NUTRITIVE REQUIREMENTS OF SWINE - USDA

NUTRITIVE REQUIREMENTS

OF SWINE

by N. R. Ellis and J. H. Zeller '

I 11 I O article deals with the more technical aspects of swine feeding,

outlining results of some of the research work that has been done on the

requirements of the pig for energy, protein, minerals, and vitamins. The

practical feeding of hogs, based on these requirements, is considered in a later article.

THE HOG excels other livestock as an economical converter of feed into body tissue, the products of which are largely meat and fat. Fundamentally, the nutritive requirements of swine are not so complicated as those of other classes of livestock. The swine ration is largely made up of concentrated feeds with only a small proportion of roughage, aside from good pasture. Hogs grow rapidly and most of them reach market weight at 7 to 10 months of age. They also reproduce at a much younger age than most farm animals. Well- developed gilts are usually bred to farrow their first litters at approximately 1 year of age.

The growth of swine follows the same general law as that of other animals, but they grow much faster in proportion to their body weight than the larger farm animals. Growth curves showing the rate of increase have been published by various investigators. The curves given in figure 1 show a somewhat faster rate than most of the other United States data. These curves are based on records kept on litters used in record-of-performance tests at the Agricultural Research Center, Beltsville, Md., for the autumn farrows of 1936 and 1937 and the spring farrows of 1937 and 1938. The sows and the pigs of all four farrows were handled under essentially identical conditions except for the diflierences due to season of the year. Besides the ration of yellow corn and a protein mixture with mineral supplements incor- porated, the sows grazed on rye pasture. The pigs were weaned either at 8 or at 10 weeks and a large proportion were placed on the record-of-performance test. For the most part, the animals were removed from the feed lot when they attained a weight of approxi-

1 N. R. Ellis is Senior Chemist, Animal Nutrition Division, and J. H. Zeller is Senior Animal Husband- man, Animal Husbandry Division, Bureau of Animal Industry.

706

REQUIREMENTS OF SWINE 707

mately 225 pounds. Tlie pigs were self-fed whole yellow corn and a mixture (known as the trinity mixture) of 50 parts tankage, 25 parts linseed meal, and 25 parts alfalfa-leaf meal, plus 5 parts of a mineral mixture composed of 50 parts ground limestone, 27.97 parts steamed bonemeal, 20 parts common salt, 2 parts iron oxide, 0.01 part copper sulfate, and 0.02 part potassium iodide. The average birth weight of 1,377 pigs was 2.91 pounds.

Because of the divergence in rate of growth between fall- and spring- farrowed pigs, separate growth curves are shown for the two groups. It will be noted that the average weight of the fall pigs (fig. 2) at the age of 22 weeks was approximately 145 pounds and of the spring pigs, 130 pounds. This difference of 15 pounds was probably associated with temperature. The hot summer months were apparently not so conducive to growth as the cool fall months. Beyond the age of 22 weeks the growth rates were approximately parallel. During the last 8 weeks the growth rate averaged 1,65 pounds a day. Further refer- ence to the feed consumption of record-of-performance pigs will be found elsewhere in this article.

COMPOSITION OF THE PIG'S BODY

In studying the nutritional needs of the pig it is well to consider first the percentage composition of the body. Some figures based on analyses made at the Agricultural Research Center are shown in table 1. These percentages are subject to wide variations owing to

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AGE OF PIGS (WEEKS) 22 24 26 28 30

Figure 1.—increase in live weight of pigs in 30 weeks, based on averages of numbers of pigs shown in parentheses.

708 YEARBOOK OF AGRICULTURE, 1939

ll-laini«iil pigs grazing on ry

differences in type, agce, and nutritional condition. They do, however, show the general trend as the pig grows and fattens. Water is an essential constituent of the body, found in tiie largest amounts in the blood and muscle tissues and constituting 40 to 4y percent of the weight of the average 225-pound market hog. The percentage of protein, which is found in every cell of the muscles, tendons, and soft tissues, is highest in the young animal and decreases as the pig fattens. The percentage of fat increases as the pig fattens. Because of the small skeleton of the pig the percentage of mineral matter is small and does not vary widely.

T.\BI.E 1.—Body composition of su i ne

Gond tion of íatnes.s Weight at slaughter

Body substance

Components of body substance

Water Protein Fat Asb

Thin Poundt

106 162 219 230 3(3

Pounds 100 154 210 219 327

Percent 56.3 49.2 44.3 41.4 37.7

Percent 14.« 13.7 12.6 10.5 10.8

Percent 25.8 34.2 40.6 4.'). 9 49..')

Percent 3.1

Moderately fat -.. 2.« Fat . .. 2.5 Veryfat 2.3 Extremely ffit 2.1

REQUIREMENTS FOR ESSENTIAL NUTRIENTS

Problems relating to the nutritive requirements of swine, along with those of other farm animals, have engaged the attention of scientific investigators since the middle of the nineteenth century. The classi- cal experiments of Lawes and Gilbert {665) - at the Rotliamsted H\- poriment Station in England, on the composition of tiie body increase of swine in relation to the composition of the feed ingested have been cited many times by nutrition workers in the past 80 years. Among

' Italic numbers in parentheses refer to Literature Cited, p. 1075.


other findings, this worl^ formed an important and incontrovertible link in the evidence that body fat is formed from the carbohydrate as well as the fat in foods.

During the third quarter of the last centur}^, the concept was firmly established that the fundamental nutritive needs of the animal body were primarily for energy, with enough protein for maintenance and the building of muscle tissue. Much of the early work on feed requirements was done by German investigators. The feeding standards formulated by Wolff, which have come down to the present day in various modifications, was first published in 1864 {32, p, 689). These standards listed the amount of digestible crude protein, carbo- hydrates, and fat required daily by the different classes of farm animals, including s wane.

The idea that energy and protein were the only essentials to be considered, in feed requirements persisted well into the present century. Indeed, Armsby, who was responsible for the introduction of the German feeding standards in this countr^^, w^rote in 1912 {31) that ^'the chief function of the feed aside from a minimum of protein, is to supply energy.^' It is true that the need for a few mineral elements, such as the calcium and phosphorus found in bones, and sodium chloride to satisfy salt hunger, was recognized. The needs of livestock, with the possible exception of swine, for minerals were considered to be satisfied by the ordinary feeds that would meet energy requirements. The discovery that swine often needed additional mineral supplements did much to promote research on the requirements of other species and to extend inquiries to a wide range of mineral elements.

Qualitative differences in proteins w^ere also recognized early in the present century. Corn had become the staple hog feed at an early date in this country. With the recognition of the fact that the proteins in corn are of low quality owing to the absence of certain essential amino acids, numerous hog-feeding trials demonstrated the value of various supplementary feeds rich in protein.

Early research on feed requirements was directed more to the needs of cattle and sheep, and even the horse, than to those of swine. Much of the work on swine was concerned with such questions as the relative advantages of grinding, soaking, and cooking grain, and the influence of the nutritive ratio between energy and protein on the live- weight gains and the proportion of lean to fat in the carcass. Later, when the complications of mineral essentials and protein qualit35^ came to be recognized in swine feeding, the inexactness of the various sets of standards based on quantity of energy and protein were clearly evident.

Today, the problem of fundamental nutritive requirements is broader and more complex. To the list of the more common and plentiful mineral elements such as calcium, phosphorus, potassium, sodium, magnesium, chlorine, iron, and sulfur have been added iodine, copper, manganese, cobalt, and zinc. Others are still in the doubtful class. The problem of vitamin requirements is a complex and ex- panding subject. The role of diet in relation to hormones is not well understood. Finally, it is more and more evident that the requirements of swine for the various essential nutrients are different from those of other farm animals.


ENERGY

Much attention has been given to the energy requirements oí tlie animal body for maintenance. Because the pig is a fast-grownig animal and the great majorit}^ of the pigs on farms are in the growing and reproductive stages, the question of maintenance of body weight is less important than it is in the case of horses and cattle, where mature animals are kept for extended periods. Nevertheless, the amount of food needed for maintenance should be evaluated as fundamental to the needs for body increase^ and i-eproduction.

One of the chief difBculties in the expression of the energy requh-ed for maintenance has been the segregation and evaluation of the portion above the basal metabolism (when the animal is completely at rest) that is expended (]) in eating, digestion, and assimilation of food, and (2) in exercise and activity. Some investigators have considered these expenditures a large, and others a small proportion of the total energy requirement. Likewise, certain of the reports show^ a definite allotment of energy for these secondary expenditures, wdnle others have simply divided the total energy requirement into (1) net energy required for maintenance, and (2) energy required for body increase and reproduction. Some of these problems have been discussed by Mitchell and Kelley (802),^

In 1917, Armsby summarized the existing information on maintenance requirements of swine (32) and found that the net energy needed per 100 pounds live w^eight was 1,199 calories a day. Since that date there have been a number of contributions. Some English breeds of swine wxre studied by Deighton, using a calorimeter, and from these data on castrated male and female pigs, along with additional data obtained at the Missouri Agricultural Experiment Station, Brody et al. (157) have derived prediction equations by means of which the basal metabolism of different w^eights of pigs may be calculated.^ Brody and his coworkers have also proposed a feeding standard for total maintenance, which is twice that of their basal metabolism standard. Furtherniore, they have expressed the feed requirements in terms of total digestible nutrients. Danish experiments by Breirem (Ï50) on. bacon-type pigs yielded a formula somewhat different from that of Brody.^

In Sweden, Edin and Helleday (S04) have derived ajiother equatioii from Swedish, American, German, and Russian feeding and slaughter tests for estimation of the maintenance and production requirements.

In a study of the energy and protein requirements of growing swine, Mitchell and Hamilton (799) found that 1 pound a day per 100 pounds live weight of a diet consisting of yellow corn, middlhigs, and tankage was required for maintenance of body weight in pigs weighing approximately 225 pounds, while 1.5 pounds per 100 pounds live weight was required by 60-pound pigs.

3 The equation for castrated male and female pigs over 50 kilograms (110 pounds) live weight is represented

as ■o-=34«-o-oii M-hlO, where Q is the basal heat production in calories per day, j\'J is the weight of the pig

in kilograms, and e is the base of natural logarithms. Brody and coworkers have derivc<î a general equation for relating the basal metabolism in calories to body weight for animals as a group (see the article on Factors Aiïecting Maintenance Nutrition, Peed Utilization, and Health of Farm Animals, p. 437). This equation, Q=70.5 M ^■'^*, whore Q is the basal metabolism in calories and A/is the body weight, yields values generally comparable with those of the foregoing.

(W) ^ E=21?.i^ -^j— 5/9, where E is the daily requirement of net energy and IT is the live weiuht in kilograms.

TABLE 2.—Comparison of different estimates of maintenance energy requirements of pigs per day

Weight of pig (pounds)

50_ 100 150 200 25{) 300 400

Basal metabolism

Deighton (English)

Brody

Female

Therms i 1.01 1.33 1.78 2.05 2.24 2.40 2.66

Therms 0.82 1.34 1.68 1.91 2.11 2.28 2.61

Male

Therms 0.92 1.50 1.92 2.24 2.54 2.83 3.42

General

Therms 0.71 1.16 1.56 1.93 2.28 2.62 3.27

Mitchell and

Hamilton

Therms 1.00 1.80 2.50 3.00 3.00

Resting

Deighton (English)

Therms 1.41 2.25 2.72 2.96 3.11 3.22 3.38

Brody

Female Male

Therms 1.55 2.47 3.03 3.31 3.48 3.60 3.78

Therms 1.48 2.40 3.03 3. 40 3. 09 3.94 4.42

Mitchell and

Hamilton

Therms 1.32 2.37 3.29 3. 95 3.95

Daily maintenance (European)

Practical maintenance

Breirem

Therms 0.93 1.37 1.72 2.01 2.28 2.52 2.90

E din and Helleday Brody

Therms Therms 1.17 1.37 1.98 2.28 2.40 3.06 2.47 3. 79

4.40 5.07 O

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' A unit of heat and energy equal to 1,000 calories.

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A summary of the maintenance requirements as determined or compiled by different investigators is given in table 2. As airead}^ indicated, it has not been possible to express all requirements strictly on the basis of economic maintenance or basal maintenance. Con- siderable variability is noted in the figures. However, they are be- lieved to present a fair picture of the probable range under reasonably restricted environmental conditions.

The production requirements over and above maintenance must be considered from the standpoint of the product. In growing and fattening pigs, the product is largely fat and protein. Because of the increase in proportion of fatty tissue to muscular tissue with increasing weight, there is a steady increase in the energy content of each additional pound of gain. Mitchell and Kelley (802) have estimated the values for different w^eights of pigs reared according to American feeding practice. For a 75-pound pig, 1,625 calories are stored, while for a 225-pound pig 2,600 calories are stored in 1 pound of live-weight gain. The feed required to furnish these energy values have been estimated in a number of studies also cited by Mitchell and Kelley. The experiments of Mitchell and Hamilton (799) would indicate that 5.4 pounds of a ration of corn, tankage, and middlings would be required for a 2-pound gain in a 225-pound pig.

Pregnant gilts have a considerable amount of energy stored in body tissue as fat and protein besides the portion required for the embryos. Older sows also store a large amount of fat that is later utilized during lactation in the formation of milk. The demands of lactation for energy are much greater than those of pregnancy. It is the exception rather than the rule for a sow nursing a fair-sized litter even to main- tain her weight, much less to increase it. The situation is quite comparable to that with the milking cow.

Numerous so-called energy feeding standards for swine have been proposed. For the most part they express the combined requirements for economic maintenance and production. On the one hand, economic maintenaî)ce, which includes the quota necessary to cover the normal muscular activity in addition to the energy expended in maintenance/ has been difficult to determine precisely, while on the other variability in production requiremeiits and feeding practices has caused the proponents of most standards to set up values permitting a wide latitude of feed allow^ances.

Investigators have used several forms for expressing the energy requirements, so that there has been considerable confusion in inter- preting results for the evaluation of feeds and rations. Because of its wide use over an extended period, the net energy basis has been utilized in the present discussion as the common ground upon which to com- pare different standards.^ It has been found that the net energy value of a given feed varies with the body function being supported. It is higher for maintenance than for fattening. Undoubtedly the values for other functions are also different from those of either maintenance or fattening. Likewise, the energy values for different combinations

5 See Factors AfiCecting Maintenance Nutrition, Feed Utilization, and Health of Farm Animals, p. 431. ó Net energy is an exDression of the energy of the feed actually useful for body functioning, and the net

energy values are intended to show the amount of body product which may be expected from a unit weight of feed.


of feeds are variable and are not necessarily the cumulative total of the individual components determined separately. Processing methods employed in preparation of feeds also influence the digestibility and thereby the available energy. The most exact measurements are accordingly those on a given mixture fed under well-defined conditions.

Table 3 gives several of the standards in abbreviated form to illustrate some of the differences encountered in them. The table also shows the changing requirements for different functions—growth, fattening, pregnancy, and lactation. In order to express the data on a comparable basis, it has been necessary in some cases to modify the figures from their original form. It will be noted that therms of net energy (a therm is 1,000 calories) are given in each of the five standards. Along with the net energy requirements are estimated amounts of feed mixture required. These are on an as-fed basis and of the type appropriate to accepted practice. The data of Mitchell and Hamilton {799) are based on results from swine type studies in which carcass analyses and digestibility experiments were conducted. The Fraps standard {38S) is a tentative one based on digestion and growth data expressed in terms of production values for the more common American hog feeds.

TABLE 3.—Comparison of standards for total daily energy requirements of swine

Class of hogs

Growing and fattening pigs: 50 pounds 100 pounds 150 pounds 200 pounds 250 pounds 300 pounds

Pregnant gilt (300 pounds) : First week Sixteenth week

Pregnant sow (400 pounds) : First week Sixteenth week

Lactating sow (400 pounds) : Second week Eighth week

Mitchell and Hamilton

Net energy

P'eed mixture

Therms 2.18 3.53 4.89 6.08 6.33

Pounds 2.6 4.3 6.0 7.4 7.7

American practice

Net Feed energy mixture

Therms 2.40 4.00 5.50 6.90 8.30 9.25

5.26 4.28

4.79 3.68

8.30 6. 51

Pounds 2.9 4.9 6.6 8.1 9.7

10.7

6.2 5.0

5.8 4.4

European practice

Net Feed energy mixture

Therms \ 1.89 I 3.10 1 5.04 ¡

Pounds 2.5 4.1

6.35 8.12

8.5 10.8

3.4 4.6

4.0 5.3

11.6 15.5

Class of hogs

Growing and fattening pigs: 50 pounds 100 pounds 150 pounds 200 pounds 250 pounds 300 pounds

Pregnant gilt (300 pounds) : First w^eek Sixteenth week

Pregnant sow (400 pounds) : First week Sixteenth week

Lactating sow (400 pounds) : Second week Eighth week

Fraps

Produc- tion

values

Therms 1.80 3.15 4.25 5.30 6.00 6.70

Feed mixture

Pounds 2.6 4.1 5.7 7.1 7.9 8.0

Net energy

Therms 2.00 3.45 4.60 5.35 5.90 6.45

4.4 3.6

4.6 3.6

9.3 7.9

Feed mixture

Total I digestible i nutrients

Pounds 2.7 4.7 6.1 7.2 8.0

6.0 4.9

6.2 5.1

12.8 10.4

Pounds 2.20 3.75 4.95 5.80 6.45 7.00

4.8 4.0

5.0 4.0

10.0 8.5

Beltsville

R. O. P.i feed

consumed

Pounds 2.7 4.7 6.3 7.3

1 In record-of-performance tests.


Tlie figures for American practice and European practice are based on the data of Mitchell and Kelley {802), who intended them as typifying feeding methods rather than as actual standards in common use. The feed mixture used in calculating the allowance in the Ameri- can practice was a combination of corn and a trinity mixture of tankage, alfalfa-leaf meal, and linseed meal with a mineral supplement proportioned for the appropriate nutritive ratio and based on a 10- percent moisture content. The feed mixtures in the other standards were likewise adjusted in accordance with the type of production involved. Mitchell and Hamilton used a mixture of corn, tankage, middlings, and alfalfa-leaf meal. A combination of corn, barley, wheat middlings, and fish meal was used for the European practice. Morrison^s standards (819) are well known and need no further expla- nation. The total digestible nutrients can be calculated for the standards other than Morrison's by the use of the total digestible nutrient values for the feeds in question.

It will be noted that the values given under ^*American practice'' for growing and fattening pigs are the most liberal. Such a standard will probably promote a faster rate of fattening than the others. On the other hand^ the allowance for the Eiu^opean practice is lower than the American, as might be expected from the greater emphasis on the production of bacon in Europe, but it does not differ greatly from the other standards.

The estimates in the standard for American practice {802) for pregnant gilts and sows were based on the assumption that the gilts would be permitted to gain approximately 100 pounds and the sows 65 pounds during the gestation period.

Brody's data indicated a higher maintenance requirement for boars. Adequate data for the total requirements of boars are apparently lacking.

The last column in table 3 lists some typical figures for average daily feed, consumption by growing and fattening pigs in record-of- performance tests at the Agricultural Research Center. These pigs have been self-fed on corn and a mixture of oO parts tankage, 25 parts alfalfa-leaf meal, and 25 parts linseed meal. Until 1937, a mineral mixture was self-fed in a third compartment of the feeders, but since then this has been mixed with the protein mixture in the proportion of 1 part minerals to 20 parts protein concentrate.

It is noteworthy that the consumption figures for the self-fed ration agree closely with those in the Morrison standard.

The general use of self-feeders for the feeding of growing and fattening pigs in this country has largely submerged the interest in the choice of a suitable standard for popular use. Much of the interest has been directed to the problem of finding the mixtures that will promote the most rapid gains in live weight and the most economical conversion of feed into live-weight gain. As information on protein, mineral, and vitamin requirements has become available and has been applied in the rationing of swine, much greater uniformity has been achieved by hog producers in the rapidity of gains and economy of feed utilization. There is thus good reason to believe that energy standards will continue to serve a very useful purpose in evaluating the success of improvements in rationing with respect to other nutritive essentials.


PROTEIN

The problem of protein requirements is closely associated with that of energy and in. actual practice is generally of more concern. Prob- ably the first major advance of recent times in swine nutrition was the finding that an exclusive corn diet supplied too little protein both in quality and quantity for the growing pig. This deficiency and the mineral deficiencies were met by the addition of such feeds as milk or milk byproducts, tankage, fish meal, linseed meal, soybean meal, and similar products.

Much of the supply of these supplements must be purchased by the farmer to supplement the home-grown cereals. Usually the cost of the protein supplements is higher than that of the cereals. It is not profitable to feed excessive amounts of protein beyond the requirements since protein ranks slightly lower than starch as a source of energy.

In computing the protein requirements, it is necessary first to figure the amount of protein that will supply the nitrogen used by the body tissues for upkeep or maintenance. Additional protein above the maintenance requirement is used for growth, reproduction, and lactation. It is possible, by means of balance experiments in which the intake and outgo of nitrogen are determined and also through analyses of the entire bodies of the pigs, to secure rather accurate figures on the amounts of protein actually broken down or built into the body. The determination of the total quantit^^ of feed protein required is complicated by a number of factors. Among these is the fact that the digested protein is a highly variable quantity. The approximate content of total digestible protein has been determined for many swine feeds. For most of the common feeds, 60 to 90 percent of the total protein is digestible. But even after the total digestible protein in a given ration has been estimated, there is another variable to be figured—the portion of the digestible protein that is biologically usable in building tissue. The proteins in many of the common rations have a biological value not greatly in excess of 50 percent.

As an example of the way the protein requirement w^orks out, the following may be cited: Mitchell and Hamilton (799) as a result of their swdne-type studies concluded that growing pigs of 100 pounds weight required 0.029 pound of protein for maintenance and 0.103 pound for growth, or a total of 0.132 pound daily. On the basis of a biological value of 50 percent for proteins of their ration of corn, middlings, and tankage, the digestible protein required was estimated as 0.264 pound. The digestible protein in the ration constituted approximately 67 percent of the total protein, hence the requirement of total protein was 0.396 pound (50 percent more than 0.264 pound).

Various sets of values have been proposed for the protein requirements of pigs. In most of these the quantity has simply been related to body weight. The relation of the protein required for maintenance to the protein required for basal metabolism has been studied by Smuts {1086). On the basis that the protein requirement is proportional to a power of the body weight, he has proposed the use of an adaptation of Brody's equation—P=0.88M°'^^'\ in which P is the daily protein requirement in grams and M the body weight in


kilograms. This equation is intended to yield generalized values applicable to all species. The values calculated for various weights of pigs are shown in table 4 in comparison with other estimates of protein requirements. The Armsby figures were based on early German and American experiments. Lund (698), a Swedish worker, has furnished data for both maintenance and production. It is significant that the figures of Lund and of Smuts agree closely even though obtained by difterent methods. Among the German investigations the standards of Kellner (31) and of Lehmann (1245) have been widely quoted, w^hile that of Peterson (91Ii) is of comparatively recent origin in Sweden. Fraps of the Texas Agricultural Experi- ment Station has made extensive studies (888) on the digestibility of typical American swine feeds and rations. The source of the data of Mitchell and Hamilton has already been indicated. Their figures for actual protein are 50 percent of those for digestible protein^ as are those of Smuts. Brody (157) estimated the digestible protein required as four times the endogenous protein (the minimum protei^i used for maintenance).

TABLE 4.—Comparison of staiiilards for (iaily ¡noteiii roifuirements of swine for maintenance

AniJsl)y , Limd ■ iMitcliell and Jiani- ilton S I!] Tits

Weight of pig (pounds) Digest-

ible protein

50-_ 100_ 150. 200 _ 250- 300-

Pounds 0.024 .048 .072 . 096

Digest- I i ble pro- ■

tein ;

Pomids 0. 044 .066 . 086 .106

Actual protein

Pounds 0.017 .030 .035 .038

.Digest- ible pro-

tein

Pounds 0.034

. 059

.071

.075

Actual ])rotein

Digest- ■ iblc pro-

tein

Brody

Pownds i (1.019 i .032 I .043 i .053 : .063 : .071

Pounds 0.038

.064

.086

.106

. 126

.142

Endoge- nous pro-

tein

Digest- ible pro-

tein

Pounds Pounds 0. 020 0. 070

.032 . 130

. 043 . 175

. 054 .216

. i)63 . 254

.073 .291

The combined requirements for maintenance and growth are shown in table o as digestible protein. As in previous cases, the suggested requirements of a number of workers, both European and American, are given for purposes of comparison. The values are intended for use in conjunction with the energy-requirement figures of the same author or authors given in table 3. For full details on the use of these feeding standards, the reader should consult the references given for each. The figures in the last column are estimates based on the data used for the feed mixture consumption figures in table 3 for record- of-performance pigs at the Agricultural Research Center. The intake of crude protein in the free-choice consumption of the corn and the protein mixture was first obtained, and then digestible protein was estimated as 80 percent of the total crude protein.

When protein-rich feeds are relatively high in price, it is desirable to restrict the protein allowance to the level that most economically meets the needs for maintenance and growth. Up to a certain point, the protein content of the ration has an important bearing upon the leanness of pork. Beyond the point where growth requirements are satisfied, additional protein has little effect. Much of the variation between the proposed requirements shown in table 5 Hes in the margin


of safety provided, although variations in production requirements exist owing to special factors peculiar to the type of hog being produced.

TABLE 5.—Digestible protein requirements per day of growing and fattening swine

European standards ; American standards

Weight of pig (pounds) Kellner

(true protein)

Leh- mann

Pound 0.35 .63 .76 .80

Lund

Pound 0.37 .52 .56 .53

Peterson Armsby

Pound 0.30 .38 .45 ,51 .55

Mitchell and

Hamil- to

Traps Morri- son

Belts- ville

50 Pound

0.31 .45 .52 .60 .60

Pound 0. 149 .238 .283 .288

Pound 0.216 .264 .308 .304 .282

Pound 0.335 .495 .618 .712 .790 .745

Pound 0.39 .55 .70 .78 .85 .90

Pound 0 40

100 . .. _ 60 150 72 200 250

.74

300 . ! 1

The lack of influence of the level of protein intake on the nature of the nitrogenous substance added to the body was studied a number of years ago at the Illinois Agricultural Experiment Station (331), The bodies of pigs from each of three groups that had received 0.32, 0.70, and 0.94 pound, respectively, of digestible protein per 100 pounds live weight showed no significant difference in the relative content of total nitrogen, soluble nitrogen, protein nitrogen, and nonprotein nitrogen. The influence of high protein intake on the protein metabolism of the bacon pig was studied recently by Woodman, Evans, and Turpitt {1259). Their data on pigs averaging 189 pounds in weight showed approximately equal protein retention on a normal daily intake of approximately 65 grams (0.14 pound) of digestible protein and on a high daily intake of 85 grams (0.19 pound).

Often protein requirements are expressed as a percentage of the total ration. On such a basis the protein requirement may be too low or too high, depending on the needs of the animal or the feed consumed. Carroll and Mitchell of the Illinois station {612) have reported data which showed that for pigs of 100 pounds live weight or less the ration should contain approximately 18 percent of protein, while for pigs over 100 pounds the percentage of protein may be dropped to 15 percent. The daily total feed intake has an important bearing on the proper protein content of the diet. This fact, as well as the importance of an adequate supply of protein, was shown in a study by Ellis and Hankins {317). Three diets varying in protein content from 12.4 to 18.9 percent were fed at a level of 3 pounds of feed per day per 100 pounds live weight. The rates of gain of the pigs increased with increasing protein content of the diet. At 100 pounds live weight, the estimated daily consumption of digestible protein on the one highest in protein content was 0.46 pound and the rate of gain in weight approximately 0.72 pound a day. These data suggest that some of the figures given in table 5 may be too low for adequate protein metabolism, while at the same time they support the medium high values for general application.

Controlled feeding work, such as the foregoing, on the effect of limitation of feed directed particularly at restriction of the energy intake is an effective means of studying the requirements for various elements. Studies on hogs in the 'Department of Agriculture {320)


have shown that moderate restriction of feed intake although reducing the rate of gain may at the same time reduce the feed requirement per unit of gain. Work in Great Britain has also given results favor- able to restriction as related to efficiency of feed utilization. The Department's work clearl}^ demonstrated that the lean tissue of the carcass, which represents the protein content, can be maintained or even increased by restriction, of the energy intake.

This suggests certain problems for further investigation. By work- ing with diets fed at restricted levels it is entirely possible that improvements in the balance of dietary essentials can be effected which will still further increase the economy of gain. It should then be possible to determine the most practical feeding standard commen- surate with optimum functional performance, whether it be growth or lactation, and the most economical use of the diet as a whole.

MINERALS

The body of a 225-pound pig contains approximately o pounds of ash, or mineral material. Of this amount nearly 4 pounds is in the skeleton, about 0.8 pound in the meat, about 0.2 pound in the organs including the alimentary tract, and slightly less than 0.1 pound each in the skin and the blood. Calcium and phosphorus are the two pre- dominating inorganic elements in the skeleton as well as in the entire body. Following are some estimates of the total quantities of the more common mineral elements in a 22o-pound pig:

Pounds Founds CalciuiTi I. 46 Sodium 0. 16 Phosphorus .88 Chlorine .13 Potassium .34 Magnesium .06 Sulfur . 20 Iron . 03

Smaller quantities of copper, manganese, iodine, cobalt, and zinc are to be found. All the elements named are known to be required in the nutrition of certain animal species, but the need for adding manganese, cobalt, and zinc to swine rations is uncertain. The requirements are undoubtedly very low and the usual diversified ration probably contains adequate amounts. It has been stated that 1 part per million of cobalt in the diet is adequate for animals that have been studied.

The requirements for calcium and phosphorus for bone formation have been fairly well determined. A lack of calcium or phosphorus retards normal skeletal development and gain in live weight (fig. 3). The bones become fragile and easily broken. In the prevention of these conditions it is important that vitamin D be supplied and that the proportion of calcium and phosphorus be kept within certain limits. The optimum range appears to be within the limits of one and two times as much calcium as phosphorus. Some approximate values for calcium and phosphorus requirements (803), expressed as percentage of the dry ration and as net requirements for body needs, are given in table 6.

Ordinarily the requirements as given can be met by the proper selection of feeds. The cereals and cereal products are generally adequate in phosphorus. Protein supplements such as tankage and fish meals contain calcium as well as phosphorus. A concentrate

REQUIREMENTS OF SWINE

Figure 3.—A ration too low in calcium causes such rachitic conditions as afflict this pig.

ration of 9 parts of corn and 1 part of tankage by weight will ordinarily meet the calcium and phosphorus needs of a 50-pound pig grazing on legume pasture.

TABLE 6.—Daily vaUiiun and phosphorus requirements of hogs

Condition and weiplit « piîï (pounds) Calcium Pliosphorus

Dry ration Amount Dry ration Amount

OrowÍDg pig: 50

Percent 0.4 .3 .2

.25

.4

.45

Grams 2.5 3.0 3.6

4.0 7.0

10.0

Percent 0.3 .26 .2

.2

.3

Grams l.S

150 2.5 250 3.1

Prcenant gilt: 250, early 3.5 250,lute 5.0

Laetatinc sow: 400 .35 8.0

A lack of salt is marked by poor appetite, unthrifty condition, and failure to grow. Tankage and milk products supply a fair amount of salt, and on the usual ration, swine will ordinarily not consume more than a fraction of an ounce a day when allowed free access to it at all times.

A lack of iodine such as occurs in goitrous areas of the Northwestern States leads to goiter and hairlessness in pigs. It is especially necessary that iodine be present in proper amounts in the ration of the pregnant sow to permit the birth of healthy pigs. It has been stated that a loO-poimd hog requires about 0.1 milligram and a sow 0.2 milligram of iodine a day. A common method of supplying iodine when it is shown to be inadequate in the ordinary ration is by adding potassium iodide to the mineral mixture. It is essential to use the utmost care to avoid harmful overdosages.


In addition to iron, copper has been found necessary for the building of the hemoglobin in red cells. There is some evidence that manganese and possibl}^ cobalt are involved. Milk is lacking in an adequate supply of iron and copper for the needs of the nursing young. If suckling pigs are prevented from obtaining an outside supply from the dirt of the hog barn, from dry feed, or from some other source, they may suffer from anemia. Affected pigs show paleness of tlie mucous membranes, sluggishness, lack of vigor, and failure to grow normally. There are various procedures for preventing the occur- rence of anemia among suckling pigs. Medication witli iron and copper salts is sometimes necessary, though the amounts required are small. An eff'ective method in winter, when the animals are confined, consists in dissolving 10 grams of ferrous sulfate and 1.5 grams of copper sulfate in water and sprinkling the solution on 50 pouiids of soil, which is placed inside the pen. The needs of the pregnant sow^ should not be overlooked. During the late weeks of pregnancy, several times her normal daily body needs are built into the embryos.

A few suggested mineral mixtures containing various elements that may be lacking in the sw^ine ration are given hi table 7. These mixtures may be made available in a self-feeder or mixed in the feed at the rate of 1 to 2 pounds per 100 pounds of the feed mixture. The minerals usually can be mixed at home much more cheaply than they can be purchased in a commercial mixture,

T A B LE 7.—Sugges ted in in era I in ixtu res for h ogs

Mixturo No. Ground limestone

Steamed bonemeal Salt Iron

oxide Copper sulfate

Potassi- um iodide Charcoal AVood

ashes

1 Pounds

33 50 40 25 75

Pounds 23 27. 97 40 50

75

Pounds 33 20 20

5 25 25

Pounds Poundu Pounds Pounds Pounds

2__. . 2 0.01 0.02 .03 3

4 10 ]0 5 ._ 6

VITAMINS

Thus far the experimental work on vitamin requirements of swine has shown a definite need for vitamins A and D. The requirement for vitamin C, if any,^ is very small. Eecent work has shown that several of the factors in the vitamin B complex are needed. These include ribofiavin, nicotinic acid, the fractions obtained by extraction and separation by chemicals (called the eluate and filtrate fractions), and probably vitamin Bi. The identity of substances essential for the pig in the eluate and the filtrate fractions of liver, rice bran, yeast, and other sources is still obscure. Vitamin Bg, lack of which causes rat dermatitis, has been identified in the eluate fraction. The development of dermatitis in chicks has been found to be due to lack of a factor or factors in the filtrate fraction.

Night blindness appears as the first easily recognized evidence of a lack of vitamin A in the hog ration. It has been found that pigs may lack normal vision in semidarkness and yet gain normally. If the dietar}^ deficiency persists, growth will be retarded sooner or later, and other physical manifestations will be evidenced such as diarrhea, muscular incoordination, and paralysis of the hind legs (545), Addi-


tion of vitamin A, or of carotene, the precursor of vitamin A, either in concentrated form or more properly in natural sources available on the farm as green feed, yellow corn, or bright-green alfalfa hay or leaf meal to the ration will cure or prevent the symptoms of vitamin A deficiency.

Work at the California Agricultural Experiment Station {Jj-Ifí) has shown that the minimum requirements for vitamin A to prevent night blindness and promote normal growth and general thrift are approximately proportional to body weight for various species of animals. It is stated that 1.0 to 1.30 milligrams of carotene from plant material or 0.3 milligram of vitamin A from cod-liver oil per 100 pounds body weight meets these requirements.

Reproduction may be impaired or prevented by an inadequate supply of vitamin A. At the Texas Agricultural Experiment Station (4^^) sows on a vitamin A-deficient ration have farrowed litters with a variety of defects including blindness, failure to develop eye tissue, cleft palate, and harelip. Gilts reared at the California Agricultural Experiment Station on diets low in vitamin A have failed to conceive {054). The difficulty was corrected by addition of cod-liver oil to the ration. The exact requirements for reproduction and lactation are not known. Possibly additional amounts over the minimum suggested oji a body-weight basis are needed. It should be possible to determine fairly accurately the amount needed for lactation in the sow to insure an adequate intake for the nursing pig.

Vitamin D, the sunshine vitamin, is associated with the utilization of calcium and phosphorus in forming bone. When the calcium and phosphorus supply in the diet is abnormal either in content or in proportion of one element to the other, lack of sufficient sunshine or dietary vitamin D is especially serious and leads to the development of stiffness, enlarged joints, lameness, poor grow^th, and other evidences of rickets or other maldevelopment of bones. Providing calcium and phosphorus in the amounts and proportions already indicated usually suffices for the prevention of rickets when the pigs are exposed to sunshine in the fields or outside pens. Winter confinement in the northern latitudes or in cloudy areas with little or no exposure to sunshine sometimes leads to the development of rickets. Under these conditions it is advisable to add vitamin D to the diet. The cereals used in hog feeding are generally low in vitamin D. Of the protein supplements, blood meal, tankage, and fish meal are of questionable value, although the latter is sometimes eft'ective in the prevention of rickets. Alfalfa, especially when cured in the suii, has proved a very useful supplement for winter feeding.

Nicotinic acid, which appears to be the substance that cures human pellagra, was found necessary for the growth and well-behig of swine by Chick, Macrae, Martin, and Martin {202) of England in 1938. Pigs fed a diet of corn, purified casein, and salt mixture developed diarrhea, dermatitis, and loss of appetite. The skin became a dirty yellow color, covered with scabs and largely denuded of hair. The addition of nicotinic acid to this diet entirely cured or prevented the development of these disturbances.

Hughes of the California Agricultiu^al Experiment Station {556) has reported experiments that confirmed the English work on the need for nicotinic acid and also showed that a lack of riboflavin was asso-

141394°—39 47


ciated with, poor growth and poor feed iitihzatioii. The California work also suggested that thiamin (vitanún BJ and substances in both the filtrate fraction and the eJuate fraction were necessary foi' the nutrition of the ])ig. It appeared to be necessary to add several of the factors in the vitamin B complex to the basal diet to secure healthy, fast-growing pigs.

In cooperative studies with the Bureau of Animal Industry on the growth requirements of pigs, Wintrobe (1^41) of Johns Hopkins University, foiuid that growth was accelerated when either thiamin or riboflavin was added to a basal diet essentially free of the water- soluble vitamin factors.

The English workers have continued their investigations on the requirements of the pig for the components of the vitamin B complex (203). Besides recognition of the need for riboflavin and nicotinic acid, they have found that botli the eluate a.nd filtrate fractions were necessary for health and growth. A lack of the filtrate fraction from liver extract leads to a cessation of growth, development of a flaccid palsy of the hindquarters, and eventually death. Deprivation of the eluate fraction from liver caused a certain type of anemia, with low corpuscular volume and low hemoglobin, and also epileptic fits.

More work needs to be done on the relation of vitamin ^ to fertility in swine.

Much work remains to be done to establish the quantitative requirements of swine for the vitamin factors, the content of these factors in hog feeds, and the conditions under which swine diets require special supplementation. Yellow corn is known to be a good source of vitamin Bi aiid riboflavin as well as of vitamin A. It is low in nicotinic acid but a.p])arently furnishes an adequate supply of the factors in the eluate and filtrate fractions when fed as the main part of the diet. Wheat, barley, and especially brewers' rice are low in riboflavin. Although processing methods probably result in some destruction, of the vitamins, animal and marine byprockicts, including skim milk, buttermilk, whey, tankage, and meat and fish meals, undoubtedly have high value as supplenieiits for supplying vitamins as well as protein and minerals. Finally the leafy forages have demonstrated their general usefulness as protective feeds.

WATER

The importance of water in tJie economical production of hogs should not be overlooked. A certain amonnt is supplied daily in wet slops when this system of feeding is used. With self-feeding, hogs need access to good fresh water at all times. Otherwise tliey will not consume sufficient dry feed to make the most rapid growth. Water may also be a carrier of certain mineral elements such as iron, calcium, magnesium, and sulfur. Evvard (351) of the Iowa Agricul- tural Experiment Station found spring pigs consimied more water than fall pigs up to ap])roximately 200 pounds hi weight. The amount of water consumed daily at'will by spring pigs averaged 3.3 pounds for the 25-pound pig and increased to 11.5 pounds for the 175-pound hog. As the pig gets older it requires proportionately less water, because it consumes less feed per unit of weight and the water content of the body is decreasing.

NUTRITIVE REQUIREMENTS OF SWINE - USDA

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