Sow mortality is a long-standing issue in sow herds, and any sow death harms the farm’s profitability. Replacement gilts typically do not become profitable until their second or third parity, so an increase in sow mortality is not only a health issue but also a direct economic one. Sow mortality is likely caused by multiple factors and needs to be addressed through a multidisciplinary approach involving disease, nutrition, management, genetics, and employee observation. The following 12 questions outline the issues currently faced, possible causes, and key points for prevention and control.
One: Reproductive performance and limb health are fundamental
1. Are the gilts equipped for good reproductive performance? Over the past 20 years, the reproductive capacity of commercial sows has changed dramatically. The industry target of producing 35 weaned piglets per sow per year places high demands on reproductive performance. High reproductive capacity is due in part to genetic selection for more robust replacement gilts with mature reproductive capacity and healthy legs. From a reproductive perspective, when gilts reach sexual maturity, they should have a well-developed vulva and at least 7 pairs of functional teats; if the number of teats cannot meet the litter size, they must produce more piglets in the next litter to remain in the herd.
2. Are the sow’s legs healthy? Skeletal health is a key area to check when replacement gilts enter the group and to reassess frequently as they mature. Lameness is one of the leading reasons sows are culled prematurely or euthanized. Features such as bowed front legs, upright hocks on the hind legs, toes on both sides split and flattened, and a swaying hindquarters can all affect a sow’s productive lifespan. Efficient sow utilization depends on sound skeletal structure when replacement gilts are introduced.
3. Are sow selection criteria feasible? Selecting lower-quality replacement gilts may adversely affect their productive lifespan and profitability, but unsuitable sows may still be selected at the outset in production. Is this being done to make up the numbers, do employees need better training in selection, or is the selection process not strictly controlled? These issues may all lead to higher sow mortality.
Two. Nutritional factors are integral to bone health, reproduction, and immunity.
4. Are amino acid levels adequate? A program must be provided to meet the nutritional needs of sows and gilts. There are four major nutritional areas worth further study: protein and/or amino acids, energy, macro minerals, and micronutrients. A sow trial in Kansas showed that feeding more than 1.05% lysine had no effect on sows, while many industry formulations now increase lysine to 1.20%, and there is disagreement in the industry about the optimal recommended level. Before reducing added amino acids, it is also necessary to study whether nonessential amino acids are adequate, because collagen and ligaments are composed mainly of nonessential amino acids, while most nutritionists currently add higher levels of crystalline amino acids and lower levels of crude protein to sow diets.
5. Are fatty acid levels adequate? Feed is typically formulated based on metabolizable energy, net energy, or the lysine-to-net-energy ratio, but the effects of different types of fatty acids are generally not considered. Long-chain polyunsaturated fatty acids are precursors to inflammatory mediators; in 2014, Michigan State University demonstrated that adding protected fish oil to the diet increased DHA in the cartilage of replacement gilts and multiparous sows, but the small sample size did not allow physiological or apparent differences to be determined. Different fatty acids affect not only sow performance but also piglet survival and growth performance, so a better understanding of sow fatty acid nutrition is needed.
6. Are the calcium and phosphorus levels in the formulation appropriate? Bones are composed of approximately 60%–70% minerals, mainly calcium and phosphorus. Recommended levels in the industry vary widely: the NRC (2012) recommends 0.60%–0.76% calcium; the PIC (2016) recommends a total calcium requirement of 0.85% for sows; and new research from the University of Illinois suggests switching to a digestible calcium-to-total calcium ratio. Research on calcium requirements for sows remains limited, and further research on both macrominerals and trace minerals is needed to optimize sow nutritional requirements.
7. Are vitamin D levels adequate? Vitamin D is crucial for calcium absorption, balance, and bone formation, and also plays an important role in the immune system. A 2014 U.S. survey found that vitamin D levels in feed for gestating and lactating sows ranged from 1100 to 2222 IU/kg, while the NRC (2012) recommended level was 800 IU/kg. An Iowa State University Veterinary Diagnostic Laboratory survey found that, compared with the recommended level, a lower level was recommended if sows were not deficient in vitamin D in their serum. DSM research also showed that the source of vitamin D may matter: adding 25-OH vitamin D₃ can increase serum calcium levels and reduce the number of stillborn piglets at farrowing.
8. Can collagen and elastin play a role? Human medical literature shows that women with uterine prolapse before menopause have lower collagen levels, and lower desmosine levels in uterosacral ligament tissue, suggesting altered elastin metabolism. Collagen plays an important role in the support tissue of the uterine ligaments, while elastin is essential for the ligaments to stretch during pregnancy as the fetus gains weight. Lameness remains the leading cause of death and culling in sows. Whether changes in collagen and elastin synthesis are associated with lameness and uterine prolapse warrants investigation of upstream nutritional factors.
9. What is the function of vitamin C? Pigs are capable of synthesizing vitamin C via gulonolactone oxidase, but hereditary vitamin C deficiency was found in a Danish pig herd. It was characterized by weakness, reluctance to move, swelling around the joints, and pain on touch, and was cured by vitamin C supplementation. Vitamin C is essential for collagen synthesis and is also involved in the differentiation of embryonic cell connective tissue. A deficiency can directly affect sows and their offspring.
10. Do mycotoxins cause more problems? Zearalenone is the main mycotoxin responsible for reproductive disorders in sows. Increasing evidence shows that zearalenone levels as low as 75 μg/kg can affect the reproductive tract within just 6 d of exposure; a study of gilts weighing 10.8 kg found that feeding contaminated feed increased the length and weight of the reproductive tract. Traditionally, pigs of this body weight are raised under a nursery program rather than a specialized gilt development program. Formulation should also take into account that mycotoxin detoxification may bind essential vitamins and other nutrients; vitamin C has been shown to mitigate zearalenone-induced damage in pigs.
11. Are relevant trace minerals being overlooked? There is trial evidence that organic trace elements can help prevent lameness in sows, but some trace minerals that may be biologically essential may be overlooked. Boron is an essential element for plants. Broiler studies indicate that boron can stimulate growth and may, to some extent, prevent leg deformities caused by vitamin D deficiency. Increasing evidence suggests that boron plays a role in bone mineralization and structure, and is also associated with energy metabolism, insulin sensitivity, the immune system, and embryonic development.
Three. Management oversight and employee capabilities are the last line of defense
12. Do sows need better observation? Recent Danish research concluded that most deaths (excluding euthanasia) occur in the farrowing house and among gilts (parities 1–3). This means either that sows die from acute conditions with a rapid course, such as intestinal or organ torsion, heart failure, or farrowing complications, or that sows are not observed frequently enough for subtle signs of illness to be noticed. The industry does a good job of managing piglets and caring for piglets at 1 days of age, but may not have enough time to observe, manage, and assess sow condition, or to investigate the real causes of sow deaths. Training employees to perform a post-mortem examination on each sow, identify or photograph abnormalities, and work closely with a veterinarian are key steps in finding the real reason for the increase in sow deaths.
Four. Summary table of 12 key points
Sow mortality cannot be explained by a single cause. Prevention and control should begin with the selection and limb assessment of replacement gilts, expand nutritional formulation beyond “meeting energy and lysine requirements” to include fatty acids, the calcium-to-phosphorus ratio, sources of vitamin D, vitamin C, and trace minerals, and incorporate mycotoxin control into daily routines. Farrowing rooms and first-parity sows should be key areas of observation. Employee training, necropsies, and collaboration with a veterinarian can help identify the actual causes of mortality on the farm. Only by connecting nutrition, physiology, health, and management can a measurable, practical sow mortality prevention and control plan be developed.