40 Feeding orphan and sick foals
It is essential to understand the nutrition of the healthy neonatal foal in order to manage the nutrition of a neonate compromised either by disease or loss of the dam. For the purposes of this chapter the foal under a month of age will be discussed.
The neonatal foal has a high metabolic rate and low hepatic glycogen reserves that only last a few hours (Ousey 2003). Newborn foals are dependent on frequent ingestion of good quality colostrum and then milk. Foals that fail to nurse even for a few hours will rapidly become hypoglycemic, hypovolemic, hypothermic and start to break down body tissue to meet their metabolic needs. During the first week of life, healthy foals suckle five to seven times per hour with each bout lasting just under 2 minutes (Carson & Wood Gush 1983). Over the first month of life, the frequency and duration of the suckling bouts decreases as the foals suckle more efficiently.
Ingestion of adequate quantities of good quality colostrum within the first few hours of life is essential for transfer of maternally derived immunoglobulins (transfer of passive immunity). Thoroughbred mares produce an average of 1–2 liters of colostrum. For maximum efficiency of this specialized but short-lived process for transfer of colostral antibodies, foals should ingest colostrum within 4 hours of birth. Colostrum provides immunoglobulins, complement, lysozyme and lactoferrin and large numbers of B-lymphocytes that are essential for the development of the foal’s immune system. It also contains growth factors and hormones important for development and maturation of the gastrointestinal tract. Ingestion of the non-nutrient factors in colostrum plays a vital role in the preparation of the gut of the newborn foal for digestion of enteral feed (Ousey 2006).
During the first 24 hours post partum foals consume about 15% of their bodyweight as milk (8 liters for a 50-kg foal); this increases to 12–15 liters by the end of the first week of life (Ousey et al 1996). The first month of life is a period of very rapid growth. Thoroughbred foals gain 1.5–2 kg/day (Jelan et al 1996, Martin Rosset & Young 2007), and most Thoroughbred foals will have doubled their birthweight by a month of age. Growth rate in healthy foals is breed, age and month of birth dependent (Chapter 12 provides data on normal growth rates of foals).
From about 2 days of age foals begin nibbling feed, grass and hay copying the feeding behavior of the dam. They start being able to digest solid feed from about 3 weeks of age. Levels of lactase and cellobiase increase in the fetus until birth (Roberts 1975) and then steadily decline from 4 months of age reflecting the change in the foal’s nutrient sources. Hind gut fermentation is not fully established until foals are 3–4 months of age.
It is well established that in order to produce a sound, healthy athlete a smooth growth curve should be maintained rather than periods of restriction and compensatory growth. Although moderate restriction in growth can be compensated for to some extent, capacity for compensation decreases with age. In general, differences in growth rates have little influence on mature size after the rapid neonatal growth phase is completed (Martin Rosset 2005). The reader is referred elsewhere in this book for a more complete discussion on foal growth and development (Chapter 12).
The management of an orphan foal will depend on the age at which the foal loses its dam. In the author’s experience foals <2 months of age require a milk -based diet in order to maintain a satisfactory growth curve. The older the foal, the smaller the proportion of milk required in the diet.
The author considers fostering to a nurse mare to be the best option for foals less than 6–8 weeks of age. Although this option may be considered labour intensive and expensive initially, it is likely to provide the most satisfactory outcome for the foal in the long term.
The most common causes of orphan foals are death of the mare, rejection by the mare or persistent agalactica. The situation is often sudden and, for non-professionals, unexpected so they are frequently unprepared. Good short-term management of the nutritional needs of the foal will allow time for the best long term option to be put in place.
First, in newborn foals it is important to ensure ingestion of adequate quantities of good quality colostrum. In foals >18 hours of age, blood samples should be taken to determine immunoglobulin G concentrations. Mare milk replacers are available worldwide and are preferred when mare’s milk is not available. If mare milk replacers are not immediately available, either unmodified goat milk or semi skimmed (2% fat) cow milk with 20 g/l of dextrose added can be used. Sugar (sucrose) should not be used as young foals lack the enzymes to digest sucrose (Table 40-1).
Ousey (1999, 2003) recommends that foals under 2 days of age are fed hourly, then every 2 hours for a further 12 days, after which there should be a gradual decrease in the frequency and increase in the volume fed such that by 8 weeks of age the foal is receiving four feeds daily.
In the authors’ experience, an average daily gain (ADG) >2 kg/day is excessive for a Thoroughbred foal up to 30 days of age (see Chapter 12). For other breeds, data on ADG should be consulted. Farm-specific data on foal growth rates provides the best guide. Alternatively, many international feed companies are able to provide optimum growth curves for various breeds. To avoid excessive or erratic growth rate, the foal should be weighed at least weekly, with feeding rates adjusted as needed.
Mare milk replacer prepared per manufacturer’s instructions tends to have a higher energy density than mare’s milk, so smaller volumes are required than would be the case for a foal suckling from its dam. Feeding a more dilute milk replacer solution at higher volume than recommended during the initial few days will help the orphan foal adapt to milk replacer. The author usually reduces the quantity of milk powder added to each liter of water by about 25% and increases the volume fed each day by the same percentage. Over the course of several days these dilutions and volumes can be changed in line with manufacturer’s recommendations. Alternatively it can be made up to provide an energy density similar to that of mare’s milk (2.13 MJ/l).
Foals digest mare’s milk very efficiently (e.g. gross energy [GE] digestibility of 97–99%). However, GE digestibility is lower (approximately 90%) for the first few days of feeding when foals are provided mare milk replacer (Ousey 2006).
• Stage of lactation – if there is a significant disparity between the stage of lactation and foal age it may be necessary to consider mineral supplementation as milk mineral levels change throughout lactation.
Fostering is a labour intensive process that may take several days. It is most likely to succeed with experienced, patient and confident personnel. Successful fostering usually requires someone to be with or close to the mare and foal at all times during the first 1–2 days. The use of a fostering crate or gate will allow the foal to be left unattended with the mare. However, the foal should remain under observation with someone available to quickly intervene if necessary.
If a suitable foster mare is not available, foals can be successfully hand reared. Although foals reared on milk replacer or goat’s milk grow and develop satisfactorily, long-term behavioural problems can develop unless they are carefully managed.
Manufacturers of mare milk replacer provide guidelines on quantities of milk to be fed. With newborn foals it is sensible to gradually increase the quantities fed over the first few days and follow directions regarding the concentration of replacer used. Naylor and Bell (1985) suggest that milk replacer should be fed at 10–15% dilution which is greater than recommended by some manufacturers, although over the last few years, manufacturer’s recommendations have changed to be more in line with this recommendation.
It is important to maintain high standards of hygiene with the preparation of the milk, and utensils used for preparation and feeding. Any unused prepared milk should be stored in a refrigerator until the next feed.
It is preferable to teach the foal to drink from a bucket so that the milk can be put in the stable and the foal left to feed. This minimizes the association between feeding and the handlers. It is preferable for the foal to drink smaller quantities at frequent intervals rather than fewer large feeds, which are more likely to overwhelm the digestive system. Episodes of feeding-associated diarrhea are common as the foal’s digestive system adapts to mare milk replacer. The use of probiotics can be helpful.
Little evidence on the efficacy of probiotics for treatment or prevention of on infectious diarrhea is available. The author prefers preparations made specifically for horses but does not recommend probiotics for use in foals under 24 hours of age or in foals with compromise to the integrity of the mucosal barrier of the gastrointestinal tract. If an episode of diarrhea persists, reducing the concentration of milk replacer may help in some instances. However it is important not to overlook other possible causes of diarrhea.
Foal creep rations designed for use in foals under 3 months of age are available. These feeds are designed to be readily digested by young foals with immature hindgut fermentative capacity and usually contain a significant proportion of milk pellets. These can be introduced from a few days of age. Manufacturers’ recommendations should be followed; however a rule of thumb for feeding concentrates to foals is 450 g per day per month of age up to a maximum of 3 kg per day. It is recommended to consult with an equine nutritionist when these feeds are used to ensure appropriate nutrition.
Exercise is extremely important in the development of a sound healthy individual and therefore it is important to ensure that orphan foals receive adequate exercise. Some owners prefer to manage these foals in a stable with no turnout, a practice that should be discouraged. If a paddock is unavailable a large barn may be suitable providing there is a suitable footing and dust levels are not excessive.
Orphan foals often become excessively “humanized”; this usually results in serious behavioral problems as the foal matures. Orphan foals should be treated in the same way as foals with their dams, and the company of humans must not replace that of horses.
The author considers it essential that orphan’s foals be provided an equine companion without delay. An old, quiet pony mare or gelding is a suitable companion. The foal and companion can be turned out together once acquainted and, when housed (e.g., in a stall), a partition can allow them to be fed separately yet maintain social contact. With an older foal it may be possible to keep them with the group of mares and foals they had previously been with if weaning from the paddock has started. However the safety of this will depend on the temperament of the orphan and others in the group.
Although the use of prophylactic antiulcer medication in sick neonatal foals remains controversial the author routinely uses prophylactic antiulcer medication in orphan foals. Whether the foal is fostered or hand reared, the loss of the mother and changes in management for the young foal are undoubtedly stressful. The choice of drug will depend on age of foal, assessment of risk and licensed products available to the clinician. The most commonly used drugs are omeprazole, ranitidine and sucralfate.
It is important to monitor weight and height regularly and compare to standard growth curves for breed and sex. The use of condition scoring is also a useful technique. Similar growth curves can be expected for hand-reared foals to those reared on mares (Cymbaluk et al 1993). However in the author’s experience it is a common complication for inexperienced personnel to feed hand-reared foals to appetite, which tends to produce excessive growth rates and associated problems (e.g., physitis). As mentioned, it is important to adjust feeding in accordance with growth rate.
One study found that fostered Thoroughbred foals grew more rapidly than those reared on their dams by 0.0366 kg/day. The authors suggested that the nurse mares (e.g., part and pure bred Tennessee Walkers) are selected for their mothering and milk producing ability, whereas Thoroughbred dams are selected on race performance (Willard et al 2005). In the UK, cobs or larger ponies are most commonly used as foster mares, selected principally for placid temperament and mothering ability.
Key Points –
Feeding orphan foals
Healthy foals aged 1–4 days spend approximately 12 hours standing and active, increasing to nearly 14 hours per day by day 7, whereas sick foals are often recumbent for much of the time. This behavioral difference reduces energy expenditure by approximately two thirds. On the other hand, environmental temperatures below the lower critical temperature (24°C in sick foals) will increase metabolic rate and so can increase energy requirements for maintenance (Ousey 1997, Ousey et al 1997).
Although studies on the requirements of sick foals are sparse, research suggests that the energy requirements of sick neonatal foals are considerably less than their healthy counterparts. Studies of immature foals and foals with perinatal asphyxia syndrome showed they have a lower metabolic rate, requiring only 260–290 kJ/kg/day (13–14.5 MJ/day for a 50 kg foal) compared to 540–600 kJ/kg/day for healthy foals (Ousey et al 1996, Ousey 2003).
A recent study using indirect calorimetry in sick foals reported energy requirements of approximately 188 kJ/kg/day (Paradis 2001). Historically, it was thought that conditions such as sepsis and systemic inflammatory response syndrome (SIRS) in young as well as mature patients produced a hypermetabolic state and therefore increased energy requirements. However, recent studies (Taylor et al 2003, Turi et al 2001) in children have refuted this theory, finding that children do not become hypermetabolic during critical illness. Turi et al (2001) speculated that this is due to diversion of energy for growth into the recovery process.
Recent studies in humans having found that the overfeeding of critically ill patients has an adverse affect on outcome (Dandona et al 2005). Similarly, McKenzie & Geor (2009) have suggested a conservative approach to calorie provision for sick neonatal foals. Providing excess carbohydrate can result in hyperglycemia, which may increase production of proinflammatory cytokines and increase production of CO2, which can worsen hypercapnia in foals with respiratory compromise. Excessive dietary protein increases protein catabolism which can produce azotemia, while excessive feeding of lipids results in hypertriglyceridemia. One study reported that triglyceride concentrations >200 mg/l (>2.25 mmol/l) were associated with non-survival in neonatal foals receiving parenteral nutrition (Myers et al 2009).
Mare’s milk has high carbohydrate (lactose) content. Insulin secreted by the beta cells in the pancreas is essential for regulation and homeostasis of blood glucose in the face of high carbohydrate intake. Maturation of beta cells in the pancreas occurs very late in gestation and is dependent on the prepartum cortisol surge which prepares the fetus for birth in the few days before parturition (Holdstock et al 2004, Fowden et al 2005).
Foals that have not been subjected to this cortisol surge often exhibit insulin resistance and have poor regulation of blood glucose concentrations (e.g., premature/dysmature foals, foals delivered by early caesarean section). Various disease processes such as sepsis can also result in a degree of insulin resistance or low levels of insulin secretion.
Buechner-Maxwell and Thatcher (2004) have suggested that crude protein requirements for neonates are 4–6 g protein/100 non-protein calories. However, other authors have recommended a lower protein requirement (2–5 g/kg/day) for foals with normal plasma protein concentrations, and a higher rate of provision (6.5 g/kg/day) for sick neonates that are hypoproteinemic (Stratton-Phelps 2008). The criteria for diagnosis of hypoproteinemia will depend on factors such as foal age, disease process, and laboratory reference ranges.