Effect of altrenogest treatment before weaning on reproductive performance and production efficiency in primiparous and multiparous sows

Most sows will experience negative energy balance during lactation resulting in impaired follicular development. This study aimed to treat 28-day lactating sows with altrenogest (ALT) to suppress follicle enlargement during lactation, and to assess the estrus and reproductive performance post-weaning. In this study, we conducted two trials. In trial 1, we monitored the follicular development of lactating sows including 10 primiparous sows and 10 multiparous sows during the whole lactation to confirm the ALT administration time. In trial 2, a total of 42 primiparous and 111 multiparous sows were allocated to three treatments: Ctrl (control group, n = 51): no treatment; TAI (timed artificial insemination group, n = 51): sows were injected with equine chorionic gonadotropin (eCG) after weaning 24 h and gonadotropin-releasing hormone (GnRH) when they expressed estrus; and AT-TAI (ALT treatment-timed artificial insemination group, n = 51): base on the process of TAI group, the sows were fed with 20 mg ALT per day before weaning 10 days. All sows were artificially inseminated twice at 12 h and 36 h after estrus. The follicle size changes and serum hormone levels were explored in this process. Although the follicle size of multiparous sows was larger than primiparous sows during the whole lactation (P