NUTRITION OF HORSES AND MULES by Ear! B. Krantz and S. R. Speelman ^ I H t first part of this article deals with the nutritional requirements of horses insofar as these have been determined; actually, there has not been very much experimental work in this field. The second part discusses practical feeding under different conditions, including suggested rations and the use of concentrates, roughage, and mineral supplements. THE PRINCIPLES of the nutrition of horses and mules ^ fundamentalh^ are not unlike those of other domestic livestock. Thus^ for body building and maintenance, for growth, and for production, the horse and mule have need for protein, carbohydrates, fats, minerals, and vitamins, much as these essentials are required for similar vital processes by cattle, sheep, swine, and poultry. The relative importance of the various nutrients and the quantities required by horses and mules are, however, not the same as for the other farm animals. Nor do the requirements of horses and mules necessarily remain the same from day to day or from period to period. The stage of life, the kind and degree of activity, climatic conditions, the kind, quality, and amount of feed, the system of management, the health and individuality of the animal, and perhaps other equally important factors are all continually exerting a pow^erful influence in the deter- mination of nutritive needs. How^ well the individual feeder or experi- menter understands, anticipates, interprets, and meets these require- ments usually determines the success or failure of the ration and of horse or mule keeping. The present discussion of the nutritive requirements of horses and mules considers the subject briefly from the standpoints of adequacy of rations, feed economies, and feeding practices. 1 Earl B. Krantz was formerly Animal Husbandman, and S. R. Speelman is Associate Animal Husband- man, Animal Husbandry Division, Bureau of Animal Industry. 2 Although most of the research and investigational work in the field of nutrition has not considered mules, the results obtained from some tests and from practical experience indicate that their requirements for feed are essentially the same as those of horses. The nutritive needs of horses and mules are accordingly treated as one in this article. 763 764 YEARBOOK OF AGRICULTURE, 1939 NUTRITIVE REQUIREMENTS PROTEIN Horses and mules of all ages and kinds need adequate amounts of protein of suitable quality. Protein is required for building new tissues and for replacing protein lost from the body in the general wear and tear of normal body processes. Actual protein requirements for these processes can be described in terms either of nitrogen used by the body or of amounts of a theoretically complete or perfect protein which contains all the amino acids needed in exactly the proportions required by the body. In this respect no one food protein is perfect, and proteins from various sources vary widely in their biological value. Knowledge concerning the actual protein requirements of horses is rather scant, but feeding standards have been established as a result of experiments as well as of practical experience that suggest amounts of crude digestible protein estimated to cover the protein requirements with a suitable margin of safety. These standards take into account the variability in nutritional value of different food proteins, as well as some variations in quantitative requirements. During the stage of growth and development of the young horse or mule, particularly the first year, the relative need for protein is greater than at any other time of life. The amounts needed daily for 100 pounds of live weight are usually greatest at the earliest ages and smallest weights, declining gradually as the animal ages and increases in size. The needs of the growing animal for protein for building new tissues are responsible for most of the excess in its protein requirements over those of mature animals. The relative demands for protein of colts and of mature horses of various classes are shown in recommen- dations for the daily intake of this nutrient in some feeding standards, such as those of Morrison {819^ pp. 1006-1007),^ which are given in table 1.^ Morrison suggests that the daily protein needs of the 500- pound draft colt are amply covered by 0.18 to 0.20 pound per 100 pounds of live weight, while for the 1,000-pound mature idle work horse the quantity specified is 0.06 to 0.08 pound. In ordinary feeding practice it is assumed that the quantitative needs for protein among young growing animals are the same for both sexes. A report by Mitchell {796)^ however, states that * ^females put on gains containing a smaller percentage of calories in protein than males.^' This indicates that the protein requirements of the growing female may be somewhat less than those of the male, but the difference is probably not of importance in practical feeding. Estimates for the combined amounts of protein required daily for growth and main- tenance in draft colts weighing 400 to 1,200 pounds, as made by Morrison {819, p. 1007\ are given in table 1. The optimum and minimum quantitative needs of colts for protein during the growth period are unknown at the present time, except for information developed from practical experience. The need for experimental research on this subject is evident. » Italic numbers in parentheses refer to Literature Cited, p. 1075. * The Morrison standards have been selected for purposes of discussion because their recommendations cover the nutrition of horses of various kinds and because they are applicable to many of the methods that have been found to be practical and economical under average and normal conditions. NUTRITION OF HORSES AND MULES 765 TABLE 1.—Morrison''s feeding standards for horses Requirements per head daily Type and weight (in pounds) of animal Total Nutritive Dry matter Digestible protein digestible ratio.i 1 Net energy nutrients to — Horses, idle: Pounds Pounds Pounds Therms ^ 1,00() 13.0-18.0 0.&-0.8 7.0-9.0 10.0-12.0 5. 6-7. 2 1,200 14.8-20. 6 .7- .9 8.0-10.3 10.0-12.0 6.4-8. 2 1,400 16. &-23.0 .8-1.0 8.9-11.5 10.0-12.0 7.2-9. 2 1,600 . 18.3-25. 4 .8-1.1 9.9-12. 7 10.0-12.0 7.9-10.1 1,800 20.0-27. 6 .9-1.2 10.8-13. 8 10.0-12.0 8. 6-11.1 llorses at light work: 1,000.-.: 15.0-20.0 .8-1.0 9.0-11.0 9.0-11.0 7. 5-9.1 1,200 17. 4-23.1 .9-1.2 10. 4-12. 7 9.0-11.0 8.7-10. 5 1,400 19. 6-26. 2 1.0-1.3 11.8-14.4 9.0-11.0 9.8-11.9 1,600 21. ^29. 2 1.2-1.5 13.1-16.0 9.0-11.0 10. &-13. 3 1,800 24.0-32.0 1.3-1.6 14.4-17. 6 9.0-11.0 12.0-14. 6 Horses at medium work: 1,000 16.0-21.0 1.0-1.2 11.0-13.0 9.0-11.0 9.4-11.1 1,200 18. 8-24. 6 1.2-1.4 12.9-15. 2 9.0-11.0 11.0-13.0 1,400 21.5-28.2 1.3-1.6 14. 8-17. 4 9.0-11.0 12. 6-14. 9 1,600 24.1-31. 6 1. 5-1. 8 16. 6-19. 6 9.0-11.0 14. 2-16. 7 1,800 26. 7-35.0 1. 7-2.0 18. 3-21. 7 9.0-11.0 15. 7-18. 5 Horses at hard work: 1,000 18.0-22.0 1. 2-1.4 13.0-16.0 9.0-11.0 11. 3-13. 9 1,200 21.3-26.1 1.4-1.7 15. 4-19.0 9.0-11.0 13. 4-16. 5 1,400 24. 7-30. 2 1.&-1.9 17.8-21.9 9.0-11.0 16. 5-19.1 1,600 28.0-34. 2 1. &-2. 2 20. 2-24. 8 9.0-11.0 17. 5-21. 6 1,800 31. 2-38.1 2.1-2. 4 22. 5-27. 7 9.0-11.0 19. 6-24.1 Brood mares nursing foals, not at work: 1,000... 15.0-22.0 1.2-1.5 9.0-12.0 6. 5-7. 5 7. 6-10. 0 1,200 17. 4-25. 5 1.4-1.7 10. 4-13. 9 6. 5-7. 5 8.8-11. 6 1,400... 19. 6-28. 8 1. 6-2.0 11. 8-15. 7 6. 5-7. 5 10.0-13.1 1,600 .. 21.9-32.1 1. 7-2. 2 13.1-17.5 6. 5-7. 5 11.1-14. 6 1,800 24.0-35. 2 1.9-2.4 14.4-19.2 6.5-7.5 12.2-16.0 Growing draft colts, after weaning: 400 . 9.2-11.3 .8- .9 5.6-7.2 6. 5-7.0 4.9-6.3 500 10.9-13. 3 .9-1.0 6. 6-8.4 6.6-7.1 5. 7-7.3 600 12. 4-15. 2 1.0-1.2 7.6-9.6 6.7-7.2 6. 5-8. 3 700 13.9-17.0 1.1-1.3 8.