Got milk?

Compared to adult horses, foals are poorly adapted to cope with periods of nutritional deficit.  Energy stores in the neonatal foal are minimal when compared to the neonates of other species.  Glycogen stores in the neonate, contained in liver and muscle, are only sufficient to maintain normal body temperature for less than one hour.¹  Hypoglycemia is therefore common in even the healthy neonate.  The ingestion of adequate amounts of colostrum (see Colostrum it’s what’s for dinner), not only for immunological needs but also for caloric, is therefore essential to carry the neonate over the initial neonatal period until intake is sufficient to meet needs.  In situations where neurological or physical compromise to the ability of the foal to suckle the mare are present, energy levels can rapidly diminish.

Considerable calories are needed not only to support basal metabolic needs, but to maintain a growth rate that approaches 2.5% of bodyweight daily in the healthy foal during the neonatal period.  Up to 150kcal/kg may be required initially, this decreasing to approximately 120kcal/kg by 3 weeks, before settling in the range of 80-120kcal/kg by one to two months of age² being calculated indirectly based on the volume of milk consumed voluntarily and the known digestible energy content of milk (0.48 kcal/L).  The requirement for healthy growing foals has been estimated as 120 kcal/kg/day by this method.³

As the resting energy expenditure requirement (RER) of critically ill foals is not standardized it is difficult to determine adequate nutrition levels.⁴  Underfeeding is undesirable as it leads to loss of condition, decreased growth, impaired healing and possibly impairment of immune responses.  Overfeeding is also problematic, leading to hyperglycemia, hyperlipemia and dysfunction of multiple organ systems.⁵  Sick, recumbent foals have been shown to require significantly less energy than healthy active foals,⁶ and excessive calories are actually deleterious in critically ill foals.⁷

By comparison, healthy active foals must consume a considerable amount of milk – between 20 and 25 percent of bodyweight daily.^3;8  This milk provides between 500 and 600 kcal per liter.⁸  Small amounts of hay, grass, and grain are ingested starting as early as the second day of life.  Maternal feces are ingested also, which likely provide the microbial flora required to enable digestion of these sources of roughage, although adequate digestion of roughage is unlikely until several weeks of age when transition from a milk-based diet begins.

During the first month of life, an average daily weight gain for a Thoroughbred foal has been shown in the range of 1.5-1.7 kg/day.^9;10  Foals will mimic mare behavior by attempting to eat solids however the gastrointestinal tract, particularly the large colon, is initially unable to digest roughage.  Time is needed for adaptation of the microbial population to enable the foal to be supported as a herbivore.  Should the foal be orphaned as well, to provide an environment more attune to that of a mare-reared foal, provision of high quality leafy hay and creep feed to the milk replacer fed foal is of great benefit.  A companion horse to aid in the development of appropriate behavior is highly desirable once the foal is strong enough to benefit from the interaction.

Should supplementation by mare’s milk be needed, during the first 24 hours a suggested initial rate of milk delivery is 2ml/kg body weight per hour.  This provides 2.4L of milk to a 50kg foal, being near 5% of bodyweight.  This feeding rate can be gradually increased to achieve 10% to 15% of body weight as milk intake daily.  Extreme care is required to avoid aspiration of milk in the compromised neonate if supplementation is by bottle feeding, especially where pharyngeal function may be depressed.  Placement of an indwelling feeding tube transiently is recommended.  Additional calories can be provided intravenously (dextrose solution, parenteral nutrition).  These cases are complex and require veterinary input.

Another time I will talk about milk replacers and intravenous feeding.  For now, don’t let them go hungry.

1. Ousey JC, McArthur AJ and Rossdale PD. Metabolic changes in thoroughbred and pony foals during the first 24 h post partum. Journal of reproduction and fertility Supplement 1990;44:561-70.

2. Ousey JC, Prandi S, Zimmer J, et al. Effects of various feeding regimens on the energy balance of equine neonates. Am J Vet Res 1997;58(11):1243-51.

3. Martin RG, McMeniman NP and Dowsett KF. Milk and water intakes of foals sucking grazing mares. Equine Veterinary Journal 1992;24(4):295-9.

4. Buechner-Maxwell VA. Nutritional Support for Neonatal Foals. The Veterinary clinics of North America.Equine practice 2005;21(2):487-510.

5. Klein CJ, Stanek GS and Wiles CE, III. Overfeeding macronutrients to critically ill adults: metabolic complications. J Am Diet Assoc 1998;98(7):795-806.

6. Paradis M. Nutrition and indirect calorimetry in neonatal foals. Proceedings of the American Association of Equine Practitioners, Denver, CO 2001;47:245-7.

7. McKenzie III and Geor RJ. Feeding Management of Sick Neonatal Foals. Veterinary Clinics of North America: Equine Practice 2009;25(1):109-19.

8. Oftedal OT, Hintz HF and Schryver HF. Lactation in the horse: milk composition and intake by foals. The Journal of nutrition 1983;113(10):2096.

9. Pagan JD, Jackson SG and Caddel S. A summary of growth rates of thoroughbreds in Kentucky. Pferdeheilkunde 1996;12:285-9.

10. Pagan JD, Brown-Douglas CG, Caddel S. Body weight and condition of Kentucky Thoroughbred mares and their foals as influenced by month of foaling, season, and gender. In: Pagan JD, editor. Nottingham University Press; 2009. p. 137-45.