Follicular development of sows at weaning in relation to estimated breeding value for within-litter variation in piglet birth weight

Supplementing a carbohydrate-rich diet from late lactation to insemination increased glucose and insulin levels in weaned sows, leading to improved subsequent piglet birth weight

Premating maternal nutrition is crucial for postweaning follicle growth, thereby influencing piglet birth weight in subsequent litters. The present study investigated the impact of supplementing a carbohydrate-rich premating diet in sows on metabolic hormones, subsequent piglet birth weight and reproductive performance. Sows were distributed into three groups, control (n=42) received standard diets; treatment I (n=41) received the same diets supplemented with 500 g of a carbohydrate-rich premating diet from weaning until insemination; treatment II (n=42) received the same diets supplemented with 500 g of a carbohydrate-rich premating diet from 7 days before weaning until insemination. Blood samples were taken from sows around weaning to measure serum insulin-like growth factor-1 and insulin, and blood glucose after feeding. The study found that sows on a carbohydrate-rich diet (treatment II) had higher postprandial glucose (P<0.05) and insulin levels (P=0.06) than others. This diet did not affect overall reproductive performance, but it did increase piglet birth weight and reduce the number of low-birth weight piglets compared to the control (P<0.001) and treatment I groups (P<0.05). Supplementing a carbohydrate-rich premating diet for 7 days before weaning until insemination enhanced postprandial glucose and insulin concentrations in weaned sows. This dietary intervention led to improved subsequent piglet birth weight and reduced the proportion of low-birth weight piglets.

The importance of optimal body condition to maximise reproductive health and perinatal outcomes in pigs

Overnutrition or undernutrition during all or part of the reproductive cycle predisposes sows to metabolic consequences and poor reproductive health which contributes to a decrease in sow longevity and an increase in perinatal mortality. This represents not only an economic problem for the pig industry but also results in poor animal welfare. To maximise profitability and increase sustainability in pig production, it is pivotal to provide researchers and practitioners with synthesised information about the repercussions of maternal obesity or malnutrition on reproductive health and perinatal outcomes, and to pinpoint currently available nutritional managements to keep sows' body condition in an optimal range. Thus, the present review summarises recent work on the consequences of maternal malnutrition and highlights new findings.

Physiological and metabolic aspects of follicular developmental competence as affected by lactational body condition loss

Metabolic demands of modern hybrid sows have increased over the years, which increases the chance that sows enter a substantial negative energy balance (NEB) during lactation. This NEB can negatively impact reproductive outcome, which is especially evident in primiparous sows causing a reduced second parity reproductive performance. The negative effects of the lactational NEB on reproductive performance can be partly explained by the influence of the premating metabolic state, during and after lactation, on the development of follicles from which oocytes will give rise to the next litter. In addition, the degree and type of body tissue mobilization during lactation that is, adipose tissue or lean mass, highly influences follicular development. Research investigating relations between the premating metabolic state and follicular and oocyte competence in modern hybrid sows, which experience higher metabolic demands during lactation, is limited. In this review we summarize current knowledge of physiological relations between the metabolic state of modern hybrid sows and follicular developmental competence. In addition, we discuss potential implications of these relations for current sow management strategies.

Fibroblast growth factor 21 (FGF21) promotes porcine granulosa cell estradiol production and proliferation via PI3K/AKT/mTOR signaling

The proliferation and steroidogenesis of mammalian ovarian granulosa cells (GCs) are related to follicular development. Previous studies found that fibroblast growth factor 21 (FGF21) regulated female fertility through the hypothalamic-pituitary-gonad axis. However, FGF21 receptors are expressed on GCs, so we speculate that it might affect female reproduction by regulating their physiological activities. Here, we showed that FGF21, fibroblast growth factor receptor-1(FGFR1), and beta-klotho (KLB) were expressed in porcine GCs. ELISA assays showed that estradiol (E₂) production was increased significantly when treating GCs with recombinant FGF21 (rFGF21). In addition, rFGF21 upregulated the mRNA and protein levels of E₂ synthesis-related genes including StAR, CYP11A1, and CYP19A1 in porcine GCs. Correspondingly, FGF21 siRNA inhibited E₂ levels and its synthesis-related gene expression. After rFGF21 treatment, CCK8 showed increased cell viability, and flow cytometry showed that the number of S phase increased, and cycle-related genes also increased. However, treatment with FGF21 siRNA to porcine GCs suppressed the cell cycle, viability, and EdU positive cell number. Consequently, FGF21/FGFR1/KLB forms a complex to activate the phosphatidylinositol-3-kinase (PI3K)/AKT/mTOR signaling pathway and further promote the proliferation and E₂ synthesis in porcine GCs. Collectively, these findings suggests that FGF21 regulates porcine ovarian folliculogenesis.

Follicular fluid steroid profile in sows: relationship to follicle size and oocyte quality†

Identification of reliable characteristics of follicle quality and developmental competence has been pursued in numerous studies, but with inconsistent outcomes. Here, we aimed to identify these characteristics by analysis of the follicular fluid (FF) steroid profile in relation to cumulus-oocyte complex (COC) morphology and follicle size, followed by molecular substantiation. Multiparous sows at weaning were used to facilitate analysis at the start of the follicular phase of the oestrus cycle. Sows with a higher average follicle size (≥5 mm vs. < 5 mm) had a higher follicular fluid β-estradiol concentration, but did not differ in other measured steroids. Sows with high compared to low percentage high-quality COCs (<70% vs. ≥70% high-quality) had follicular fluid with a higher concentration of β-estradiol, 19-norandrostenedione, progesterone, and α-testosterone, while the concentration of cortisol was lower. Transcriptome analysis of granulosa cells of healthy follicles of sows with a high percentage high-quality COCs showed higher abundance of transcripts involved in ovarian steroidogenesis (e.g., CYP19A2 and 3, POR, VEGFA) and growth (IGF1) and differential abundance of transcripts involved in granulosa cell apoptosis (e.g., GADD45A, INHBB). Differences in aromatase transcript abundance (CYP19A1, 2 and 3) were confirmed at the protein level. In addition, sows with a high percentage high-quality COCs lost less weight during lactation and had higher plasma IGF1 concentration at weaning, which may have affected COC quality. To the best of our knowledge, this study is also the first to report the relation between FF steroid profile and COC quality.

Consequences of negative energy balance on follicular development and oocyte quality in primiparous sows†

Metabolic demands of modern hybrid sows have increased over the years, which increases the chance that sows enter a substantial negative energy balance (NEB) during lactation. This NEB can influence the development of follicles and oocytes that will give rise to the next litter. To study effects of a lactational NEB on follicular development, we used 36 primiparous sows of which 18 were subjected to feed restriction (3.25 kg/day) and 18 were full-fed (6.5 kg/day) during the last 2 weeks of a 24.1 ± 0.3 day lactation. Feed restriction resulted in a 70% larger lactational body weight loss and 76% higher longissimus dorsi depth loss, but similar amounts of backfat loss compared to the full fed sows. These changes were accompanied by lower plasma insulin-like growth factor 1 (IGF1) and higher plasma creatinine levels in the restricted sows from the last week of lactation onward. Ovaries were collected 48 h after weaning. Restricted sows had a lower average size of the 15 largest follicles (−26%) and cumulus–oocyte complexes showed less expansion after 22 h in vitro maturation (−26%). Less zygotes of restricted sows reached the metaphase stage 24 h after in vitro fertilization and showed a higher incidence of polyspermy (+89%). This shows that feed restriction had severe consequences on oocyte developmental competence. Follicular fluid of restricted sows had lower IGF1 (−56%) and steroid levels (e.g., β-estradiol, progestins, and androgens), which indicated that follicles of restricted sows were less competent to produce steroids and growth factors needed for oocytes to obtain full developmental competence.

Consumption of Dietary Fiber from Different Sources during Pregnancy Alters Sow Gut Microbiota and Improves Performance and Reduces Inflammation in Sows and Piglets

Although the direct effects of dietary fiber on gut microbiota composition have been studied extensively, systematic evaluation of different fiber sources on gut health and inflammatory responses of sows and their offspring has rarely been conducted. Excessive reactive oxygen species produced by overactive metabolic processes during late pregnancy and lactation of sows leads to increased endotoxin levels, disordered gut microbiota, decreased SCFA production, and secretion of proinflammatory factors, which in turn causes local inflammation of the gut, potential damage of the gut microbial barrier, increased gut permeability, increased blood endotoxin levels (resulting in systemic inflammation), and ultimately decreased sow and piglet performance.

In pregnant and lactating sows, metabolism and immunity undergo drastic changes, which can lead to constipation, abortion, and intrauterine growth restriction (IUGR) and reduce production performance. Dietary fiber can regulate animal gut microbiota, alleviate inflammatory responses, and improve performance. Here, 48 sows (Large × Landrace) were randomly allocated to groups including, control, and with alfalfa meal (AM), beet pulp, and soybean skin dietary supplementation for 60 days of gestation. The AM diet decreased IUGR, increased food intake during lactation, and promoted the reproductive performance and physical condition of sows. Further, the AM diet significantly reduced markers of intestinal permeability (reactive oxygen species and endotoxin) in sow serum, and of systemic inflammation (interleukin-6 [IL-6] and tumor necrosis factor alpha) in sow feces and serum, as well as piglet serum, while it increased the anti-inflammatory marker, IL-10, in sow serum and feces. The AM diet also significantly affected gut microbiota by increasing the relative abundance of proinflammatory bacteria, while decreasing anti-inflammatory bacteria. Moreover, the total short-chain fatty acid (SCFA) content was higher in feces from sows fed an AM diet, with butyric acid content significantly higher during lactation, than in controls. Sow performance was correlated with intestinal permeability, inflammation, and gut microbiota, which were also vertically transmitted to piglets. Our results are significant for guiding feed management in the pig breeding industry. Further, the “sows to piglets” model provides a reference for the effect of dietary fiber on the gastrointestinal function of human mothers and infants.

IMPORTANCE Although the direct effects of dietary fiber on gut microbiota composition have been studied extensively, systematic evaluation of different fiber sources on gut health and inflammatory responses of sows and their offspring has rarely been conducted. Excessive reactive oxygen species produced by overactive metabolic processes during late pregnancy and lactation of sows leads to increased endotoxin levels, disordered gut microbiota, decreased SCFA production, and secretion of proinflammatory factors, which in turn causes local inflammation of the gut, potential damage of the gut microbial barrier, increased gut permeability, increased blood endotoxin levels (resulting in systemic inflammation), and ultimately decreased sow and piglet performance. Our results showed that supplementation of the diet with alfalfa meal in mid and late pregnancy can reverse this process. Our findings lay a foundation for improving the gut health of sows and piglets and provide insights into the study of the gastrointestinal tract function in human mothers and infants.

Coping with large litters: the management of neonatal piglets and sow reproduction

As a result of intensive breeding, litter size has considerably increased in pig production over the last three decades. This has resulted in an increase in farrowing complications. Prolonged farrowing will shorten the window for suckling colostrum and reduce the chances for high-quality colostrum intake. Studies also agree that increasing litter sizes concomitantly resulted in decreased piglet birth weight and increased within-litter birth weight variations. Birth weight, however, is one of the critical factors affecting the prognosis of colostrum intake, and piglet growth, welfare, and survival. Litters of uneven birth weight distribution will suffer and lead to increased piglet mortality before weaning. The proper management is key to handle the situation. Feeding strategies before farrowing, management routines during parturition (e.g., drying and moving piglets to the udder and cross-fostering) and feeding an energy source to piglets after birth may be beneficial management tools with large litters. Insulin-like growth factor 1 (IGF-1)-driven recovery from energy losses during lactation appears critical for supporting follicle development, the viability of oocytes and embryos, and, eventually, litter uniformity. This paper explores certain management routines for neonatal piglets that can lead to the optimization of their colostrum intake and thereby their survival in large litters. In addition, this paper reviews the evidence concerning nutritional factors, particularly lactation feeding that may reduce the loss of sow body reserves, affecting the growth of the next oocyte generation. In conclusion, decreasing birth weight and compromised immunity are subjects warranting investigation in the search for novel management tools. Furthermore, to increase litter uniformity, more focus should be placed on nutritional factors that affect IGF-1-driven follicle development before ovulation.

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

Follicle development and timing of ovulation are indicators of the reproductive performance of sows. The present study aimed to determine factors influencing pre-ovulatory follicle diameter and weaning-to-ovulation interval (WOI) in spontaneously ovulating sows in tropical climates with special emphasis on breed, parity and backfat thickness at weaning. In total, 80 sows were included in the study. Follicle development was determined by using transrectal real-time B-mode ultrasonography every 6 hr after standing oestrus. Weaning-to-oestrous interval (WEI), oestrous-to-ovulation interval (EOI), WOI and the diameter of graafian follicles were investigated in relation to breed, parity number (1, 2-3 and 4-7) and backfat thickness (low, moderate and high) of sows. Overall, WEI, EOI, WOI and the pre-ovulatory follicle diameter were 92.5 ± 21.6 hr, 64.3 ± 19.3 hr, 156.3 ± 29.1 hr and 10.3 ± 2.0 mm, respectively. Pre-ovulatory follicle size was smaller in primiparous sows compared with sows of greater parity, 4-7 (9.7 ± 0.51 and 11.7 ± 0.52 mm, respectively, p < .05). Weaning-to-ovulation interval was positively correlated with WEI (r = 0.75, p < .001) and EOI (r = 0.66, p < .001), but negatively correlated with size of the graafian follicle (r = -0.34, p < .01). Sows with a shorter WEI had a larger pre-ovulatory follicle diameter (at 64 hr after oestrus) (r = -0.37, p < .01). Sows with low backfat thickness had a WOI 23.4 hr longer than those with moderate backfat thickness (p < .05) and 17.6 hr longer than sows with a high backfat thickness (p = .140). The follicle diameter in primiparous sows with high backfat thickness (11.7 ± 1.1 mm) was higher than in those with low (8.9 ± 0.7 mm, p < .05) or moderate (8.6 ± 0.8, p < .05) backfat thickness. In conclusion, factors influencing follicle diameter and WOI in sows included parity number and backfat thickness at weaning. The impact of backfat thickness on follicle diameter, WEI and WOI was most pronounced in primiparous sows.

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

Simple Summary

In 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.

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.

Steroid profile of porcine follicular fluid and blood serum: Relation with follicular development

The aim of this study was to identify follicular fluid (FF) steroids which reflect follicular development in the early stages of the follicular phase and to establish whether the levels of these FF steroids correspond to their levels in serum. If these relations are established, serum steroid profiles may be used to monitor follicular development already in this early stage of the follicular phase. We used samples of two experiments, one with multiparous sows at the onset of the follicular phase (weaning) and one with primiparous sows at the midfollicular phase (48 hr after weaning). Complete steroid profiles were measured in pooled FF of the 15 largest follicles and serum using high-performance liquid chromatography-tandem mass spectrometry. In experiment 1, pooled FF volume, as a measure for average follicle size, tended to be positively related to higher FF 17β-estradiol levels (β = 0.56, p = .08). In experiment 2, a larger FF volume was related not only to FF higher 17β-estradiol levels (β = 2.11, p < .001) but also to higher levels of β-nortestosterone (β = 1.15, p < .0001) and its metabolite 19-norandrostenedione (β = 1.27, p < .01). In addition, FF volume was related to higher FF 17α-OH-pregnenolone (β = 1.63, p = .03) and 17α-OH-progesterone (β = 1.83, p < .001), which could indicate that CYP17,20-lyase activity is limiting for 17β-estradiol production in larger follicles at the beginning of the follicular phase. In serum, most of the steroids were present at lower levels compared to FF, except for the corticosteroids. Serum progestins and androgens were never related to follicle pool volume and steroid levels did not differ in the midfollicular phase compared to the onset of the follicular phase in the second experiment. Serum steroid levels therefore poorly reflect the developmental stage of the follicle pool in the first half of the follicular phase of the estrous cycle in sows.

Factors affecting estrus and ovulation time in weaned sows with induced ovulation by GnRH administration in different seasons

Follicle development in post-weaning sows is influenced by various factors. To control ovulation time using hormone, factors that influence ovulation should be investigated. The present study was performed to evaluate the effect of GnRH (buserelin) administration in relation to season and sow parameters on ovulation time in weaned sows. Seventy-seven weaned sows were divided into the following groups: control (hot season, n=21; cool season, n=16) and treatment (hot season, n=22; cool season, n=18). Sows were kept in a close house equipped with an evaporative cooling system. Ovulation time was determined every 6 hr using transrectal ultrasonography. Administration of 10 µg buserelin at 72 hr after weaning affected estrus-to-ovulation interval (EOI) and weaning-to-ovulation interval (WOI) in sows (P<0.05). The percentage of sows that ovulated between 44–56 hr after injection was higher in the cool season than in hot season (P<0.05). Weaning-to-estrus interval (WEI) and injection-to-estrus interval (IEI) were affected by season (P<0.05). Body condition score (BCS) of sows influenced EOI (P<0.01). Sows with low backfat thickness, lactation length <20 days, or litter weight ≥67 kg, had delayed injection-to-ovulation interval (P<0.05). In conclusions, buserelin administration (10 µg, at 72 hr after weaning) advanced ovulation. Hot season prolonged ovulation time. Sows that were weaned with lactation length of at least 20 days, litter weight less than 67 kg, or BCS of at least 3, had better responses to buserelin injection. High backfat reserve after weaning is important for ovulation induction response by buserelin injection.

In ovaries with high or low variation in follicle size, granulosa cells of antral follicles exhibit distinct size-related processes

Antral follicle size might be a valuable additive predictive marker for IVF outcome. To better understand consequences of antral follicle size as a marker for reproductive outcome, we aimed to obtain insight in follicle size-related granulosa cell processes, as granulosa cells play an essential role in follicular development via the production of growth factors, steroids and metabolic intermediates. Using the pig as a model, we compared gene expression in granulosa cells of smaller and larger follicles in the healthy antral follicle pool of sows, which had a high variation versus low variation in follicle size. Selected gene expression was confirmed at the protein level. Granulosa cells of smaller antral follicles showed increased cell proliferation, which was accompanied by a metabolic shift towards aerobic glycolysis (i.e. the Warburg effect), similar to other highly proliferating cells. High granulosa cell proliferation rates in smaller follicles might be regulated via increased granulosa cell expression of the androgen receptor and the epidermal growth factor receptor, which are activated in response to locally produced mitogens. While granulosa cells of smaller follicles in the pool are more proliferative, granulosa cells of larger follicles express more maturation markers such as insulin-like growth factor-1 (IGF1) and angiopoietin 1 (ANGPT1) and are therefore more differentiated. As both higher IGF1 and ANGPT1 have been associated with better IVF outcomes, the results of our study imply that including smaller follicles for oocyte aspiration might have negative consequences for IVF outcome.