a consequence, better overall physiological condition of the animals. This observation is in agreement with Caroprese et al. (2007), who noted that machine milking requires a stricter compliance to management techniques, which has a positive effect on animal health in general.

The structure of the pathologies detected is typical for productive horse breeding. The high proportion of ovarian diseases is probably due to the significant stresses on the mare's body when combining lactation and new foaling under herd conditions and possible energy and nutrient deficiencies, also noted by Duncan et al. (1984) and Dell et al. (2021) as a key factor in reproductive stress.

The average gestation rate (78.8%) and successful foaling rate (76.0%) are high for local herd breeds and indicate good adaptive potential of the Kazakh and Mugalzhar breeds. These indicators are in line with the goals of sustainable development and conservation of native breeds, the importance of which is emphasized by Prišenk et al. (2022) and Atroshchenko et al. (2023). The low percentage of abortions, stillborn and weak-born foals indicates the efficiency of the reproduction management system in the studied farms and good foaling performance of the mares.

The obtained data on age dynamics are in full agreement with the concepts generally accepted in zootechnics. The lowest performance of mares under 5 years of age (gestation - 74.4%, foaling - 65.6%) is explained by their incomplete physiological maturity and adaptation to the first lactation. The most productive age period of 6-9 years (gestation - 88.0%, foaling - 79.5%) confirms that by this age mares reach the peak of their physical and reproductive form.

A slight decrease in performance in mares over 10 years of age (foaling - 74.6%) is expected and is due to natural aging processes and accumulation of chronic pathologies of the reproductive tract. An important practical conclusion is the confirmation of the thesis that with competent management, high-yielding mares can be effectively used in reproduction up to 12-13 years of age.

The set of methods used in the study to determine the optimal insemination time is the gold standard in modern equine reproductive management. The recommendation to inseminate between 13 and 20 h after the first signs of estrus and at specific cervical mucus condition is a practical and valuable guide for horse breeders to maximize the percentage of fertilization with a minimum number of cages.

The optimal parameters of reproduction management presented in this paper are scientifically justified and critical for the economic efficiency of productive horse breeding. The emphasis on balanced feeding, prevention of inbreeding and timely etiotropic therapy of endometritis fully corresponds to the conclusions of such authors as Gupta et al. (2014), Koveshnikov et al. (2019) and Assanbayev et al. The established etiology of postpartum endometritis confirms the relevance of prescribing broad-spectrum drugs, as recommended in modern works (Ganiev et al., 2024; Stepochkina et al., 2024).

Thus, the results of this study not only provide specific data on reproduction of Kazakh and Mugalzhar breeds, but also fit well into the global scientific paradigm of productive horse breeding. They confirm that the key to high reproduction rates is not only the genetic potential of indigenous, well adapted breeds, but also strict compliance with technological standards of feeding, housing, veterinary control and reproductive management.

Additionally, it should be noted that the productivity of first-lactating mares differed significantly between farms: the highest average daily milk yields (8.7 L) and milk yield over 150 days of lactation (1421.7 kg) recorded on the “Ertai” farm, which correlates with a slightly higher fat content (1.85%) and protein (2.31%) in the milk of these mares. whereas the lactose and ash levels remained stable in all farms. These findings confirm that improved management and feeding practices on dairy-oriented farms positively affect not only reproductive performance but also milk productivity and its chemical composition.

5. Conclusion

When analyzing the reproduction indicators of the Kazakh horse population, conducted on statistical material from current information sources and primary data from zootechnical reporting, trends were identified in the reduction of pregnancy rates and successful foaling rates against the background of an increase in the proportion of abortions, weak-born foals and stillborn offspring in the group of mares over 10 years old, compared to mares aged 6-9 years.

Fillies reach sexual maturity between 12 and 18 months of age. Therefore, it is recommended that colts and fillies be housed separately once they are 1 year old. Although young horses can breed, this is not recommended. Mares bred before maturity will require additional care and nutrition, especially during lactation and the last 3 months of pregnancy (due to the risk of dystocia), to ensure that she and her foal reach their genetic potential.

It is recommended to maintain mares and test their performance before breeding to assess their quality. If they perform well, the value of their foals increases.

In managing reproduction in horse breeding, zootechnical and veterinary methods are used. In the line of veterinary medicine in reproduction, it is necessary to carry out post-foaling measures and control the precise fertilization of mares. In this case, the use of hormones takes place to bring animals into estrus with subsequent manual mating by a stallion.

Following recommended husbandry practices and understanding the basics of mare reproductive science will improve the mare's chances for reproductive health and success.

The absence of a reliable difference in the pregnancy rate (88.0-82.0%) and successful foaling (79.5-74.6%) between mares aged 6-9 years and mares over 10 years old is explained by the fact that the mares on the farms are either the most fertile mares that regularly produce healthy foals or the mares that are the most valuable from a selection point of view, and to which more attention is paid.

Differences in milk performance among farms demonstrate the impact of feeding quality and herd management on dairy productivity. Mares from dairy-oriented farms showed significantly higher milk yields and slightly enhanced chemical composition, supporting the notion that improved management practices positively influence both reproductive and productive traits.

Overall, the study confirms that sustainable reproduction in Kazakh and Mugalzhar horse populations depends on the integration of balanced nutrition, proper estrus detection, regular gynecological monitoring, and adherence to optimized reproductive management protocols. These findings contribute valuable knowledge for the conservation and efficient utilization of Kazakhstan’s indigenous horse genetic resources and support the further development of mare's milk production as a promising branch of the national livestock sector.

Acknowledgements

This research was funded by the Ministry of Agriculture of the Republic of Kazakhstan, grant number BR22887106, under the project titled “Application of molecular genetic methods for horse genetic resources management optimization and efficient horse breeding innovative technologies development”.

Data Availability Statement

The entire data set that supports the results of this study was published in the article itself.

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Edited by

• Editor:
  Takako Matsumura Tundisi

Publication Dates

• Publication in this collection
  30 Jan 2026
• Date of issue
  2025

History

• Received
  21 Aug 2025
• Accepted
  18 Nov 2025