Abstract
Simple SummaryIn this field study, the ovaries of weaned (n = 191, experiment 1) and lactating (n = 40, experiment 2) sows were transrectally scanned to measure the diameter of the follicles. Both the weaned and lactating sows showed great variability in the diameter of the ovarian follicles, indicating that the variability at weaning already existed during early lactation and was carried over to weaning. Sows with small follicles at weaning showed low reproductive performance and were more frequent among those with fewer farrowings and those weaned in summer–autumn.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.
Highlights
Pig production is an economic activity whose profitability relies largely in an efficient reproductive management of sows [1,2]
In the number of piglets born per litter
The results of the present study showed that sows had clear differences in the diameter of the ovarian follicles at weaning and that those with smaller follicles had seriously compromised their following reproductive performance
Summary
Pig production is an economic activity whose profitability relies largely in an efficient reproductive management of sows [1,2]. Achieving such efficiency involves reducing non-productive days, which will allow more piglets to be weaned per sow and year [3]. Sows with one or more farrowings represent around 80% of the total sow population in breeding pig farms They are inseminated at the first estrus. A variable number of weaned sows do not show estrus within this period, which delays their insemination and increases the number of non-productive days [5,6]. Long weaning-to-estrus intervals are related to increased pregnancy losses, decreased farrowing rates, and smaller litter sizes [5,7]
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