Postembryonic development of Mughalzhar breed fillies from directed selection

Desenvolvimento pós-embrionário de potras da raça Mughalzhar por meio de seleção dirigida

Abstract

Extensive horse breeding is an important sub-branch of animal husbandry in Kazakhstan, where the Mughalzhar horse breed is of high value due to its adaptation to pasture-based management and high productivity. However, the effectiveness of classical selection methods under the conditions of regional populations in the southern part of the country has been insufficiently studied, which necessitates assessing their impact on the growth and development of young stock. The study was conducted in 2024–2026 at the peasant farm “Senim” (Turkestan Region). From 285 mares of reproductive age, a selection group (n = 233) was formed. For selective mating, 18 mares of the “elite” and Class I categories and one elite-class breeding stallion were selected. Growth and development were evaluated in 10 fillies (aged 3 days to 24 months) based on live weight, four main body measurements, and absolute gain. The milk productivity of the dams was determined in the third month of lactation using the test milking method. The data were processed using methods of variation statistics. The results showed the selection group was characterized by high uniformity in conformation (Cv = 3.21% for live weight) with moderate variability in milk productivity (Cv = 13.93%). The average daily milk yield of the mares was 4.17 ± 0.28 kg. Offspring from selective mating demonstrated high growth intensity: during the first 6 months of life, live weight increased 3.09 times (from 39.0 to 159.5 kg). By 24 months of age, the fillies reached a live weight of 303.9 ± 11.06 kg and a height at the withers of 140.3 ± 4.84 cm, corresponding to the breed standard. The coefficient of variation for live weight in the offspring group decreased to 5.46% by the age of 2 years, indicating high herd uniformity in productive traits. The highest intensity of live weight gain was observed during the period from 3 days to 3 months of age, after which relative and average daily gain gradually decreased, while the positive dynamics of absolute gain were maintained up to 24 months of age. Directed selection of parental pairs using elite and Class I animals ensures the stable production of uniform offspring with growth intensity exceeding average population indicators. The milk productivity of mares (4.17 kg/day) can serve as an indirect predictor of offspring growth rate. The results confirm the effectiveness of classical selection methods in extensive horse breeding in the southern region of Kazakhstan and can be used to optimize breeding programs.

Keywords:
horses; Mugalzhar breed; fillies; milk yield; body conformation traits; body weight

Resumo

A criação de cavalos em sistema de rebanho é um importante sub-ramo da pecuária no Cazaquistão, no qual a raça de cavalos Mughalzhar apresenta alto valor devido à sua adaptação ao manejo em pastagens e à elevada produtividade. No entanto, a eficácia dos métodos clássicos de seleção nas condições das populações regionais do sul do país ainda é insuficientemente estudada, o que exige a avaliação de seu impacto sobre o crescimento e o desenvolvimento dos animais jovens. O estudo foi realizado no período de 2024 a 2026 na fazenda camponesa “Senim” (região do Turquestão). A partir de 285 éguas em idade reprodutiva, foi formado um grupo de seleção (n = 233). Para o acasalamento dirigido, foram selecionadas 18 éguas das categorias “elite” e Classe I, bem como um garanhão reprodutor de classe “elite”. O crescimento e o desenvolvimento foram avaliados em 10 potras (com idade de 3 dias a 24 meses) com base no peso vivo, em quatro principais medidas corporais e no ganho absoluto. A produtividade leiteira das mães foi determinada no terceiro mês de lactação pelo método de ordenhas de controle. Os dados foram processados por métodos de estatística variacional. Verificou-se que o grupo de seleção foi caracterizado por alta uniformidade de conformação (Cv = 3,21% para peso vivo), com variabilidade moderada na produtividade leiteira (Cv = 13,93%). A produção média diária de leite das éguas foi de 4,17 ± 0,28 kg. A progênie proveniente do acasalamento dirigido apresentou alta intensidade de crescimento: nos primeiros 6 meses de vida, o peso vivo aumentou 3,09 vezes (de 39,0 para 159,5 kg). Aos 24 meses de idade, as potras atingiram peso vivo de 303,9 ± 11,06 kg e altura na cernelha de 140,3 ± 4,84 cm, o que corresponde ao padrão da raça. O coeficiente de variação do peso vivo no grupo da progênie diminuiu para 5,46% aos 2 anos de idade, indicando elevada consolidação do rebanho quanto às características produtivas. A maior intensidade de ganho de peso vivo foi observada no período de 3 dias a 3 meses de idade, após o qual o ganho relativo e o ganho médio diário diminuíram gradualmente, mantendo-se uma dinâmica positiva do ganho absoluto até os 24 meses de idade. A seleção dirigida de pares parentais, com o uso de animais das categorias “elite” e Classe I, garante a obtenção estável de descendência homogênea com intensidade de crescimento superior aos indicadores médios populacionais. A produtividade leiteira das éguas (4,17 kg/dia) pode servir como um preditor indireto da intensidade de crescimento da progênie. Os resultados confirmam a eficácia dos métodos clássicos de seleção na criação de cavalos em sistema de rebanho na região sul do Cazaquistão e podem ser utilizados para otimizar programas de melhoramento genético.

Palavras-chave:
cavalos; raça Mugalzhar; potras; produção de leite; características de conformação corporal; peso vivo

1. Introduction

Extensive horse breeding is a traditional and economically significant sub-branch of productive livestock farming in Eurasian countries, including Kazakhstan (Orazymbetova et al., 2023). Historically, horses ensured the functioning of the economic systems of nomadic and semi-nomadic peoples. Under modern conditions, productive horse breeding retains strategic importance for rural areas, contributing to employment and the production of high-value food products such as meat and milk. As of 2020, the number of productive horses in Kazakhstan exceeded 4 million head, of which about 2 million were breeding mares. The gene pool is represented by four domestic breeds (Kazakh, Mughalzhar, Kushum, Aday), as well as two intra-breed types of the Kazakh breed (Jabe type and steppe type) (Kabylbekova et al., 2024; Baimukanov and Iskhan, 2022; Baibolsyn, 2023).

Among domestic breeds, the Mughalzhar horse breed is of considerable scientific and practical interest. It was developed in 1969–1998 through selective breeding of Jabe-type Kazakh horses with the aim of improving meat and milk productivity. The Mugalzhar breed is one of the most valuable native herd horse breeds, as it combines high meat and milk productivity with stable adaptation to extreme environmental and climatic conditions, as well as the ability to be kept on pasture year-round (Kalzhanov, 2023; Seleuova et al., 2018; Shamshidin et al., 2025). According to evaluation data, the average live weight of mares is 440–490 kg, height at the withers is 141–146 cm, oblique body length is 147–152 cm, chest girth is 178–183 cm, and cannon bone girth is 18.5–19.5 cm. Breeding stallions reach a live weight of 460–510 kg with a height at the withers of 143–148 cm (Assilbekov et al., 2021).

As of 2020, the population of the Mughalzhar breed numbered 16,290 head, including 7,026 mares. The main breeding area is concentrated in the northwestern regions of Kazakhstan, primarily in Aktobe and West Kazakhstan regions, as well as in bordering regions of the Russian Federation. The distribution of the breed is associated with steppe and semi-desert zones due to its high adaptability to year-round grazing (Akimbekov et al., 2025). At the same time, some local populations, including those in the southern regions of the country, are formed under conditions different from the main habitat, which requires clarification of growth and development parameters of animals in specific environmental and management conditions.

One of the promising areas for the use of productive-type horses is the production of mare’s milk, traditionally used to produce kumis-a fermented beverage with high nutritional and biological value (Kondybayev et al., 2021). Mare’s milk has a unique composition: the ratio of casein to whey proteins is approximately 1:1, making it similar to human milk and ensuring high digestibility (Shokrollahi et al., 2025). It contains biologically active components, including lysozyme (0.2–2 g/L), lactoferrin (0.08–0.20 g/L), immunoglobulins, and α-lactalbumin, which provide antimicrobial, immunomodulatory, and antioxidant properties (Shaikh et al., 2021). During fermentation, bioactive peptides with antihypertensive, anti-inflammatory, and prebiotic effects are formed, allowing kumis to be considered a functional food product (Kossaliyeva et al., 2025). The milk productivity of mares can also serve as an indirect predictor of offspring growth intensity, which justifies its inclusion in breeding programs.

Kazakhstan has accumulated a significant body of experimental data on the use of local horse breeds for mare’s milk production under herd conditions (Sharapatov et al., 2023). However, traditional selection methods based on selection and mating are characterized by relatively low rates of genetic progress. This is due to the high variability of milk production traits and their dependence on individual animal characteristics (Iskhan et al., 2019a). An additional limiting factor is the relatively low heritability of these traits in horses (on average 0.20–0.35), as well as the influence of non-genetic factors, including the age of mares, feeding conditions, stage of lactation, and reproductive status (Sharapatov et al., 2022). In modern horse breeding, genomic selection methods are increasingly used to improve the accuracy of breeding value assessment (Pozharskiy et al., 2023). In the genome of the Mughalzhar breed, a number of candidate genes associated with adaptation to harsh climatic conditions have been identified, and no significant harmful segregating mutations have been found, indicating a sufficient level of genetic diversity (Kassymbekova et al., 2025). At the same time, the implementation of genomic technologies requires a reliable phenotypic base, and the evaluation of the effectiveness of traditional selection methods in specific populations remains a relevant task.

Recent studies indicate that the productivity and growth of young horses are determined by a combination of factors, including management conditions, physiological characteristics, and the genetic basis of traits. In recent years, particular attention has been paid to the genetic determinants of adaptability and productivity in indigenous breeds. Whole-genome sequencing of Kazakh horses has revealed a high level of genetic diversity and adaptive potential (Assanbayev et al., 2024). Furthermore, studies on gene polymorphism confirm its influence on growth performance and developmental efficiency in animals (Kazhgaliyev et al., 2026). In addition, mare milk productivity represents a key factor influencing the development of productive traits in young stock, as it is affected by age, stage of lactation, and management conditions (Toishimanov et al., 2025).

Despite the importance of the Mughalzhar breed, issues of directed selection of parental pairs using controlled mating in specific regional populations remain insufficiently studied and fragmented (Iskhan et al., 2019b). In particular, there is a lack of systematized data on the patterns of growth and development of young stock obtained through targeted selection in the southern regions of Kazakhstan. Meanwhile, it has been established that monitoring the growth and development of young animals, assessed by live weight and morphometric parameters at different ages, is of key importance in breeding work (Asilbekov et al., 2018). Morphometric parameters of foals change with age and reflect their overall development level, which allows their use in selection (Sydykov et al., 2022). The growth intensity of young stock is closely related to the formation of meat productivity and the economic value of horses (Akimbekov et al., 2019).

It is hypothesized that directed selection of parental pairs using elite-class breeding stallions and mares of at least Class I reproductive status will make it possible to obtain offspring with improved growth and development indicators compared to average population values. At the same time, the milk productivity of mares, assessed in the third month of lactation, can be considered an additional predictor of offspring growth intensity.

The aim of the study is to determine the patterns of postembryonic development of Mughalzhar breed fillies obtained through directed selection of parental pairs.

2. Materials and Methods

The research was conducted at the peasant farm “Senim” (Sozak District, Turkestan Region, Republic of Kazakhstan) during the period 2024–2026. The horses were kept under herd pasture conditions. Feeding was based on natural pastures, while in the winter period supplementary feeding with hay and concentrates was provided in accordance with the zootechnical standards adopted on the farm.

The object of the study was Mughalzhar breed horses of the Sozak population. At the beginning of the study, the farm herd consisted of 285 mares of reproductive age and 22 breeding stallions.

From the total number of mares, a selection group of 233 animals (81.7% of the total mare population) was formed using the pair-analog method (taking into account age, live weight, body measurements, and class). For selective mating, 18 mares of the “elite” and Class I categories, as well as one elite-class breeding stallion, were selected. The assessment of growth and development was carried out on the offspring obtained from selective mating in 2024-10 fillies that were monitored at the ages of 3 days, 3, 6, 12, 18, and 24 months.

Bonitation and class evaluation. The bonitation of horses was carried out in accordance with the Instruction for the Bonitation of Horses. Based on body measurements and live weight, the animals were assigned to the “elite” and Class I categories.

Four main body measurements were taken: height at the withers, oblique body length, chest girth, and cannon bone girth. Measurements were performed using a measuring stick and a measuring tape with an accuracy of 0.5 cm. Live weight was determined by individual weighing on electronic scales (CAS model, accuracy 0.5 kg). Weighing was carried out in the morning before feeding.

Milk productivity of mares was recorded in the third month of lactation using the test milking method over two consecutive days (morning and evening milking) without separating the foals. The average daily milk yield (kg/day) was calculated.

Milk productivity was recorded in mares aged 7–9 years, which were in the third month of lactation, using the control milking method over two consecutive days, including morning and evening milking, without separating the foals from the mares. The average daily milk yield was calculated (kg/day).

Based on live weight at different age periods, the dynamics of absolute and relative live weight gain were studied using the following Equations (1) and (2):

$\text{ALWG}=\text{W}2-\text{W}1$ (1)

$\text{RLWG}=\left(\text{W}2-\text{W}1\right)/\text{W}1\text{*}100\text{\%}$ (2)

where ALWG is absolute live weight gain, RLWG is relative live weight gain, W₁ is the initial live weight, and W₂ is the final live weight.

The data were processed using methods of variation statistics with the use of Microsoft Excel (version 2019) and Statistica 10.0 software. For each sample, the arithmetic mean (M), standard error of the mean (±Sxˉ), standard deviation (σ), coefficient of variation (Cv), and limits (lim) were calculated. The significance of differences between mean values of traits was assessed using Student’s t-test at a significance level of p < 0.05 (Welham et al., 2014; Holmes and Huber, 2019).

3. Results

According to the results of bonitation at the peasant farm “Senim,” 233 mares (81.7%) out of 285 of reproductive age were selected to form the breeding (selection) group. The average body measurements and live weight of Mughalzhar horses of the Sozak population met the requirements of the bonitation instruction (Table 1).

Table 1
Average body measurements and live weight of Mughalzhar horses of the Sozak population (M ± Sx̄).

Sex and age groups	n	Height at the withers, cm	Oblique body length, cm	Chest girth, cm	Cannon bone girth, cm	Live weight, kg
Breeding stallion	22	149.5±3.2	155.7±4.1	187.2±8.3	20.2±0.21	511.7±28.2
Mare	285	143.5±1.5	152.1±2.6	181.8±5.8	19.2±0.17	468.2±22.1
Filly (2.5 years)	38	141.2±1.7	142.6±2.1	169.8±5.2	17.2±0.18	389.3±35.5
Filly (1.5 years)	31	135.8±1.2	132.5±1.9	141.7±4.4	15.4±0.14	259.6±19.2
Colt (2.5 years)	19	144.6±1.4	144.3±1.7	172.9±6.8	17.4±0.19	409.9±16.5
Colt (1.5 years)	24	135.8±1.8	135.9±1.8	145.2±4.3	15.6±0.16	276.8±14.4

For selective mating, 18 mares of the “elite” and Class I categories (aged 4.5–12.5 years) and one elite-class breeding stallion (aged 5.5–14.5 years) were selected. The class composition and productive traits of the animals are presented in Tables 2 and Figure 1-2. The average foal crop from the breeding animals used was 92.7%.

Table 2
Class composition and age of animals selected for the breeding group.

Group	Number of animals (head)	Elite class (head)	Class I (head)	Average foal crop, %	Age, years
Breeding stallion	19	19	-	92.7	5.5-14.5
Mare	128	20	108	-	4.5-12.5
Replacement stallions	4	4	-	-	4.5
Replacement fillies	68	68	-	-	3.5

Figure 1
Body measurements of parental animals obtained from planned mating (M ± Sx̄). Note: Breeding stallion (n=1), Mares (n=18).

Figure 2
Live weight and milk productivity of parental animals obtained from planned mating (M ± Sx̄). Note: Breeding stallion (n=1), Mares (n=18).

The selected mares showed variation in traits as follows: live weight 460–500 kg, height at the withers 140–149 cm, oblique body length 145–155 cm, chest girth 180–186 cm, cannon bone girth 18.5–19.5 cm, and average daily milk yield in the third month of lactation 3.1–5.1 kg. The coefficient of variation was 3.21% for live weight and 13.93% for milk yield, indicating sufficient uniformity of the herd in terms of conformation traits and moderate variability in milk productivity

The dynamics of growth and development were evaluated in 10 fillies born in 2024, from the age of 3 days to 2 years. Table 3 presents summary data on live weight and body measurements across the studied age periods.

Table 3
Dynamics of body measurements and live weight of Mughalzhar breed fillies obtained from selective mating (n = 10).

Age	Parameters	Height at the withers, cm	Oblique body length, cm	Chest girth, cm	Cannon bone girth, cm	Live weight, kg
3 days	M±Sx̄	90.30±3.60	70.20±3.04	80.30±3.64	10.15±0.15	39.00±2.75
	σ	10.81	9.11	10.92	0.46	8.25
	Cv, %	5.99%	6.49%	6.80	2.26%	10.57%
	lim	79-96	64-78	73-89	10.0-10.5	32-45
3 months	M±Sx̄	104.70±3.72	95.80±4.05	102.00±1.29	12.55±0.23	122.10±6.28
	σ	11.17	12.16	11.10	0.70	18.84
	Cv, %	5.34%	6.35%	5.44%	2.79%	7.71%
	lim	98-113	83-103	95-110	12.0-13.0	109-135
6 months	M±Sx̄	119.30±5.43	116.00±5.63	126.00±5.29	13.50±0.21	159.50±8.05
	σ	16.30	16.90	15.87	0.63	24.15
	Cv, %	6.83%	7.28%	6.30%	2.34%	7.57%
	lim	107-130	103-124	115-136	13.0-14.0	135-178
12 months	M±Sx̄	125.10±5.12	127.50±4.78	137.90±4.48	14.35±0.21	219.10±11.56
	σ	15.37	14.35	13.43	0.64	34.69
	Cv, %	6.14%	5.63%	4.87%	2.23%	7.92%
	lim	115-136	117-138	128-147	14.0-15.0	190-234
18 months	M±Sx̄	135.50±5.93	132.90±5.78	149.00±5.04	15.30±0.16	259.60±16.83
	σ	17.78	17.33	15.13	0.49	50.50
	Cv, %	6.56%	6.52%	5.08%	1.60%	9.73%
	lim	121-148	119-144	137-158	15.0-15.5	229-292
24 months	M±Sx̄	140.30±4.84	139.20±4.84	162.70±4.70	16.25±0.20	303.90±11.06
	σ	14.53	14.53	14.09	0.50	33.17
	Cv, %	5.18%	5.22%	4.33%	1.54%	5.46%
	lim	128-152	127-150	150-173	16.0-16.5	276-325

The highest growth intensity was observed during the first 6 months of life. During this period, live weight increased 3.09 times (from 39.0 to 159.5 kg), height at the withers increased by 29.0 cm (32.1%), oblique body length by 45.8 cm (65.2%), chest girth by 45.7 cm (56.9%), and cannon bone girth by 3.35 cm (33.0%). In subsequent age periods, growth rates decreased; however, by 24 months all indicators reached values close to those of the 2.5-year-old mare group presented in Table 1.

Comparison of live weight of fillies at 18 and 24 months with the population averages (Table 1) showed that offspring from selective mating (259.6 and 303.9 kg, respectively) were comparable to the average values (259.6 and 389.3 kg for 1.5- and 2.5-year-old fillies, respectively). At the same time, at 2 years of age, a closer correspondence to the breed standard in body measurements was observed: height at the withers 140.3 cm (with a standard of 141–146 cm), chest girth 162.7 cm (standard 178–183 cm - the attainment of adult mare values is expected at an older age).

The coefficients of variation for live weight at different age periods ranged from 5.46% to 10.57%, indicating low variability of the trait and stability in the formation of meat-producing qualities in the offspring from the selected parental pairs. The lowest variability was recorded at 24 months of age (Cv = 5.46%), which indicates increasing uniformity of the animals as they mature.

In accordance with the requirements for studying live weight dynamics during the postnatal period, relative and absolute live weight gains were determined (Figure 3).

Figure 3
Dynamics of live weight gain in Mugalzhar fillies. Note: By age period: values are presented as M ± Sx̄.

The data presented in Figure 3 indicate that the maximum growth intensity of Mugalzhar fillies was observed during the period from 3 days to 3 months of age. Subsequently, as the animals’ age and live weight increased, relative and average daily gains gradually decreased. Nevertheless, absolute gain remained at a relatively high level up to 24 months of age, confirming the continued active growth and development of the fillies during the postnatal period.

4. Discussion

The results of the conducted research indicate the high efficiency of directed selection of parental pairs using elite-class breeding stallions and mares of no lower than Class I for improving the productive traits of Mughalzhar breed offspring under the conditions of the Sozak population. The obtained data are consistent with the concept that targeted selection based on phenotypic evaluation of conformation and milk productivity makes it possible to achieve significant genetic progress even in the absence of whole-genome evaluation methods, especially in breeds with high adaptive potential (Hayes et al., 2009).

The dynamics of growth and development of fillies obtained from selective mating demonstrate classical age-related patterns typical of meat-type horses. The highest growth intensity, recorded during the first six months of life, is due to the high milk production potential of the dams (average daily milk yield 4.17 ± 0.28 kg) and corresponds to the biological optimum described for dairy mares in (Reiter and Reed, 2023). The increase in live weight by 3.09 times by 6 months of age exceeds the average indicators for herd populations of the Kazakh breed, indicating the effectiveness of selecting parents based on milk productivity. This fact allows the average daily milk yield of mares in the third month of lactation to be considered a reliable predictor of offspring growth intensity, which is especially important for breeding programs under pasture conditions, where direct weighing of young animals is difficult (Auclair-Ronzaud et al., 2022).

A comparative analysis of morphometric parameters showed that by 24 months of age, the fillies of the experimental group reach values close to the breed standard, while the coefficient of variation of live weight decreases to 5.46%. The low variability of traits in the final rearing period indicates a high degree of herd consolidation in terms of conformation and constitution types and the effectiveness of selection. Previous studies have shown that the Mughalzhar breed is characterized by moderate heritability of measurements (h² = 0.25–0.40); however, with targeted selection of parents homogeneous in class, it is possible to significantly increase the accuracy of predicting offspring phenotype. Our data confirm this position: offspring from elite and Class I parents demonstrate not only high absolute growth indicators but also uniformity within the group, which simplifies further breeding work and reduces the risk of producing individuals that do not meet bonitation requirements.

Particular attention should be paid to the analysis of milk productivity of mares included in the selection group. The observed variability of milk yield (Cv = 13.93%) with uniformity of conformation traits (Cv = 3.21%) indicates the presence of a reserve for selection for milk productivity. This is consistent with data showing that milk production traits in horses have low heritability but can be effectively improved using indirect evaluation methods, including offspring growth and conformation indices (Chirgin et al., 2021). In our study, the average milk yield of mares (4.17 kg/day) in the third month of lactation exceeds the average breed values (3.5–3.8 kg/day), which is likely due to both genetic factors and optimal feeding conditions at the “Senim” farm.

The obtained results indicate that the growth intensity of young stock is determined by a combination of physiological and external factors, including mare milk productivity and management conditions. The relationship identified in the present study is consistent with the findings of Sharapatov et al. (2025a), who reported that the average daily milk yield of Kazakh Jabe-type mares varied from 4.09 to 7.48 kg across different months of lactation, whereas in Novoaltai–Kazakh crossbred mares this parameter ranged from 2.18 to 2.95 kg, reflecting breed-specific and adaptive characteristics.

Furthermore, milk productivity was shown to be strongly influenced by management conditions and behavioral activity. According to Sharapatov et al. (2025b), during the winter period, an increase in daily travel distance to 8300–8400 m resulted in a decrease in milk yield to 4.67 ± 0.14 L/day, whereas under lower activity levels (5200–5300 m/day), milk yield reached 7.20 ± 0.12 L/day. These findings confirm the significant impact of climatic factors on productivity.

Thus, the results are consistent with current understanding of the multifactorial nature of productive trait formation, determined by the interaction of physiological, environmental, and behavioral factors.

An important aspect is the adaptive potential of the obtained offspring. The Mughalzhar breed was historically formed under the sharply continental climate of northwestern Kazakhstan; however, the successful rearing of young animals in the southern region (Turkestan Region), characterized by higher temperatures and a different pasture phytocenosis, indicates a wide reaction norm of this breed. This confirms conclusions about the high plasticity of the Mughalzhar breed and the possibility of its breeding in various ecological and geographical zones without loss of productive qualities, provided that the breeding core is preserved.

In the context of modern breeding approaches, the obtained results are of practical importance. Despite the active introduction of genomic technologies, phenotypic evaluation and classical selection based on pedigree remain relevant for populations with limited access to genomic selection (Burrow et al., 2021). This study demonstrates that even with the use of traditional bonitation and selection methods, it is possible to achieve improvement in key economically valuable traits, which is especially important for small and medium-sized farms where the implementation of expensive genetic technologies is economically impractical.

At the same time, the limitations of this study should be considered. The relatively small sample size of the offspring (n = 10) and the absence of a control group obtained from non-directed mating do not allow for a high degree of statistical certainty in separating the effects of selection and non-genetic factors. Further studies should be aimed at assessing the lifetime productivity of the raised fillies, including their milk and meat productivity, as well as at genetic analysis of polymorphisms associated with growth processes in this population.

5. Conclusion

The studies conducted at the peasant farm “Senim” (Sozak District, Turkestan Region) showed that directed selection of parental pairs of the Mughalzhar breed using elite-class breeding stallions and mares of no lower than Class I ensures the production of offspring with high growth and development indicators. Fillies obtained from selective mating were characterized by intensive growth during the first six months of life (an increase in live weight by 3.09 times), which correlated with the level of milk productivity of the dams (average daily milk yield 4.17 ± 0.28 kg). By 24 months of age, the live weight of the experimental animals reached 303.9 ± 11.06 kg, and height at the withers was 140.3 ± 4.84 cm, which corresponds to the breed standards for this age.

The low variability of body measurements and live weight in the offspring group (Cv = 5.46% at 24 months) indicates a high degree of herd consolidation in terms of conformation and constitutional types and the effectiveness of the applied selection methods. The milk productivity of mares included in the selection group showed moderate variability (Cv = 13.93%), indicating the presence of potential for further improvement of this trait.

Analysis of the dynamics of live weight gain showed that the maximum growth intensity occurred during the early postnatal period, from 3 days to 3 months of age, whereas in subsequent age periods the relative gain decreased, which corresponds to the general biological patterns of young animal growth.

The practical significance of the obtained results is determined by their potential use in improving breeding programs for the Mugalzhar breed as one of the most promising breeds in productive herd horse breeding.

The obtained data confirm the proposed hypothesis about the possibility of effectively improving the growth traits of Mughalzhar breed young stock under the conditions of the southern region of Kazakhstan using classical selection methods. The results of the study can be used in the development of breeding programs in farms engaged in extensive horse breeding, and may also serve as a basis for further assessment of the genetic structure of the population and the identification of markers associated with high growth intensity.

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.

References

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Edited by

• Editor:
  Takako Matsumura Tundisi

Publication Dates

• Publication in this collection
  27 July 2026
• Date of issue
  2026

History

• Received
  30 Mar 2026
• Accepted
  24 May 2026