The effect of double administration of PGF2alfa in gilts treated before corpus luteum acquisition of luteolytic capacity

The effect of double administration of PGF2alfa in gilts treated before corpus luteum acquisition of luteolytic capacity Fabio De Rensis1, Gatano Donofrio1 , Mongkol Techakumphu2, Padet Tummaruk2 1Dipartimento di Salute Animale, Facoltà di Medicina Veterinaria, Parma, Italy 2Department of Obstetrics, Gynaecology and Reproduction, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand E-mail address: fabio.derensis@unipr.it; Mongkol.t@chula.ac.th; Padet.t@chula.ac.th Introduction Prostaglandin F 2alpha (PGF2 ) is known to have the ability to regress the corpus luteum (CL) in many domestic animals and is used for estrus synchronization in cattle, ewe and goat. However, in female pig, single PGF2 administration is effective in induce luteolysis only after day 12 of estrus cycle or multiple injections are required. In a recent study in mini pigs, two administration of 3.0 mg PGF2 (cloprostenol) within 12 hours interval can induce luteolysis as early as 7 days after ovulation [1]. These data suggest that double PGF2 administration can induce luteolysis also before day 12 of luteal phase of estrus cycle. Also the route of PGF2 administration is important and intra vulvosubmucosal (IVSM) route is more effective than intramuscular (IM) route. The aim of this study is to evaluate the possibility to reduce the length of estrus cycle by the double administration of PGF2 given IVSM at high doses at day 8 of estrus cycle, before CL acquisition of luteolytic capacity. Material and Methods Experiment 1: Eight gilts at day 8 of estrous cycle were treated with 75 μg di Cloprostenol destrogiro (1 ml of Dalmazin–Fatro) 2 times at interval of 6 h IVSM. Heat detection was effectuated for 10 days after end of treatment. Experiment II: 10 gilts at day 8 of estrous cycle were treated as in experiment I. In these animals, blood sample were taken on the day of PGF2 administration and 24 and 42 h later to determine plasma progesterone (P4) levels. Based on the decrease of P4, the gilts were classified as: complete luteolysis (HLL), partial luteolysis (HLH) and no luteolysis (HHH). Heat detection was performed every day until estrus occurs. Intensity of estrous symptoms were scored 1=very low, 5=very evident. Results Experiment I: Two gilts showed estrus within 8 days after PGF2 treatment, while 6 gilts showed estrus at longer than 10 days. Experiment II: In 6 gilts, estrus occured 10 days after PGF2 treatment indicating that length of estrous cycle was not modified, in 2 gilts, estrus occured at 7 days and in 2 gilts estrus occured at 8 days after PGF2 treatment. Based on progesterone plasma levels, 1 gilt was HHH, 7 gits were HLH and 4 gilts were HLL. The score for estrous signs tended to be reduced compared the other gilts (5.0 vs 3.7, P=0.051). The P4 levels before treatment were lower in gilts in which complete luteolysis occurs. 0 1 2 3 4 5 6 7 day 6 day 7 day 8 day 9 day 10 day 11 and more N u m b e r o f g il ts Days after PGF2alfa administration Number of gilts and Interval treatment-estrus Figure 1 Number of gilts and interval from treatment to estrus Discussion The results of this study indicate that in gilts the response to a high dose of PGF2 administered twice at perivulvar level is high variable and shortened estrous cycle only in 30% of animals. In the other animals an incomplete luteolysis occurs. The reason for such high variability could be related the number of CLs because luteolysis occurred in gilts with lower progesterone levels before treatment. Usually in cows average interval between PGF2 administration and estrus is 4-5 days while in this study in gilts that responded to treatment estrus occurred 7-8 days after treatment. This suggests that to synchronize estrus in gilts with PGF2 is difficult also because the mechanism of recruitment and maturation of ovulatory follicles required more time compared to cow. Furthermore intensity of estrus expression is reduced. In conclusion the results of this study indicate that in gilts response to PGF2 administration at day 8 of estrous cycle in terms of luteolysis is highly variable and that the length of estrus cycle can be partially reduced only in a minority of treated animals. In this study a tendency for a correlation between plasma P4 levels before treatment and luteolysis has been detected. Reference 1. Kuge, T., et al., 2006. J. Reprod. Dev. 52:391-396