FOLLICULAR DEVELOPMENT AND OVULATION IN SOWS - EFFECT OF HCG AND GNRHTREATMENT

Follicular growth, chronology of ovulation and embryo morphology were compared in sows ovulating spontaneously and sows, in which the ovulat ion was attempted induced by hCG or GnRH. Indwelling catheters were pl aced on day 1 (weaning = day 0) in the ear veins of 18 sows, which wer e then randomly divided into 3 groups: a control group (N = 6), a grou p (N = 6) given 750 iu hCG (Physex(R)) im 76h after weaning (hCG group ) and a group (N = 6) given 500 mu g GnRH (Fertagyl(R)) im 76h (N = 3) or 100h after weaning (N = 3) (GnRH group). Follicular diameter and t ime of ovulation were monitored by ultrasonography every 4h from day 3 until ovulation or development of cysts by means of a sector scanner fitted with a 5.0/7.5 MHz multiangle probe. Heat detection was per for med every 8h from day 3 until ovulation. On day 13, the sows were slau ghtered, the number of corpora luteae (CL) was counted, and embryos we re flushed from the uteri. The control group showed clear heat symptom s, and on day 3, the follicles were typically 3-7 mm and grew up to 7- 10 mm over 2 days, where they remained for approximately 24h until ovu lation took place 41h +/- 9h after first sign of standing heat. The hC G group exhibited no signs of heat, and the follicles only reached 5-8 mm in diameter at time of ovulation, which occurred 40h +/- 1h after hCG-injection. The GnRH group exhibited inconsistent signs of heat, an d the follicles reached a maximum size of 7-12 mm in diameter where th ey remained for more than 24h. Only 2 sows in this group ovulated with in 84-92h after the GnRH injection, and development of bursa cysts and cystic follicles was a common finding. The average number of CL was 1 8.2 +/- 5.7 per sow (N = 16, range: 3-27) with no significant differen ce between the groups. Total embryo recovery was 79 +/- 13 % with no s ignificant difference between groups. The embryo diversity calculated as standard deviation of the maximum diameter was higher in the hCG gr oup as compared with the control group. It is concluded that (1) trans rectal ultrasonography can be used in sows for accurate assessment of follicular growth and ovulation; (2) the use of hCG results in lack of heat symptoms and reduced follicle size at the time of ovulation when injected 76h after weaning; (3) administration of a single injection of GnRH, if given before the first signs of heat, results in inconsist ent heat symptoms and no or late ovulations.