Factors Affecting Estrus Response and Conception Rates Following Artificial Insemination in Dairy Farms of Northeast Algerian

1. Introduction
Reproductive efficiency in dairy herds has shown a steady decline over recent decades, mainly as a consequence of the genetic and management emphasis on milk yield [1]. In Algeria, dairy cattle provide nearly 80% of the national milk supply, yet the overall herd size has diminished in recent years. The national dairy herd is estimated at about one million head, among which imported dairy breeds—principally Holstein (H), Montbéliarde (MB), and Fleckvieh (FV)—represent approximately 30% [2].
The Sétif region, located in northeastern Algeria, is one of the country’s leading dairy production zones, with around 77,000 cows [3]. Despite this potential, reproductive inefficiency remains a limiting factor for productivity. Declining fertility indices and longer calving intervals have hindered the goal of achieving one calf per cow per year, thereby affecting farm profitability.
Reproductive management tools such as estrus synchronization and artificial insemination (AI) are widely used to enhance fertility and accelerate genetic improvement [4, 5]. However, variable results among farms highlight the influence of local conditions and management practices. This study provides new insights by directly comparing the reproductive performance of cows treated with prostaglandin F₂α (PGF₂α) alone with that of cows treated using combined hormonal protocols under field conditions in Sétif. We also investigated how breed, parity, and the interval from calving to first insemination (IC–AI1) influence estrus expression and conception rates, aiming to generate practical recommendations for improving fertility management in Algerian dairy herds.

2. Material and Methods 
2.1. Study location
This research was carried out on two intensive dairy farms situated in the Sétif region of northeastern Algeria (36°11′N, 5°24′E; 1,080 m elevation). The trial was carried out during spring (March–June), characterized by moderate temperatures (18–28 °C) and low thermal stress. A total of 105 cyclic cows and heifers were selected after confirming normal reproductive status by rectal palpation. The group included 39 primiparous (PP) and 66 multiparous (MP) animals, aged between 2 and 5 years. The herd consisted of 66 MB and 39 Prim’Holstein (PH) cows. All animals were clinically healthy, free from structural defects, and maintained a body condition score (BCS) greater than 2 on a 1–5 scale, as described by Campanile et al. (2010) [6]. Reproductive procedures were conducted between 55 and 90 days postpartum.
Throughout the experiment, all cows were managed under uniform housing, feeding, and breeding conditions. Animals presenting any postpartum disorders (retained placenta, metritis, or endometritis) were excluded from the study population. Animals were kept apart from the general herd until AI was completed.
Reproductive performance indicators were assessed as follows:
Estrus response rate (ER): defined as the total number of cows/heifers observed in estrus divided by the total number of females subjected to reproduction in each group ×100.
Conception rate: defined as the total number of cows/heifers pregnant divided by the total number of inseminated females in each group ×100.

2.2. Experimental protocols 
The cows were randomly distributed into three experimental groups of 35 animals each. One group received two injections of PGF₂α alone, while the other two groups were treated with PGF₂α in combination with either a single (GP) or double (GPG) administration of gonadotropin-releasing hormone (GnRH).

2.3. Determination of factor effects 
Three main factors were evaluated in this study: breed, parity, and the interval between calving and IC–AI1.
● The cows belonged to two genetic groups: PH and MB.
● Animals were also categorized according to parity into PP and MP groups.
● The calving-to-insemination interval was classified into two periods: Class 1 (55–69 days postpartum; n=76) and class 2 (70–90 days postpartum; n=29).
2.4. Estrus detection and pregnancy diagnosis
Estrus detection was performed through direct visual observation, as automated detection systems were unavailable on the participating farms. Despite its limitations, visual detection remains a valid approach in field conditions when performed by trained staff [7, 8]. Lack of heat-detection aids (tail chalking, pedometers, activity monitors) may have underestimated estrus expression, representing a known limitation of this study. 
AI was performed when cows exhibited visible signs of estrus. Heat detection was carried out through visual observation twice daily, each session lasting approximately 30 minutes. To eliminate operator bias, all inseminations were performed by a single experienced veterinarian from National Center for AI and Genetic Improvement (CNIAAG). The presence and consistency of cervical mucus on the day of insemination were also considered to confirm estrus. Pregnancy was diagnosed by ultrasonography 30 days after insemination and verified through rectal palpation at 45 days post-AI.
Semen used for insemination was supplied by the CNIAAG. It originated from two bulls: INDOR (MB breed) and HAELTOP (H breed). All inseminations were conducted by a CNIAAG-certified veterinarian. The potential influence of the sire was additionally evaluated with respect to conception rate and offspring sex ratio.
To ensure semen consistency, inseminations were carried out using semen from two CNIAAG-proven bulls with similar fertility indices, and the same semen batch was used across all treatments.

2.5. Statistical analysis
Data analysis was performed using SAS software (version 9.12). The main objective was to evaluate how different synchronization treatments influenced estrus response, pregnancy, and conception rates among the experimental groups. Differences in reproductive performance between groups were tested using the chi-square (χ²) test, and results were considered statistically significant at P<0.05. The normality of continuous variables was verified using the Shapiro–Wilk test. Chi-square analysis was complemented by descriptive statistics (Mean±SD), and 95% confidence intervals (CI) were calculated where appropriate.

3. Results
3.1. Evaluation of reproductive performance
This experiment assessed reproductive performance in PH and MB dairy cows, focusing on estrus response and conception rates. Table 1 summarizes the overall outcomes for these parameters.

Estrus detection was based on behavioral observation, particularly when a cow stood immobile while being mounted by another. Fecundity was evaluated using the interval from IC–AI1, while fertility was measured through the conception rate.
Out of 105 cyclic cows subjected to synchronization treatments using either prostaglandin alone or prostaglandin combined with GnRH, 57 animals (53%) exhibited visible estrus, and 40 of these (70%) conceived successfully. The prostaglandin-only protocol produced the most favorable reproductive outcomes, with an estrus response of 60% and a conception rate of 75%, compared to 50% and 65% in the combined PGF₂α + GnRH groups, respectively.

3.2. Factors influencing fecundity and fertility
The study examined several sources of variation, namely breed, parity, and the IC–AI1. The influence of these factors on reproductive performance is summarized in Table 2.

With regard to breed, MB cows showed a slightly higher ER compared to PH cows (56.06% vs 51.28%; P=0.497). Similarly, conception rates were comparable between the two breeds (70.72% vs 70%; P=0.966). These results indicate no statistically significant differences (P>0.05) in either estrus response or conception performance between breeds.
For parity, out of the 57 cows that displayed estrus, 16 were PP (16/39; 41.02%) and 41 were MP (41/66; 62.12%). This difference was significant (P<0.05), indicating that older cows expressed estrus more frequently than younger cows. Conception rate also varied slightly between these groups, with 62.5% (10/16) in PP and 73.17% (30/41) in MP cows (P=0.106), though this difference was not statistically significant.
Concerning the IC–AI1 interval, average estrus detection was similar between cows inseminated within 55–69 days and those inseminated between 70–90 days postpartum (62.53% vs 58.62%; P=0.393). However, conception rate was significantly higher in cows bred after 70 days postpartum (82.35%) compared to those inseminated earlier (65%; P<0.05). This suggests that extending the interval between calving and insemination improves conception outcomes.

4. Discussion
The ER obtained in this study was higher than that reported by Demetrio et al. [1] in H cows but lower than those observed by Colazo and Ambrose [9] and Raphalalani et al. [10], who recorded 68% and 75%, respectively. This difference may be attributed to variations in synchronization protocols, especially those using hormonal combinations beyond prostaglandins. Non-responding cows might have failed to exhibit behavioral signs of estrus due to the absence of mounting partners or silent heat episodes. Çevik et al. [11] noted that estrus detection rates below 50% are frequent in dairy herds, particularly in high-yielding cows, where increased milk production is associated with lower circulating estradiol and shorter estrus periods. Furthermore, as Rao et al. [12] indicated, mounting frequency tends to increase when several cows are simultaneously in heat, improving detection rates.
The conception rate reported in this study is comparable to that obtained by Mouffok et al. [13] in eastern Algeria (64%) and Belay et al. [14] in Ethiopia (60.4%). Such variation could be related to differences in hormonal treatments, environmental conditions, and management systems. Nutritional and metabolic status are known to affect fertility, especially during early lactation when energy deficits are common [5, 15]. Additionally, environmental stresses such as high temperature and prolonged drought may impair fertilization and embryo survival [16].
Regarding breed influence, MB cows showed slightly higher ERs than PH cows, although the difference was not significant. Literature indicates that fertility varies among breeds; Hs typically exhibit lower reproductive performance and longer calving-to-conception intervals compared to dual-purpose breeds [17–19]. The weaker estrus signs in PH cows could be related to shorter or silent heat, as reported by Tada et al. [18]. Bouamra et al. [19] also found a longer calving-to-first-AI interval in Hs compared to MBs. The present results were lower than those reported by Ben Salem et al. [20] in Tunisia and by Mouffok et al. [13] in Algeria. Breed differences in estrus behavior, including shorter estrus duration and fewer mounting activities, were also highlighted by Orihuela [21], who noted that cattle raised on pasture spend less time expressing estrus. Similarly, Zebu breeds are known to exhibit shorter and less intense estrus compared to exotic breeds [22].
With respect to fertility parameters, PH cows achieved a conception rate of 70%, which exceeds the 40% reported by Ben Salem et al. [20]. Since all animals were kept under identical management and nutrition, this variation is likely due to genetic differences and reproductive history, particularly postpartum recovery and milk yield. High-producing cows are more prone to thermal stress, which negatively affects fertility [23, 24]. This highlights the need to balance selection for milk production with reproductive performance. However, as fertility traits are generally low in heritability and difficult to measure, indirect indicators such as BCS or milk fatty acid profile, as proposed by Miglior et al. [15], may be useful alternatives in selection programs.
Concerning parity, our results showed that MP cows exhibited higher estrus expression than PP cows, although conception rates were not significantly different. While some studies [25] suggest that PP cows respond better to estrus synchronization, this discrepancy may reflect differences in energy balance, milk production, or management conditions. In our study, MP cows may have expressed estrus more visibly due to stronger behavioral signs, even if their overall conception advantage was minimal. Lane et al. [26] also reported that parity had no significant effect on fertility (P>0.05), supporting the idea that observed differences in estrus expression do not necessarily translate to large differences in conception outcomes.
Regarding the interval between calving and IC–AI1, most dairy farmers tend to increase this interval for high-yielding cows, believing it improves conception rates. Buckley et al. [27] reported higher first-service conception rates when this interval exceeded 75 days, while Pursley et al. [28] found lower pregnancy rates in cows inseminated between 60 and 75 days postpartum. This has been attributed to the negative energy balance and incomplete uterine recovery occurring during the early postpartum period [16]. Extending the voluntary waiting period allows the reproductive tract and the hormonal system to return to normal function before insemination. 

5. Conclusion 
This study demonstrates that fertility in dairy cows is influenced by several factors, particularly parity and the interval between calving and IC–AI1. Although breed differences were not significant, MB cows tended to show slightly better estrus response. Prolonging the IC–AI1 interval beyond 70 days postpartum improved conception success.
However, some methodological limitations should be acknowledged. Estrus detection was performed only visually, twice daily, without the use of detection aids such as tail chalking, pedometers, or activity monitors, which may have led to an underestimation of estrus expression. Another limitation of this study is the unbalanced sample sizes between IC–AI1 groups (76 vs 29), which may have affected the statistical power and precision of the comparison. Finally, nutritional status and health parameters were not systematically recorded, which could influence estrus expression and conception outcomes.
Future studies involving larger herds and considering additional health, nutritional, and genetic parameters are needed to better identify the key determinants of reproductive efficiency in Algerian dairy systems.

Acknowledgements
We would like to thank all the breeders who took part in this study. 

Compliance with ethical guidelines
Experimental procedures were approved by the Institutional Committee for the Protection of Animals of the National Administration of Higher Education and Scientific Research of Algeria (98-11, Act of 22 August 1998).

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
Conceptualization and study design: Ahmed Boucif and Abdelmadjid Noui; Experiment: Ahmed Boucif and Abdelmadjid Noui; Data analysis and interpretation: Nassim Ouchene and Nadjet Amina Khelifi Touhami; Writing the original draft: Mustapha Nabi, Omar Salhi, and Nadjet Amina Khelifi Touhami; Review and editing: Ahmed Boucif, Abdelmadjid Noui, Nassim Ouchene, and Nadjet Amina Khelifi Touhami.

Conflict of interest
The authors declared no conflict of interest.

Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.

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