Pregnancy associated laminitis
Insulin resistance in pregnant mares can be detrimental to both mother and foal. DR JENNIFER STEWART explains why it happens and what can be done to help prevent it.
Known as ‘gestational diabetes’ or GDM, pregnancy diabetes affects between 4% and 12% of women. An equivalent condition occurs in mares and increases their risk of pregnancy associated laminitis. In both human and horse, the condition is associated with changes in blood glucose and insulin regulation.
The role of insulin is to move glucose out of the blood and into the body tissues (mostly into muscle and liver). At around 27 weeks (6-7 months) insulin sensitivity in mares begins to drop. This is known as insulin resistance, an evolutionary adaptation which means the mother’s tissues become less sensitive to the effects of insulin so that less glucose is taken out of the blood and more glucose can be delivered to the foetus and placenta. In addition to reduced sensitivity to insulin, the amount of insulin released from the pancreas is increased during pregnancy and blood insulin levels rise.
In all horses, irrespective of breed and discipline, elevated blood insulin is the number one cause of laminitis. Due to the natural development of insulin resistance during pregnancy, mares are at increased risk for laminitis from six months gestation. And it’s not just the effect of higher insulin levels on the feet – additional stress comes from the increasing body weight borne by the hooves, and lack of regular hoof care and farriery. Further, the risk of pregnancy associated laminitis increases with every pregnancy.
The choice of feed can either protect pregnant mares or increase the risk of laminitis. Feeds that are high in starch and sugar compound the risks (Table 1). Insulin levels rise faster, peak higher and remain elevated for longer in pregnant mares and this is particularly pronounced with high starch/sugar feeds. Both starch and sugar stimulate insulin release and because pregnant mares already have elevated insulin, they need to be protected from surges caused by diet mistakes and inappropriate feed choices. Regardless of the statements and descriptions on feed bags and labels, researching the website and reading the ingredient list is the best protection for your mare.
Certain feed ingredients and certain feed processing methods (Table 1) have harmful effects on blood glucose and insulin responses and can be unsafe for pregnant mares. These include all grains (oats, wheat, barley, corn) and all grain by-products i.e. cereal by-products and cereal co-products such as bran, pollard, millmix, and millrun. Many feeds are variously described as ‘low GI’, ‘cool’ or ‘low starch’ (Table 2) and are marketed as safe for certain equine clinical conditions. However, relying on the branding, labelling and description can be detrimental.
Stomach ulcers and peri-natal colic
Although horse owners often roll and boil cereal grains, the most common commercial processes are grinding, micronising, extruding/expanding and flaking – the objective being to increase the nutritional value of the feeds by enhancing the availability of starch. Starch is transformed into glucose by bacteria, digestive juices and enzymes in the stomach and small intestine. Compared to grinding, micronising and extruding increase the rate of starch fermentation and breakdown in the stomach. But this is not necessarily a good outcome as the starch alters the microflora in the non-glandular portion of the stomach, eventually causing conditions such as ulcers. Starch-rich feeds also delay stomach emptying, prolonging exposure of the stomach to acid, another risk factor for stomach ulcers (ESGD and EGGD). Feeds high in starch also increase the risk of colic.
Both the amount of starch in the feed and the type of feed processing have a significant impact on blood glucose and insulin. The misapplication of these factors can result in abnormally high insulin levels and laminitis. Although horses in hard work and needing high grain intakes benefit from these processing methods, they are not appropriate for horses with insulin dysregulation (PPID, EMS) and pregnancy. And, it’s not just the mare that experiences faster, higher and longer rises in insulin, it impacts the growing foal too.
The foal: insulin and developmental orthopaedic diseases
Blood glucose and insulin flow through the placenta from the mare to the developing foal. Here they influence the organs and systems that control glucose and insulin dynamics including the structure of the pancreas and the development of joint cartilage. After birth, foals of mares fed starch/sugar concentrates during pregnancy have higher insulin levels for up to 18 months. They are also more susceptible to osteoarticular lesions, including all forms of developmental orthopaedic diseases (DOD) such as bone cysts, physitis and OCD. Foals from mares on high sugar/starch feeds have abnormal insulin and inflammation from 160 days to 12 months of age. This is the major risk period for developmental orthopaedic diseases and even moderate amounts of starch/sugar during pregnancy predispose the foal to osteochondral lesions between 7 and 12 months of age.
The pregnant mare presents a difficult challenge since feed supplementation is indicated for at least the last four months to support rapid foetal foal growth. Being a broodmare has been identified as a risk factor for obesity and laminitis and it can be hard to manage increasing body weight in pregnant mares. Mares increase their body weight by around 15% during pregnancy, with the majority gained between 230 and 290 days gestation. The last third of pregnancy is the time of increased foetal foal growth – which often coincides with poor winter pastures – and pregnant mares need more nutrients, but the primary need is for protein and minerals, not energy. Energy requirements increase with lactation, not so much during pregnancy. All care must be taken to ensure the feed is low in starch and sugar and mares don’t become overweight. It’s important to keep in mind that pregnant mares in lean or normal body condition can become insulin resistant on feeds high in starch. Even in normal, non-pregnant, healthy horses, starch and sugar are associated with insulin resistance, obesity and laminitis.
Because mismanagement of pregnant mare nutrition has profound health effects for the mare and the foal, it’s important to avoid diet mistakes and indiscretions. We need to avoid mares being subjected to concurrent factors that favour the development of laminitis. Reading labels carefully (Table 2) and feeding a diet based on roughage with added oil (250–500ml/day) plus a balancer more closely mimics the natural grazing state of pasture and allows for adaptation of glucose and insulin levels to pregnancy and lactation. Low starch/sugar feeds combined with high roughage, oil-enriched diets have little effect on insulin and have been shown to protect against the development of laminitis in mares and DOD in foals.
Detecting laminitis:
Recent studies have revealed how difficult it can be to diagnose laminitis, and that up to 45% of cases may not be recognised or may be mistaken for colic, tying-up, foot abscess, bruised soles, hock lameness or navicular disease. From this research comes valuable information and a clear check list to alert owners that the laminae are undergoing damage and weakening:
- Difficulty turning
- Shifting weight from leg to leg
- Reluctance to walk
- Short, stilted gate
- Bilateral forelimb lameness
- Increased digital pulse
- Resistance to foot lifting
Also watch out for a stilted, wooden gait, rigid head carriage at the walk, less spontaneous movement, reluctance to trot or make sharp turns, hesitancy on hard ground, tension through shoulders, back and rump, and a drop in social status. Importantly, the typical laminitis stance and divergent hoof growth rings are present in less than 50% of cases. You can read more in this study.
The risk of over-feeding energy and calories is increased with complete feeds if the amount fed is increased to meet the increased amino acid (protein), vitamin and mineral needs of pregnancy. However, if a complete feed is fed below recommended amounts, it’s likely there will be underfeeding of vitamins and minerals. Feeding a correctly formulated, complementary balancer containing amino acids, minerals and vitamins allows you to increase or decrease energy intake without compromising vitamin and mineral intake.
The effect of sugar and starch on blood glucose and insulin are alike in horse and human, with some of the same health complications (weight gain and insulin resistance) and for horses, laminitis, osteochondritis and polysaccharide storage myopathy. Pregnancy represents a unique metabolic state which must be considered when choosing feeds and nutrition. The old adage ‘she gives it all to the foal’ is, after the fifth month of pregnancy, exactly as nature designed: the large demand for glucose by the growing foal is met by a reduction in the amount the mare uses.
Dr Jennifer Stewart BVSc BSc PhD is an equine veterinarian, a member of the Australian Veterinary Association and Equine Veterinarians Australia, CEO of Jenquine and a consultant nutritionist in Equine Clinical Nutrition.
All content provided in this article is for general use and information only and does not constitute advice or a veterinary opinion. It is not intended as specific medical advice or opinion and should not be relied on in place of consultation with your equine veterinarian.
