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THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
17
or in evaluation of nutritlonal or management treatments than we now
have from a measure of the end-product of the process is yet to be determined. As nearly as it can be projected today this information should
be extremely important in certain cases but as a general rule its use is
likely to be limited because of the extreme complexity of the physiological processes involved.
I N T E R R E L A T I O N S B E T W E E N E N D O C R I N E S , METABOLISM,
A N D P R O D U C T I V E EFFICIENCIES I N F A R M A N I M A L S *
SAMUEL BRODY
University of Missouri
W e are presenting several questions, with explanatory notes, on the
interrelations of endocrines, metabolism, and productive efficiencies in
farm animals. Orientations for these questions, including references to
the literature, will appear in the March (1939) issue of the Journal of
Nutrition.
The questions are illustrated b y - t h e best known endocrine, the
thyroid, and the best known type of metabolism, that referred to as
"basal metabolism", which is the minimum heat production. This "basal
metabolism" is very important in Computing productive efficiency because the digestible feed cost of maintenance is proportional to it. Productive gross efficiency is the ratio of the output, such as milk energy
produced, to the input (the digestible nutrient energy consumed) which
includes the maintenance cost.
1. W h a t is the relation between the rate of endocrine activity and
the rate of metabolism, that is, heat production?
Quantitative and causal relations between endocrine activity and
heat production have been established only for the thyroids. About
189~ Magnus-Levy and others discovered that loss of the thyroids reduces the basal heat production to about half the normal level, and
that feeding thyroid increases the basal heat production up to about
twice the normal level. It was thus established that thyroxin is a powerful metabolic (especially heat-producing) catalyst.
2. Has it been established that thyroxin influences the rate of productive processes in farm animals?
* Paper No. 186 in the Herman Frasch Foundation for Research in Agricultural
Chemistry. Paper No. ~88 in the Missouri Agricultural Experiment Station
Journal Series.
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THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
There is no doubt that thyroid influences the rate of productive processes. It had long been known that thyroidectomy (removal of thyroids)
in young animals not only depresses heat production, but also arrests
growth and development. On feeding thyroid to such thyroidectomized
animals heat production is increased, and growth and development are
promptly resmned. Recently Graham and associates, at the Reading
and the Missouri Stations, discovered that thyroidectomy profoundly
depresses milk production, which is promptly resumed to the original
level, and even increased above the normal level, by thyroid feeding or
thyroxin injection. Winchester, at the Missouri Station, demonstrated
a similar effect for egg production in domestic fowls.
3. What is the nature of the relationship between the metabolismaccelerating and the production-accelerating properties of thyroid?
The nature of this relationship is as yet unknown. Some metabolic
catalyzers, as thyroxin, accelerate the productive rate; other metabolic
catalyzers, as dinitrophenol, do not accelerate productive rate. Likewise
sterility associated with tow metabolism is often remedied by thyroxin
administration (which raises metabolism to the normal level) but probably not by dinitrophenol (which may also be used for raising metabolism
to the normal level).
4. Is high metabolism in non.producing mature animals (e,g. dry cows)
associated with potentially high productivity? (e. g. milk production).
Is metabolism rate an index of potential productivity?
High-producing cows when lactating have higher basal heat production rates than low-producing cows. However, our data are not
sufficient to indicate whether or not there are differences in metabolic
rates between potentially high and low milk producers when they are
dry. This statement hold with regards to other productive processes.
5. Is high metabolism in young animals (e.g., Calves, or colts) associated with high productivity at maturity (e.g., high milk production
in dairy cows or high racing performance in horses?) Is there a possibility of predicting future performance from metabolic rates in young
animals?
This question, involving for demonstration the correlation between
the metabolic rate of young animals and their subsequent productive
performance, has been suggested by a practical breeder of dairy cattle
and race horses who thought that we should develop what he called a
"'metabolic test" for predicting performance. This breeder based his suggestion on the belief that the thyroid glands, which condition the
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
19
metabolic rate, and often stimulate high general activity in humans,
may also condition high performance in dairy cattle and race horses.
W e have been collecting data on this problem for some time.
6. Does an increase in the rate of production following thyroxin administration in "normal" animals imply an increase in productive
efficiency (ratio of output to input)?
Not necessarily; it depends on the speed of increase in the rate of
production as compared to the speed of increase in basal metabolism
(and therefore to maintenance cost to which it is proportional) with
increasing thyroxin dosage. If the maintenance cost increases more
rapidly than the rate of production, the production efficiency will obviously tend to decrease rather than increase.
7. Would an increase in productive efficiency foliowing thyroxin
administration in "normal" animals indicate the desirability of routine
thyroid administration? Assuming that high thyroid activity is associated with high productivity and efficiency, would it be desirable to
breed animals for high thyroid act!vity?
Not necessarily; it would depend on the long-range after-effects;
that is, it would depend on the relative influence of thyroid hormone
level on immediate efficiency on one hand, and on later rates of production, and on longevity, and fertility on the other. Thyroid hormone
accelerates the "rate of living"; and there is good evidence by Rubner,
Loeb, Pearl, and others that increasing the rate Of living decreases longevity. Long.range efficiency may thus not be compatible with immediate
efficiency. That is, the immediate gains and success may be offset my unfavorable after effects with long.range failure.
8. To what extent are the above questions illustrated by the influence
of thyroid on metabolism and on efficiency applicable to other productive
stimuli?
This question needs experimental investigation, as does indeed the
thyroid-metabolism-efficiency question. The organismic viewpoint leads
to the inference that in the course of evolution the component parts of
the body developed to function in an organismic harmony, which would
be disturbed with unfavorable after-effects, and therefore reduced longrange efficiency, either by dosing the animal with, or breeding for,
one productive stimulator and leaving the remainder of the body unimproved. However, the influence of the time factor can not be predicted. Thus, the unfavorable after effects may not become marked
until after the animal has reached the end of the desired productive
process. This complex problem of immediate vs long-range efficiency
needs careful formulation and investigation.