In order to attack the problem, the first necessity was to establish the relative amounts of food material the animal retained for its own use. The chemical analysis of a feeding-stuff was of little value for this purpose, as the chemical analysis of a feeding-stuff, in the absence of any other data, gives no measure of the nutritive value.
The method adopted in order to assess the value of a feeding-stuff was to feed known weights of a given feeding-stuff to an animal, collect, weigh and analyse the excreta, whence by deduction the amounts of the feeding-stuff that were actually absorbed into the system, and were thus available for maintenance of bodily activity, growth, repair of tissues and other purposes, were obtained. The results of these somewhat tedious, patient researches are comprised in tables giving the chemical analyses of the chief feeding-stuffs and their digestible constituents, the most recent table of British figures being contained in Miscellaneous Publication No. 32, published by the Ministry of Agriculture.
This proved, however, only a partial solution of the problem, as it quickly became evident that the value of the digested nutrients varied according to the nature of the feeding-stuff from which these nutrients were derived. As a result of further research these difficul- ties were overcome, and a method was devised whereby it is possible to assess the true value of any given feeding-stuff for any required purpose. The chief facts discovered, stated briefly, are as follows :
The value of a feeding-stuff may be divided into two portions: (a) its value as a supplier of protein ; and (6) its value as a supplier of energy. The protein is required by the animal for the formation of flesh, the repair of waste tissue and the protein portion of milk; the energy is required for the maintenance of the bodily activities of the animal and the production of fat, milk, work and heat. A certain quantity of the digestible nutrients is required for main- taining the animal in health ; this portion is generally called the main- tenance requirement : the rest is available for the production of meat, work or any other purpose. The excess of protein beyond the ani- mal's daily requirement is also available for the production of energy, but since the protein portion of a food is dearer than the non-protein portion, the use of protein as a source of energy is wasteful. Kellner, by a series of carefully controlled experiments, compared the relative values of digestible protein, fat and carbohydrate for the purpose of fat production. The method adopted was to adjust an animal's diet so that it neither gained nor lost weight, and then add a stated quantity of pure protein, fat or starch, to the diet and find the amount of fat produced. This gave a comparison between the fat-producing or energy-producing power of the various constituents of a food, and Kellner decided to express this energy value in the form of starch, which figure he called the "starch equivalent." Thus I part digestible protein was found to equal 0-94 parts starch, I part digestible fat 2-3 parts starch, and I part of digestible carbohydrate I part starch. This gave the necessary data for calculating the starch equivalent from any food-stuff, given the digestibility figures.
It was found on computation that the theoretical starch equivalent as computed differed from the actual values as found by experiment. This difference was due to the fact that the work of digestion of the feeding-stuffs varied considerably, and the energy thus required formed a prior charge on the digested nutrients, only a proportion of which was thus available for fat production. For this reason a " value number " was given to the different classes of feed ing -stuffs, and this enables us with fair accuracy to compute the starch equiva- lent of a new feeding-stuff from the digestible nutrients.
Kellner's starch equivalent represents the fattening capacity of loo Ib. of a feeding-stuff expressed as starch. Thus 100 Ib. of a feed- ing-stuff whose starch equivalent is 75 would produce as much work, fat or energy as 75 Ib. of starch. Through this work, the prob- lem of relating food requirement to milk production became simple.
An animal requires two essential substances, proteins for repair of tissues, and fat, protein or starchy material for energy. The average requirements of a cow for protein and energy for mainte- nance of bodily activity were ascertained and experiments soon established the relationship between gallons of milk produced and requirements of energy and protein. The results thus obtained form the basis of a scientific feeding standard for milch cows and are given in the following table :
Digestible
protein
Ib.
70
84
. -98
Starch
equivalent
Ib.
6-25
7-50
8-75
Maintenance Ration
A cow weighing 1,000 Ib. requires A cow weighing 1,200 Ib. requires A cow weighing 1 ,400 Ib. requires
Production Ration. In addition to the maintenance ration a cow will require approximately -58 Ib. of digestible protein and 2-50 Ib. starch equivalent for every gallon of milk produced.
From the above table it will be quite easy to compute a suitable ration for a dairy cow giving a known quantity of milk. An example will suffice to illustrate the method.
Let us assume that a dairy cow weighing 1,200 Ib. gives 3 gallons of milk, and that the foods available are mangolds, oat straw, linseed cake and palm-kernel cake. From a table of analyses similar to that given in the Miscellaneous Publication No. 32, already referred to, it is found in British practice that
I Ib. oat straw contains . I Ib. mangolds contains . I Ib. linseed cake contains I Ib. palm-kernel cake
Now the maintenance requirements of
a 1 ,2OO-lb. cow are 3 gallons of milk require
Total requirements of a 3-gallon cow = A suitable ration would be :
20 Ib. oat straw
60 Ib. mangolds
8 Ib. palm-kernel cake
3 Ib. linseed cake
Digestible protein Ib.
Starch equivalent Ib.
OI
005 24 16
17 06
74 75
Digestible protein Ib.
Starch equivalent Ib.
84 i-74
7-50 7-5
2-58
15-00
Digestible protein Ib.
Starch equivalent Ib.
20 30 1-28
3-4 3-60 6-00
72
2-22
2-50
15-22
The above ration would represent a suitable ration for a cow giving 3 gallons of milk a day on the limited foods available. It is possible by this method to feed the entire herd according to their actual milk yield. As a matter of practice, the whole of the herd are given the same maintenance ration, hay, roots and straw, and the cakes and meals are varied according to the milk yield. As a rough working rule it generally takes 3^ to 4 Ib. of cake for every gallon of milk produced. The chief value in the scientific valuation of food re- quirement for a dairy herd lies, however, in the possibility of checking the adequacy of the actual ration fed to a herd and of enabling the computer to suggest a suitable alternative ration in cases where an unsuitable ration is being fed.
Much useful work in this direction is now being done in parts of England by agricultural organizers. The system adopted is for the farmer to fill up a food-record sheet, in which he enters the number of cows in the herd, the total milk produced and the actual weights of foods fed. From this the agricultural organizer computes the food value of the rations given and the scientific requirement. Compari- son of the two sets of figures obtained enables him at once to state whether any alteration in feeding is necessary, and to suggest a possibly cheaper ration.
Other systems of feeding for dairy cows deserve mention here. A method based on the fat content of milk is in use in America. According to the Haecker-Savage standard, the food requirements are stated! in digestible protein and total digestible nutrients, and the amounts to be added to the maintenance ration vary according to the fat content of the milk.
A system in common use in Denmark depends for its existence on its simplicity, a simplicity which has only been arrived at by sacri- ficing a certain amount of scientific accuracy. The Danish food-unit system consists of a table of equivalent values of various feeding- stuffs compared with a standard. The values arrived at have been based mainly on the extensive experiments carried out by Fjord and his co-workers with milch cows and swine. In Denmark the standard unit is I Ib. of grain; in Sweden the standard unit is I kgm. (2-2 Ib.) of mixed concentrates. A table is generally given showing the quantities of feeding-stuffs equivalent to one unit, and in computing rations all the feeding-stuffs are reduced to units. It is thus quite easy to ascer- tain the number of food units used to produce a gallon of milk, and enables quick and ready comparisons to be made between different cows or herds of cows. For this reason it has been greatly appreciated, and has proved of great value, especially in cooperative efforts to improve Danish dairy cattle and their feeding.
It is, however, only of value where the conditions ruling, both as to foods fed and to type of farming adopted, are similar, and the Danish food-unit system cannot be applied with safety to the variable conditions of English farming practice.
The Hygiene of Milk Production. Milk, owing to its composi- tion and liquid nature, forms an ideal medium for most bac- teria, whether beneficial or otherwise. The rapidity with which bacteria will multiply in milk and the ease with which milk is contaminated when handled under ordinary conditions have impressed upon certain sections of the population the necessity of taking steps to improve the quality of the milk supply.
The American Medical Milk Commissions have already acted, and have reached general agreement as to the conditions under which milk should be marketed in the United States. The standards are based fundamentally on the bacterial content, and, similarly to the English custom, standards also exist as to fat content and total milk solids. Four grades of milk are recog-
