Lokesha E, Kalyan De, Vishal Rai, Meera K, Nitin M Attupuram, Priyajoy Kar, Satish Kumar and Jaya
ICAR – National Research Centre on Pig, Rani, Guwahati, Assam
Introduction
Iron is a crucial trace element in the diet of piglets, and its deficiency contributes to nearly 10% of piglet mortality before weaning. This deficiency results in microcytic hypochromic anaemia, impacting the synthesis of haemoglobin (Hb). Approximately 80-90% of iron in piglets is utilized for Hb synthesis, and a deficiency in Hb (< 9 g/dL) in 2-4 week old suckling piglets indicates iron deficiency anaemia. Naturally, sow milk lacks sufficient iron (1.4 – 2.6 mg/L), providing only 1 mg/d to piglets, while their daily requirement is 7-16 mg. Consequently, piglets are highly susceptible to anaemia. Iron plays a crucial role in vital life stages such as growth, pregnancy, lactation, and the transition from weaning to starter. Additionally, iron is essential for the early development of digestive functions, including stomach acid secretion. Deficiency in iron affects intestinal morphology, impairing nutrient digestion and absorption, and compromising the barrier function of the intestine, leading to conditions like endotoxemia and suppressed immunity. Genetic selection for higher litter size and growth rate in piglets increases their iron requirements. Larger piglets are more prone to iron deficiency than smaller ones, while those born to primiparous sows with lower body weight have a reduced risk of anaemia compared to those born to multiparous sows. Furthermore, older sows have lower body iron storage than new sows. Vitamin-K deficiency is another potential cause of anaemia, leading to bleeding, especially in the navel region. Piglets raised on concrete floors may lack access to soil iron (20 – 40g/kg), increasing their susceptibility to anaemia. Additionally, creep feed with a high zinc concentration (>500 ppm), designed to prevent diarrhoea from E. coli infection, may also induce iron deficiency anaemia.
Clinical signs
Anaemic piglets exhibit various noticeable symptoms. They appear weak, with a pale mucus membrane, rough body coat, wrinkled skin, and often suffer from diarrhoea. The reduced oxygen-carrying capacity of their blood leads to laboured breathing. Fluid accumulation occurs around different internal organs, particularly in the brisket and throat regions. Behaviorally, iron-deficient piglets demonstrate signs of memory loss, struggle to identify their feed, show reluctance in returning to the mother or feeding space, and tend to avoid playing with their siblings. Post-mortem examinations typically reveal oedematous lungs and pericardium, indicating the severity of the anaemic condition in these piglets.
Diagnosis of iron deficiency anaemia in piglets
Diagnosing decreased iron levels in the body involves utilizing various haematological measures, (normal values provided in brackets) include: Haemoglobin (Hb, 11-13 g/dL), Mean Corpuscular Volume (MCV, 50-68 fL), Mean Corpuscular Haemoglobin (MCH,17-21 pg), Serum Iron (21.7 ± 5.9 µmol l−1 ), Ferritin ( 20.8 ± 14.7 ng/ml), Total Iron Binding Capacity (TIBC, 56.8 ± 6.8 µmol l−1 ), Transferrin ( 215–380 mg/dl). Subclinical iron deficiency, indicating the availability of iron for new red blood cell production for the next 3-4 days, can be estimated by measuring reticulocyte haemoglobin (CHr, 1.07±0.08 fmol). These diagnostic parameters help assess the iron status in individuals and provide valuable insights into potential deficiencies.
Iron supplementation
Boosting the iron content in the diet of pregnant animals has a limiting effect on the trans-placental transfer of iron to piglets. Similarly, in lactating animals, it restricts the enhancement of iron in the milk. The unabsorbed iron in the excreta of sows becomes the sole source for piglets reared on concrete floors to access iron, which is not an ideal situation. Sprinkling soil over the concrete floor to obtain iron poses risks, including the potential for parasitic infestation and increased microbial infection. Therefore, the most effective way to enhance the iron status of piglets is through external iron supplementation. Preventing piglet anaemia involves providing additional iron in the form of iron salts through either oral administration or injection. Experimental findings suggest that supplying a total of 200 mg of iron within seven days of birth is sufficient to prevent anaemia and promote pre-weaning and post-weaning growth. Alternatively, a recommended regimen involves administering 100 mg of iron on the 3rd or 4th day, followed by a booster dose on the 14th day of age. This strategic iron supplementation is essential for ensuring the optimal health and development of piglets.
Methods involved in administration
When it comes to administering iron, the most common methods are oral or parenteral routes. Oral supplementation is provided in various forms such as tablets, syrup, pastes, or by pasting iron salts (Ferrous sulphates) over the udder of sows. Enriching iron in the creep feed is considered late to counter the early onset of anaemia, as the normal practice of introducing creep feed starts after the second week of parturition. However, oral dosing of iron salts has a disadvantage of lower absorption. Iron absorption is naturally limited through the gastrointestinal system, and in piglets, DMT1 (Divalent Metal Transporter 1) and HAMP (Hepsidin Antimicrobial Peptide) responsible for iron absorption and homeostasis are not fully active at an early age, limiting absorption. Diarrhea symptoms in piglets further decrease the absorption capacity. Alternatively, taking advantage of the temporary ability of the intestine to absorb large molecules from colostrum, iron oral supplements like iron dextran syrups can be given at a dose rate of 200 mg within 12 hours or a maximum of 24 hours after birth. Weaning animals’ diets supplemented with organic iron sources, such as iron gluconate, ferrous fumarate, yeast iron, or ferric glycinate, are reported to be more bioavailable than inorganic salts like ferrous sulphate. Organic irons are more stable, and less excretion of unabsorbed excess iron decreases environmental pollution. Heme iron sources, including meat meal, bone meal, and fish meal, are superior to plant-origin sources due to higher bioavailability. Commonly used cereals and oil cake extracts contain higher amounts of phytate (0.8-0.9%), hindering iron absorption. Supplementation of phytase enzyme (>1500 FTU/kg) aids in utilizing bound iron. New findings report novel sources of iron for oral supplementation in piglets, such as sucrosomial iron, iron oxide nanoparticles (IONP) complexed with phospholipids, iron nanoparticles, or nano iron coated with dextran. These sources show better results when fed on a daily basis at a rate of 6 mg/d from the 5th day after birth to the 28th day of life. ICAR-CIARI has developed oral feeding of ferrous sulphate at a rate of 30 mg/kg body weight on the 2nd, 7th, 10th, and 15th day after birth.
Parenteral administration of iron is a widely practiced method for iron supplementation due to its advantage of quicker absorption into the systemic circulation. However, disadvantages may include improper restraint during injection causing pain, muscle staining, decreased pork value, necrosis at the injection site, or arthritis. Sudden iron overload can lead to hypersensitivity reactions, respiratory failure, and cardiac arrest. Iron injection in piglets deficient in Vitamin E and/or Se makes them susceptible to iron toxicity due to a lack of enzymes to utilize iron. Symptoms such as swelling at the injection site, lameness, anaemia, laboured breathing, icterus, weakness, ataxia, and death may occur within 24 hours. Unutilized iron causes oxidative stress through free radical formation, leading to cytotoxicity, inflammation, and sometimes cardiovascular collapse and death. Unlike iron supplementation, vitamin E and selenium are capable of transport across the placenta and to piglets. Increasing vitamin E (100 I.U. /kg feed) and selenium (0.3 ppm) levels in piglets can be achieved by supplementing them in the sow’s diet. The colostrum or milk concentration of vitamin E and selenium can be improved through supplementation in the sow’s diet, ensuring sufficient levels to utilize a high dose of iron. Hepcidin, a peptide hormone secreted by the liver in response to high iron levels, plays a crucial role in iron homeostasis. Injected iron enters macrophages, stored as ferritin or transported through ferroportin to circulation. A sudden supply of a high iron dose (200 mg) through injection triggers the release of hepcidin, which acts by blocking ferroportin, preventing iron release to circulation, and inhibiting intestinal iron absorption. Therefore, it is advisable to administer iron injections in split doses, with one at 3rd or 4th days and the second dose at 10-14 days of age in piglets, at a rate of 40 mg/kg body weight.
Iron toxicity in piglets
An experimental study conducted with a higher dietary level of iron (~3000 ppm) revealed significant impacts on intestinal morphology and barrier function, leading to a decrease in nutrient absorption. Iron absorption proteins, such as DMT1, also decreased under elevated dietary iron levels. This imbalance resulted in increased reactive oxygen species in the intestine, promoting cell death. Additionally, the study found alterations in the microbial diversity of the intestine, characterized by a decrease in beneficial bacteria and an increase in harmful bacteria. It’s noteworthy that many feeds and salts commonly used, including dicalcium phosphate and limestone, are inherently good sources of iron. However, when supplementation goes beyond the recommended levels, it can lead to gastrointestinal discomforts such as diarrhea, vomiting, or nausea. This underscores the importance of maintaining a careful balance in iron supplementation to avoid adverse effects on intestinal health and overall well-being.
Iron and other minerals
Effective absorption of iron is intricately connected with the dietary status of other trace elements, such as copper and zinc. Copper-containing proteins like ceruloplasmin and hephaestin play a crucial role in mediating the absorption and transportation of iron. A deficiency of copper can negatively impact the efficient absorption of iron. Furthermore, zinc and iron have an antagonist relationship. Excess zinc in the diet, typically around 1500 ppm, diminishes iron absorption. On the other hand, a deficiency in zinc suppresses DMT1 and ferroportin, which are responsible for the effective absorption and export of iron, respectively. Therefore, simply having iron present in the diet may not be sufficient for treating anaemia, and maintaining a balance with other trace elements, particularly copper and zinc, is essential for optimal iron absorption and overall health.
Conclusion Iron deficiency anaemia in piglets poses a significant threat, contributing to about 10% of pre-weaning mortality. Increased genetic selection for higher litter size and growth rate raises the demand for iron, particularly putting larger piglets at a greater risk of deficiency. Key preventive measures involve oral or parenteral routes for iron supplementation. Before initiating any iron therapy, it is crucial to ensure that animals are not deficient in selenium and vitamin E. The limitations of oral iron supplements can be overcome by using novel sources. Parenteral iron supplementation is highly beneficial and safe, especially when administered in split doses. Additionally, recognizing the interplay of iron with other trace elements, such as copper and zinc, underscores the importance of a balanced approach to effectively address piglet anaemia and promote overall health.