Chapter 50 Nutrition of the Sick Animal
The influence of nutrition on the recuperation of veterinary patients is often overlooked, although the effects of nutritional status on recuperative ability are well known. Many patients are in a state of protein calorie malnutrition when first presented to the clinician. Early intervention with supplemental calories, protein, and other essential nutrients provides the patient with the dietary resources needed to optimize immune function, promote wound healing, and improve the recovery of the animal.
Multiple research studies have demonstrated that the immune response of an animal is directly related to the nutritional state of the animal.1-4 A deficiency of calories, protein, minerals, or vitamins alters the production of inflammatory cytokines, adversely affects leukocyte function, and decreases host resistance to bacterial infections.1,2 Clinical studies in hospitalized horses have demonstrated an improved recovery after gastrointestinal surgery in patients supplemented with intravenous nutrition.5
Different forms of diet therapy may be employed, depending on the clinical condition of the animal and the ability of the animal to tolerate different types of supplemental nutrition. Large animal patients that have a functional gastrointestinal tract and can tolerate placement of a nasogastric (NG) or esophageal feeding tube are candidates for treatment with liquid enteral nutrition. Glucose can be added to a patient’s intravenous fluids to provide an energy source. Parenteral nutrition (PN) is ideal for animals that have gastrointestinal ileus, that have an obstructive lesion in the gastrointestinal tract, or that are recumbent.
ASSESSMENT OF NUTRITIONAL STATUS
Before initiation of dietary therapy, the large animal patient must be examined to determine its nutritional needs. Animals may be anorectic owing to systemic disease, or they may be dysphagic owing to a mechanical (foreign body, abscess, poor dentition) or neurologic (botulism, tetanus, viral encephalitis) disease. Assessment of the nutritional status of the patient should include a measurement of the body weight (BW) and body condition score (BCS) of the animal. BW measurements should be taken at the time that the large animal patient is presented to the clinician and as frequently as possible during hospitalization. If a scale is not available, estimations of BW can be made with a weight tape or by using length and girth measurements (see Chapter 9). When a scale or weight tape cannot be used, the animal’s BCS should be used to evaluate the nutritional status of the patient. The BCS system enables the clinician to subjectively assess the endogenous protein and lipid stores in a large animal patient. A list of BCS descriptions for different species is provided in Chapter 9. Changes in weight or BCS are often easily overlooked in day-to-day observations of the patient if a concerted effort is not made to detect them. Palpation of the animal (ribs, dorsal vertebral processes) is necessary in sheep with a heavy fleece, camelids with long fiber, and horses with a thick winter hair coat. Animals with a low BCS (1 to 3 of 9; 1 to 1.5 of 5) have minimal protein and lipid stores and are at greater risk for developing protein calorie malnutrition after a period of anorexia. Large animal patients with a high BCS (7 to 9 of 9; 3.5 to 5 of 5) that are anorectic may have an increased risk for developing complications (hyperlipemia, hepatic lipidosis) from abnormal lipid metabolism. A clinician should initiate dietary therapy in a large animal patient that loses 3% to 5% of its initial BW or whose BCS diminishes by ≥1 grade.
Biochemical tests provide another method to evaluate the nutritional status of the large animal patient. Endogenous protein catabolism is a normal physiologic response to anorexia in animals. To date, few biochemical tests are available to assess protein malnutrition in large animals. Although anemia and hypoproteinemia (hypoalbuminemia) are occasionally seen in cases of malnutrition, they are not specific and frequently are associated with another primary disease process such as parasitism or protein-losing enteropathy. Severe protein malnutrition can result in abnormally low serum urea nitrogen (SUN) concentrations in horses and ruminants. Liver disease also decreases the formation of urea nitrogen and must be ruled out when evaluating the animal. Protein malnutrition can result in an increase in the urinary excretion of 3-methylhistidine, a myofibril amino acid that is not metabolized. Measurement of this metabolite in the future may be a useful tool to monitor protein catabolism in large animal patients.
Underfed horses develop a mild hyperbilirubinemia (unconjugated) that, although not directly related to nutritional status, is readily reversed when food intake resumes.6,7 Animals that are in negative energy balance also use endogenous lipid as an energy source. Serum nonesterified fatty acids (NEFAs) and/or triglycerides are expected to rise in these animals. Once nutritional support or refeeding is initiated, these lipid metabolites usually decrease. Pathogenic elevations in serum triglyceride (>500 mg/dL) develop in some equine patients that are anorectic and that have a high daily energy requirement (lactation, pregnancy), insulin resistance (Cushing’s syndrome), or renal failure and in predisposed breeds (miniature horses, ponies). Ketone bodies have a glucose-sparing effect in the body and are normally produced from fatty acids and amino acids in animals that are in negative energy balance. Ketonuria develops after the excess production of ketones and can be used to indirectly monitor the severity of caloric malnutrition in ruminants. Hypoglycemia is a common complication in large animal neonates that are malnourished but is an uncommon finding in adults. Both adult and neonatal large animals may develop glucose intolerance and hyperglycemia during periods of systemic illness and may require treatment with a diet that will not exacerbate the hyperglycemia. Electrolyte and mineral derangements including hypocalcemia, hypomagnesemia, hyponatremia, hypochloremia, hypophosphatemia, and hypokalemia may develop in inappetent systemically ill large animals or during the refeeding process.8,9
NUTRIENT REQUIREMENTS OF LARGE ANIMALS DURING CLINICAL ILLNESS
Although it is generally accepted that sick animals have increased nutritional requirements, these requirements have not been quantified for specific disease conditions. The current trend in critical care nutrition is to provide adequate calories to meet the resting energy requirements of the hospitalized patient and sufficient protein to meet the maintenance requirements. These values can be calculated based on the animal’s BW (see Chapter 9) or determined by reference to National Research Council (NRC) tables.10 For adult horses, the resting digestible energy (DE) requirement is calculated as DErest (Mcal) = 0.975 + 0.021 BW(kg), and maintenance crude protein (CP) requirement is calculated as CP (g) = 1.26 BW(kg).10 For a 450-kg horse, these would equate to a 10.4-Mcal resting energy requirement and a 567-g crude protein requirement. For foals and calves, resting energy requirement is approximated as DE (Mcal) = 0.07 BW(kg) and digestible protein as DP (g) = 3.5 BW(kg), which would equate to 3.50 Mcal (3500 kcal) and 175 g of protein for a 50-kg neonate. These values represent starting points for formulating dietary therapy, and adjustment based on clinical response or specific medical conditions may be necessary.
Vitamin and mineral requirements, also available from NRC tables, can usually be met if an enteral diet is formulated with commercial complete feed pellets or pelleted hay. Parenteral solutions can be supplemented with vitamins and minerals. Although B vitamin deficiencies do not occur naturally in horses and cattle, supplementation is probably beneficial in large animals with gastrointestinal diseases that result in the disruption of the normal tract flora that produce B vitamins.
ORAL SUPPLEMENTATION
The animal’s feed intake should be monitored during treatment. If the animal is losing condition despite consuming all feed offered, more or higher-quality feed should be provided. If the animal’s appetite is poor, the patient should be offered a variety of highly palatable feeds including fresh grass, dried forages, and complete commercial feed pellets. Although sweet feeds are palatable, their use should be limited to a top dressing of other feeds. Ruminants in particular may consume small quantities of fresh feed if it is offered frequently, whereas if the same quantity is offered in one feeding, it may be ignored after a few bites. Many dairy cows can be coaxed into eating hay if it is placed in the back of the pharynx by the clinician, and oropharyngeal stimulation may result in increased voluntary feed consumption. Fresh silage and dried brewer’s grain frequently appeal to the hypophagic cow. Many sick horses and ruminants benefit from grazing if grass is available.
A hospital feeding chart can be created to facilitate monitoring of the feed consumed by a hospitalized patient. Use of an inexpensive farm scale is the most accurate way to measure the amount of feed offered to a patient. Feed that is not consumed within a few hours should be weighed and discarded to prevent the accumulation of stale, and possibly fermented malodorous feed. If the animal does not voluntarily consume enough feed to meet its resting energy requirements or its maintenance protein requirements, or if the animal loses weight or condition, dietary therapy with a liquid diet by intragastric administration should be considered. Dysphagic animals can be managed with a liquid diet that can be fed through a tube as the sole source of nutrition.
LIQUID DIETS FOR HORSES
Adult Horses
Assisted enteral feeding (AEF) with a liquid diet should be used in horses that require nutritional support to maintain their energy and protein intake during a short period (2 to 14 days) of partial or complete anorexia. Horses that are good candidates for AEF do not have gastrointestinal ileus or gastric reflux and are able to tolerate an indwelling NG tube, repeated intubation, or an esophagostomy tube. Horses fed using AEF should be standing. Diet choice will depend on product availability and on the nutrient requirements of the equine patient. Energy, protein, vitamin, and mineral requirements should be calculated for each equine patient to ensure that the appropriate concentration of nutrients is administered. Enteral diets may be administered to provide partial or complete nutrient supplementation to an adult horse.
Liquid diets may be classified into three categories: (1) complete feed blender diets consisting of liquefied or finely ground whole food suspended in water; (2) composition diets containing highly digestible whole protein (usually casein or soy), fats, and carbohydrate; and (3) commercially available liquid enteral diets sold for human use. When commercial liquid enteral diets are chosen, the source of carbohydrate should be examined, and only diets that contain a limited amount of sucrose should be used for horses.
Vital HN* and Osmolyte HN* are human liquid enteral diets that have been administered to adult horses.11,12 Ross Laboratories produces a variety of human liquid enteral products, including formulations that contain oat and soy fiber. A partial list of formulas that can be administered to adult horses is provided in Table 50-1. All human formulations are designed for administration through a small-diameter tube and are an option for horses that can tolerate only an 18 Fr feeding tube (Mila NG18100).† Most products contain approximately 1 kcal/mL and 4.1 to 4.2 g of protein per 100 kcal. Almost 10.5 L of a human enteral product would be required to meet the stall resting energy requirement of 10.4 Mcal for a 450-kg horse, at an approximate cost of $120/day. The protein content (approximately 440 g) in 10.5 L of Osmolyte or Vital HN will not meet the requirement of 567 g of protein for a 450-kg horse, and supplemental protein (casein, lactalbumin, whey, soy) may need to be added to each formulation to ensure adequate protein intake. The nutrient composition of a human formulation should be evaluated to ensure that the horse is receiving the most appropriate product. Diets that contain a high (>15%) proportion of calories as fat are contraindicated in horses with hyperlipemia and hepatic lipidosis. The soluble carbohydrates included in a human enteral formulation may not be tolerated by horses that have a compromised gastrointestinal tract or by horses with hyperglycemia. Any commercial human product should be fed starting at approximately 25% of the final maintenance requirement, with the volume gradually increased over 4 to 7 days to the target quantity.
Although they may be inconvenient, complete feed blender diets have the advantage of being inexpensive ($5 to $10/day), and the ingredients are usually available. Most products contain 14% to 25% crude fiber (dry matter [DM]) and vary in energy density from 2.6 to 3.1 Mcal/kg of diet. A list of commercial feeds that can be fed as a liquid enteral diet is provided in Table 50-2. From 3.4 to 6.0 kg of diet per day is required to meet the resting energy requirements of a 450-kg horse. In some equine patients, protein supplementation may be required. Some patients may also benefit from vitamin and mineral supplementation. This type of a diet may be prepared either by grinding one quarter to one third of the daily requirement of dry pellets in a blender and suspending the blended product in water, or by soaking the pellets in water before blending to create a slurry. The total amount of water that is added to the preparation should be recorded and added to the daily fluid administration log for the patient. The preparation should be fed three to six times daily to horses that require complete feeding or once or twice daily if only partial supplementation is required. Hay pellets or alfalfa meal can be blended into a liquid enteral diet; however, the nutrient content and quality of pelleted forages is often more variable than those of commercial feeds.
An ingredient-based composition diet can be designed using structural carbohydrate and protein ingredients that are available in the local region. One such diet (Table 50-3) composed primarily of dehydrated cottage cheese, dextrose, and alfalfa meal requires considerable preparation by the clinician.13 Corn, canola, or soy oil (113 to 227 mL) can be added as an energy source. Diets with high concentrations of oil and dextrose should be avoided. Structural carbohydrate should comprise 50% to 75% of the diet DM. The approximate cost for complete supplementation with the homemade equine diet is $30 to $40 per day for a 450-kg horse. As indicated in Table 50-3, the homemade diet is introduced gradually over a period of 7 days.
Table 50-3 Suggested Feeding Regimen for a Liquid Diet for a 450-kg Adult Horse11*
The consistency of any formulation can be adjusted by blending the ingredients with water to ensure that the formulation can be delivered through the NG tube that has been selected for administration. Larger diameter NG tubes (>0.65 cm inner diameter) must be used when fiber is included in the diet. The diet should be tested using the NG tube before the tube is placed in the animal to ensure that the tube will not be clogged with the feed. The total volume of enteral diet should be divided into at least three feedings per day and should be administered slowly enough to ensure that feed does not reflux around the NG tube. No more than 6 to 8 L of total volume should be administered at one time. This volume must be appropriately lowered when treating a pony or miniature horse. Before feeding, the amount of residual fluid in the stomach should be checked. Horses with ≤2 L can be fed the meal, but if the volume of gastric fluid is >2 L, the feeding should be delayed for 2 hours. Horses with persistent gastric reflux should not be fed enterally, and instead the clinician should consider treatment with PN. After the horse has been fed, the tube should be flushed with at least 500 mL of water before the tube is capped. Excessive distention of the stomach must be avoided. If the NG tube will remain in place between feedings, a muzzle may be used to prevent the horse from removing the tube. During treatment, horses should be offered palatable feeds to encourage a transition to voluntary food consumption. The equine patient can gradually be weaned from AEF once it is consuming 75% of its DErest on a daily basis.
All liquid enteral diets may result in a mild, self-limiting diarrhea when fed as the sole source of nutrition, possibly because of lack of dietary fiber or because of fermentation of the highly soluble ingredients in the large colon.11,13,14 This may be ameliorated by addition of a fiber source such as alfalfa meal.
Foals
Mare’s milk is the ideal supplemental feed for orphan or critically ill foals. Neonatal foals with normal gastrointestinal tract motility can initially be fed a volume sufficient to meet 10% of BW (100 mL/kg BW) each day. The volume should be incrementally increased until the foal is consuming 20% of its BW (200 mL/kg/day). Neonatal foals should be offered milk every 2 hours as long as the feedings are tolerated and should be encouraged to nurse from their dams once they develop a strong suckle reflex. A small-diameter NG feeding tube can be used for milk supplementation until the foal can nurse voluntarily. Foals have minimal endogenous energy stores and require supplemental nutrients within 6 to 12 hours of losing the ability to nurse. Any foal that cannot tolerate enteral feedings should be placed on PN to ensure that its dietary requirements are met.
Orphan foals can be fed 20% of their BW per day using a commercial foal milk replacer (Mare’s Match*, Mare’s Milk Plus†, Foal Lac‡) if a nurse mare or mare’s milk is not available. If a foal milk replacer is not available, goat’s milk can be fed as a short-term substitute but is not recommended for long-term use because the nutrient profile is different from that of mare’s milk. Because indigestion occurs relatively commonly when using milk substitutes in foals, dietary changes should be instituted gradually over a period of 1 to 2 days at a minimum. If indigestion occurs, both the frequency and volume of feeding should be decreased until the indigestion resolves. Foals that are 2 weeks of age or older can be fed every 4 to 8 hours, with a decreased frequency of feeding as the foal ages. Orphan foals should be fed from a pan or bucket because it forces the foal to actively ingest and swallow the milk and decreases behavioral complications that can develop when an orphan foal is bottle-fed. If a foal will be bottle-fed, the nipple should be checked to ensure that milk does not freely flow from the nipple. Improper use of a bottle can result in aspiration pneumonia if the foal does not have a normal swallow response.
LIQUID DIETS FOR RUMINANTS
In most cases the most practical and least expensive way to force-feed ruminants is the blender-type or slurry diet. Hypophagic adult cattle may be force-fed a suspension of alfalfa meal and dried brewer’s grain (3 to 5 kg each in 20 L of water) two or three times daily. If a ruminal fistula is necessary (e.g., tetanus), the diet may be directed into the rumen. Presumably similar preparations would be suitable for sheep and goats, although published reports are scarce. Administration of ruminal liquor obtained from a healthy donor cow provides a good source of microflora as well as volatile fatty acids as an energy source in hypophagic cows.15
INTRAVENOUS FEEDING
Intravenous Dextrose
The simplest and least expensive form of intravenous feeding is the supplementation of intravenous crystalloid fluids with dextrose. This represents a short-term solution for boosting caloric intake when a rapid return to normal feed consumption is anticipated. Dextrose can be added to make a final solution with a concentration that ranges from 2.5% to 10%. If the fluids are infused at a rate to meet maintenance fluid requirements (2.2 mL/kg/hr), the patient’s renal threshold of glucose (10 mmol/L or 180 mg/dL for adult horses; 12 mmol/L or 216 mg/dL for foals) will usually not be exceeded. The energy provided may be calculated based on 3.4 kcal/g of dextrose. A 450-kg horse treated with fluids supplemented with 2.5% dextrose and infused at a maintenance rate of 1 L/hr (24 L/day) will receive 2040 kcal from the dextrose (close to 20% of the patient’s DErest). Although protein is not provided with the dextrose therapy, the supplemental energy will blunt the catabolism of endogenous lipid and protein stores. Dextrose-supplemented fluids can be administered as the sole source of nutrition for 24 to 48 hours. If a patient consumes <75% of its maintenance protein requirement and/or <75% of its resting energy requirement, supplemental nutrition should be administered. Patients that have complications with glucose regulation may be able to tolerate therapy with a 2.5% solution of dextrose, but if complications with glucose regulation persist, alternative methods of nutritional supplementation should be initiated.
Parenteral Nutrition
Intravenous feeding or PN is a means of providing nutritional support to animals that do not have a functional digestive tract or animals that cannot tolerate placement of an NG tube. Because of the greater expense (approximately $80/day for foals and $450/day for adult horses), the need for special infusion supplies, and the risk of complications when compared with enteral feeding, PN should be reserved for cases in which bowel rest is necessary. Possible indications for PN include neonatal diarrhea in cases in which oral feeding exacerbates the diarrhea, postoperative feeding after gastrointestinal surgery, nonsurgical intestinal obstruction or ileus (proximal jejunitis, botulism), dietary supplementation in a laterally recumbent patient, gastrointestinal intolerance in premature neonates, and hypoxic ischemic gastrointestinal syndrome. Because enteral nutrition provides nutrients directly to the enterocytes and promotes both intestinal barrier function and immune system function, a small volume of a liquid enteral diet should be administered whenever possible in a patient receiving PN.
PN formulations are composed of dextrose and lipids as an energy source, and amino acids as a protein and nitrogen source. Compatible vitamin and mineral supplements can be added to the PN formulation. A variety of PN mixtures can be designed to meet the nutritional requirements of a clinically ill large animal patient. Sufficient calories in the PN solution must be provided in the form of carbohydrates and lipids to promote the incorporation of amino acids into protein instead of the catabolism of amino acids for energy. The ideal calorie-to-nitrogen ratio for adult horses is extrapolated from data calculated for critically ill humans, in whom the ideal ratio is 120:1 to 150:1 for healthy individuals, and 80:1 to 90:1 for acutely ill humans.16 (Glucose provides 3.4 kcal/g, amino acids provide 4 kcal/g, and lipids provide 11 kcal/g; amino acids include 0.16 g of nitrogen per gram.) Animals with systemic inflammatory diseases or severe protein loss and large animal patients recovering from major surgery will probably benefit from a therapeutic enteral or parenteral diet that has a calorie-to-nitrogen ratio that is between 80 and 100, as long as protein supplementation is not contraindicated in the patient. Although PN solutions can be formulated with dextrose alone as the energy source, addition of lipids provides many advantages. Because of the larger size of the molecule and higher energy density on a per-gram basis, replacement of dextrose with lipid lowers the PN osmolarity and/or infusion volume required to meet the energy needs of the patient and reduces the hyperglycemic effect of PN administration. The lipid content of the PN solution is usually targeted as approximately 50% but no more than 80% of the nonprotein calories in the formulation. Animals with hypertriglyceridemia (>500 mg/dL) or hepatic lipidosis that require PN should be treated with a formulation that is restricted in lipid, or that is lipid-free, whereas the concentration of dextrose or the PN administration rate should be restricted in animals with hyperglycemia. If long-term administration (>5 days) is expected, calcium (200 mg/kg/day), phosphorous (110 mg/kg/day), and other micronutrient supplementation of the PN solution should be considered. Commercial multiple vitamin (e.g., MVI-12*) and trace mineral (e.g., Multitrace5†) supplements are available for addition to the PN mixture but may add as much as $20/day to the cost of the formulation.
All parenteral solutions must be mixed aseptically. A laminar flow hood should be used to prepare the formulation, but if this equipment is not available, the solution can be mixed in a clean room with low traffic such as a surgical instrument preparation room. Alternate options for PN compounding include human hospitals, human parenteral compounding companies, and the commercial compounding pharmacy CAPS (Central Admixture Pharmacy Services, http://www.capspharmacy.com). The formulation can be made in a 2- or 3-L all-in-one infusion bag (Vitalmix‡), in a sterile glass container, or in a sterilized carboy. Single-use infusion containers are preferred. Guidelines for PN compounding are listed in Box 50-1.
Box 50-1 Instructions for Compounding a Parenteral Nutrition Solution
Parenteral solutions should be administered through a dedicated line in a large-diameter or central vessel (jugular, vena cava) to reduce complications from phlebitis but can be administered in a peripheral vein (lateral thoracic, cephalic) if the osmolarity of the solution is <900 mOsm/L. A multilumen polyurethane catheter§ is ideal for PN infusion because one port can be reserved exclusively for PN infusion while the other port(s) can be used for blood sampling and medication or fluid infusion. In many settings, when this is not feasible, dual infusion ports can be added to a single-lumen Arrow catheter. Patient medications may not be compatible with the PN solutions and should be given through a separate line, or the PN line flushed with saline before and after administration. Correction of electrolyte abnormalities in separate crystalloid supplemental fluids is best because rapid adjustments in the electrolyte supplements can be made without discarding an expensive PN solution.
The PN solution should first be administered at 25% to 33% of the total infusion rate, and if the patient tolerates the PN the rate should be gradually increased over 12 to 36 hours. A fluid administration pump facilitates a constant rate of infusion. During PN therapy the patient should be monitored for hyperglycemia, hypertriglyceridemia, and serum electrolyte abnormalities. Hyperglycemia and hypertriglyceridemia should be managed first by reducing the rate of infusion and then by lowering the concentration of dextrose or lipid in the PN solution. If hyperglycemia is persistent, treatment with subcutaneous Ultralente insulin (0.2 to 0.3 IU/kg, q12-24h) or regular insulin as a continuous rate infusion (0.005 to 0.01 U/kg/hr) may improve glucose use and permit increased caloric intake without further hyperglycemia. Similarly, heparin (40 IU/kg q12h) may be administered if hyperlipemia persists. At the conclusion of therapy, PN should be gradually discontinued over 18 to 36 hours.
PARENTERAL NUTRITION IN HORSES
Adult Horses
The stall resting digestible energy (DErest) and maintenance protein requirements, calculated as shown earlier, should be used as guidelines when formulating a PN solution for an adult horse. Although the exact energy requirements during a clinical illness have not been determined for the equine species, provision of enough nutrients to meet the stall resting requirements should provide the adult horse with sufficient energy to blunt the catabolic effect of anorexia and illness. Horses with a limited medical budget can be managed with a PN solution that provides a portion of the DErest energy.
The preferred way to formulate a PN solution is first to meet the calculated protein requirements of the horse with the amino acid solution and then to meet the remaining energy requirements with a combination of dextrose and lipid calories. A formula with approximately 50% of nonprotein calories as lipid and 50% as dextrose is recommended. The final composition of the solution can be altered to manage patients with hyperglycemia or hypertriglyceridemia. An example of a worksheet used to facilitate calculations for PN formulation for an adult horse is shown in Fig. 50-1. Alternatively, the clinician can calculate the daily requirements of dextrose, amino acids, and lipids on a dose per BW basis. The formula listed in Table 50-4 provides 2.8, 1.3, and 0.8 g of dextrose, amino acids, and lipids, respectively, per kilogram per day, providing the resting stall DE and maintenance protein requirements with a calorie:nitrogen ratio of 108:1, with 48% of nonprotein calories as lipid and an osmolarity of 1026 mOsm/L. Approximate cost is $450/day not including administration sets. If the clinician is willing to forgo the benefits of lipid inclusion, the lipid component in Table 50-5 can be replaced with an additional 2.8 g/kg/day of dextrose, at a savings of nearly $200/day.
Table 50-4 Parenteral Nutrition Formulation for Adult Horses
| Ingredient | Dosage Rate | Volume per Day (450-kg horse) |
|---|---|---|
| 50% Dextrose | 2.8 g/kg/day | 2500 mL |
| 10% Amino acids* | 1.3 g/kg/day | 6000 mL |
| 10% Lipid† | 0.8 g/kg/day | 3500 mL |
| Begin administration at 0.3 mL/kg/hr and gradually increase to target of 1.1 mL/kg/hr (12 L/day for a 450-kg horse). | ||
* Available as Aminosyn II, Hospira, Lake Forest, IL; or Travasol, Baxter Healthcare (Clintec), Deerfield, IL.
† Available as Liposyn II, Abbott Laboratories, N. Chicago, IL; or Intralipid, Baxter Healthcare, Deerfield, IL.
Table 50-5 Parenteral Nutrition Formulation for Foals
| Ingredient | Dosage Rate | Volume per Day (50-kg Foal) |
|---|---|---|
| 50% Dextrose | 10 g/kg/day | 1000 mL |
| 10% Amino acids | 3.5 g/kg/day | 1750 mL |
| 10% Lipid | 2 g/kg/day | 1000 mL |
| Begin administration at 0.7 mL/kg/hr and gradually increase to target of 3.1 mL/kg/hr (3750 mL/day for a 50-kg foal). | ||
A commercial amino acid and dextrose admixture (Clinimix, 5% Aminosyn II, 25% dextrose *) is a convenient alternative that does not require special preparation. However, because these products do not contain lipids, the osmolarity (1539 mOsm/L) is higher than that of the PN solution in Table 50-5. The increased cost of these products may be partially offset by the savings in sterile mixing containers and time costs of PN preparation.
Foals
The nutrient density of PN solutions for foals is higher than that for adult horses. The PN formula in Table 50-5 is designed to provide 10, 3.5, and 2 g of glucose, amino acid, and dextrose, respectively, per kilogram per day. This formula will provide 70 kcal/kg/day at a calorie:nitrogen ratio of 125:1 and an osmolarity of 1139 mOsm/L, with 40% of the nonprotein calories as lipid. Once the full flow rate is achieved, additional caloric density can be achieved by increasing the proportion of lipid emulsion, and if fluid volume restriction is required, 20% or 30% lipid emulsion can be used instead of 10%. Further increases in caloric intake require increased flow rates.
PARENTERAL NUTRITION IN RUMINANTS
Because of cost, use of PN is usually limited to calves, and little information exists on the use of PN in the adult bovine or the ovine and caprine species. The most common indication for the use of PN in calves is diarrhea, particularly in chronic cases accompanied by weight loss.17 In such cases, if sufficient milk is fed to meet the calf’s nutritional needs, the diarrhea is exacerbated, and PN allows the quantity of milk to be reduced without compromising the nutritional status of the patient. The PN regimen provided for foals in Table 50-5 would also be suitable for calves. However, because amino acids and lipids are the most expensive components of PN, a modified formula based on a 10:2:1 glucose:amino acid:lipid ratio has been used with success.17 For a 50-kg calf, this would result in administration of 1 L of 50% dextrose, 1 L of 10% amino acids, and 500 mL of 10% lipids daily, at an approximate cost of $60 per day. Eliminating the lipid emulsion from the formula is an acceptable alternative that will reduce the cost approximately 15%. A multiple B vitamin product may be added to the formula (approximately 1 mL of supplement per liter of PN), but trace minerals are not usually necessary for the short-term administration that is most common in calves.
Catheter-related complications are rare in calves, and a central venous catheter, although preferred, is not required. I (RWS) have had success with 16-gauge, 3¼-inch, Teflon-coated, over-the-needle catheters available from several distributors. These are placed in the jugular vein, sutured or glued to the overlying skin, and left in place for up to 10 days if no signs of phlebitis or sepsis occur.
SPECIAL DIETS
Numerous diseases require specific alterations in the therapeutic ration because of metabolic disturbances that accompany these conditions. Recommendations are discussed in the individual chapters dealing with these diseases and include alterations in dietary protein for hepatic disease and restrictions in the protein and calcium content of the diet for horses with chronic renal failure. A nutritionist can develop therapeutic enteral and parenteral formulations to meet the unique nutritional requirements of individual patients.
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10 National Research Council. Nutrient requirements of horses, sixth revised edition, Washington, DC: National Academies Press, 2007.
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