A study of the effect of the periods of gestation and lactation upon the growth and composition of swine
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Growth is at the base of organic production. In recent years an increasing importance has been attached to its study and to the conditions affecting it. Davenport says: "The importance of the study of growth cannot be over estimated. The maintenance of the human race depends upon that property which protoplasm alone displays of increasing itself for an indefinite time and to an indefinite amount. The supplies of the world are produced largely by growth each year [...] the only thing then that limits growth is the limitations in the conditions of growth." The same author defines organic growth as increase in volume which may result from increase in volume of either the living substance or the formed matter of which organisms are composed. It is well known that there are many factors that influence growth and development. Among these are light, temperature, moisture, oxygen supply, food, climate, season of year, age, and species. Among factors less easily analyzed and explained, but dependent in greater or less degree upon the foregoing, may be mentioned the inherent tendency to reach a certain size and form, cell activities, and glandular secretions and excretions. Certain pathological conditions, pregnancy, and lactation may exert very marked influences on growth and development. The purpose of this study was to find the effect on growth of the conditions of pregnancy and lactation. It seems reasonable to expect that the production of milk would greatly check growth. The common observation of animals becoming thin in flesh while producing milk is sufficient evidence that the food is used for milk production even when there is not an excess over the amount the animal could use for the maintenance of its own body or for the increase of its own substance. It is well established that under conditions of insufficient nutrition, material may be drawn from the tissues for the production of milk.
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