Open Veterinary Journal, (2025), Vol. 15(9): 4255-4264

Research Article

10.5455/OVJ.2025.v15.i9.32

Effects of birth season and reproductive performance in Romanov-derived F1 ewes in terminal crossbreeding

Fatih Ahmet Aslan¹* and Ebru Emsen²

¹Ordu University, Ulubey Vocational School, Ordu, Turkey

²Department of Integrative Agriculture, College of Agriculture and Veterinary Medicine, United Arab Emirates University, Al Ain, United Arab Emirates

*Corresponding Author: Fatih Ahmet Aslan. Ordu University, Ulubey Vocational School, Ordu, Turkey. Email: fatihahmetaslan [at] gmail.com; faslan [at] odu.edu.tr

Submitted: 03/07/2025 Revised: 18/08/2025 Accepted: 26/08/2025 Published: 30/09/2025

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ABSTRACT

Background: Terminal crossbreeding strategies combine prolific maternal lines with growth-oriented sires to enhance lamb productivity and carcass traits. Lamb meat production sustainability depends on genetic efficiency and seasonal adaptability.

Aim: This study aimed to evaluate the effect of birth season and maternal genotype on reproductive performance, survival rates, and growth traits in lambs produced by Charollais rams crossed with Romanov × Akkaraman (RA) and Romanov × Morkaraman (RM) F1 ewes.

Methods: Charollais rams (n=4) were used to artificially inseminate RA (n=40) and RM (n=40) F1 ewes. Reproductive traits, survival rates, and weaning data were recorded. The influence of seasonal lambing (spring vs. summer), hormonal synchronization protocols, and type of parturition on lamb productivity was analyzed. Statistical analyses were conducted to assess the significance of litter size and growth metrics.

Results: RM ewes showed a 13% higher lamb number at birth, whereas RA ewes had a 4.9% advantage at weaning. The survival rates were 12% higher in lambs from RA ewes. Spring lambing resulted in significantly larger litter sizes than summer lambing (p < 0.01). Lambs born in summer exhibited superior body weights. Hormonal synchronization positively influenced the outcomes of birth and weaning.

Conclusion: F1 maternal lines derived from Romanov crosses, especially under managed breeding strategies, offer promising results for enhancing lamb production efficiency and productivity under semi-intensive conditions.

Keywords: Birth season, Lamb productivity, Maternal genotype, Reproductive performance, Terminal crossbreeding.

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Introduction

Global population growth has outpaced agricultural production, prompting the need for intensified farming systems. While intensification can increase food output, it simultaneously raises concerns about long-term sustainability. In Türkiye, sheep and goat farming is prominent due to unique characteristics such as heterogeneous soil structures, diverse pasture availability, rural demographic trends, and cultural practices, including transhumance and nomadism (Koyuncu et al., 2010).

Türkiye leads Europe and ranks seventh globally in sheep population, housing approximately 43.4 million sheep, 93% of which are indigenous breeds (Turkish Statistical Institute (TurkStat), 2024). National breeding policies, such as the “Sheep and Goat Breeding Strategy,” aim to enhance the productivity of local genotypes. Although escalating input costs pose significant challenges to efficiency, most producers operate within semi-intensive frameworks. According to current reports, sheep contribute 13% of Türkiye’s red meat (210,600 tons) and 5.8% of milk production (1.34 million tons), alongside notable outputs in wool and hides (Ministry of Agriculture and Forestry, 2024; Turkish Statistical Institute (TurkStat), 2024).

Sheep (Ovis aries) were first domesticated from the Asiatic mouflon (Ovis orientalis) approximately 11,000 years ago in Southwest Asia (Zeder, 2008; Larson and Fuller, 2014). Several millennia of selective breeding under various environmental pressures have led to the development of distinct breeds suited to diverse production systems. Modern breeding programs prioritize crossbreeding as a strategy to combine favorable traits for commercial productivity, particularly through the use of heterosis and complementary breed characteristics (Van Eenennaam, 2025).

Crossbreeding programs worldwide focus on improving lamb meat quality and yield by pairing prolific maternal genotypes with growth-optimized terminal sires (Ünal, 2002). Selection criteria vary depending on carcass weight targets: lighter market demands favor fast-growing lambs (typically 40–45 kg), whereas larger breeds with enhanced marbling and dressing percentages are required. Recent studies have emphasized the role of initial body weight and genetic background in determining carcass traits and market suitability (Bohrer et al., 2023; Norman et al., 2024). For instance, heavier lambs tend to yield fatter carcasses with higher marbling scores, whereas lighter lambs show better feed conversion and leaner profiles.

Since the 1970s, Türkiye has pursued strategic crossbreeding to enhance fertility and milk yield, resulting in locally adapted breeds such as Türkgeldi, Tahirova, Sönmez, and Acıpayam (Kaymakcı et al., 1999). More recent efforts aim to improve carcass traits through targeted mating schemes. For example, Bafra × Akkaraman crosses have demonstrated superior fertility relative to pure Akkaraman ewes (Güngör et al., 2022).

Three-way crossbreeding has emerged as an effective method for maximizing heterosis by combining adaptability and performance traits. International studies highlight successes such as Hu × Charolais × Australian White crosses exhibiting favorable rumen microbiota (Wang et al., 2024) and Poll Dorset × Southdown lambs with enhanced growth rates (Zhang et al., 2024). Within Türkiye, combinations such as German Black Head × Kivircik and Chios crosses have resulted in improved birth weights, weaning outcomes, and survival rates (Özcan et al., 2001). Genetic markers, such as CLPG, have also been linked to better growth efficiency in crossbred lambs (Wang et al., 2022).

Although crossbreeding strategies have been extensively studied in sheep production, the influence of birth season on reproductive and growth traits within three-way cross systems remains underexplored. This study aims to address this gap by evaluating how seasonal timing interacts with genetic background to affect performance outcomes.

The birth season is a critical environmental factor that can influence the reproductive efficiency and growth performance of lambs. Seasonal variations in photoperiod, forage availability, and ambient temperature may alter hormonal cycles, nutrient intake, and maternal behavior, thereby affecting offspring development (Forcada and Abecia, 2006; Rutter, 2006).

The length of daylight plays a central role in regulating the reproductive cycles of sheep, particularly through melatonin secretion and its downstream effects on gonadotropin release (Forcada and Abecia, 2006). Additionally, forage availability fluctuates seasonally, influencing maternal nutrition and milk yield, which are key determinants of lamb growth (Rutter, 2006).

Seasonal variation, particularly between winter and summer, has been shown to significantly influence reproductive efficiency in sheep, with winter mating often yielding higher conception rates due to optimal photoperiod and hormonal profiles (Forcada and Abecia, 2006; Rutter, 2006).

Terminal crossbreeding, particularly within structured three-way systems, remains a cornerstone of lamb meat production. Maternal genotypes should ideally exhibit high fertility and moderate size, whereas sires should contribute to carcass quality and growth potential (Jones et al., 2004; Yaqoob et al., 2004).

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Materials and Methods

This study was conducted using F1 crossbred Romanov × Akkaraman (RA) and Romanov × Morkaraman (RM) ewes with an average age of 2.5 years, raised at the Erzurum Er-Gen Biotechnology Research Farm. Charollais (C) rams with an average age of 3 years served as terminal sires.

Artificial insemination was performed in November and February using fresh semen collected from the artificial vagina of Charollais rams. The semen was pooled and diluted with OVIPOR (Ceva Sante Animale, France) extender in a 32°C dry bath to achieve a dose of 100 million motile spermatozoa per 0.4 ml. Laparoscopic intrauterine insemination was performed 48–52 hours post-estrus onset. Estrus was detected using vasectomized rams, and only ewes with at least one recorded estrus cycle were selected.

Estrus synchronization was performed using intravaginal sponges containing 60 mg medroxyprogesterone acetate (Intervet, Netherlands) and was retained for 14 days. Following sponge removal, 400 I.U. of equine chorionic gonadotropin (Gonaser, HIPRA, Amer, Spain) was administered intramuscularly. Before insemination, the selection criteria were as follows: minimum 10 weeks postpartum interval, average body weight of 50–55 kg, no oral or foot anomalies, and body condition scores ≥3. Pregnancy diagnosis was performed on days 45 and 60 post-insemination using real-time B-mode ultrasonography (5–7.5 MHz; Draminski, Poland).

Ewes grazed on a 27,000-decare highland pasture in Kevenlik village (Pasinler, Erzurum) without supplementary feeding from June. In July, all animals underwent shearing, vaccination [including those for foot-and-mouth disease and Coglavax^® (Ceva-Phylaxia, Budapest, Hungary)], and parasite treatment. Vitamins (A, D, E) and mineral supplementation were provided from October to January.

Photographs of the animal materials used in the study are presented in Figures 1 and 2 to represent the general characteristics of the sample.

Fig. 1. a: (Morkaraman): A native fat-tailed breed known for its hardiness and meat quality. b: (Akkaraman): A common indigenous breed in Anatolia, valued for climate adaptability. c: (Romanov): A Russian breed with high prolificacy that is widely used in crossbreeding programs. d: (Charollais): A French terminal sire breed selected for rapid growth and high carcass yield.

Fig. 2. a: (Romanov × Akkaraman F1): F1 cross combining litter size of Romanov with the adaptation traits of Akkaraman. b: (RM F1): F1 cross combining the litter size of Romanov with the adaptation traits of Morkaraman. c,d: (Terminal Cross): Terminal crossbreeding (Charollais × F1).

During the last six weeks of gestation, each ewe was fed 1.5 kg of dry alfalfa hay and 500 g of finishing feed daily, along with free access to water and mineral lick stones. Clostridial vaccination and vitamin E + selenium injections (Yeldif^® Istanbul, Turkey) (Ceva-Dif, Libourne, France) were administered in the final 4 weeks.

After birth, the lambs remained with their dams and suckled freely until weaning. No creep feeding or supplementary concentrate was provided. Lambs had continuous access to natural pasture, which consisted of native highland flora, including Festuca spp., Trifolium spp., and Poa spp. The pasture quality varied seasonally, with spring forage offering moderate protein and fiber levels, while summer pastures provided higher biomass and energy density due to peak vegetative growth. These seasonal differences in forage quality likely influenced lamb growth performance during the pre-weaning period.

Lambs produced from Charollais × RA (CRA) and Charollais × RM (CRM) mating were born in April and July, respectively. A total of 30 lambs were born from 14 RA ewes in spring and 26 lambs from 16 RA ewes in summer. Similarly, 45 lambs were born from 19 RM ewes in spring and 32 lambs from 18 RM ewes in summer. Their growth traits and overall flock productivity were analyzed. Table 1 presents lamb distributions by maternal genotype and birth season.

Table 1. Number of terminal crossbred lambs according to the birth season and dam line genotype.

Statistical analysis

The study was structured as a two-factor (2 × 2) factorial design. The first factor was the maternal genotype (RA and RM), and the second factor was the birth season (spring and summer). Each combination formed a distinct experimental group, and ewe selection and insemination scheduling were randomized. To minimize environmental variation, hormonal synchronization protocols were uniformly applied across all groups. Adequate replication was achieved with 14–19 ewes per group, allowing for robust statistical comparisons.

All data were analyzed using the Minitab LLC (2012) statistical software package (Minitab LLC, 2012). Descriptive statistics were calculated for all variables. Group comparisons were performed using one-way analysis of variance, and differences among means were evaluated using Duncan’s multiple range test. Statistical significance was considered at (p < 0.05) and (p < 0.01) levels.

Ethical approval

Ethical approval was not required for this study as the data were collected before the enforcement of national regulations on animal experimentation (Official Gazette No. 28914).

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Results

Flock productivity

The reproductive performance and flock-level productivity of RA and RM F1 dam lines were assessed following laparoscopic artificial insemination with diluted fresh semen from Charollais rams. The lambing rate was 78% for insemination conducted during the breeding season (November) and 70% for inseminations performed outside the breeding season (February). The seasonal effect on lambing rate was not significant.

This study defines reproductive performance as the number of lambs born and weaned per ewe, and calculates total productivity based on the total weaning weight per lambed ewe. In spring lambing, five lambs were stillborn, and one lamb was lost due to dystocia. Two stillbirths were recorded during summer lambing. Mastitis was observed in three ewes, one in spring and two in summer, resulting in failure to wean at least one lamb. Lambs stillborn or lost to dystocia were included in the lambing totals but were excluded from the survival rate calculations.

The incidences of stillbirth and mastitis were evaluated statistically across genotypes (RA vs. RM) and birth seasons (spring vs. summer). No significant differences in stillbirth rates were observed between genotypes or seasons (p > 0.05). Similarly, mastitis cases did not vary significantly across the groups (p > 0.05). Statistical analysis showed that neither genotype nor birth season had a measurable impact on the occurrence of stillbirth or mastitis in this study population.

No statistically significant differences were found between the RA and RM genotypes in terms of the number of lambs born, number of lambs weaned, lamb survival rates, or total weaning weight per ewe (Table 2). RA ewes exhibited a 4.9% advantage in weaning rate, whereas RM ewes showed approximately 13% higher lambing rates at birth (p > 0.05). The lamb survival rates were ~12% higher in the RA crosses. The observed 3.11 kg difference in weaning weight per ewe between dam lines was not significant (Table 2). Ewes lambing in spring had a significantly higher number of lambs born per ewe compared with those lambing in summer (p < 0.01), whereas the survival rate, weaning rate, and total productivity did not differ significantly between seasons.

Table 2. Number of lambs at birth and weaning, lamb survival rates, and total productivity according to dam line genotypes and birth seasons.

The dam line genotype and birth season had varying effects on lamb number, weaning number, survival rate, and total productivity. The effect of genotype on lamb number was not statistically significant (F ≈ 2.1, df ≈ 1, 58, p > 0.05). RA ewes produced an average of 1.83 ± 0.13 lambs, whereas RM ewes produced 2.07 ± 0.12 lambs. No significant differences in the number of weaning or survival rates were observed (p > 0.05). However, the birth season significantly affected lamb numbers (F ≈ 7.5, df ≈ 1, 58, p < 0.01); spring-born ewes (2.26 ± 0.13) had higher lamb numbers than summer-born ewes (1.65 ± 0.13). Genotype × season interactions were not statistically significant for any trait (p > 0.05), indicating that genotype effects were consistent across seasons.

The growth performance and overall flock productivity of triple-crossed lambs (CRA and CRM) were recorded and evaluated.

Growth characteristics

Live weights and average daily weight gains at various ages

This study evaluated lamb development from birth to weaning and assessed live weights (LW) at 15, 30, and 150 days of age in triple-crossbred CRA and CRM lambs born in spring (April) and summer (July). LW of lambs were recorded on days 15, 30, 75 (weaning), and 150. All measurements were performed using a high-precision digital livestock scale with 100-g sensitivity. Table 3 (April-born lambs) and Table 4 (July-born lambs) present the mean values, SEs, and results of the Duncan multiple comparison test.

Table 3. Mean LW, SEs, and multiple comparison test results of lambs at different developmental stages born in April.

Maternal genotype and lamb sex had no statistically significant effect on birth weight, 15th day weight, 30th day weight, weaning weight, or 150th day weight (p > 0.05). However, birth type had a significant impact on growth traits up to weaning (p < 0.05).

No significant differences were found between CRA and CRM lambs in terms of LW from birth to weaning and up to day 150 (p > 0.05). For example, CRA lambs born in April had a birth weight of 3.78 ± 0.18 kg, whereas CRM lambs had 3.91 ± 0.15 kg (Table 3). Similarly, genotype-related differences were not significant among July-born lambs. The effect of sex was also non-significant across all growth stages (p > 0.05). However, birth type (single, twin, triplet) had a significant impact on several growth parameters (p < 0.05); single-born lambs generally exhibited higher LW and ADG (Table 4).

Table 4. Mean LW, SEs, and multiple comparison test results of lambs at different developmental stages born in July.

Among lambs born in spring, birth type significantly influenced birth weight, whereas summer-born lambs did not. In CRA and CRM lambs born in April (Table 3), triplet lambs had significantly lower LW and average daily gains (ADG) on day 15 compared with singles and twins (p < 0.05). By day 30, triplet lambs had caught up in weight with singles, whereas twins showed the lowest LW and ADG values.

Weaning weights of triplets and twins were similar, whereas those of singles were the lowest. Regarding ADG until weaning, singles exhibited the highest growth rate (251 g/day) (Table 3), followed by triplets (233 g/day) and twins (208 g/day).

For summer-born lambs, significant differences were observed in 15th day weights among singles, twins, and triplets (p < 0.05). Singles gained 100 g more than twins, and twins gained 60 g more than triplets. By day 30, the gap between twins and singles had narrowed. A significant reduction in weaning weight was noted with increasing litter size (p < 0.05). Unlike spring-born lambs, high ADG values observed until weaning were not maintained in summer-born lambs (Table 4).

Extended weight assessment and terminal productivity

The 15th and 30th day weights of CRA and CRM lambs born in summer matched or surpassed those reported for İvesi purebred and Turkish Merino × İvesi F1 crossbred lambs (Çelik, 2006). Summer-born lambs exceeded the 30th day weight of İvesi lambs by day 15 and had a 1.64 kg advantage over Turkish Merino × İvesi F1 crosses by day 30 (Fig. 3).

Fig. 3. Comparative schematic of the 15th and 30th day LW of CRA and CRM lambs born in summer in relation to İvesi purebred and Turkish Merino × İvesi F1 crossbred lambs (Çelik, 2006).

Examination of Tables 3 and 4 revealed no statistically significant effects of birth season, lamb sex, or birth type on the 150th day LW and average weight gain of CRA and CRM lambs (p > 0.05). The limited influence of environmental factors on long-term growth performance was a consistent outcome in both seasonal cohorts.

Compared with the Charollais-sired crossbred lambs in this study, those reported by Köyceğiz et al. achieved 5 kg higher weights on day 150, though with lower lambing and weaning rates. In contrast, the Sakiz × Kivircik F1 maternal line used in this study resulted in higher numbers of birth and weaning lambs.

By day 150, total productivity reached 46.2 kg for lambs sired by German Black-Headed rams and 52.8 kg for lambs sired by Charollais, indicating a 14% productivity gain.

The lower performance of G1 lambs compared to F1 lambs supports the importance of maintaining heterotic effects in successive crossbreeding strategies. Inter-se mating and backcross designs should be carefully managed to maximize performance and avoid loss of hybrid vigor. In addition, sire prepotency should be considered when designing efficient terminal crosses.

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Discussion

This study evaluated the flock productivity and growth characteristics of Charollais-sired terminal lambs born from RA and RM F1 maternal lines. Compared with purebred Morkaraman and Akkaraman sheep, triple-crossbred lambs exhibited a 1.4- to 1.8-fold increase in total productivity, demonstrating the effectiveness of terminal crossbreeding strategies under Eastern Anatolian conditions. These values are consistent with the productivity ranges reported for established meat-oriented Turkish breeds such as Ramlıç, Menemen, Hasmer, and Hasak (Kaymakcı and Taşkın, 2008).

Out-of-season lambing (spring–summer) achieved through estrus synchronization and artificial insemination showed minimal reproductive efficiency reduction. Although the number of lambs weaned dropped by approximately 17% during off-season mating, the total productivity per ewe remained stable. These results suggest that the reproductive performance of Romanov-based maternal lines is well maintained across breeding seasons. Similar findings were observed by Kutluca et al. (2011) in RM and RA crosses, where productivity remained high despite the absence of hormonal treatments and natural mating.

Although stillbirth and mastitis rates did not significantly differ between genotypes or seasons, these outcomes remain critical indicators of flock health and management efficiency. Factors such as maternal nutrition, environmental stress, and peripartum care practices may influence their occurrence. The lack of statistically significant differences in this study could be attributed to the uniform management conditions or sample size limitations. Future studies should explore these variables in more detail to better understand their impact on reproductive health.

Early-maturing genotypes that reach slaughter weight in shorter timeframes improve meat quality and reduce operational costs, making them ideal for meat-oriented sheep farming systems.

Higher rates of stillbirth during spring lambing, coinciding with the breeding season, highlight the importance of nutritional management during the final stages of pregnancy. These challenges, particularly in Romanov F1 genotypes, echo findings from Aşkın (1982), Başaran and Dellal (1996) and Hancı (2006), who reported that lambing success is linked to hormonal protocols and ewe condition.

In this study, the ADG of terminal crossbred lambs reached approximately 230 g/day, which may indicate a performance advantage over Akkaraman lambs, although further studies are needed to confirm long-term consistency (Esen and Yıldız, 2000). This performance remained consistent across different birth types (single, twin, and triplet), indicating strong postnatal growth potential. Lambs born in summer outperformed spring-born lambs in early growth stages, possibly due to access to fresh forage and potential improvements in maternal lactation. Variations in grazing conditions and nutritional availability between spring and summer may also influence these seasonal differences in growth performance. Similar seasonal effects were reported by Çelik (2006) in İvesi and Turkish Merino × İvesi F1 lambs.

Although genotype × season interactions were not statistically significant, their inclusion in the model confirmed the stability of genotype performance across seasonal conditions. The significant effect of birth season on lamb number may be attributed to differences in pasture quality and nutritional availability. Spring-born ewes likely benefited from richer forage conditions, which may have contributed to higher productivity. These findings highlight the potential influence of environmental factors on reproductive and growth traits.

The preservation of heterotic advantage in terminal lambs from RM F1 ewes is consistent with previous studies (Köycegiz et al., 2009), which demonstrated superior growth traits in crossbred genotypes. Comparisons with other crossbreeding schemes such as Sakiz × Akkaraman (Akçapınar et al., 2000), Kivircik × Akkaraman (Esen and Yıldız, 2000), and Corridale × Morkaraman (Arslan et al., 2003) suggest that the LW gains observed in RM terminal lambs are promising and may be comparable to or exceed those reported in previous studies. However, as highlighted by Mundan and Özbeyaz (2004), the reduced growth performance in G1 crosses underscores the need for long-term and economic evaluations to confirm the sustainability of heterotic advantages. However, lower growth performances reported in G1 crosses by Mundan and Özbeyaz (2004) suggest a reduction in heterotic effects in successive generations, underlining the importance of carefully selecting breed combinations for continued improvement.

The 5-month LW recorded in this study were similar to those reported for Morkaraman lambs (Özbey and Akcan, 2001; Arslan et al., 2003) and were notably higher than the Akkaraman benchmarks reported by Esen and Yıldız (2000). Values were in alignment with those found by Akçapınar et al. (2000) and Yakan et al. (2012).

Crossbred lambs of Sakiz × Akkaraman, Kivircik × Akkaraman, and Corridale × Morkaraman F1 genotypes showed comparable performance to the CRA and CRM lambs in this study, with the exception of RM F1 lambs, which had superior outcomes (Köycegiz et al., 2009).

At 150 days, CRA and CRM lambs reached LW higher than those previously reported for F1 and G1 genotypes. Terminal lambs achieved similar slaughter weights approximately 1 month earlier than stabilized genotypes like Bafra (Ünal et al., 2004), indicating their suitability for early finishing systems. Early-maturing genotypes, such as those in this study, offer economic advantages by reducing feed costs and better aligning with fluctuating market prices.

Development of new sheep types for the Black Sea Region, such as Bafra sheep (Sakiz × Karayaka G1), has targeted improved adaptation and meat traits. The 180th day weights of Karayaka, F1, G1, and stabilized Bafra lambs ranged from 23.30 to 32.65 kg (Arıtürk et al., 1987; Aydoğan and Gül, 1992; Ünal et al., 2004). In this study, the CRA and CRM lambs achieved comparable weights by day 150.

Akkaraman and various F1 and G1 crosses reached 180th day weights between 21.65 kg and 36.02 kg (Akçapınar et al., 2000; Mundan and Özbeyaz, 2004), with terminal lambs in this study reaching similar or greater weights by day 150. CRA and CRM lambs exceeded the weights of older G1 lambs by approximately 10 kg.

Shrestha et al. (2008) investigated the reproductive traits of reciprocal crossbred ewes between Romanov and Finn breeds and the meat production of Suffolk-sired lambs. The number of lambs born and weaned per ewe for RF and FR crosses was 3.2 and 2.5, respectively, higher than the present study’s findings. This difference is likely because both parental breeds used in that study are among the most prolific sheep breeds globally. Additionally, while RF and FR ewes reached a total lamb weight of 22 kg per ewe within 30 days postpartum, it took approximately three more weeks to reach the same weight in the present study.

The lambing rate at birth for the RA F1 maternal genotype was 2.14, which is higher than the rates reported in previous studies on Akkaraman ewes treated with various doses of eCG (Aşkın, 1982; Başaran and Dellal, 1996; Daşkın, 2001; Hancı, 2006). Compared with lambing rates reported for Morkaraman sheep (Emsen, 2002; Kutluca, 2005; Atsan et al., 2007), the lambing rate of 237% observed in RM F1 ewes was notably higher. This suggests that F1 maternal lines derived from Romanov crossbreeding play a significant role in the success, efficiency, and cost-effectiveness of terminal crossbreeding programs. Atsan et al. (2009) evaluated the economic impact of natural and laparoscopic artificial insemination between local fat-tailed Morkaraman and Tuj breeds with Romanov rams, reporting that Romanov F1 females demonstrated a sevenfold superiority in total productivity compared to local breeds. In the present study, the total productivity values of RM genotype ewes over the first 18 months were found to be comparable to those of Romanov F1 females.

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Conclusion

Terminal crossbreeding using Romanov × Akkaraman and RM F1 maternal lines with Charollais sires showed promising short-term improvements in lamb productivity, growth performance, and seasonal adaptability. The integration of reproductive synchronization and out-of-season lambing appeared to enhance flock efficiency during the study period. Although these findings suggest the potential benefits of hybrid vigor and early maturing sire lines under semi-intensive systems in Eastern Anatolia, long-term impacts and economic feasibility remain to be evaluated. Future research should focus on multi-season trials and cost-effectiveness analyses to validate and expand upon these results.

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Acknowledgments

This study was derived from a doctoral thesis.

Conflict of interest

The authors declare that there are no conflicts of interest.

Funding

The Scientific and Technological Research Council of Türkiye (TÜBİTAK) supported this study under the 1507 SME R&D Start-up Support Program (Project number: 7100360).

Authors’ contributions

Fatih Ahmet ASLAN: Conceived and designed the study, performed fieldwork and experimental procedures, analyzed data, and drafted the manuscript. Ebru Emsen: Contributed to the development of the methodology, supervised hormonal synchronization protocols and artificial insemination procedures, and critically revised the manuscript for important intellectual content. All authors have read and approved the final version of the manuscript prior to submission.

Data availability

The data supporting the findings of this study were generated as part of a PHD thesis and are not openly accessible due to institutional and privacy considerations. However, they are available upon reasonable request from the corresponding author.

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References

Akçapınar, H., Özbeyaz, C., Ünal, N. and Avcı, M. 2000. Possibilities of using Akkaraman, Sakiz, and Kivircik sheep breeds in developing maternal and paternal lines for lamb meat production. I. Fertility in Akkaraman sheep; survival and growth of lambs in Akkaraman, Sakiz × Akkaraman F1 and Kivircik × Akkaraman F1 crosses. Turk. J. Vet. Anim. Sci. 24, 71–79.

Arıtürk, E., Akçapınar, H., Aydoğan, M. and Bayrak, S. 1987. Improvement of the Karayaka sheep breed through crossbreeding. Doga. Turk. J. Vet. Anim. Sci. 11(1), 1–6.

Arslan, M., Yılmaz, Ö. and Ateş, C.T. 2003. Growth in Morkaraman and Corriedale × Morkaraman F1 lambs. YYU. Vet. Fac. J. 14(1), 46–49.

Aşkın, Y. 1982. Possibilities of controlling estrus synchronization and fertility using exogenous hormones in Akkaraman and Anatolian Merino sheep, associate professorship thesis. Ankara: University, Faculty of Agriculture.

Atsan, T., Emsen, E., Yaprak, M., Dagdemir, V. and Gimenez Diaz, C.A. 2007. An economic assessment of differently managed sheep flocks in eastern Turkey. Ital. J. Anim. Sci. 6, 407–414; doi:10.4081/ijas.2007.407

Atsan, T., Emsen, E., Yaprak, M., Gimenez Diaz, C.A., Koycegiz, F. and Kutluca, M. 2009. Comparative economic returns from artificial insemination and natural service in purebred fat-tailed and crossbred Romanov flocks. J. Anim. Vet. Adv. 8(1), 80–84.

Aydoğan, M. and Gül, I. 1992. Possibilities of developing a new sheep type through crossbreeding between Sakiz and Karayaka breeds. Doga-Tr. Turk. J. Vet. Anim. Sci. 16, 393–402.

Başaran, D. and Dellal, G. 1996. Possibilities of controlling estrus and improving fertility using progestagen and PMSG in Akkaraman sheep. Turk. J. Vet. Anim. Sci. 21(3).

Bohrer, B.M., Dorleku, J.B., Campbell, C.P., Duarte, M.S. and Mandell, I.B. 2023. A comparison of carcass characteristics, carcass cutting yields, and meat quality of barrows and gilts. Transl. Anim. Sci. 7(1), txad079; doi:10.1093/tas/txad079

Çelik, R. 2006. Studies on some performance traits of Awassi and Turkish Merino × Awassi (F1) lambs, Doctoral Thesis, Istanbul, Türkiye: Institute of Health Sciences.

Daşkın, A. 2001. Effect of PMSG injections on fertility in estrus-synchronized Akkaraman ewes. Ankara Univ. Vet. Fac. J. 48, 165–167; doi:10.1501/Vetfak_0000001602

Emsen, E. 2002. Effects of vitamin E + Se and exogenous hormone use on fertility in Awassi and Morkaraman ewes, and on growth and survival traits in lambs, Doctoral Thesis. Erzurum, Türkiye: Institute of Science.

Esen, F. and Yıldız, N. 2000. Growth, survival, and body measurements of Akkaraman and Sakiz × Akkaraman (F1) crossbred lambs. Turk. J. Vet. Anim. Sci. 24(3), 223–231.

Forcada, F. and Abecia, J.A. 2006. The effect of nutrition on the seasonality of reproduction in ewes. Reprod. Nutr. Dev. 46(4), 355–365; doi:10.1051/rnd:2006017

Güngör., Özbeyaz, C., Ünal, N., Çapar Akyüz, H., Arslan, R. and Akçapınar, H. 2022. Evaluation of genotype and nongenetic effects on some production traits: comparison of Akkaraman and Bafra × Akkaraman B1 sheep genotypes. Turk. J. Vet. Anim. Sci. 46, 755–763; doi:10.55730/1300-0128.4250

Hancı, H. 2006. Effect of oxytocin use on fertility in insemination with diluted semen in estrus-synchronized Akkaraman ewes, Master’s Thesis, Ankara, Türkiye: Institute of Science.

Jones, H.E., Amer, P.R., Lewis, R.M. and Emmans, G.C. 2004. Economic values for changes in carcass lean and fat weights at a fixed age for terminal sire breeds of sheep in the UK. Livest. Prod. Sci. 89(1), 1–17; doi:10.1016/j.livprodsci.2004.02.002

Kaymakcı, M. and Taşkın, T. 2008. Crossbreeding studies in sheep breeding in Türkiye. Anim. Prod. 49(2).

Kaymakcı, M., Sönmez, R., Kızılay, E., Taşkın, T. and Ergül, N. 1999. Studies on developing sire lines for market lamb production (Phase I project). Turk. J. Vet. Anim. Sci. 23, 255–259.

Köycegiz, F., Emsen, E., Gimenez Diaz, C.A. and Kutluca, M. 2009. Effects of lambing season, lamb breed and ewe parity on production traits of fat-tailed sheep and their lambs. J. Anim. Vet. Adv. 8(1), 195–198.

Koyuncu, M., Kaymakcı, M., Taşkın, T. and Ak, I. 2010. Organic sheep and goat farming. In Proceedings of the 1st National Organic Animal Husbandry Congress, Gumushane, pp 84–93.

Kutluca, M. 2005. Effects of different estrus synchronization methods on fertility in Awassi and Morkaraman ewes, and on growth and survival traits in lambs, Master’s Thesis, Erzurum, Türkiye: Institute of Science.

Kutluca, M., Emsen, E., Koycegiz, F., Gimenez-Diaz, C.A. and Aslan, F.A. 2011. Reproductive performance and milk traits of F1 Romanov ewes. Small Ruminant Res. 100, 34–36; doi:10.1016/j.smallrumres.2011.05.016

Larson, G. and Fuller, D.Q. 2014. The evolution of animal domestication. Annu. Rev. Ecol. Evol. Syst. 45(1), 115–136; doi:10.1146/annurev-ecolsys-110512-135813

Ministry of Agriculture and Forestry. 2024. National Sheep and Goat Breeding Program [Internet]. Ankara: Ministry of Agriculture and Forestry. Available via https://www.tarimorman.gov.tr (Accessed 24 June 2025).

Minitab LLC. 2012. Minitab Statistical Software (Version 16.1.1) [Computer software]. Available via https://www.minitab.com

Mundan, D. and Özbeyaz, C. 2004. Milk yield traits in Akkaraman, Kivircik × Akkaraman G1, and Sakiz × Akkaraman G1 sheep and growth and survival in their lambs. Lalahan Hayv. Arast. Enst. Derg. 44(4), 23–35.

Norman, T.C., Dehaan, E.R., Francis, F.L., Rusche, W.C. and Smith, Z.K. 2024. Effect of lighter and heavier initial weight on growth performance and carcass traits of single-source beef steers. Animals 14(4), 567; doi:10.3390/ani14040567

Özbey, O. and Akcan, A. 2001. Performance of Morkaraman, Akkaraman, and Awassi sheep under semi-intensive conditions: II. Growth and survival traits in lambs. Firat. Univ. Vet. J. 17(1), 57–66.

Özcan, M., Altinel, A., Yılmaz, A. and Güneş, H. 2001. Studies on the possibility of improving lamb production by two-way and three-way crossbreeding with German Blackheaded Mutton, Kivircik and Chios sheep breeds. I. Fertility, lamb survival and growth of lambs. Turk. J. Vet. Anim. Sci. 25(5), 8.

Rutter, S.M. 2006. Diet preference for grass and legumes in free-ranging domestic sheep and cattle: current theory and future application. Appl. Anim. Behav. Sci. 97(1), 17–35; doi:10.1016/j.applanim.2005.11.016

Shrestha, J.N.B., Boylan, W.J. and Rempel, W.E. 2008. Evaluation of sheep genetic resources in North America: ewe productivity of purebred, crossbred, and synthetic populations. Can. J. Anim. Sci. 88(3), 399–408; doi:10.4141/CJAS07049

Turkish Statistical Institute (TurkStat). (2024). Livestock production statistics, 2023 [Internet]. Ankara: TurkStat. Available via https://www.tuik.gov.tr (Accessed 24 June 2025).

Ünal, N., Akçapınar, H., Atasoy, F., Koçak, S. and Aytaç, M. 2004. Live weight and fleece characteristics in Akkaraman, Sakiz × Akkaraman and Kivircik × Akkaraman crosses (F1, G1) and Karayaka Bafra sheep. Lalahan Hayv. Arast. Enst. Derg. 44(2), 15–22.

Ünal, N. 2002. Survival, growth, and some body measurements in Akkaraman and Sakiz × Akkaraman F1 lambs. Turk. J. Vet. Anim. Sci. 26, 109–116.

Van Eenennaam, A.L. 2025. Current and future uses of genetic improvement technologies in livestock breeding programs. Anim. Front. 15(1), 80–90; doi:10.1093/af/vfae042

Wang, H., Zhan, J., Jiang, H., Jia, H., Pan, Y., Zhong, X., Huo, J. and Zhao, S. 2024. Metagenomics-metabolomics exploration of three-way-crossbreeding effects on rumen to provide basis for crossbreeding improvement of sheep microbiome and metabolome. Animals (Basel). 14(15), 2256; doi:10.3390/ani14152256

Wang, J.T., Wang, G.S., Gong, Y.F., Qiao, X., Li, X., Wang, G.Z., Zheng, Y.Z., Lv, J.G., Li, X.L. and Liu, Z.Z. 2022. Screening of three-way crossbred combination and genetic effect analysis of the SNP in the CLPG gene in meat sheep. Arch. Anim. Breed. 65(4), 417–426; doi:10.5194/aab-65-417-2022

Yakan, A., Ünal, N. and Dalcı, M.T. 2012. Fertility, growth, and survival traits in Akkaraman, Awassi, and Kivircik sheep breeds under Ankara conditions. Lalahan Hayv. Arast. Enst. Derg. 52(1), 1–10.

Yaqoob, M., Merrell, B.G. and Sultan, J.I. 2004. Comparison of three terminal sire breeds for birth weight of lambs kept under upland grassland conditions in the northeast of England. Pak. Vet. J. 24(4), 196.

Zeder, M.A. 2008. Domestication and early agriculture in the Mediterranean Basin: origins, diffusion, and impact. Proc. Natl. Acad. Sci. USA. 105(33), 11597–11604; doi:10.1073/pnas.0801317105

Zhang, R., Zhang, L., An, X., Li, J., Niu, C., Zhang, J., Geng, Z., Xu, T., Yang, B., Xu, Z. and Yue, Y. 2024. Hybridization promotes growth performance by altering rumen microbiota and metabolites in sheep. Front. Vet. Sci. 11, 1455029; doi:10.3389/fvets.2024.1455029