Alterations in Body Weight or Size


Chapter 9

Alterations in Body Weight or Size



Meri Stratton-Phelps, Consulting Editor



John Maas


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Slowed growth and below-normal weight gain usually happen at the same time, although occasionally they develop separately. By definition a decrease in growth and weight gain is limited to the growing animal. Similar pathogenic mechanisms cause weight loss or an emaciated condition in an adult patient. This arbitrary age division allows the clinician to consider possible causes that are more or less common for a given age group.


Potential growth and weight gain are genetically determined. They differ according to species, breed, and sex, and marked differences in potential growth exist within a breed. The potential for growth in ruminants is greater in the offspring of multiparous females than in those from primiparous females. The normal or minimum growth and weight gain rates for common breeds of the various large animal species are outlined in the section on assessment of growth and weight gains.



Mechanisms of Decreased Growth and Decreased Weight Gain


Major pathogenic mechanisms that result in decreased growth and decreased weight gain include the following:



Inadequate intake of one or more essential nutrients is an important cause of decreased growth. In many cases growing animals are not provided with a sufficient volume of feed to meet their nutrient requirements. Young animals rely on a highly digestible diet that provides energy and essential nutrients for growth. Even animals fed an appropriate volume of a poor-quality milk replacer could suffer from poor growth. Milk replacers formulated with sources of protein, fat, vitamins, and minerals that have limited nutrient digestibility may induce a state of energy, protein, vitamin, or mineral malnutrition. For some young animals, poor-quality forage is the only feed available. Weaned foals and ruminants rely on forages and cereal grains to provide essential nutrients. Hay that has been harvested at a late stage of growth usually has a lower nutrient digestibility compared with young forages. Diets low in digestible energy or protein or both reduce total daily intake in ruminants (Table 9-1) because of the increased turnover time (T1/2) in the gastrointestinal tract and subsequent decreased throughput. This compounds the problems caused by an inadequate intake of digestible nutrients. The digestibility of forages is even lower for horses than for ruminants.



Protein-calorie malnutrition (PCM) is the most common clinical cause of decreased growth and decreased weight gain in young animals. It is characterized by smaller size and lower weight than the normal minimums for age, breed, and sex. Inadequate intake of digestible energy and protein (or essential fatty acids in the neonate primarily adapted to a milk diet) results in inadequate levels of amino acids, fats, and carbohydrates for normal metabolism and growth. Diets that lack any of the other essential nutrients (essential fatty acids, vitamins, macrominerals, or trace minerals) can also decrease growth. Deficiencies of calcium, phosphorus, and magnesium result in improper skeletal formation. Deficiencies in other macrominerals (e.g., sodium, chloride, potassium), trace minerals (e.g., copper, zinc, manganese, cobalt, iron), and vitamins (e.g., A, D, E, thiamin) cause biochemical dysfunctions that lead to inefficient metabolism and growth. Large animal patients that grow slowly as a result of inadequate diets often have normal or increased appetites until they are terminally ill. Physical findings and clinicopathologic data from animals with PCM are often within the normal range until the disease process is well advanced.


Infections or inflammatory processes are important causes of decreased growth and decreased weight gain in young horses and ruminants. The decrease in growth can be of short duration followed by recovery and compensatory gain (cryptosporidiosis) or can persist (chronic bronchopneumonia). Infections or inflammatory processes can also result in nutrient malabsorption (chronic salmonellosis, acute rotavirus diarrhea, equine proliferative enteropathy), anorexia (pharyngeal abscesses, systemic disease), increased nitrogen turnover, and direct protein losses (gastrointestinal disease). Both energy and protein requirements may be increased as a result of infection and inflammation.


Parasitism often affects young horses and ruminants and results in decreased growth and decreased weight gain by increasing nutrient requirements, increasing nutrient losses, and/or decreasing nutrient absorption. The animal’s metabolic rate and nutrient requirements may also increase as a result of inflammatory and immune reactions that arise secondary to parasitism.


Genetic diseases (α-mannosidosis, dwarfism) result in decreased growth through generalized errors in the genetic code or interference with strategic reactions in one or more metabolic pathways. Congenital cardiac malformations (tetralogy of Fallot, interventricular septal defect) create physiologic inefficiencies that require energy beyond the body’s ability to supply it. Congenital renal disease (agenesis, dysplasia, hypoplasia, polycystic kidney disease) affects homeostatic mechanisms that regulate electrolyte and acid-base balance, results in the production of uremic toxins, and often results in partial anorexia and PCM. Digestive tract malformations including cleft palate, megaesophagus, and brachygnathism can reduce nutrient ingestion and impair growth.


Toxicities, although rare in growing animals, result in decreased weight gain by interfering with metabolic pathways (e.g., ammonia toxicity, zinc-induced copper deficiency with abnormal skeletal development in foals), by causing loss of body reserves (e.g., thiamin deficiency in horses, bone marrow hypoplasia and associated bleeding diatheses in ruminants associated with bracken fern toxicity), by inducing anorexia, or by a combination of mechanisms. The pathogenic mechanisms of many toxins are not yet known.


Environmental factors including extreme heat or cold or high humidity result in decreased growth and decreased weight gain. Extremely cold conditions increase an animal’s daily energy requirements. During extremely hot weather feed intake often decreases, which may contribute to decreased growth. Often, environmental conditions influence the development of disease, resulting in a subsequent increase in nutrient requirements in a growing animal (e.g., calves with PCM housed in poorly ventilated or overly humid conditions become much more susceptible to infectious pneumonia).


In many cases a combination of these diverse factors may influence the growth and weight gain of young animals. A period of increased growth rate and weight gain, called compensatory gain, often occurs after a period of restricted growth once adequate dietary energy and protein are available. In growing foals, compensatory gain should be closely monitored to prevent rapid growth and abnormal skeletal development, which could lead to developmental orthopedic disease.


Boxes 9-1 and 9-2 list many of the possible causes of decreased growth and decreased weight gain in horses and ruminants, respectively.



Box 9-1


Causes of Decreased Growth and Decreased Weight Gain in Horses







Box 9-2


Causes of Decreased Growth and Decreased Weight Gain in Ruminants









Approach to the Diagnosis and Management of Decreased Growth and Decreased Weight Gain in Horses



1. Take a general history and a diet history.


a. General history


i. Foal factors: What is the patient’s age? Was the foal born prematurely? Were any congenital defects identified during the initial examination of the foal after birth? Did the foal have any complications from sepsis? What is the vaccination history of the mare and the foal? Has the foal shown any evidence of systemic illness (diarrhea, nasal discharge, cough, pyrexia)?


ii. Environmental factors: How is the foal housed? What type of protection is provided from adverse weather conditions? Has the foal experienced any extreme weather conditions (cold, heat, humidity)? Does the foal have access to a pasture or dry lot? Are there any toxins in the foal’s environment? What is the stocking density of the herd? Is the foal exposed to a high parasite load in the environment? What is the foal’s deworming history? Have there been previous problems with gastrointestinal parasitism on the farm? Does the farm have a history of infectious disease agents (Rhodococcus equi, Streptococcus equi subsp. equi, Clostridium difficile)? Are there any sick horses on the same farm? If so, what age cohort is sick?


b. Diet history


i. Foal: If the foal is nursing, is the mare at an ideal body weight? Is the mare producing a sufficient amount of milk for the foal? If the foal is an orphan, what type of milk replacer is the owner using? What is the daily energy and protein intake of the foal? Is the owner mixing the milk replacer properly? Does the foal have access to a creep feed? What is the owner using as a creep feed? How much of the creep feed does the foal consume daily?


ii. Weanling: When was the foal weaned? Does the foal compete with other foals for feed? Has the owner changed the foal’s diet recently? If yes, what changes were made? Does the foal have a good appetite? Has the foal’s appetite changed recently?


(1) Forage: What type of forage is fed to the foal? Does the foal have access to pasture? How long is the foal turned out in the pasture? What is the nutritional quality of the hay or pasture? Is there gross evidence of dirt, mold, or weed contamination in the hay? Has a hay analysis been performed? If so, what is the digestibility of the hay? How much hay is offered to the foal (in weight) daily? How much forage (in weight) does the foal eat each day?


(2) Supplemental Feeds and Grain: What type of supplemental feed or grain is fed to the foal? Is the feed of high quality and appropriate for a growing foal? What is the nutrient composition of the supplemental feed? How much of the supplemental feed or grain (in weight) does the foal eat each day?


(3) Vitamins and Minerals: Is the foal offered a vitamin and mineral supplement? Is the vitamin and mineral supplement appropriate for a growing foal? Is the vitamin and mineral supplement offered free choice? How much of the supplement (in weight) does the foal eat each day? Could any nutrients be consumed in a toxic amount? Has the owner provided any supplemental parenteral vitamins or minerals to the foal?


2. Perform a physical examination.


a. What is the body weight of the foal (measured by using either a scale or weight tape if the foal is 3 months of age or older)? What is the body condition score (BCS) of the foal (see Table 9-22)? Is the foal small, thin, or underweight according to growth charts (Table 9-2; Figs. 9-1 and 9-2)?





b. Does the foal have evidence of a congenital abnormality (cardiac, renal, gastrointestinal, oral)?


c. Does the foal show any signs of infectious disease (current or resolved)?


d. Does the foal have any musculoskeletal abnormalities?


3. Examine the feces. What is the consistency of the feces? Refer to Chapter 17 for the diagnosis and management of neonatal diarrhea; refer to Chapter 7 if the foal is older and has evidence of diarrhea. Is there evidence of sand in the manure? Perform a fecal egg count. If the foal has a positive fecal egg count, follow the parasite control program recommendations in Chapter 49. If a negative fecal egg count is reported but parasitic infestation is still suspected, repeat the test in 2 to 3 weeks or follow the deworming protocols in Chapter 49. Evaluate the feces for occult blood. If the foal has a positive fecal occult blood test, review the medical management for melena in Chapter 7.


4. Perform blood analyses.


a. Perform a complete blood count (CBC) and include a plasma protein and fibrinogen concentration. If the foal is anemic, determine the cause of the anemia following the guidelines in Chapter 24. If the foal’s CBC indicates inflammation, review Chapters 25 and 26 and select appropriate ancillary diagnostic tests to identify the source of the infection or inflammation.


b. Perform a serum biochemical analysis. Evaluate the results for evidence of systemic disease. Serum albumin is usually within normal limits with PCM until the condition is terminal. Serum glucose is usually normal, but it may be decreased in neonatal foals with sepsis. Serum glucose may be elevated in stressed animals. Serum urea nitrogen and creatinine concentrations are elevated in foals with renal disease. Serum urea nitrogen decreases in cases of chronic protein malnutrition.


c. If the foal has evidence of systemic disease, perform ancillary diagnostic tests to identify the source of the illness and then manage the case with appropriate medical or surgical intervention.


5. Analyze the diet and improve the feeding program.


a. Determine whether the energy, protein, mineral, and vitamin content of the diet meets the requirements of the growing foal (Table 9-3). Use the Nutrient Requirements of Horses free companion computer program as a reference for all essential nutrients (www.nap.edu, search word “horse”).


i. Dietary protein and essential amino acids are especially important in young growing horses. Lysine is the first, and threonine is the second limiting amino acid in the equine. Growing foals should consume 4.3% of their crude protein requirement as lysine (multiply the crude protein requirement by 4.3%).6 Growing foals should also consume at least 0.5% threonine dry matter (DM) in their diet. Soybean meal and alfalfa hay contain approximately 3.3% and 0.9% lysine (DM), respectively. Cereal grains are poor sources of lysine.


ii. Milk replacer: If the foal is consuming a milk replacer, review the guaranteed analysis and ingredient list of the product. Review the mixing instructions with the owner or farm manager. Develop a feeding program appropriate for the foal’s age.


iii. Forage: Determine the nutrient content of forage or pasture with an analysis. Forage sampling instructions and forage analysis companies are listed in Boxes 9-3 and 9-4. University extension services often provide a forage analysis service. If the client does not purchase a large volume of hay, or if analysis cannot be performed, forage tables from the Nutrient Requirement Council reference books (www.nap.edu) and nutrient tables from the Equi-Analytical Laboratories forage laboratory database (www.equi-analytical.com) can be referenced to estimate the concentration of different nutrients in common forages and supplemental feeds. Use the daily nutrient requirements (see Table 9-3) to recommend the type and amount of forage the foal should consume on the basis of the nutrient content of the forage.


iv. Commercial feeds and grain mixes: The guaranteed analysis on the feed tag label provides the nutrient content of certain ingredients. Contact commercial feed companies for the energy content of their product. Make recommendations about the appropriate use of commercial equine feeds, grain, or grain mixes to complement the forage-based ration for growing foals on the basis of the clinical health of the foal.


v. Vitamins and minerals: Ensure that the ration meets the vitamin and mineral requirements of the foal and that proper mineral ratios are maintained in the ration. Supplement the ration if necessary.



TABLE 9-3


Daily Nutrient Requirements for Growth in Equines of Various Mature Body Weights












































































































































































































































































































Mature Body Weight (kg/lb) Category Weight Daily Gain Digestible Energy (Mcal) Crude Protein (g) Lysine (g) Calcium (g) Phosphorus (g)
(kg) (lb) (kg) (lb)
Ponies 200 kg (440 lb) Nursing foal (4 mo old) 67 147 0.34 0.75 5.3 268 11.5 15.6 8.7
Weanling (6 mo old) 86 189 0.29 0.64 6.2 270 11.6 15.5 8.6
Yearling (12 mo old) 128 282 0.18 0.40 7.5 338 14.5 15.1 8.4
Long yearling (18 mo old) 155 341 0.11 0.242 7.7 320 13.7 14.8 8.2
2-year-old (24 mo old) 172 378 0.07 0.154 7.5 308 13.2 14.7 8.1
Horses 400 kg (880 lb) Nursing foal (4 mo old) 135 297 0.67 1.47 10.6 535 23.0 31.3 17.4
Weanling (6 mo old) 173 381 0.58 1.28 12.4 541 23.3 30.9 17.2
Yearling (12 mo old) 257 565 0.36 0.79 15.0 677 29.1 30.1 16.7
Long yearling (18 mo old) 310 682 0.23 0.51 15.4 639 27.5 29.6 16.5
2-year-old (24 mo old) 343 755 0.14 0.31 15.0 616 26.5 29.3 16.3
Horses 500 kg (1100 lb) Nursing foal (4 mo old) 168 370 0.84 1.85 13.3 669 28.8 39.1 21.7
Weanling (6 mo old) 216 475 0.72 1.58 15.5 676 29.1 38.6 21.5
Yearling (12 mo old) 321 706 0.45 1.0 18.8 846 36.4 37.7 20.9
Long yearling (18 mo old) 387 851 0.29 0.64 19.2 799 34.4 37.0 20.6
2-year-old (24 mo old) 429 944 0.18 0.40 18.7 770 33.1 36.7 20.4
Horses 600 kg (1320 lb) Nursing foal (4 mo old) 202 444 1.01 2.22 15.9 803 34.5 46.9 26.1
Weanling (6 mo old) 259 570 0.87 1.91 18.6 811 34.9 46.4 25.8
Yearling (12 mo old) 385 847 0.54 1.19 22.5 1015 43.6 45.2 25.1
Long yearling (18 mo old) 465 1023 0.34 0.75 23.1 959 41.2 44.5 24.7
2-year-old (24 mo old) 515 1133 0.22 0.48 22.4 924 39.7 44.0 24.4
Horses 900 kg (1980 lb) Nursing foal (4 mo old) 303 667 1.52 3.34 23.9 1204 51.8 70.3 39.1
Weanling (6 mo old) 389 856 1.30 2.86 28.0 1217 52.3 69.5 38.7
Yearling (12 mo old) 578 1272 0.82 1.80 33.8 1522 65.5 67.8 37.7
Long yearling (18 mo old) 697 1533 0.51 1.12 34.6 1438 61.8 66.7 37.1
2-year-old (24 mo old) 773 1701 0.32 0.70 33.7 1386 59.6 66.0 36.7


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Modified from National Research Council (NRC). 2007. Nutrient requirements of horses. National Academies Press, Washington, DC.



Box 9-3


Forage and Large Animal Feed Sampling Instructions







b. If the foal or weanling has a nutrient deficiency, the problem should be corrected by a change in the ration or through appropriate parenteral supplementation.


c. If the diet history indicates that nutrients for maintenance and growth have been available and steadily consumed, the search for another cause of decreased growth and decreased weight gain should continue.


6. Perform ancillary diagnostic tests. If the cause of the decreased growth and/or poor weight gain has not been determined, additional diagnostic tests should be performed. Possible tests include, but are not limited to, ultrasound, radiographs, serum or whole blood trace mineral analysis, and carbohydrate absorption tests (oral d-glucose, d-xylose).



Approach to the Diagnosis and Management of Decreased Growth and Decreased Weight Gain in Ruminants



1. Take a general history and a diet history.


a. General history


i. What is the age of the animal? When was a decrease in growth observed? How many animals in the herd are affected? What are the ages of the affected animals? Has the herd had historical problems with growth of the young?


ii. Identify the problem as acute, subacute, or chronic.


iii. Check for signs or history of previous infectious disease in the herd.


iv. Determine the parasite control procedures for the animal or herd.


v. Examine the environment, including feed preparation areas and equipment, for possible toxic substances (e.g., zinc from galvanized buckets). Ensure cleanliness of bottles and equipment used with nursing animals.


b. Diet history


i. Obtain an accurate diet history, including diet information when milk or a milk replacer is being fed (birth to 2 or 3 months of age). Note the age and condition of the dam if patient was suckled before weaning. An accurate postweaning dietary history is essential. Suckled animals are developed ruminants at weaning, but hand-reared animals (dairy calves, bummer lambs, and dairy kids) are usually not fully developed ruminants at the time they are weaned from milk.


ii. Inspect all forages and concentrates for quality, signs of spoilage, or abnormal color or odor. Has an analysis been performed on the forage or feed? Is the feed formulated appropriately for a young growing animal? Is the feed stored appropriately?


iii. Because ruminants are often fed in groups, note whether all animals have adequate space to eat simultaneously.


2. Perform a physical examination.


a. Determine the patient’s age and weight. Is the patient growing appropriately on the basis of age and weight charts (Figs. 9-3 to 9-6)?






b. Does the animal show any signs of infectious or parasitic disease?


c. Does the animal show any signs of congenital abnormalities?


3. Examine the feces. Perform flotation, sedimentation, and Baermann’s procedures to detect patent parasitic infestation. Perform a fecal occult blood test; if the result is positive or if there is evidence of diarrhea, see the section melena or diarrhea in Chapter 7. If diarrhea is noted in neonatal calves, refer to Chapter 20 for diagnostic and therapeutic management.


4. Perform blood analysis.


a. Perform a CBC, including plasma protein and fibrinogen. Calculate the erythrocytic indices, and document and characterize the anemia if present. If a herd problem exists in a selenium-deficient region, measure the whole blood selenium concentration or glutathione peroxidase activity.


b. Perform a serum biochemical analysis. Serum albumin is decreased late in PCM. Albumin is normally lower in neonates (≈1 g/dL less) than in adults. The blood urea nitrogen (BUN) level is often low in ruminants as a result of urea recycling through saliva. Total serum calcium may be decreased with hypoalbuminemia (ionized serum calcium remains normal), anorexia, or hypocalcemic syndromes (milk fever). Serum phosphorus may be increased during severe starvation or decreased with anorexia. Hypophosphatemia may be the result of dietary deficiency or Brassica feeding, or it may be associated with copper deficiency. Measure serum (plasma) copper if a herd problem exists in a copper-deficient region (or a region with excess molybdenum or sulfate or both). Copper (serum or plasma) concentrations below 0.5 µg/mL (ppm) indicate deficiency. The concentration of copper in the liver is even more indicative of status. Serum glucose may be increased with stress or decreased or normal near death.


5. Analyze the diet and improve the feeding program. Compare nutrient intake with the requirements for maintenance and growth of the various ruminant species (Tables 9-4 through 9-11). If the neonate is being fed a milk diet, evaluate the quality of the product and ensure that the animal’s intake meets the dietary requirements (see Tables 9-4 and 9-5). Requirements for other breeds and life stages can be found in the nutrient requirement textbooks for dairy cattle, beef cattle, and small ruminants. Ensure that the milk replacer is mixed properly. If the ruminant is consuming a grain mix or forage, ensure that the quantity and the quality of the feed are adequate to allow sufficient intake in developed ruminants (see Table 9-1). Forage sampling instructions are listed in Box 9-3. If anorexia is present, look for more specific signs of a primary disease process. If the diet supplies adequate nutrients for maintenance and growth, consider decreased growth and decreased weight gain to be caused by a primary disease condition.



TABLE 9-4


Daily Energy and Protein Requirements for 50-kg Calves on a Milk Diet
























Digestible Energy Requirements Digestible Protein Requirements
Maintenance 45-55 kcal/kg body weight 0.5 g/kg body weight
Gain 300 kcal/100 g gain in body weight* 22 g/100 g of weight gain†
0.5 kg daily gain 1500 kcal
1 kg daily gain 3000 kcal


* A 50-kg calf gaining 0.75 kg/day would have a daily energy requirement of 5000 kcal of digestible energy (2750 kcal maintenance + 2250 kcal/0.75 kg of gain).



† A 50-kg calf gaining 0.75 kg/day would have a daily protein requirement of 190 g of digestible protein (25 g of maintenance + 165 g of gain).



TABLE 9-5


Net Energy (NE) Requirements of Young Lambs on Milk-Replacer Diets*










































































Body Weight in Kilograms (Pounds)
Average Daily Gain (g) 5 (11) 7.5 (16.5) 10 (22) 12.5 (27.6) 15 (33)
NEm Required, kcal/day

358 487 603 712 817
NEg Required, kcal/day
100 127 172 214 253 290
150 193 262 325 383 440
200 261 353 438 518 594
250 330 447 555 355 751
300 401 543 674 796 913
350 473 641 796 940 1078
400 547 742 921 1088 1247


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* Protein requirements for young lambs on a milk-replacer diet are approximately 20 g, 40 g, and 60 g for weight gains of 0, 100, and 200 g/day, respectively.


NEg, Net energy of gain; NEm, net energy of maintenance.


From Chiou PWS, Jordan RM. 1973. Ewe milk replacer diets for young lambs. IV. Protein and energy requirements of young lambs. J Anim Sci 37:581.



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Aug 11, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Alterations in Body Weight or Size

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