Gilts often reach puberty just before the beginning of breeding. Gilts that are near spontaneous puberty may respond to daily exposure to a boar and be in estrus in four to 10 days. A gonadotropin, either eCG (500 to 1200 IU) or PG600® (200 IU hCG + 400 IU PMSG) may also be injected to induce puberty and the peak response in estrus is generally five to six days after injection.

Suckling by the litter prevents resumption of estrous cycles and is widely used to synchronize estrus in sows. Suckling usually inhibits estrus during at least the first four weeks after farrowing and may be effective as long as six weeks. Most sows return to estrus between three and seven days after their litter is weaned. Gonadotropins may be administered at weaning or 24 h after weaning, to further regulate the follicular phase and increase the percent of sows promptly returning to estrus.

Once estrous cycles are initiated, they can be modified in a variety of ways. Many of the synthetic progestins used for synchronizing estrus in other species result in a high incidence of follicular cysts and infertility in pigs. A progestin that is effective in pigs is altrenogest. The dose for gilts is 15 mg per day mixed in the diet or top-dressed. A 14- to 18-day feeding period produces good synchrony of estrus[5] (see [1] in Fig. 1). Altrenogest synchronizes estrus when treatment has continued beyond the time of spontaneous luteolysis in all females in the group. With small groups and when the date of last estrus is known, it may be possible to shorten the treatment period by delaying treatment until the first gilt or sow reaches day 14 of her cycle.

[1] Horses and pigs

Feed altrenogest for 14 days-pigs 15 days-horses

Watch for estrus and Al -

Pregnant or pseudopregnant


Watch for estrus and Al

18 to 40 days

Pregnant or pseudopregnant


Watch for estrus and Al

18 to 40 days o iV

eCG or PG600

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