NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE STOCK.
291
of an animal are to be expressed. Apart from nutrition, perhaps the most striking
effect on egg-production derived from control of extraneous environmental in-
fluence is that which follows increased exposure to light.
Just as we have a measure of the intensity of inheritance from observations
on parent and offspring in breeding practice, so to determine quantitative effects
of environmental factors on gene expression, it is necessary to have stock whose
genetical constitution is known.
There is yet another phase of genetical inquiry that may perhaps be con-
sidered of mainly academic interest, but from which we now have indications
that it may lead shortly to more practical and less tedious methods of controlling
heredity than that outlines earlier in this paper. In the final genetical analysis
the gap in our knowledge which exists between the presence of the gene, on the
one hand, and the exhibition of its end-product—the character—on the other hand,
must be bridged.
Hammond [ 7 ] has given us a suggestion as to the type of mechanism that
may lie between the genes and their characters. In the experiments on the
increased productivity due to an increased light ration, it is his opinion that
light acts by stimulating the anterior pituitary gland to increased secretion,
and this substance circulating in the blood stimulates in turn the ovary
to increased production. He further suggests that the level of this substance
in the blood may explain the difference between high and low egg-producing
strains and breeds.
It would be interesting to determine which of the five qualities outlined
previously as leading to increased egg-production are likely to be affected by
this stimulus.
Early sexual maturity.—The relation existing between sexual maturity
and the anterior lobe of pituitary is too well known to need labouring but the
work of Domm [ 8 ] in Chicago merits a brief notice. By suitable injections of
a preparation of this gland, he was able to produce precocious development in
the sex glands and secondary sexual characters of fowls, so that some of his male
chicks were crowing nine days after hatching, and began to tread when only a
fortnight old.
Persistency.—The length of time a bird continues laying after the production
of her first egg is limited by the time of appearance of the moult. In one of our
birds we were able to eliminate the moult by implanting anterior pituitary glands
from other birds (Greenwood [ 9 ]).
Broodiness.—From extracts prepared in our laboratory, Professor F. A. E.
Crew has been able to produce the typical behaviour of broodiness in Leghorn
fowls, a breed in which it rarely occurs. Even young hens reacted to the stimulus
before sexual maturity was reached.
292 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III
Intensity and no winter pause.—Gutowska [ 10 ] has shown that oral adminis-
tration of anterior lobe of pituitary leads to an increase in egg-number. There
was an increase in the number of follicles in the ovary, and also an increase in
their size. The results were most striking in the early part of the year (before
spring).
Finally, Parkes [ 11 ] has shown recently that the removal of this gland leads
to the atrophy of the sexual glands. I have purposely avoided entering into
too much detail with regard to these extremely significant observations, since
at the present time control of heredity by these means remains still in the realm
of possibility and has hardly reached the fringe of probability. An immense
amount of work still remains to be done.
SUMMARY
1. Selection methods practised along the right lines tend to increase pro-
ductivity, particularly in unimproved stock, but progress is slow in improved
stocks because of the inability of the breeder to control heredity.
2. It has been shown that the desirable qualities to select for are inherited
and that their mode of transmission from parent to offspring has been deter-
mined.
3. Such knowledge need not necessarily affect selective breeding practice
because of the present inability to distinguish between hetero- and homo-zygous
forms of these genes.
4. The application of genetical knowledge to breeding requires either a method
of distinguishing these forms by their production records, or an accessible technique
whereby the genetical constitution of an animal may be accurately determined.
With this knowledge at disposal, the fixation of desirable characters in a flock
can be readily made.
5. The field of work of the geneticist covers not only the mode of transmission
of characters under optimum conditions, but also the effect of variations in the
environment on the resultant expression of gene action. For this it is essential
to deal with animals of known genetic constitution.
6. The final phase in the genetical analysis concerns the relation between
the gene and the mechanism by which the end result—the character—is produced.
The possibility of the control of heredity through the control of physiological
processes is foreshadowed.
THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE STOCK.
293
REFERENCES
1. M. A. Jull, Poultry Husbandry, McGraw-Hill Book Co., Inc., New York, and London,
1930.
2. L. C. Dunn, quoted by Jull.
3. H. D. Goodale and R. Sanborn, Changes in Egg-production in the Station Flock,
Mass. Agric. Expt. Stat. Bull., No. 211, 1922.
4. D. R. Marble, and G. O. Hall, A Statistical Analysis of the Results of Breeding
High-line and Low-line Leghorns, N. Y. (Cornell) Agric. Expt. Stat. Bull., No. 533,
1931.
5. F. A. Hays, and R. Sanborn, Breeding for Egg-production, Mass. Agric. Expt.
Stat. Bull., No. 307, 1934.
6. E. B. Babcock, and R. E. Clausen, Genetics in Relation to Agriculture, Hill Pub-
lishing Co., London, 1918.
7. J. Hammond, Fertility in Poultry, Eggs, Aug. 29, 1934.
8. L. V. Domm, and H. B. van Dyke, Precocious Development of Sexual Characters
in the Fowl by Daily Injections of Hebin. Proc. Soc. Expt. Biol. and Med.,
1932, 30, 349.
9. A. W. Greenwood, Observations on Egg-production, Harper Adams Utility Poultry
J., 1933,18.
10. M. S. Gutowska, Effects of Prolonged Oral Administration of Large Doses of Pitui-
tary Anterior Lobe to Laying Hens, Q. J. Expt. Physiol., 1931, 21, 197.
11. A. S. Parkes, Proc. Roy. Soc., 1934, 115.
THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE
STOCK
IV. WOOL
J. E. NICHOLS
(Wool Industries Research Association)
The general title of these papers suggests a wider field for consideration than
that simply of the inheritance of wool-characters, which has been reviewed recently
by Miller [1]. In the first place, it is to be remembered that the fleece, as a covering
during life, contributes to the hardiness of the animal in its ability to survive
the rigours and changes of environment, and is, therefore, concerned in the other
activities of the sheep, for meat-production, for breeding surplus stock, in some
countries for milk, and so on. It is an agent, though indirect, in promoting the
efficiency of the sheep as a producer of those commodities which the sheep-breeder
hopes will be profitable to him. Herein it gives rise to problems in productivity
rather remote from those occurring in the other animal products dealt with in these
articles.
Fibre-growth is a more intimate function of the sheep's activity than is, say,
milk-production of the cow's and egg-production of the hen's. It begins in early
foetal life and ends only at death. There would thus appear to be three different
primary sets of environmental conditions to which it is exposed, viz. (1) the rela-
tively constant foetal environment, during which, however, the follicles inter se are
affected by the sequence and density of their development [2], (2) the early post-
natal, representing a change in life-habit towards (3) the post-weaning, quite
independent life, in which the animal attains maturity, becomes a functional
ruminant, and so exposed to all the exigencies of nutritional environment inciden-
tal to free-grazing animals.
The changes that occur with general development are obvious in many breeds.
Many Merino lambs are born hairy; the birth-coat hairs are shed or lost, and
leave the growing lamb with a fleece of practically pure wool. The lambs of some
of our Down breeds, especially the Suffolk, are more or less darkly coloured at
birth; by shedding and replacement, the relatively pigment-free adult coat is
acquired; from maturity onwards we find other changes in fleece character.
Recent work on time or age changes, from birth to maturity is pervaded with the
idea that definite relationships exist between natal and adult coats, and that
selection for desirable adult fleece-characters can be exercised early in life [3].
It is clear that not only is the follicle-population variable in time, but also the forms
of the fibre-product are alterable.
( 294 )
THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE STOCK.
297
But in surveying the wool-producing countries, one cannot help being impressed
by the remarkable way in which certain localities are pre-eminent for selection and
improvement, constituting in effect centres for the breed from which emanate
stock for commercial use in other areas. The type most successfully or most
readily developed in one breeding centre is, however, not necessarily very like
that from another. Further, they do not perforce react in precisely the same way
when transported to yet another environment.
A few instances from the many may be quoted. In the British Isles, is a
multiplicity of breeds, almost every one possessing a territory within which it
either predominates or produces stock for crossing, and there are also local varia-
tions in type of practical importance. In Australia, among the Merinos, are the
South Australian, the Riverina, and other New South Wales forms of strong wools;
stocks of strong or medium wool origin exhibit different characters when pastured
in fine wool areas, whlist among the fine wools, distinction can be made, for
example, between the Tasmanian, Victorian, and New South Wales types. Parts
of the Karroo areas in South Africa form fountain heads of improved breeding
stock for use in other regions of the Union, and in New Zealand, among the
Romneys, different localities apparently demand different strains.
In all cases it is, or should be, the general balance of fleece-characters that is
borne in mind. Only a few days ago, discussion with a New Zealand breeder
revealed that he had been attempting to increase his fleece-weights by selecting
for greater staple-length, but he had found that at a certain stage the wool suffered
by the tips of the staples becoming more weathered and wasted. Thus, it was
better to sacrifice the extra length and weight for soundness throughout the staple.
All these considerations add force to the principle that the pre-requisite for
selection is that environment which allows the clearest expression of genotype.
In the field of wool-productivity, to aid in the recognition of genotype and to gain
accurate knowledge of phenotype to which it gives rise in other environments, are
objectives which the zoologist may well pursue.
REFERENCES
1. W. C. Miller, Empire J. Expt. Agric. 1933,1, 173.
2. A. B. Wildman, Proc. Zool. Soc., London, 1932, 257.
3. F. W.Dry, N. Z. J. Agric., 1933, 46, 10, 141, 279 ; 47, 289.
4. J. E. Nichols, J. Text. Inst., 1933, 24, T 333.
5. A. T. King, and J. E. Nichols, Nature, 1933,132, 966.
6. J.-A. Hill, 34th Ann. Rept. Wyoming Agric. Expt. Stat., 1923-4.
7. C. B. Davenport and E. G. Ritzman, New Hamp. Agric. Expt. Stat. Tech. Bull.
No. 31, 1926.
8. J. E. Nichols, J. Agric. Sci., 1933, 23, 473.
THE INHERITANCE OF PRODUCTIVITY IN FARM
LIVE STOCK
V. DISCUSSION OF PRECEDING CONTRIBUTIONS
J. L. LUSH
(Iowa State College, Ames, Iowa, U. S. A.)
Clarity may be served by discussing these four papers from two stand-points:
firstly, the inheritance of productivity as a scientific fact, or series of interrelated
facts, and secondly the methods of using those facts and interrelations most
efficiently to advance the aims of animal breeders. Efficient application of funda-
mental knowledge to the solution of present problems may not automatically
follow the discovery of that knowledge. Research in methods of application may
be quite as necessary as research in discovery of the principles themselves.
So far as concerns the inheritance, each paper has stressed the complexity of
the topic. It seems certain that for each trait there are many genes involved.
No doubt these genes interact with each other and with the environment in many
ways besides the simple additive way that may be expressed most readily in gene-
ralized formulae.
Each paper has also stressed the necessity for keeping the animals in an envi-
ronment that would permit differences in productivity to develop, although the
philosophical explanation for this necessity varies among the speakers. Dr.
Hammond holds that the genes change adaptively in direct response to the environ-
ment, whereas most of us hold that such gene-changes have not been demonstrated
experimentally, even by the many experiments expressly intended to find them,
and, moreover, are not necessary to explain the facts, either of animal breeding
or of evolution. Hence, we would argue that there is no necessity for invoking such
a supposed direct effect of environment of genes, even as a working hypothesis.
The necessity for keeping animals under an environment that will permit them to
show their differences in productivity, arises from the fact that conscious selec-
tion for such differences is possible only when and as far as such differences are
permitted to develop to a recognizable degree.
The sharp line which Dr. Hammond proposes between ' developmental' and
' mutational' characteristics will not, I think, be accepted as valid by many
workers, either in animal breeding or in more classical branches of biology. Most
of us would hold that all characteristics are developmental, depending for their
full expression upon the interactions of the genes with each other and with environ-
ment as well. From this standpoint, highly hereditary characteristics are those in
which most of the variance we ordinarily see, is due to differences in the genes
( 298 )
302 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III
varying degrees of knowledge about each. These illustrations have been used to
show what kinds of knowledge are needed,.and how one should proceed to make a
business-like estimate of the probable gains to be derived from various methods of
selection, progeny-testing, etc. Not until such a valid estimate is made, is one in
a position to decide whether a given procedure is likely to provide gains that
will more than offset its costs. In preparing these estimates, there is
work in plenty to be done in measuring reproductive rates, selection differentials
reasonably attainable, the genetic portion of the observed variance, etc.
In addition to the genetic variance that can be expressed by an additive
scheme, there is a portion (perhaps a very large portion in stocks that are already
improved) of the variance which is genetic in a broad sense, but cannot be
expressed additively because the gene combination interact in other ways. Such
gene interactions include inhibitory, multiplicative, complementary and epistatic
effects, and also what may be a very common class of cases where that which is
optimum in the breeder's opinion is genetically intermediate.
No of Plus Genes.
SCALE OF THICKNESS OF BACK FLESH.
Diagram illustrating the case where the maximum of desirability may
be produced by an intermediate combination of genes. In such a case
selection usually produces noticeable results in the first few generations
it is practised, but rather quickly approaches a limit beyond which
progress is not made, although hereditary variability still remains.
Further progress can often be made if some combination of inbreeding
and outbreeding is practised along with continued selection.
304 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III
will accrue from a complete and detailed knowledge of the technical genetic situa-
tion in each case. We are far from agreeing on the importance which inbreeding
and outcrossing should receive in breeding for productivity.
I hope that such discussion as this, which of itself solves no problems, may
nevertheless contribute to their solution by formulating them more clearly and
particularly by presenting to our colleagues in more classical branches of biology
some view of the nature and complexity of the problems that are still unanswered.
Measurement looms large in such problems. This explains the importance of
quantitative methods in applied genetics.
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