Preparing and protecting your gilts for optimum lifetime performance

Gilts are arguably the most valuable animals on a swine farm as their success or failure will dictate the future productivity and profitability of the sow herd. However, often they are treated no differently than their meat-producing counterparts from a nutritional perspective. The modern gilt has been selected for prolificacy first and foremost. Recent data from leading genetic companies are reporting the reproductive performance of over 40 piglets per sow per year from their top-producing herds (SEGES report 2136, 2021). These gilts are growing faster and are leaner than their predecessors. Growing at such a fast rate with minimal backfat can make it difficult for adequate bone and mammary gland development to occur to support a long and productive life. The cost of raising a gilt is an investment that is not returned until at least her third parity however many gilts fall out of the herd before this stage. To optimize the longevity of gilts, a holistic and adaptative approach is required, encompassing nutritional strategies dedicated to optimum bone and joint development, immune competency, and reproductive organs' health and maturity. These approaches include providing optimum mineral and vitamin nutrition, as well as safeguarding the gilts against the potential risks of mycotoxins.

Reproductive health and development

Reproductive failure is the leading cause of premature culling of gilts, accounting for between 25-47% of cases, followed by common disease and lameness (Wang et al., 2019). Gilts are especially sensitive to mycotoxins that can have a direct effect on the development and functionality of the uterus and ovaries, impacting oocyte development and disruption of pregnancy hormones. Due to its similarity to estrogen, zearalenone (ZEN) binds to estrogen receptors and causes hyperestrogenism. Enlargement of external reproductive organs such as the vulva is a clear sign of hyperestrogenism with ZEN-intoxication as the most important differential diagnosis. Gilts are even more sensitive to the effects of ZEN than sows, which is reflected in EU guidance levels which are 250 ppb for sows and 100 ppb for gilts, respectively.

Another example of mycotoxins impacting reproduction is the group of trichothecenes. These Fusarium-toxins are well known for compromising feed intake and causing leaky gut syndrome which can indirectly impact reproductive performance. There is also evidence that these mycotoxins, which often co-occur with ZEN, also directly impact reproduction. Incubation of ovaries collected from gilts with deoxynivalenol (DON) – a mycotoxin belonging to the family of B-Trichothecenes, resulted in toxic effects on ovaries and negative effects on follicular development (Gerez et al., 2017). ZEN and DON are only two of the most prominent representatives within the huge group of mycotoxins with known effect on fertility.

The reproductive health and performance of gilts can be benefited not only by guaranteeing the safety of their feed but also by optimizing its micronutrition. Data in humans have started to draw correlations between the vitamin D status of mothers and the birthweight of their offspring. Low levels of circulating vitamin D3 in the blood (25-OH-D3) in early gestation have been shown to be associated with low birth weight or even preeclampsia (Benachi et al., 2020). Research in pigs has shown that feeding vitamin D3 in the form of 25-OH-D3 which is a more bioactive metabolite of vitamin D3 was able to increase the muscle fiber number of piglets in-utero thereby impacting the future growth potential of these pigs. A recent review has summarized all the extensive benefits of maternal 25-OH-D3 supplementation including increased sow performance, improved milk composition, and enhanced bone characteristics in sows and piglets, promoting skeletal muscle development and influencing gut bacterial metabolites of piglets compared with vitamin D3 (Zhang et al., 2021).

Skeletal health

Lameness is among the top two reasons for premature culling of gilts and can account for as high as 15% of the reasons for gilts not making it past their first parity (Wang et al., 2019). Consequently, prioritizing optimal skeletal development during the growing period and the initial gestation/lactation phases becomes imperative to optimize the lifetime performance of sows.

The importance of vitamin D3, specifically the active form, 1-25-dyhydroxyvitamin D3 for calcium metabolism and hence skeletal health and function of the locomotory system is well known. Lower serum 25-OH-D3 levels have been reported in lame pigs in commercial settings versus their healthy counterparts (Williams et al., 2023 in press). Feeding the bioactive form of vitamin D3, 25-OH-D3 has been shown to successfully increase serum 25-OH-D3 levels compared to feeding the same levels of classical vitamin D3 resulting in increased bone breaking strength, better gait scores and increased gilt selection rates (France, 2014; unpublished field trial). Both the liver and kidney are key organs in the normal metabolism of vitamin D3. These organs are also the main targets of some of the most prevalent mycotoxins (e.g., ochratoxins and aflatoxins) found in feed ingredients fed to gilts. Damage to these organs as a result of mycotoxin contamination will directly impact the ability of gilts to properly mineralize their bones and develop cartilage in joints predisposing these animals to lameness issues.

Damaging the liver and kidney are not the only mechanisms by which mycotoxins can impact bone metabolism. Some emerging research has demonstrated an interaction between vitamin D metabolism in different body tissues and the negative systemic effects of mycotoxins leading to bone fragility and arterial function (Malvandi et al., 2022). Aflatoxins have been shown to affect vitamin D receptor expression which can decrease vitamin D efficiency (Costanzo et al., 2015). Other finding in pigs has demonstrated a decrease in vitamin D receptor expression in intestinal mucosa when mycotoxins are present, lowering the efficacy of vitamin D metabolism (Sauve et al., 2021). Oxidative stress is a well-known effect of mycotoxins. Oxidative stress has a direct effect on bone metabolism by promoting the activity of osteoclasts (cells responsible for bone dissolution) whereas it suppresses the activity of osteoblasts (bone forming cells). This modulation of bone homeostasis leads to a delay of fracture healing as well as skeletal fragility (Sun et al., 2015).

Immune competency

Immune competency development serves as a foundation for a healthy start and long lifetime performance of sows. Gilts need to be prepared for introduction to the sow herd by well-managed and farm-specific processes including a vaccination regime. Health is also challenged by pathogens circulating in the herd, for which gilts might not have required immunity previously. Mycotoxins can modulate response of the immune system to pathogens and vaccination antigens and hence hinder an adequate immune response.

Porcine reproductive and respiratory Syndrome (PRRS) is one of the diseases with the highest impact on economy and is the focus of many activities in research. It is a common procedure to vaccinate gilts before introduction to a farm positive for PRRSV, even if the herd is clinically stable. Several papers show that exposure to DON modulates response to PRRSV-vaccination. Effect is not only on antibody response (Savard et al., 2015, Rückner et al., 2022, Pierron et al., 2023) and cell-mediated immune system (Pierron et al., 2023) but also on clinical outcome. In a vaccination-challenge trial vaccinated piglets exposed to DON were not protected and were affected by the disease in the same way as an unvaccinated animal (Rückner et al., 2022). Vaccination failure does not only affect susceptibility of respective gilts to disease but may lead to uneven immunity of the herd, circulation of the virus and hence instability of herd health.

The role of vitamin D on the immune system has been well researched particularly in recent years in the context of COVID-19. Vitamin D3 has been found to have a pivotal role to play in numerous aspects of the immune response with most major immune cells subsets of the innate immune system as well as the adaptive immune system expressing its receptors (Di Rosa et al., 2011). The active form of vitamin D3 has a regulating effect on the immune system by promoting the secretion of anti-inflammatory cytokine IL-4 and suppressing proinflammatory signals IL-2, IFN gamma, IL-17, IL-21 (Yang and Ma, 2021). Therefore, inadequate circulating levels of 25-OH-D3 which is often the case in gilts can result in a suboptimum immune response characterized by excessive inflammation which wastes energy and nutrients or a weak immune response in the face of challenge leading to disease.

The adaptive nutritional approach for gilts

An adaptive nutritional approach is necessary to prepare and protect gilts entering the herd. This approach begins with a thorough assessment of the risks facing these gilts. One of the key risks threating the reproductive development and success of gilts is mycotoxins. Gilts are even more sensitive to mycotoxins than sows and their feed should be analyzed in a comprehensive way to include not only the most common mycotoxins but also emerging and modified mycotoxins. Protecting gilts from mycotoxins and it’s harmful effects requires advanced risk management including prediction, precise quantification and deactivation of the mycotoxins in gilt feed. A unique biotransformation technology present in in the Mycofix® product line, combining patented specific enzymes and biological components that convert harmful and widespread toxins into non-toxic, environmentally safe metabolites is the most advanced available solution in the market to protect gilt wellbeing and performance.

Another risk to gilt longevity that largely goes unnoticed is suboptimum vitamin D3 status. Sub-optimal vitamin D levels have implications for optimum Ca and P metabolism having the potential to compromise gilt health and diminish performance. Precisely assessing 25-OH-D3 blood status and providing adequate amounts of a bioactive form of vitamin D3 (Hy-D®) to guarantee target 25-OH-D3 blood levels can ensure faster and more efficient uptake of vitamin D from feed to blood, supporting stronger bone development, enhanced reproduction, and immune competency.

The evolving characteristics of the modern gilt, such as increased leanness, faster growth rates and hyperprolificity demands an adapted gilt preparation strategy to ensure longevity in the herd. Mycotoxins, known as endocrine disruptors, have the potential to adversely impact reproductive organ development, gilt maturity, immune competency, and bone health. On the other hand, adequate vitamin D nutrition plays a pivotal role in promoting bone, cartilage, and joint formation, as well as supporting immune competency and reproduction. By effectively managing mycotoxins risks and ensuring proper vitamin D nutrition, gilts can be prepared and protected to achieve optimum lifetime performance.