Synchronization of estrus and ovulation in sows not conceiving in a scheduled fixed-time insemination program

A field study was conducted to investigate the effectiveness of a treatment with altrenogest, eCG and hCG or the GnRH-analogue D-Phe 6-LHRH to synchronize estrus and ovulation of sows diagnosed as non-pregnant in order to reintegrate them back into a scheduled fixed-time insemination program. Sows ( n = 531) diagnosed as non-pregnant by ultrasonography on days 21–35 after insemination were subjected to one of three treatments: (1) 16 mg altrenogest/day/animal orally for 15 days to block follicular growth, followed by injection of 1000 IU eCG intramuscularly (i.m.) 24 h after withdrawal of altrenogest to stimulate follicular growth and 500 IU hCG i.m. 78–80 h after eCG to induce ovulation; (2) similar to (1) except that 20 mg altrenogest and 800 IU eCG were used and (3) similar to (2) except that 50 μg D-Phe 6-LHRH was used to induce ovulation. Females were artificially inseminated (AI) twice at 24 and 40 h, respectively, after hCG/D-Phe 6-LHRH. Success of treatments was checked by ultrasonography of the ovaries. Rates of conception and farrowing (CR, FR), and number of total and live born piglets (TB, LB) were recorded and compared to those of synchronized first served sows. Females had differing ovarian structures prior to treatment. Altrenogest effectively blocked follicular growth in >80% of the females irrespective of dosage, but 16 mg increased the development of polycystic ovarian degeneration. Four to 18% of the females still had corpora lutea after altrenogest. Most females ovulated either between both inseminations or thereafter ( P < 0.05). Females treated with D-Phe 6-LHRH tended to ovulate earlier than those injected with hCG. The CR and FR were up to 25% lower for sows diagnosed as non-pregnant than for sows after first service ( P < 0.05). Among sows diagnosed as non-pregnant the CR was higher in females treated with D-Phe 6-LHRH ( P < 0.05). No differences were found in regard to numbers of TB and LB. In conclusion, a treatment with 20 mg altrenogest per day per animal, followed by 800 IU eCG and 50 μg the GnRH-analogue D-Phe 6-LHRH is appropriate to synchronize estrus and ovulation of sows diagnosed as non-pregnant. Whether there might be a need to feed altrenogest for a longer interval of 18 days has to be investigated.