Progesterone and estradiol in biodegradable microspheres for control of estrus and ovulation in mares

Comparison of different treatments for oestrous induction in seasonally anovulatory mares

The aim of this study was to evaluate the effects of different treatments for induction and synchronization of oestrus and ovulation in seasonally anovulatory mares. Fifteen mares formed the control group (C), while 26 mares were randomly assigned to three treatment groups. Group T1 (n = 11) were treated with oral altrenogest (0.044 mg/kg; Regumate(®) ) during 11 days. Group T2 (n = 7) was intravaginally treated with 1.38 g of progesterone (CIDR(®) ) for 11 days. In group T3 (n = 8), mares were also treated with CIDR(®) , but only for 8 days. All mares received PGF2α 1 day after finishing the treatment. Sonographic evaluation of follicles, pre-ovulatory follicle size and ovulation time was recorded. Progesterone and leptin levels were analysed. Results show that pre-ovulatory follicles were developed after the treatment in 88.5% of mares. However, the pre-ovulatory follicle growth was dispersal, and sometimes it was detected when treatment was not finished. While in mares treated with intravaginal device, the follicle was soon detected (1.5 ± 1.2 days and 2.3 ± 2.0 days in T2 and T3 groups, respectively), in T1 group, the pre-ovulatory follicle was detected slightly later (3.9 ± 1.6 days). The interval from the end of treatment to ovulation did not show significant differences between groups (T1 = 13.1 ± 2.5 days; T2 = 11.0 ± 3.6 days; T3 = 13.8 ± 4.3 days). The pregnancy rate was 47.4%, similar to the rate observed in group C (46.7%; p > 0.05). Initial leptin concentrations were significantly higher in mares, which restart their ovarian activity after treatments, suggesting a role in the reproduction mechanisms in mares. It could be concluded that the used treatments may be effective for oestrous induction in mares during the late phase of the seasonally anovulatory period. Furthermore, they cannot synchronize oestrus, and then, it is necessary to know the reproductive status of mares when these treatments are used for oestrous synchronization.

Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 and diestrus: 1.6-10.8 ng mL(-1); P<0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2+/-3.1 ng mL(-1)h(-1)) followed by estrus (25.1+/-2.7) and anestrus (21.0+/-0.4 ng mL(-1)h(-1); P<0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations (R=0.5; P<0.05), but it did not correlate with the interval from PRID removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6+/-28.6 ng mL(-1)h(-1)) when compared to estrous and diestrous mares (349.7+/-53.3 and 370.5+/-40.3 ng mL(-1)h(-1); P<0.05). Follicular size at PRID insertion had no effects on the intervals from PRID removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID were significantly correlated with the interval from coil removal to estrus (R=-0.55, P<0.05) and ovulation (R=-0.72, P<0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.

Seasonal effects on attempts to synchronize estrus and ovulation by intravaginal application of progesterone-releasing device (PRID™) in mares

To investigate seasonal effects on the efficacy of estrus synchronization in mares, we administered a progesterone-releasing device (PRID) intravaginally to eight Haflinger mares for 11 days. In January 3 of 8 mares responded to the treatment with estrus and ovulation, in March 7 with estrus and 6 of 7 mares with ovulation, in June 6 of 7 and in October 7 of 8 mares with estrus and ovulation. Follicle distribution patterns at PRID insertion were different between January/October, March/June and June/October (P<0.05). Number of follicles decreased during PRID treatment in January, March and June (difference of number of follicles at Day 12 minus number of follicles at Day 1: -4.2+/-2.7, -0.9+/-0.9 and -4.9+/-1.5 follicles), while it increased in October (3.9+/-1.2 follicles; P<0.05). Mean progesterone concentrations were lowest in January (0.3+/-0.1 ng mL(-1)) when compared with March (3.5+/-1.8 ng mL(-1); P=0.063), June (4.4+/-1.4 ng mL(-1); P<0.05) and October (2.2+/-0.9 ng mL(-1); P<0.05). At Day 2 of PRID treatment, mean progesterone concentrations significantly increased in all mares. Except from January, mean LH concentrations decreased within one day after PRID insertion and remained at low levels during treatments in January and March. Total secretion of LH during PRID-treatment was significantly lower in January and March when compared with June and October. In the 5 of 7 mares that ovulated during PRID treatment a distinct increase of plasma LH concentrations after ovulation was detected. Administration of the progesterone releasing intravaginal device PRID combined with the PGF2alpha analogue cloprostenol was able to induce estrus and ovulation in mares at different times of the year. However, efficacy of the treatment was not satisfactory concerning effectiveness in relation to season and synchrony of intervals from removal of PRID to ovulation in mares.

Modified release drug delivery in veterinary medicine

To successfully research and develop an animal pharmaceutical dosage form, a diverse array of issues covering basic medicine, pharmacology and technology must be addressed. Societal concerns regarding animal and public health, as well as the rapidly changing farming and economic environments, provide additional challenges that require integration into an already complex web of issues. Here, we examine the drive towards reducing the frequency of administration to animals and the closing of gaps between the human and veterinary drug product development.

Recent advances in bovine reproductive endocrinology and physiology and their impact on drug delivery system design for the control of the estrous cycle in cattle

When methods of drug intervention are being developed to control estrous cycles, a thorough understanding of the endocrine and functional changes together with the reproductive behavior of the animals are essential. This review presents our current knowledge on reproductive endocrinology, physiology and behavior, and the methods of drug intervention to control estrous cycles. It also describes current efforts to develop advanced drug delivery systems that meet the animal scientist's demands to control the estrous cycle in cattle.