Preovulatory follicle dynamics and ovulatory efficiency in sows with thrifty genotype and leptin resistance due to leptin receptor gene polymorphisms (Iberian pig)

This study compares follicular function and ovulatory efficiency in 20 sows with obesity/leptin resistance genotype (Iberian pig) and 20 females of lean commercial crosses (Large White × Landrace; LW × L). Estrous cycle was synchronized with progestagens; ovulation was induced with eCG and hCG, in half of the females of each group, to determine its effect. In females of both breeds not treated with gonadotropins, the number of follicles larger than 4.9 mm and the estradiol secretion increased throughout the follicular phase (P < 0.05); estradiol values were similar at estrus detection (22.5 ± 1.2 vs. 26.5 ± 0.6 pg/ml respectively, for Iberian and LW × L sows). Moreover, ovulation rate was higher in Iberian pigs (15.3 ± 1.3 CLs) than in LW × L (10.2 ± 1.3 CLs; P < 0.05), with mean progesterone values being 18.1 ± 0.7 ng/ml in Iberian and 16.8 ± 0.6 ng/ml in LW × L pigs. Thus, the preovulatory follicular growth and the ovulatory efficiency seem not to be the main limiting factors for reproductive efficiency in Iberian swine. The gonadotropins induced a significant increase, when compared to untreated females (P < 0.05), in the number of follicles larger than 4.9 mm growing throughout the follicular phase; however, estradiol values at estrus were lower (P < 0.05) in both breeds (9.2 ± 0.7 pg/ml in Iberian vs. 8.6 ± 0.8 pg/ml in LW × L), when compared with the nontreated animals, which suggests defective follicular function after gonadotropin stimulation. There were also no differences between genotypes in ovulation rate (15.2 ± 1.3 vs. 12.7 ± 1.8) and progesterone secretion (21.2 ± 0.8 ng/ml in Iberian and 20.9 ± 0.7 ng/ml in LW × L sows) in the treated animals. In conclusion, the current findings indicate that preovulatory follicular growth and ovulatory efficiency are not main limiting factors for prolificacy in a pig model of leptin resistance and obesity.

Research highlights
► This study is the first describing follicle dynamics of obese sows by ultrasonography.
► Follicular turnover and ovulation rate are not limiting prolificacy in obese pigs.
► A lower prolificacy may be more likely determined by a lower embryo survival.