Ovarian Follicle Growth during Lactation Determines the Reproductive Performance of Weaned Sows

Abstract

Factors causing variability in ovarian follicle size among weaned sows are not well known. This field study aimed to disclose influencing factors and evaluate if the differences at weaning were established during lactation. Ovaries were scanned using transrectal ultrasound. The first experiment was conducted over a year with 191 randomly chosen sows that were hierarchically grouped (p < 0.001) according to ovarian follicle diameter reached at weaning: Small (0.20–0.30 cm; n = 37), medium (0.31–0.39 cm; n = 75), and large (0.40-1.00 cm; n = 69). Sows with small follicles showed a higher incidence of post-weaning anestrus (p < 0.01), longer wean-to-estrus/ovulation intervals (p < 0.01) and farrowing smaller litters (p < 0.05). Ovaries with small follicles were more common among sows weaned in summer–autumn than in winter–spring (p < 0.01) and among sows of lower parity (1–3) (p < 0.05). In the second experiment, with 40 sows randomly chosen at farrowing, the ovaries were scanned at 7, 14, and 21 d post-partum. Sows showed great variability in ovarian follicular size during lactation with a consistent relationship between the three measurement times (r = 0.84, p < 0.01). Follicle size was smaller in sows nursing in summer–autumn than in winter–spring (p < 0.05). In conclusion, early lactation dictates the great variability in ovarian follicular diameter at weaning shown by sows. Sows with smaller follicles at weaning had longer intervals for estrus and ovulation and smaller litters at farrowing and they were in greater numbers among sows weaned during the summer and fall and among those with fewer previous farrowing.

Identifying Risk Factors for Low Piglet Birth Weight, High Within-Litter Variation and Occurrence of Intrauterine Growth-Restricted Piglets in Hyperprolific Sows

“…However, WII did not affect CV PBW or the occurrence of mIUGR or sIUGR piglets, which is difficult to explain without knowing the underlying mechanisms of the effect of the length of WII. The size of the follicles at weaning is determined during lactation, and sows with small follicles at weaning have a longer weaning to estrus interval [ 29 ]. The effect of WII seen in this study might reflect if the sow was in the right nutritional state during lactation and after weaning, when follicles developed.…”

Factors influencing pre‐ovulatory follicle diameter and weaning‐to‐ovulation interval in spontaneously ovulating sows in tropical environment

“…Briefly, the ultrasound transducer was inserted into the rectum and the ovaries were located by rotating the probe to the left and the right sides of the sow. Numerous spherical anechoic structures on the ovary with diameter up to 10 mm, showing thin borders and sometime with irregular outlines, were defined as ‘follicles’ (Lopes et al., 2020). Both ovaries were examined, and the diameters of 4–8 large follicles in each ovary were measured.…”

Releasing Hormone and Vitamin Efficiency in the Treatment of Obstetric and Gynecological Pathologies in Breeding Sows

“…A difference in the number and size of follicles is also observed depending on the season [5]. In summer, most sows have yellow masses instead of follicles [6].…”