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Background: The intensive reproductive management in the dairy farms requires inclusion of a large group of replacement heifers in the breeding program for a shorter period. In this aspect, a creation of effective estrus synchronization protocols with timed artificial insemination (TAI) by sexed semen and optimization of the current ones have a crucial role for obtaining high pregnancy rate. These protocols are beneficial, because they led to reduced interval to first AI, lack of need for estrus detection, and allow obtaining a large group of female calves for on time. Because of limited fertilizing potential of sexed spermatozoa this type of semen is applied mainly for heifers, as fertility is higher compared to lactating cows. The main objective of the present study was to investigate the effect of ovarian status on the reproductive performance in dairy heifers subjected to estrus synchronization and timed artificial insemination with sexed semen. Materials, Methods & Results: Forty-eight Holstein healthy heifers separated in 2 groups were subjected to PGF2α-GnRH pre-treatment and Ovsynch or PRID-5-day estrus synchronization protocol and timed artificial insemination (TAI) with sex-sorted semen, staring 6 days after end of the hormonal pre-treatment. The ovarian status (presence of follicles with or not a corpus luteum) of the heifers at the begin of the treatment, on day of TAI and pregnancy rate in different groups were determined and compared. Additionally, the ovarian status at the begin of the treatment, ovarian status and size of preovulatory follicle (PF) on day of TAI and total values for both groups according to reproductive performance (pregnant or non-pregnant) were also analyzed. On day of TAI the animals with PF and a lack of corpus luteum (CL) in both groups were more that those with PF and CL (39.3% and 30% vs. 60.7 % and 70%), with significant (P < 0.05) difference in PRID-5-day group. The pregnancy rate tended to be higher in PRID-5 day than Ovsynch treatment (65% vs. 35.7%). A higher percentage (100% and 67.9%) of the pregnant animals in both treatments had not CL on day of TAI, and the size of the PF (1.58 ± 0.12 cm and 1.64 ± 0.13 cm) was increased (P < 0.05). Similar effects of the ovarian status on reproductive performance were obtained after a comparison of the total values between pregnant and non-pregnant animals. The percentage of heifers with observed PF without CL on day of TAI was significantly greater (P < 0.05) in pregnant compared to non-pregnant group (91.3% vs. 40%). The opposite dependence was determined for the parameter presence of follicles and corpus luteum (8.7% vs. 60%; P < 0.05). Furthermore, the size of the PF measured immediately before TAI was increased in animals became pregnant (1.60 ± 0.12 cm vs. 1.34 ± 0.17 cm; P < 0.05). Discussion: The analysis of the obtained results showed that the ovarian status on day of TAI affects the reproductive performance in dairy heifers subjected to estrus synchronization and timed artificial insemination with sexed semen. Hormonal pre-treatment with onset of PRID-5-day protocol 6 days later and TAI with sex-sorted semen ensure acceptable pregnancy rate. The greater preovulatory follicle and a lack of corpus luteum before insemination provide significantly (P < 0.05) more pregnant animals, compared to the cases when CL is presented. Ultrasound determination of the ovarian function before insemination can be used in selection of heifers for TAI with sex-sorted semen. Keywords: heifers; estrus synchronization; sexed semen, pregnancy.

Although slow release GnRH-agonist implants have been shown to effectively suppress the estrous cycle in queens, there are still several remaining questions about their use: if the probability and frequency of estrus induction because of initial stimulation is dependent on the stage of cycle when animals are treated, if all effects are reversible, and to what extent fertility is regained after the end of efficacy. The latter is of major interest to cat breeders who want temporary suppression of estrus in breeding animals. Twenty queens (14 with known fertility) were treated with a 4.7 mg deslorelin implant; hormonal changes (progesterone [P4], and estradiol [E2]) and behavioral changes with special respect to estrus signs and subsequent fertility were assessed. Group A cats (N = 10) were treated 3.2 ± 0.8 days after the beginning of estrus and estrus stopped 4.1 ± 2.5 days after treatment. Estrus induction was observed in one queen 6 days after treatment, and one queen showed estrous signs 138 and 155 days after treatment. Progesterone increased significantly after treatment in all animals until day 14, then slowly decreased reaching basal levels on day 56 without any further increase. Group B cats (N = 10) were treated 7 days after the end of estrus; nine cats had P4 > 1.5 ng/mL and basal E2, one cat (B10) had basal E2 and P4. In cat B10 estrus induction occurred after treatment, but in none of the others; however, E2 increased in all group B cats 1 day after treatment but reached pretreatment concentrations on Day 7 again and remained basal. The implant was still effective in one animal of the estrus group with a duration of efficacy >1102 days, in the others duration of efficacy varied between 483 and 1025 days. Eight queens were mated afterwards and gave birth to a healthy litter with 3.3 ± 1.5 kittens. This study proves that (1) the incidence of estrus induction—although very low—is highest after treatment in estrus or postestrus, (2) the duration of efficacy varies between 16 and 37 months, and (3) estrus suppression is reversible and animals remain fertile after the treatment effect has expired.

Suppression of oestrus is of major interest in feral cat populations, but also in breeding queens temporarily not intended for breeding. Slow release gonadotropin-releasing hormone (GnRH) agonist implants are a new off-label approach for reproduction control in cats. However, initially, oestrus induction may occur and no data exist regarding what happens if previously mated queens are treated. This case report presents a queen mismated 9 and 8 days before treatment with a 4.7 mg deslorelin implant. The queen delivered four healthy kittens 66 days after mismating, but showed no interest in the kittens and lactation was not adequate. Progesterone and oestradiol concentrations were monitored and the queen was followed until the return of oestrus and subsequent breeding. The next oestrus was observed 498 days after treatment and the queen was mated in the second oestrus afterwards, became pregnant and delivered two healthy kittens, both of which were raised successfully by the queen. This case report clearly shows that pregnancy following a GnRH-agonist implant may go to term, but maternal care might be influenced owing to hormonal changes induced by treatment. In addition, this is the first report demonstrating reversibility of effects induced by long-term treatment with a deslorelin implant (return to oestrus, fertility and normal maternal care).