Use of Progesterone as a Strategy to Improve Reproductive Efficiency in Cattle

Abstract

Progesterone (P4) is a key hormone in the reproductive physiology of cattle, playing a crucial role in regulating the estrous cycle and establishing and maintaining the pregnancy. In the context of reproductive efficiency, the use of P4 has been a strategy increasingly used on rural properties to anticipate puberty, increase pregnancy rates and reduce gestational loss. A common application is the administration of P4, often in the form of intravaginal devices or, more recently, with long-acting injectable progesterone. These methods help synchronize ovulation, allowing more precise management of reproductive programs, facilitating the use of artificial insemination, and contributing to genetic improvement. The synchronization of ovulation in beef and dairy cattle allows insemination at a pre-determined time without the need for estrus detection. These treatments increase the number of inseminated animals and, consequently, the number of pregnant animals. Overall, the strategic use of P4 in livestock management serves as a valuable tool for increasing reproductive efficiency, facilitating better control of reproductive cycles, and contributing to increased pregnancy rates and better overall reproductive performance in cattle herds.

1. Introduction

In cattle, one of the factors causing infertility is related to the inadequate functioning of the corpus luteum (CL), which is characterized by a low peripheral concentration of progesterone. A deficiency in the secretion of this steroid hormone by the CL can contribute to the occurrence of embryonic and fetal losses, negatively impacting reproductive efficiency.

Progesterone is related to the maintenance of pregnancy and has a positive effect on the possibility of embryonic survival. In this context, strategies to increase the plasma concentration of progesterone would benefit embryonic development, improve pregnancy rates and reduce gestational loss.

As an attempt to improve the productive and reproductive indices of dairy and beef cattle, several studies have been carried out based on hormonal protocols for inducing puberty, synchronizing estrus and ovulation, promoting an increase in pregnancy rate and reducing gestational loss, with progesterone and progestins present among these studied hormones [1].

Common strategies implemented in cattle farming include (i) applications of human chorionic gonadotropin (hCG) or gonadotropin-releasing hormone (GnRH) to provide final support for follicular development and formation of an accessory corpus luteum [2]; (ii) exogenous P4 supplementation via slow-release intravaginal devices, orally, subcutaneously or even the use of long-acting injectable progesterone. All of these strategies aim to increase the concentrations of circulating P4 directly or indirectly, contributing beneficially to the elongation of the conceptus and the establishment of pregnancy in cattle, as already demonstrated in studies [3, 4].

2. Importance of progesterone in cattle

Substances capable of maintaining pregnancy and promoting the modification of the proliferative endometrium into a secretory one are classified as gestagens [5]. Among these substances, progesterone is of great relevance. Progesterone is a steroid hormone derived from cholesterol [6, 7], synthesized in the corpus luteum by small luteal cells and mainly by large luteal cells [8].

According to Binelli [9], P4 is related to the process of ovulation and the maintenance of pregnancy. It modulates follicular growth and exerts several functions in the growth of the endometrial and tubuloalveolar glands of the mammary gland. P4 acts in the regulation of gonadotropin secretion, in blocking the expression of estrus and ovulation by hypothalamic action; it also has an influence on the secretory activity of the oviduct and in the endometrial glands for the development of the zygote before its implantation and acts in the inhibition of contraction uterus and the maintenance of pregnancy [9, 10, 11, 12, 13].

Progesterone receptors are expressed during the luteal phase and are directly regulated by the concentration of P4 [14]. According to Wiltbank et al. [7], the concentration of P4 is regulated by the development of the CL after the pulsatile wave of luteinizing hormone (LH), more precisely by the number of granulosa cells that undergo the luteinization process, becoming large luteal cells, which begin to produce progesterone.

In cattle, plasma progesterone concentrations exhibit variation throughout the estrous cycle, with concentrations below 1 ng/ml during estrus and on the 10th day of the cycle, these concentrations vary between 2 and 3 ng/ml for zebu cows [15] and 16 ng/ml in taurine cows, such as the Holstein breed [16].

According to Bazer et al. [17], it is believed that P4 induces changes in gene expression and secretion and trophoblast formation, probably affecting the development of the conceptus. An increase in P4 concentration during metestrus and at the beginning of diestrus was related to the establishment of pregnancy after embryo transfer [18]. Other authors suggest that the concentration of P4 has an indirect effect on embryonic survival and development through the positive modulation of interferon-τ (IFN-τ) production, related to the recognition of pregnancy and inhibition of prostaglandin secretion and consequent luteolysis [4, 10].

Thus, females with reduced P4 concentrations at the beginning of diestrus could have an impaired pregnancy rate due to interference with fetal development and maternal recognition of pregnancy, with P4 being implicated in the process by stimulating the expression of some genes that favor embryo development, and the production of IFN-τ at the most appropriate time [9].

Although there is evidence that increasing P4 concentration has a positive effect on embryo development and fertility results, the results of studies that aimed to increase plasma concentrations of P4 are still inconclusive and conflicting [19].

Numerous anti-luteolytic strategies have been studied to enhance embryonic quality and reproductive efficiency in cattle. Among the strategies used are the formation of an accessory corpus luteum, through the application of hormones such as hCG or GnRH or even exogenous P4 supplementation via slow-release devices, orally, subcutaneously, or even the use of long-acting injectable progesterone [20, 21, 22].

3. Use of progesterone in inducing puberty in heifers

In the context of reproductive efficiency, age at first calving is directly related to the female’s reproductive lifespan. By starting the heifer to reproduce earlier, the young female will have a greater production of calves throughout her productive life [23]. Therefore, the sexual precocity of females is a characteristic of great economic impact and has significant importance in reducing the generation interval, as the sooner the females can reproduce and become pregnant, the shorter the generation interval will be and the greater the genetic gain [24].

Aiming to improve productivity and reproductive efficiency, protocols with P4 supplementation were developed before timed artificial insemination (TAI) protocols to promote earlier puberty in heifers. The justification for this association is to increase the number of pubescent heifers at the beginning of the ovulation synchronization protocol and, consequently, maximize conception rates in TAI [25]. These protocols have used intravaginal devices [26], melengestrol acetate – MGA [27], and long-acting injectable P4 [25] as sources of progestin.

The anticipation of puberty and increased fertility of a herd directly reflect on profitability. Females younger than their first birth spend less time in the herd, leading to an increase in the number of calves born and, consequently, a greater economic return to the producer. However, achieving this goal is especially challenging in Bos indicus cattle because puberty generally occurs at older ages than in Bos taurus, ranging from 16 to 40 months. Possible causes of delay in reaching puberty are associated with genetic and environmental factors, including nutrition, disease, temperature, humidity and time of birth.

Breeding systems with heifers’ first calving age at 24 months have higher productivity compared to those with first calving at 36–48 months of age. In induction protocols, progesterone in association with estrogen allows the induction of puberty in heifers, as P4 artificially simulates the functional state of the CL, allowing follicular growth, which results in greater estrogen production by the ovarian follicles and LH peak. Treatments with only progestins are capable of inducing puberty in heifers, although the result is influenced by the age, weight, body and follicular development of the heifers before treatment, highlighting that the exclusive use of P4 would be capable of inducing puberty only in those in which the negative estrogen feedback would have already started to decline [28].

The use of P4 as a pre-synchronization strategy is based on the fact that this hormone leads to a reduction in the number of estradiol receptors in the hypothalamus, interfering with the negative feedback caused by this hormone in GnRH secretion [29]. Furthermore, the use of P4 can increase receptors and their sensitivity to estrogen in the regions most sensitive (mediobasal hypothalamus) to the effect of estradiol on LH secretion [30].

Intravaginal progesterone devices that have already been used at least once have lower amounts of P4, and this results in a more efficient response in induction protocols, as they induce the formation of larger follicles, a higher estrus detection and conception rates, when compared to females treated with new devices [31]. High concentrations of progesterone are not beneficial for pre-pubertal heifers, as they can suppress LH pulsatility, thus impairing follicular development and ovulation, consequently affecting the results of puberty induction [32].

Anderson et al. [33] reported a positive effect of P4 (norgestomet) for 10 days on the induction of puberty, frequency of LH pulses and uterine weight of pre-pubertal heifers slaughtered 1 day before device removal. The authors observed anticipation of puberty (P4: 22 ± 9 d vs. control: 63 ± 12.5 d), increased uterine weight (P4: 222.3 ± 30 g vs. control: 72.7 ± 10.9 g), and increased number of LH pulses in heifers treated with P4. These authors concluded that treatment with progestins is effective in anticipating puberty and sexual maturity in cattle.

It has been demonstrated that progesterone is an efficient alternative for inducing puberty in cattle, aiming to facilitate management, reduce the generation interval and accelerate genetic gain. Vrisman et al. [34] monitored the luteal dynamics of Nellore heifers that were subjected or not to puberty induction with an intravaginal P4 device for 10 days, followed by the application of GnRH 48 hours after removing the device. In conclusion, the authors showed the importance of exposing pre-pubertal heifers to progesterone, as indicated by the higher percentage of CLs with normal function in the first estrous cycle compared to animals in the control group.

Satisfactory results of puberty induction and pregnancy were also reported by Lima et al. [25] by supplementing pre-pubertal Nellore heifers with long-acting injectable progesterone and, 10 days later, applying estradiol benzoate and prostaglandin. Twelve days after the end of the protocol, the animals were synchronized to observe heat and perform artificial insemination. The pregnancy rates reported by the authors were 46% for the group with puberty induction by P4 versus 38.3% for the control group.

Regarding the time between puberty induction and the beginning of the synchronization protocol to perform TAI, some studies indicate that an interval of more than 30 days between the beginning of induction and insemination provided a higher reproductive tract score and a higher pregnancy rate after TAI, compared to animals subjected to TAI a maximum of 30 days after induction [35].

It is important to highlight that in treatments to anticipate puberty, there are individual variations in the response to the administration of progesterone, and the effectiveness of P4 in anticipating puberty can be influenced by factors such as genetics, nutritional and environmental conditions.

In summary, the literature suggests that administering progesterone can effectively accelerate puberty in cattle, offering advantages in terms of reproductive and economic efficiency. Nonetheless, it is crucial to adopt an individualized approach and comprehend the factors that might impact the response to progesterone therapy.

4. Strategies for increasing progesterone after insemination

4.1 Exogenous progesterone supplementation

The current understanding of the role of progesterone during the early stage of pregnancy and in embryonic development has led to a series of studies on P4 supplementation after insemination, with a direct relationship between the ability to secrete P4 by the corpus luteum and embryonic growth, and the establishment of pregnancy [36]. This way, high concentrations of P4 during the initial phase of diestrus in cattle are fundamental, as they help with endometrial secretions, favoring embryonic development and the production of interferon-τ, related to the recognition of pregnancy and inhibition of prostaglandin secretion and luteolysis [10, 17, 36, 37].

The ability to produce interferon-τ in sufficient quantities depends on uterine stimuli, with P4 being involved in the process by stimulating the expression of some genes that favor embryonic development [9]. Therefore, females with low concentrations of P4 at the beginning of diestrus could have lower pregnancy rates due to interference in embryonic development and pregnancy recognition.

Exogenous P4 supplementation is an alternative to increase plasma progesterone concentrations. This supplementation can be carried out through the use of an intravaginal P4 device, administration of daily injectable doses of P4, administration of long-acting injectable P4, and supply of progestins in the diet, such as the use of melengestrol acetate [12, 22, 38, 39].

In a meta-analytic study, Wiltbank et al. [7] observed that P4 supplementation during diestrus, between days 3 and 7 of the estrous cycle, significantly increased the size of the conceptus on days 13 and 16 [4, 10]. Ababneh et al. [40] evaluated the effect of P4 supplementation (vaginal device) at different times of the estrous cycle of Holstein cows and observed a better conception rate between days 2 and 7 compared to cows treated between days 7 and 16. In another study, a better conception rate was observed with P4 supplementation (CIDR®) between days 5 and 19 compared to non-supplemented cows when evaluating the effects of post-insemination P4 administration in Holstein cows (control = 25%, CIDR = 56%) [41].

In a meta-analysis study carried out by Yan et al. [12] focusing on post-insemination progesterone supplementation in cattle, the authors observed that the strategy proved to be efficient when supplementation was carried out between days 3 and 7 after insemination, harmful when animals were supplemented before day 3 (for induce early luteolysis) and indifferent when performed after 7 days. These same authors also pointed out that supplementation is only efficient in herds in which the animals have compromised fertility (i.e., conception rate < 45%), resulting from ovulation deficiency or even insufficient concentrations of progesterone to sustain pregnancy in the initial phase.

The optimal timing for progesterone (P4) supplementation remains a subject of inquiry, as certain studies have reported neutral or even adverse outcomes. Parr et al. [42], when supplementing dairy cows with a P4 device between days 4 and 9 post-insemination, they observed a lower conception rate for treated animals. Possible explanations for this result involve a failure in CL development or even early luteolysis related to the previous increase in P4 exogenously. To prove these explanations, these same authors, in another study [43], showed that heifers with failed CL development, when supplemented with exogenous P4 from D4 to D10 (D0 = day of insemination), did not reverse these effects, demonstrating that P4 has a negative effect on the useful life of this CL, however, when supplemented from D4 to D7, there was a recovery of CL area. These results may be directly related to LH pulsatility in this initial phase, since there is an inverse relationship between P4 concentration and LH pulse, where the primary developing CL depends on LH receptors in theca and granulosa cells, thus making it very vulnerable to hormonal variation [29].

In addition to the variation in LH pulsatility, it was demonstrated that P4 supplementation from D4 led to a decrease in the number of P4 receptors and an increase in CL oxytocin receptors on D5, but more studies are needed to investigate the effects of supplementation. of P4 on the development of CL [43].

Other forms of post-insemination P4 supplementation have already been tested, such as the use of MGA, a synthetic progestin formulated to be administered orally. Junior et al. [22] used MGA together with mineral salt, 2.28 g/day, starting 5 or 13 days after TAI, in 99 Nellore cows. The conception rate in the control group was 18% (n = 55), and in the group treated with MGA, the conception rate was 48.7% (P < 0.05). In the same study, the authors found no difference in pregnancy loss between 30 and 80 days.

Silva et al. [44] reported positive results when providing MGA to Nellore cows 13 to 18 days after TAI; however, when provided between days 5 and 10 post-TAI, the group treated with MGA showed a significant reduction in the pregnancy rate. These authors believe that this progestin in question has a different mode of action than the others, in which it does not favor the uterine environment during initial diestrus.

An alternative to increasing the concentration of P4 in the initial diestrus is the application of long-acting injectable P4 (P4LA). The aim of using this route of administration is to facilitate management, especially in beef herds, as it excludes a second management when compared to the use of intravaginal devices, which need to be removed after a few days [38]. P4LA at doses of 150 or 300 mg has been shown to increase circulating P4 concentrations for more than 3 days during the early luteal phase in beef cattle [3]. In summary, no differences were found between the use of intravaginal devices or the application of injectable P4LA for supplementation in early diestrus [12].

The use of injectable P4 has been studied for decades, as demonstrated by Johnson et al. [45], where the authors evaluated supplementation with 100 mg of P4LA on days 2, 3, 4, 5 and 9 after TAI, totaling 500 mg P4/animal, and found a higher pregnancy rate in treated animals compared to those from group control.

This strategy of supplementation with injectable P4LA has gained prominence in recent years. Pugliesi et al. [38], after several experiments evaluating the supplementation of injectable P4LA in beef cattle 4 days after TAI, demonstrated that this is an efficient strategy when there are animals with a deficient CL. For example, in animals that are in anestrus at the beginning of the TAI protocol (common in lactating beef cows raised on pasture), generating a 20% increase in the pregnancy rate. Likewise, Couto et al. [46], evaluating the supplementation of injectable P4LA on D5 in beef cattle (D0 = TAI), observed an increase in pregnancy rates and lower pregnancy loss in the treated group, highlighting the efficiency of administering P4 in early diestrus to improve herd fertility. Both studies suggest that supplementation at this stage improves the uterine environment and, consequently, the survival, elongation and implantation of the embryo, obtaining better results.

Furthermore, according to Couto et al. [47], the application of P4LA, 7 days after ovulation, was able to improve conception rates in animals with a reactive temperament, with increased cortisol levels, suggesting that supplementation is effective in animals that are subjected to some factor that could compromise basal progesterone levels, such as handling stress and low nutritional status.

According to Mann and Lamming [48], the increase in conception rates occurs only when P4 is supplemented in the first week after insemination and has no effect when exogenous P4 is supplemented in the second and third weeks after insemination.

In a study carried out with long-acting injectable P4, it was shown that a dose of 150 mg on the third day after TAI was a viable strategy to improve the conception rate; however, an anticipation of luteolysis was observed in some animals [3]. According to O’hara et al. [49], this same effect was observed in animals supplemented through an intravaginal device 3 days after TAI.

Martins et al. [50] investigated the impact of supplementing Nellore cows with long-acting injectable progesterone (P4LA) 3 days after timed artificial insemination (TAI). Their study evaluated the effect on early luteolysis and concluded that while P4 favors uterine receptivity, it can also reduce the longevity of the CL, making it difficult to establish pregnancy, since conceptus signaling cannot overcome the early luteolytic stimulus. Furthermore, early luteolysis is more related to the result of early exposure of the uterus to P4, which leads to the anticipation of the activation of the luteolytic cascade (production of PGF2alpha), than to the impairment of CL development due to the decrease in LH pulsatility. Additionally, these same authors [50] concluded that early luteolysis, due to the effect of P4 supplementation in animals that presented three follicular waves, was lower, suggesting that the number of follicular waves after AI plays a significant role in the fertility response to P4 supplementation, by regulating uterine function.

4.2 Induction of accessory corpus luteum

To counteract potential deficiencies in corpus luteum function, progesterone supplementation or the administration of luteotropic agents after ovulation is a viable approach [51]. According to Bech-Sabat et al. [52], cows normally produce a single CL after ovulation, but there are ways to induce the formation of an accessory corpus luteum to increase P4 concentrations. Administration of GnRH, GnRH agonists, or hCG at specific times after TAI can induce the formation of an accessory CL [53].

The use of these hormones and the consequent formation of accessory CL increases the plasma concentration of P4 and reduces the production of estradiol, producing a positive effect on embryonic development [54]. According to Besbaci et al. [55], studies on the subject have failed to provide a consensus on the benefits of such treatments since some report a beneficial effect of using GnRH or hCG in relation to pregnancy. In contrast, others do not show the same results [56].

Previous studies have shown that administration of GnRH, a GnRH agonist or hCG after TAI, in the presence of a dominant follicle in the first or second follicular waves, can induce the formation of accessory CL, increase P4 and reduce estrogen production [57]. According to Araújo et al. [58], ovulation of a first-wave follicle after TAI may alter follicular dynamics at the time of luteolysis, prolonging the time for luteolysis and allowing more time for embryo elongation.

Cows with an accessory corpus luteum were 0.32 times less likely to lose a pregnancy than cows with only one corpus luteum [39]. According to Lopez-Gatius et al. [59], cows that received GnRH on the day of TAI and 12 days later were 3.7 more likely to present accessory CL than cows that did not receive any dose. Beltran and Vasconcelos [53] observed that serum P4 concentrations increased from the 7th to the 12th day with GnRH injection applied on day 5 post-TAI about untreated animals.

Administration of GnRH, 5 days after TAI, in dairy cows increased P4 concentration on the 13th day after TAI; however, pregnancy rates were not different between the GnRH and control groups [60]. Ataman et al. [61] evaluated the use of GnRH (20 μg buserelin) 12 days after TAI and its effect on P4 concentration and pregnancy rate in dairy cows. Pregnant cows that received GnRH had higher P4 concentrations between days 18 and 21 compared to pregnant cows that received saline solution. Despite the difference observed in P4 concentrations between days 18 and 21, pregnancy rates between days 21 and 45 were not different.

In another study, Pinto et al. [62], evaluating induction of accessory corpus luteum and conception in embryo recipients, observed that 51% of treated animals had accessory corpora lutea while the control had 23.5% (P = 0.04). Additionally, the GnRH group demonstrated a conception rate of 38%, whereas the control group had 24% (P < 0.05).

In a meta-analytic study involving 52 articles on induction of accessory corpus luteum and the effect on pregnancy, it was observed that treatments with GnRH and hCG improve pregnancy in cows with low fertility (very low <30% and low 30.1 to 45%). On the other hand, the treatment of cows with high fertility (>60.1%) did not result in any benefit [55]. This study also reports that treatment with a medium or high dose (≥ 10 μg) of buserelin was associated with a higher conception rate than low doses of buserelin.

Stojanov et al. [63], evaluating the application of GnRH 5 days after insemination, observed an increase in the percentage of cows with more than two CLs on day 14 in the group treated with GnRH compared to the control group (82 vs. 0%). Furthermore, cows in the GnRH group that had accessory CL had higher P4 concentrations on day 14 (5.87 ± 2.04 ng/ml) compared to the control (4.21 ± 1.22 ng/ml) and the GnRH cows that did not present an accessory corpus luteum (only 1 CL on days 14–3.21 ± 1.12 ng/ml). On day 21, the conception rate was still higher in the GnRH group compared to control (65% vs. 48.3%, p < 0.05).

In a subsequent study, the effectiveness of GnRH and hCG administered 7 days post-insemination was investigated. Results revealed that 50% of animals treated with GnRH (lecerylin acetate) developed accessory corpus luteum, while in the hCG group, this proportion increased to 80%. Moreover, both the GnRH and hCG groups demonstrated significantly higher conception rates compared to the control group [64].

According to Stevenson et al. [57], there is a linear and positive relationship between the number of follicles ≥5 mm at the time of treatment (between 4 and 9 days post-AI) with GnRH or hCG and the number of CLs induced, with animals with 1 or 2 follicles ≥5 mm had fewer CLs induced than those with 4 or more follicles of the same size. In beef cows, the effect of hCG is similar to the effect in dairy cows, with this hormone capable of inducing ovulation when used 7 days after TAI. Therefore, it was observed that the number of accessory CLs was greater with hCG when compared to the use of saline (control group). Additionally, on day 33, the proportion of pregnant cows that had accessory CLs was higher in the hCG group than in the control group [56]. In another study evaluating the administration of buserelin (GnRH analog), an increase in the number of accessory corpora lutea was observed; however, this fact was not able to increase plasma concentrations of P4 and the conception rate [62].

In summary, the use of GnRH as an alternative to increase reproductive rates is well-studied, but the results are still controversial. The differences in results reported in the literature are consequences of many methodologies adopted, such as the moment of application and the GnRH analog used [47, 55, 63].

Studies aimed at evaluating the effect of the side formation of the accessory CL (contralateral or ipsilateral to the primary CL) on its maintenance during the first and second months of pregnancy have been developed. Accessory CL that was induced contralateral to the pregnancy CL tended to regress in 66% of pregnant cows around the 67th day of gestation. There were two different periods of regression of the contralateral CL in pregnant dairy cows: (I) close to the normal period of regression of a CL in non-pregnant cows (19 to 25 days of the cycle); (II) during the second month of pregnancy (30 to 60 days) [65].

Monteiro et al. [66] carried out a study to evaluate the time and serum concentrations of P4 associated with the regression of the contralateral accessory CL during the first and second months of pregnancy. The results showed that in pregnant cows, only the accessory CL contralateral to the pregnant CL underwent luteolysis. Functional luteolysis occurred quickly, with less than 24 hours for a drop in circulating P4 concentrations and between 48 and 96 hours for regression of luteal volume, both in the group that underwent early luteolysis (between 19 and 21 days) and in the group that underwent the process in the second month (between days 48 and 51). This speed and punctuality in the process suggest that the luteolytic mechanism is similar in both periods. Regarding the fact that there is no luteolysis of the CL ipsilateral to the pregnant CL, it is suggested that there is some protective mechanism for both during the second month of pregnancy. This mechanism may be related to the increase in uterine blood flow in the gravid horn.

It is known that the side of the accessory CL affects fertility, as multiparous cows have lower fertility than primiparous cows if the accessory CL is contralateral to the gravid CL. Likewise, the contralateral accessory CL is more likely to undergo early luteolysis (gestation less than 32 days) in multiparous cows than primiparous cows [65]. The regression of the accessory CL both in the early period (between days 19 and 23) and in the late period (>45 days) results in approximately 40% reduction in circulating P4 concentrations; therefore, the presence of an ipsilateral CL can be very more positive for fertility than that of a contralateral CL, especially if the regression of this accessory CL occurs during the early phase of pregnancy [66, 67].

In brief, the use of GnRH as an alternative to improve reproductive rates has been increasingly studied, but it still presents controversial and sometimes inconsistent results. The differences in results found in the literature are a consequence of the variety of methodologies used, mainly concerning the moment of application and the GnRH analog used.

5. Conclusion

The use of progesterone has been demonstrated to be an effective tool to optimize reproductive efficiency in cattle undergoing a timed artificial insemination program. The exogenous administration of this hormone makes it possible to induce puberty in heifers and control the females’ estrous cycle, synchronizing them for artificial insemination at strategically chosen times. This not only makes herd management easier but also increases conception rates and reduces calving intervals, resulting in more efficient production. However, it is crucial to consider the appropriate dosage, timing of administration and specific herd conditions to ensure the success of the insemination program. In short, progesterone plays a fundamental role in optimizing reproductive efficiency in cattle, contributing to significant improvements in the productivity and profitability of animal production systems.

Conflict of interest

The authors declare no conflict of interest.