Colostrum and Failure of Passive Transfer in Foals

Newborn foals are somewhat immunodeficient, meaning that they lack antibodies for many of the pathogens they will encounter soon after birth. Mother Nature has overcome this problem by providing your foal with colostrum – the “first” milk produced by the mare which is rich in maternal antibodies.

Colostrum is produced in the mammary gland of the mare during the last weeks of pregnancy. Immunoglobulins (maternal antibodies) are concentrated from the mare’s blood into the colostrum. Normal foals begin suckling colostrum within 1 to 2 hours of birth, and maternal antibodies are detectable in the foal’s blood within 6 hours of birth. Specialized cells in the foal’s small intestine are able to absorb these antibodies for 12 to 24 hours after birth after which time, these cells “close” and antibodies are no longer absorbed. This is why it is important that your foal receives colostrum within 12 hours of birth. The process by foals obtain antibodies via colostrum is called passive transfer. When foals fail to receive colostrum and its associated antibodies, this is called failure of passive transfer (FTP).

Ideally, your foal should be examined by a veterinarian and assessed for adequacy of passive transfer of immunoglobulins when they are between 18 and 40 hours of age. The most common method of assessing passive transfer is to measure your foal’s serum IgG concentration (IgG is a type of antibody). Foals should have a serum IgG level of greater than 800g/dL to provide optimal passive immunity. There are a variety of rapid screening test kits available for stall side assessment of passive transfer. Foals with IgG levels lower than 800g/dL are susceptible to infection and septicemia. If FTP is suspected or recognized in your foal before 12 hours of age, oral administration of good quality colostrum is indicated. Many farms keep a bank of frozen colostrum. When FTP is recognized after a foal is 18 to 24 hours of age, oral administration of colostrum is of no help because the small intestine can no longer absorb the immunoglobulins. These foals require treatment with intravenous equine plasma in sufficient quantities to increase the serum colostrum levels to above 800g/dL. Normal equine plasma with high quantities of IgG is commercially available for purchase by your veterinarian.

By the time FTP is diagnosed in many foals, it is already too late to prevent exposure to potential pathogens in the environment. Therefore, the best approach begins with aggressive prevention and early recognition of the problem. Your mare should be closely monitored at the time of foaling, and the foal should be noted to stand and suckle vigorously within 2 hours after birth. The mare should also be assessed to ensure that she is producing high quality colostrum, as some mares may leak colostrum before giving birth. Farm managers should maintain a clean foaling environment during the periparturient period. Thorough cleaning and disinfection of foaling stalls between mares, replacing bedding after parturition and washing the mare’s udder before the foal suckles for the first time may decrease the ingestion of pathogenic bacteria by the foal. A good practice is to feed the foal the mare’s colostrum via bottle immediately after birth. This way, you can be certain that the foal received a certain quantity of colostrum, and it also allows you to assess the quality of the colostrum. Good colostrum tends to be sticky, yellow and thick, however, this is a subjective assessment and not always a reliable indicator of colostrum quality. A common method for estimating colostrum quality is determination of colostral specific gravity using a colostrometer. Specific gravity correlates directly with IgG concentration. Ideally, colostrum specific gravity should be greater than 1.060, and a foal should receive 1 to 2 liters of colostrum within the first 8 hours of life.

Foals with uncomplicated FTP have an excellent prognosis if the condition is recognized early and treated appropriately. Prognosis of foals recognized with FTP after the development of sepsis or other infectious diseases depends on the nature and severity of the infection. FTP can be avoided with good management practices and close observation of foaling and suckling.

Sarah Seitz is a veterinarian that works for a company called World Vets that provides humanitarian veterinary aid to developing countries around the world, as well as veterinary disaster relief worldwide. Sarah was born in Zimbabwe and moved to South Africa when she was 10 years old. After attending high school at St Andrew’s in Johannesburg, she worked for her father for several years doing wildlife conservation and breeding endangered species. After that, she was introduced to the illustrious world of thoroughbred breeding and racing when she was employed to manage a thoroughbred stud farm for four years. This stud has produced several notable winners in its time, including a Durban July winner. Sarah decided to come the USA to study Veterinary Medicine. Far from home and lots of paperwork later, she obtained her Doctor of Veterinary Medicine degree at Washington State University in Pullman, Washington.