Abstract
Simple SummarySuccessful development of replacement gilts plays a critical role for sustainable swine production, whereas most gilts entering the breeding herd are culled at a young age. Recent advances in reproductive physiology revealed that the ovarian reserve could be considered as an important target of improving reproductive span. Therefore, in the present study, we hypothesized that ovarian follicle development and survival could be enhanced by dietary fiber. Currently there is no appropriate level of dietary fiber intake for growing replacement gilts despite the fact that dietary fiber, rather than starch, protein, or feeding allowance level, could improve the fertility of gilts. Results in the present study demonstrated that ovarian follicle development and survival were sensitive to dietary fiber levels. Our results shed light on the mechanisms underlying the beneficial effects of dietary fiber on the reproduction of sows and provided nutritional insights for enhancing the lifetime fertility of pigs by targeting the ovarian reserve.Ovarian follicle activation and survival were recently found to be controlled by nutrient sensors AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) and apoptosis related markers Caspase-3, Bax, and Bcl-2, yet their expression as regulated by dietary fiber remained uncertain for gilts. To investigate the effects of dietary fiber levels on ovarian follicle development, and the cellular molecular components related to follicle activation and survival of gilts, 76 gilts with similar bodyweight and age were fed four diets, including a corn-soybean meal based control diet, or other three diets to consume 50%, 75%, and 100% more dietary fiber than the control gilts at different experimental phases. Inulin and cellulose (1:4) were added to the corn-soybean meal basal diet to increase dietary fiber content. The growth traits, and the age, bodyweight, and backfat thickness at puberty were not affected by diets. The number of primordial follicles and total follicles per cubic centimeter of ovarian tissue linearly increased with dietary fiber level at day 30 of the experiment and at the 19th day of the 3rd estrous cycle, without negatively affecting the formation of antral follicle with diameter between 1–3 mm or larger than 3 mm. These changes were associated with altered phosphorylation of mTOR, S6, Extracellular regulated protein kinases 1/2 (ERK1/2) and AMPK, and mRNA expression of Caspase-3, Bax, and Bcl-2 in ovarian tissues. Collectively, this study demonstrated a beneficial effect of dietary fiber on the ovarian follicle reserve in gilts, which provides a basis for enhancing reproduction in the short- or long-term.
Highlights
A large proportion of gilts are maintained in swine production for the renewal of the breeding herd, emphasizing the importance of successful gilt development for overall herd performance and profitability
The age at puberty, bodyweight at puberty, and backfat thickness at puberty were not affected by consumption of different levels of dietary fiber (p > 0.05, Table 4)
The effects of dietary fiber levels on the ovarian follicle reserve were investigated in growing replacement gilts and it was found that the activation and survival of follicles were sensitive to the intake of dietary fiber, which shed a light on the importance of dietary fiber for the feeding and management of replacement gilts
Summary
A large proportion of gilts are maintained in swine production for the renewal of the breeding herd, emphasizing the importance of successful gilt development for overall herd performance and profitability. 40–50% of the replacement gilts entering the breeding herd suffer reproductive failure at a young age, and provide only 30–40 piglets in their lifetime [1,2]. The culling of sows could be ascribed to many reasons but the reproductive disorders, such as estrous initiation failure, conception failure, and small litter size, account for most of the reasons for culling [1,2]. The ovarian reserve has been observed to be controlled by several factors [5], yet the environment factors (e.g., nutrition) controlling the ovarian reserve of female pigs remains largely unknown. Activation of the ovarian primordial follicle, the first step of folliculogenesis, is closely associated with cellular nutrient sensors AMPK or mTOR, and the survival of follicles is influenced by apoptosis related proteins including Bax, Bcl-2, and Caspase-3 [5]
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