210 SECTIONAL ADDRESSES. 
A third factor with an adverse effect on mineral metabolism is the 
increasing tendency to feed large numbers of animals together. This 
necessitates for practical purposes the adoption of fixed standard rations, 
which may be fed with little or no change for months on end, or even 
through the whole life cycle of the animal. Unless such rations are almost 
perfectly constituted with regard to their mineral content, there must be 
a cumulative effect of any deficiency or lack of balance which would not 
occur in the case of either single animals or small groups, fed in a more 
haphazard fashion. As a matter of fact, in practice, the cottager’s pig, 
with a varying diet consisting largely of scraps, differing in kind from 
day to day, seems less liable to disease and more successful in bearing and 
rearing large litters than pigs fed in large numbers under what might 
almost be termed factory conditions. 
The reasons adduced above seem valid enough to justify the fear that, 
under modern conditions of intensive production in animal husbandry, 
there is a danger of malnutrition and disease arising on account of defects 
in the inorganic portion of the ration. Acting on this belief, attempts 
have recently been made to increase the rate of growth and improve the 
condition of animals by the addition of various mineral salts thought to 
be present in their rations in insufficient amounts. In many cases marked 
beneficial effects have been noted. Thus in pig-feeding, the cereal grains 
and most other foodstuffs commonly used in making up rations are 
deficient in calcium, sodium, chlorine and, in some cases, iron and iodine, 
and it has been found that growth, health, and reproductive capacity 
all tend to be improved by the addition to the food of salt mixtures con- 
taining these elements. The high requirement of the rapidly growing pig 
for minerals is now so generally recognised that it need not be further 
discussed here. Most manufacturers of pig-meals now adjust the mineral 
content of their meals by the addition of the minerals thought to be 
deficient. 
In poultry it has been found, in experiments carried out at Ohio and 
at stations in Scotland and Northern Ireland, that even though the birds 
have access to green food and lime or oyster-shell, egg-production can be 
increased by the addition to the cereal rations usually fed to poultry of a 
mixture of those salts which are present in the ration in smaller proportions 
than in egg. The increased egg-production is due to a lengthening of the 
laying period. Apparently the mineral additions prevent the depletion 
of the skeleton and other tissues which would otherwise terminate egg- 
production. 
Of all farm animals the stall-fed heavy-milking cow is the one most 
likely to suffer from depletion of minerals from the tissues and consequent 
malnutrition, on account of the fact that she loses from her body such 
relatively large quantities of mineral matter in the milk. In short tests, 
running for a few days or weeks, the adjustment of the mineral matter 
of the ration is not usually followed by increased milk production, because 
the cow will continue to give milk even though the body is being depleted 
of minerals. But the influence of adjusting the ration is seen towards the 
end of a long lactation or in a subsequent lactation. In recent tests at — 
Beltsville and Ohio and at Aberdeen, which have been carried over — 
one or more complete lactation periods, it has been found that the 
