Mid Winter Anemia in Birds Of Prey
During the winter months as the temperature drops, falconry birds kept at “flying weight” over an extended period of time, may suffer from mid-winter anemia.
Cause:
- All birds require a diet balanced in protein, carbohydrates and fat. Through metabolism of carbohydrates, glucose is produced and is necessary as an energy source, especially for the brain and central nervous system. If the diet becomes low in carbohydrates or the body has depleted the energy stores, abnormal metabolism of the body fat and protein will take place to try and maintain the proper level of energy.
- A raptor with a fully gorged crop will take approximately 24 hours to digest this meal. Often falconry birds are fed a modified amount of food to maintain the flying weight. This can lead to the digestion of the meal within 12-14 hours, leaving the raptor without the proper energy stores for 10-12 hours. Over time, this will predispose the raptor to utilize their fats and protein as an energy source. Cold snaps in the weather will exasperate this condition. As the temperature falls (32 degrees or less) the energy demand becomes greater.
- The energy reserves for each raptor will vary and affected by species of raptor (smaller raptors has less tolerance for weight loss), sex and age of the raptor, imprint vs passage and the manning protocols implemented for the raptor. Raptors maintained on their marginal diet and not fed extra to compensate for the lower temperatures, will quickly exhaust their “reserves” and develop signs of mid -winter anemia. The anemia is a result of a chronic starvation state and the inability to properly produce red blood cells. Low protein levels (hypoproteinemia) are also part of this syndrome. This devastating condition may be fatal within 24 hours of showing signs.
Clinical signs:
- The first signs of this syndrome may show a raptor not enthusiastically flying or pursuing game. This may be perceived that the raptor is too heavy and needs more food restrictions. They may sit fluffed and sleepy eyed, with decreased reaction to stimuli. They are weak and ataxic. Relying only on the atrophy of the keel muscle to determine if mid-winter anemia is present may be misleading because some raptors with this condition may appear only slightly thin over the keel muscle. Being in this metabolic imbalance, if the raptor is left outside, lost overnight or miss a meal they can “starve to death” overnight. The body weight may plummet 2-3 ounces within a short period of time. The GI tract is often functioning at a slow rate and cannot digest food properly. Crop stasis may be present resulting in endotoxemic shock and metabolic acidosis, which often leads to death.
Treatment:
- Treatment for these raptors must be aggressive. Normal body functions begin to shut down and the raptors present to the veterinarian severely dehydrated and emaciated. Laboratory evaluation will show anemia (PCV 30% or below), low total protein (less than 2 gm/dl) and elevation of the uric acid (a result of protein being broken down for energy). The blood glucose levels are often normal due to the metabolism of fats and protein. The first 24-48 hours of treatment is critical. Careful restoration of fluids and initiation of alimentation are important during their first 24–48 hours of veterinary care as well as providing external heat and minimizing stress. A raptor in this state must not be force-fed. They will not have the ability to digest food. Fluid therapy is given either intravenously, intaosseous or subcutaneously. Some raptors may require a blood transfusion if severe anemia is present or the use of colloids like hetastarch if the bird is hypoproteinemic.
Reintroduction of food must be done gradually and after the raptor is stabilized with fluids. In the beginning it is best to use an elemental diet (Emeraid Carnivore Care, Lafeber Co.) providing a protein in a simple hydrolyzed form along with amino acids and fatty acids that are easily absorbed in the gut. At this stage some raptors may require gastrointestinal (GI) motility medications to combat GI stasis. Once the gastrointestinal tract is functioning properly with gavage diets, small amounts of clean meat may be introduced and increased gradually. The whole concern when caring for a raptor with this type of condition is to avoid the “refeeding syndrome”, which can be fatal. Metabolic and electrolyte disturbances can occur if the choice of food offered is incorrect or given too early. This on top of the already compromised raptor can lead to death. Plasma electrolytes should be monitored for the first few days. The transition to chunked and whole prey items is gradual and may take up to a week. Antibiotics may be necessary for secondary infections as well as vitamin therapy, especially Vitamin B. The weight must gradually be elevated to 2-3 ounces over flying weight and maintained at this weight for a minimum of 2 weeks before any free flight training is begun.
Prevention:
- The best prevention is to fly the raptor at an elevated healthy weight and be prepared to increase the food amount with the onset of cold weather. Feeding a high quality varied diet is also important. During the colder months allowing the raptor to eat a “full crop” every 3-4 days and then rest for the next day to put the crop over may help to decrease the chance of mid winter anemia. A strict program of flying the raptor daily in adverse weather conditions should be avoided unless the raptor is at a healthy weight, not at a marginal “flying weight”.