Altrenogest treatment during the last week of lactation on ovarian traits and subsequent reproductive performance of primiparous and multiparous sows

High-quality follicles result in larger corpora lutea (CL), producing more progesterone, and having a fundamental role in pregnancy maintenance. For some sows, follicular growth takes place during lactation, and follicle selection occurs under a catabolic environment. As altrenogest inhibits follicular development, this study aimed to evaluate follicular growth, CL size, estrus expression, and subsequent reproductive performance of sows treated with altrenogest during the last seven days of a three-week lactation. A total of 81 primiparous and 319 multiparous sows were allocated to two treatments: CONT (control group) and ALT (20 mg of altrenogest/day during the last seven days of lactation). Subsamples of 20 primiparous sows and 97 multiparous were randomly selected to evaluate follicular growth and 26 multiparous sows for serum progesterone analysis at day 21 of gestation. On day 21 of pregnancy, CL measurement was performed by ultrasound. Once in estrus, sows were post-cervically inseminated with pooled semen doses with 1.5 × 109 sperm cells at estrus onset and every 24 h during the standing reflex period. Sows not showing estrus until 10 days after weaning were considered in anestrus. The variables weaning-to-estrus interval, CL size, litter size in the subsequent cycle, and piglet birth weight were evaluated using the GLIMMIX procedure and compared using the Tukey–Kramer test. Anestrus, pregnancy, farrowing, and adjusted farrowing rate were evaluated as binary responses using logistic regression. Follicular size was analyzed as a repeated measure during treatment and after weaning. Treatment was considered as a fixed effect. During the treatment period, follicular size was smaller in ALT sows than CONT sows (3.29 vs. 3.52 mm; P