Assistant Professor of Swine Medicine and Reproduction Clinic of Farm Animals, School of Veterinary Medicine, Aristotle University of Thessaloníki Greece
The significance of reproductive performance for the outcome of swine production is undoubtable. Both sides, gilts/ sows and boars are the basis of proper and financially rational production in intensive swine farms globally.
⇰ Genetic lines of hyperprolific sows, as well as high durability and increased performance boars are needed for increasing production demands and high-quality pork meat.
A variety of major issues, such as reproductive management, selection of gilts and boars, introduction of gilts to farm’s reproductive program, environmental conditions affecting reproductive performance (e.g. heat stress, etc.), along with maintenance of high health status and fulfillment of specific nutritional requirements, should be taken care during the rearing of hyperprolific sows and boars.
⇰ Controlling the major viral or bacterial swine pathogens affecting the genital tract and reproductive performance, as well as proper nutrition in terms of ingredient/ nutrient requirements and a proper feeding schedule during various stages of gestation and boar’s life, are significant parts of proper reproduction management.
Mycotoxins are secondary metabolites of certain fungi species that can be found in grains worldwide. They are produced before (fungi as plant pathogens) or after the harvest of grains, or even during storage (fungi growing saprophytically).
In particular regions, the mycotoxin menace seems to be higher resulting in severe outbreaks of intoxication (mycotoxicosis) threatening humans and animals1.
⇰ The significant impact of mycotoxins includes loss of human and animal life, increased health care and veterinary care costs, and reduced livestock production2.
The most important mycotoxin producing fungi belong to the genera Aspergillus, Penicillium, Fusarium, Alternaria y Claviceps3.
Out of more than 500 mycotoxins, some are considered extremely significant for pig health and productivity.
Namely, aflatoxins (AF) B1, B2, G1 y G2, deoxynivalenol (DON), zearalenone (ZEN), fumonisins (FB1, FB2, FB3) and ochratoxin A (OTA) are considered significant for their devastating effects on pig production worldwide.
Other mycotoxins such as T-2 toxin, nivalenol or ergot alkaloids have been suggested as somewhat significant for swine, especially in particular geographical regions1,4.
In this article, we will try to synopsize effects of the most important mycotoxins ingested separately, on the two parts of reproduction, i.e. the female part (gilts, sows and the offspring) and the male part which includes the boars.
Predominantly direct toxic effects of AF, OTA, DON, T-2, FB and ZEN are described, since presentation of indirect effects (e.g. increased susceptibility to infections due to impaired immunity that could affect reproduction, or effects of reduced protein synthesis or feed refusal on gestation and litter weight) is practically more or less extremely extensive. In vivo and in vitro effects along with aspects related to the hormonal alteration of reproduction according to relative literature are also described.
Reproductive effects of Aflatoxinas in swine
Aflatoxins (AFs) are produced mainly by Aspergillus flavus, A. parasiticus and A. nomius and are detected usually in maize, peanuts and cottonseed.
The most common AFs are AFB1, AFB2, AFG1and AFG2.
AFB1 is considered as an active hepatocarcinogen and is the most significant in terms of toxicity in swine6.
⇰ The liver is considered the primary target organ of AFB1.
AFs, apart from being hepatotoxic, they have mutagenic, and possibly teratogenic effects in animals.
They are categorized as Class 1 human carcinogens by the International Agency for Research on Cancer (IARC).
AFs decrease the absorption of nutrients and reduce weight gain in pigs, while chronic exposure to low doses results in jaundice (pale-yellowish appearance of the liver) with hemorrhaging sites in the liver and variable levels of fibrosis and cirrhosis, diffused centrilobular necrosis and fat degeneration7.
Few reports have connected AFs with reproduction in swine. Abortion is not expected at AF7.
- Sows are capable of normal gestation and reproduction when fed AF at levels between 500 and 700 ppb, whereas their piglets show growth retardation due to AF excretion in milk8,9.
- Reduced piglet birth weight has been reported after ingestion of 800 ppb AFB1 in feed of sows during the second half of gestation and the suckling period10.
It has been further suggested that AFB1 can impair porcine early embryonic development (blastocyst formation was impaired with treatment of 1 nM AFB1) through oxidative stress (excessive reactive oxygen species), induce DNA damage, disrupt DNA damage repair process, while also induces apoptosis and consequently autophagy12.
Possible adverse effects on boar reproductive efficiency have been suggested13, where lower sperm concentration, lower survival of spermatozoa, and a larger proportion of abnormal spermatozoa were found simultaneously with great levels of AFB1 in seminal plasma.
Reproductive effects of Ochratoxin A in swine
Ochratoxin A (OTA) is produced by several Aspergillus and Penicillium species, such as Penicillium verrucosum A. ochraceus, A. westerdijkiae, A. steynii, A. carbonarius and A. niger14.
Its primary target organs are the kidneys (nephrotoxicity), however it can induce several toxic effects such as teratogenic, embryotoxic, genotoxic, neurotoxic, immunosuppressive and carcinogenic14,15.
⇰ OTA has been classified by the IARC as a possible human carcinogen (group 2B).
In a previous study with boars (250 kg weight), which were given 0.08 μg/kg OTA orally for 6 weeks, reduction in sperm viability, initial forward motility, and motility were observed after 24 hours storage16.
Moreover, it was suggested that OTA (fed to boars at high concentrations) might have the potential to affect sperm production and boar semen quality by inducing a reduction of initial motility and longevity of spermatozoa17.
Additionally, OTA is able to negatively affect porcine oocyte maturation in vitro (reduced rate of porcine oocyte polar body extrusion) at levels of exposure exceeding 5 μM18.
Reproductive effects of Fuminosin B in swine
Fumonisin Bs (FBs) are mycotoxins produced mainly by Fusarium verticillioides and F. proliferatum, commonly in maize.
The predominant FB1 corresponds to 70% of FBs and is classified as a potential human carcinogen (Class 2B) by IARC19.
Its main toxic mechanism is based on the disruption of sphingolipid biosynthesis, with inhibition of ceramide synthase that results in the accumulation of sphinganine and sphingosine.
Acute intoxication of swine with high levels of FB (>100 ppm) is characterized by pulmonary edema7.
Nevertheless, FBs have been well implicated in the impairment of immune response [e.g. modification of Th1/ Th2 (T-helper 1/T-helper 2) cytokine balance], as well as in significant effects in the gastrointestinal tract.
FB1 has been associated with the induction of intestinal barrier integrity alterations and its function/permeability [e.g. decreased transepithelial electrical resistance (TEER), reduced expression of occludin and E-cadherin in ileum], as well as with the modulation of digestive and absorptive processes (e.g. reduced aminopeptidase activity in jejunum) and reduction of intestinal defense during pathogen exposure (increased colonization and shedding of Escherichia coli)7,20.
In regard to reproduction, FBs have been also linked with delay in sexual maturity and reproductive functionality alterations21.
⇰ Specifically, they have been suggested as responsible for the reduction of testicular and epididymal sperm reserves and daily sperm production in boars22,23. Additionally, detrimental effects on semen quality and motility after 6 months of exposure to FBs have been suggested23.
Furthermore in vitro, FB1 produced inhibitory effects on granulosa cell proliferation24.
- FB1 was found to influence the steroidogenic capacity of porcine granulosa cells (stimulation of progesterone production but no effect on estradiol production), as well as to inhibit their proliferation, thus it could compromise the normal follicle growth and oocyte survival in swine5,24,25.
- In vivo, la FB induced abortions 1–4 days after acute spontaneous toxicosis which was probably consequence of fetal anoxia due to severe pulmonary edema in the dam26,27.
- Concentrations of 100 ppm FB1 fed to sows in the last 30 days of gestation did not induce pulmonary edema, abortions, or fetal abnormalities7.
Reproductive effects of Trichothecenes in swine
Effects of Deoxynivalenol on swine reproduction
All trichothecenes are known to affect reproductive performance in pigs. Deoxynivalenol (DON) belongs to the trichothecene family of mycotoxins and it has been proved able to significantly inhibit protein synthesis.
⇰ Particular acetylated and modified forms of the parent toxin, such as 3-acetyl-DON (3-Ac-DON), 15-acetyl-DON (15-Ac-DON) and DON-3glucoside [DON3G, main plant metabolite of DON], occur simultaneously in grains25.
DON toxicosis has been associated with gastrointestinal signs such as abdominal discomfort, diarrhea, vomiting, anorexia and reduced weight gain.
DON heavily affects the intestinal barrier integrity and function, while can also modulate immune response7,20.
Evidence of oocyte maturation and embryo development impairment along with the reduction of feed intake are the main reasons behind the DON-induced detrimental reproductive effects in pigs.
⇰ In vivo, ingestion of DON contaminated feed by pregnant gilts, may result in reduced weight and body length of piglets28.
A significant passage of DON through the placenta from exposed sows to fetuses that could potentially affect fetal function has been demonstrated29,30.
Furthermore, several in vivo negative effects on fertility have been associated with consumption of combined DON and ZEN contaminated feed31.
DON has been associated with particular reproductive effects, mainly through in vitro studies on porcine oocytes.
- In vitro effects of DON include disturbance of porcine oocytes maturation through the induction of abnormalities of the meiotic spindles and by altering oocyte cytoplasmic maturation32,33,34.
- In addition to the DON-induced impairment of oocyte maturation, findings of autophagy/ apoptosis and epigenetic modifications in porcine oocytes have been presented35.
- Moreover, DON has been associated with dose-dependent effects on porcine granulosa cell proliferation [biphasic effect: lower concentration (0.034 mM) of DON results in increased proliferation, but greater concentration (3.4mM) have the opposite effect], inhibition of progesterone and estradiol production [induced by FSH plus Insulin-like growth factor I (IGF-I)] and CYP19A1 and CYP11A1 mRNA abundance15,36.
- Exposure of ovarian explants to 10 μM DON affected the process of follicular maturation with a decrease of the reserve pool of follicles, resulting in a significant decrease in the number of normal follicles, as well as an increase of pyknotic oocytes number in all stages of follicular development37, whereas treatment with 1 μM DON decreased the rate of polar body extrusion in porcine oocytes18.
Effects of T-2 toxin on swine reproduction
Besides DON, which is the main representative of the trichothecenes group, T-2 toxin and its deacetylated form HT-2 toxin (type A trichotecenes) can be considered as quite significant for swine, according to recent studies.
They are produced in crops (e.g. wheat, maize, barley) by various Fusarium species such as Fusarium sporotrichioides, F. poae and F. langsethiae, either in the field or during storage.
Pigs are very susceptible animals towards their effects. HT-2 toxin is a natural contaminant in cereals but is also the main metabolite of T-2 toxin, thus T-2 toxin effects can be partially attributed to HT-2 toxin.
In acute T-2 toxicosis cases, serous-haemorrhagic necrotic-ulcerative inflammation of the digestive tract, vomiting, diarrhea, leukopenia (leukocyte apoptosis), hemorrhage, shock and death, oral/dermal irritation and immunosuppression can be observed.
⇰ However, in chronic cases of mildly contaminated grains ingestion, growth retardation, weight gain suppression and feed refusal along with greater pro-inflammatory gene expression, are observed in pigs38.
Quite similarly to DON, the effects of type A trichothecenes on reproduction are mainly demonstrated through in vitro studies, since in vivo clinical reproductive disorders in pigs, that could be directly attributed to their effects have not been presented.
According to a study39, T-2 toxin may be able to alter the growth of the granulosa cell layer as well as affecting steroidogenesis.
- T-2 toxin had potent inhibitory effects on IGF-I and FSH-induced steroid production in cultured porcine granulosa cells, since dosages of 1, 3, 30 and 300 ng/mL inhibited estradiol production, but progesterone production was inhibited with a dose of 30 and 300 ng/mL. An inhibitory effect on cell number was observed at 3 ng T-2 toxin/mL.
- It has been also suggested that the treatment of porcine oocytes with 50 nM HT-2 toxin and greater concentrations significantly decreased the rate of polar body extrusion18.
- Failure of oocyte maturation after HT-2 toxin treatment has also been suggested, since the toxin inhibited porcine oocyte polar body extrusion and cumulus cell expansion, while also disrupted meiotic spindle morphology and disturbed actin distribution40.
- Oxidative stress, apoptosis and autophagy in the treated oocytes were also among the findings of the previously mentioned study.
Reproductive effects of Zearalenone in swine
Zearalenone (ZEN) is a phenolic resorcylic acid lactone mycotoxin produced by several Fusarium species, especially F. graminearum and may undergo modification in plants, fungi and animals (prehepatic, hepatic and extrahepatic) by phase I and phase II metabolism.
⇰ Major metabolites of ZEN include α-zearalenol, β-zearalenol, α-zearalanol, β-zearalanol, zearalanone (phase I), whereas conjugated forms with glucose, sulfate and glucuronic acid are the outcome of phase II25,41.
Pigs are very sensitive to ZEN, since the parent toxin is metabolized mainly to α-zearalenol in that species, which shows greater estrogenic potency than ZEN. ZEN toxicosis has also been associated with increased oxidative stress, reduction of nutrient digestibility and growth retardation.
⇰ Toxic effects of ZEN on other tissues and systems outside the reproductive tract, such as liver and immune system have already been demonstrated42,43,44.
ZEN sufficiently resembles 17β-oestradiol that allows it to bind to estrogen receptors in various organs and induce estrogenic effects.
Its effects depend on the dose, as well as on the time of administration in relation to estrous cycle5. It is considered the most important mycotoxin affecting swine reproduction and prepubertal gilts seem to be a very sensitive age group to the effects of the toxin.
For more than 40 years, researchers have demonstrated the significant reproductive disorders that can be caused after ZEN ingestion in gilts and sows in vivo (e.g. pseudopregnancy, diminished fertility, hyperestrogenism syndrome, reduced litter size).
Moreover, in vitro studies have presented its negative effects on oocyte maturation and porcine granulosa cells proliferation7,41.
Placental passage of ZEN from sows to fetuses has been confirmed, as ZEN and its metabolites have been detected in the bile of newborn piglets from sows ingesting contaminated feed45.
Hyperestrogenic effects in newborn piglets in Greek swine farms.
As regard to the effects of ZEN on boars’ reproductive function and quality of semen, results of in vivo studies have suggested reduced serum testosterone levels, testis weights and spermatogenesis, as well as feminization and suppressed libido in young boars5. Further in vitro studies on boar semen have suggested ZEN toxicity.
Multiple impairment of semen quality and kinetics, including decrease of sperm viability and progressive motility46-48 can be the outcome of boar semen in vitro exposure to ZEN.
Additionally, ZEN and α-zearalenol can reduce the ability of boar spermatozoa to bind to the zona pellucida46 and affect sperm chromatin integrity48,49.
Diagnosing mycotoxin-induced reproductive disorders in sows or boars is definitely not an easy task. As presented in this review, the extent of effects on the reproductive system of swine is vast and includes a great variety of direct and indirect mechanisms of toxicity at the cellular and genomic levels.
Furthermore, the interactions of the abovementioned toxins in vivo and their final observed effects on sow and boar’s reproductive efficiency have not been fully elucidated yet and need further clarification.
Evidence so far suggests that ZEN and α-zearalenol are the most important mycotoxins for swine reproduction and from a clinical viewpoint they are probably the first to investigate in cases of reduced fertility on farm.
⇰ However, such cases usually include concomitant DON ingestion via feed due to the “characteristically observed” combined mycotoxins contamination of pig feed.
From the diagnostic standpoint, onset of reproductive signs right after feed alterations on farm, as well as the absence of any significant impact of infectious agents or environmental or managerial factors that could induce reproductive disorders, must be considered when establishing differential diagnosis of reproductive inefficiency cases.
⇰ Feed analysis is of colossal importance along with evidence of mycotoxins/metabolites circulating in blood or detected in tissues and excreta.
Unfortunately, antidotes against mycotoxins do not exist, thus, control of such cases would need removal of contaminated feed or mixing with clear feed (usually at 1:10 rate), as well as inclusion of agents that could either adsorb or biotransform the mycotoxins to non-toxic metabolites.
⇰ Moreover, clinical support should be given to splay-leg newborns with signs of hyperestrogenism that cannot receive the appropriate amount of colostrum/milk.
In the majority of cases, removal of mycotoxins would lead to the improvement of fertility and reproductive parameters in due time through defense and repair mechanisms at cellular level50.
⇰ However, time would be needed in order to achieve previous reproductive rates again on farm.
The principle is that prevention of mycotoxicosis should be the basic tool.
Regular feed screening (enrichment materials and other fiber sources can contain significant amounts of mycotoxins, thus they should be also included in the analysis), as well as the inclusion of proper agents that would reduce the level of mycotoxins available for absorption in the gastrointestinal tract are of utmost importance51.
Proper management of sows (e.g. proper estrus detection, heat stress countermeasures) and regular semen viability and kinetics analysis, along with prevention of infectious agents (e.g. proper vaccination schedule of the breeding stock), would significantly assist on rapid detection of abnormalities that could be associated with mycotoxicosis, thus proper treatment and prevention efforts would start timely.
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