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THE EFFECT OF CLIMATE ON THE COMPOSITION OF
PASTURE PLANTS.*
BY
A. E. V. RICHARDSON, M.A., D.Sc.
Waite Agricultural Research Institute, South Australia.
Recent investigations (1) (2) have shown that the mineral and protein content
of pasture plants vary widely according to (a) species, (b) growth stage, (c) soil type,
(d) fertilisers.
Different species grown in pure cultures under similar controlled soil condi-
tions and harvested at a definite stage (flowering) show wide variations in mineral
and protein content. Growth stage exercises a dominating influence on both the
nitrogen and mineral content of pasture species. The composition of individual
species grown on different soils tends to follow the major differences in the available
supply of nutrients in each soil type. The composition of a species in any given
climatic region will therefore be dependent upon the fertility of the soil. The
application of fertilisers, particularly nitrogenous and soluble phosphatic fertilisers,
has a marked effect on the protein and phosphate content of a species. This effect
is more marked on soils low in nitrogen or phosphate than on soils rich in these
nutrients.
The precise influence of the climatic factors on the composition of pasture has
not been determined. Apart from the influence of soil type, stage of growth, and
fertilisers, it would appear that pasture species grown in tropical and sub-tropical
climates are lower in protein and in soluble ash than those in temperate regions.
The Rowett Research Institute has analysed samples from many pastures in
Britain and from many Empire sources. Godden's (3) conclusions on the composi-
tion of British pastures are summarised in the following table:—
Table showing the nitrogen and mineral content of British pastures.
British pastures.
A. Good cultivated pasture
B. Natural hill pasture (grazed)
C. Poor hill pasture (partly
grazed).
Nitrogen
N
2.82
2.50
2.54
Phoshoric
acid
P 2 O 5
.735
.67
.60
Potash
K 2 O
3.177
2.66
2.60
Lime
CaO
1.004
.66
.56
Soluble
ash
6.64
5.85
5.49
* Occasional communication No. 1 circulated by the Imp. Bureau of Animal Nutrition, Reid
Library, Rowett Institute, Aberdeen, Scotland.
( 364 )
EFFECT OF CLIMATE ON COMPOSITION OF PASTURE PLANTS
365
Aiyer and Kayasth (4) in India conclude that, though the grasses grown on
rich black soils are richer in mineral nutrients than those grown on light soils, the
grasses of both areas are poor in phosphoric acid and lime compared with British
pastures, and that they are very deficient in nitrogen. The silica free ash of the
species investigated ranged from 2.77 to 3.69 per cent. on the black soils, and
those on light soils from 1.19 to 1.69 per cent. The corresponding range for
phosphoric acid was .18 to .21 for black soils, and .035 to .073 for the light soils.
The mean content of grasses from thirteen centres was .55 per cent. nitrogen, .187
per cent. for P 2 O 5 , and 3.04 per cent. for soluble ash.
The Government Chemist for the Sudan (5) states that the chemical examina-
tion of fodder grasses grown in the Sudan showed a low mineral content when
compared with European pastures. The most striking deficiencies are in nitrogen
and phosphorus, the average being only 40 per cent. and 50 per cent. respectively
of that of a good pasture. All grasses in the White Nile Province showed a marked
phosphate deficiency.
Follett-Smith (6) states that in an investigation at Waranama, British Guiana,
seven pasture species from Savannah areas were markedly deficient in silica free ash,
phosporic acid and nitrogen. The silica free ash ranged from .83 per cent. to 4.9
per cent., with an average value of 2.3 per cent., the phosphate content from .01
per cent. to 15 per cent., with an average value of .08 per cent., and a nitrogen
content ranging from .5 per cent. to 1.31 per cent., with a mean value of .73 per
cent. The samples were collected during the rainy season, and Follett-Smith
stated that the phosphate content would probably be even lower during the dry
season.
In an unpublished report to the Rowett Research Institute natural pastures from
the Samaru district (Nigeria) average .13 per cent. P 2 0 5 . The pasture from seven-
teen other centres in Northern Nigeria showed an average content as follows—
soluble ash 3.01 per cent., nitrogen .85 per cent., phosphoric acid .34 per cent.
Husband and Taylor (7) found that the crude protein content of normal Veldt
grass was much below the standard of average of European grass. The crude
protein content at maturity reached the extraordinarily low value of 1.73 per cent.
The natural grasses suffered from a decided mineral deficiency, especially from March
onwards.
Henrici (8) shows that even the average percentage of phosphoric acid in the
hill pastures of Great Britain is about four times higher than the average percentage
of the best grasses in the Veldt.
366 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [III, IV.
Brunnich (9) analysed a large number of grasses from the pastoral areas in
sub-tropical Qeensland, where the rainfall has a marked summer incidence. Thirty-
eight samples of pasture grasses of various species, taken mostly in the growing
stage, gave a mean value of 1.5 per cent. nitrogen and .46 per cent. phosphoric acid.
Forty samples of old grass from similar areas gave mean values of .56 per cent. nitro-
gen and .16 per cent. phosporic acid. Four samples of grass hay conserved in stacks,
gave values of 1.1 per cent. for nitrogen and .336 per cent. for phosphoric acid.
The mean values for fifteen samples of Mitchell and Flinders grass taken in various
centres in Western Queensland during a droughty period in 1927 were—nitrogen .87
per cent. and phosphoric acid .20 per cent.
The results of analyses of pastures by the Rowett Institute (10) from Otjorn-
bindi, S.-W. Africa, show the following mean values for fen sepecies—nitrogen .43
per cent., phosphoric acid .065 per cent., potash .41 per cent. and soluble ash 1.89
per cent.
Samples of grass hay from British Somaliland and analysed at Rowett Institute
gave nitogen .86 per cent., phosphoric acid .24 per cent. and soluble ash 3.07 per
cent. Low values for nitrogen, phosphorus and soluble ash have also been recorded
by Orr (11) for Athi Plains, Makura and Molo in Kenya.
These analyses, representing pasture species and mixed pastures in regions of
summer rainfall (tropical and sub-tropical), show that the values for nitrogen,
phosphoric acid and silica-free ash are strikingly lower than those recorded by
Godden for pastures of Britain (Table 1), and very much lower than a series of
analyses of Kent pastures by Woodman (12) of Cambridge. These latter showed a
range of nitrogen 3.5 to 4 per cent., phosphoric acid .75 to .98 per cent., lime .79 to
1.21 per cent. and potash 3.9 to 4.1 per cent.
It would thus appear, from such records as are available, that the protein and
mineral content of pastures from tropical and sub-tropical areas are, in general,
lower than those recorded for pastures in cold temperate regions.
Pastures in Britain are more intensively grazed than those of countries of
summer rainfall and winter drought. Moreover, tropical and sub-tropical pastures,
in comparison with those of temperate countries, are notably poor in leguminous
components, which normally have a high protein content.
It may be that climatic factors, apart from those already discussed, affect the
protein and mineral contents of a pasture; and it is proposed to show that the
difference in mineral content of pastures in tropical and temperate regions may be
caused by a differential effect of climate on the rate of nitrogen and mineral uptake
EFFECT OF CLIMATE ON COMPOSITION OF PASTURE PLANTS
367
on the one hand, and rate of growth on the other. We may consider the latter
aspect first.
In tropical and sub-tropical climates the growth of pasture is rapid and
frequently the plant approaches maturity a few months after the onset of the wet
season. In cool temperate or winter rainfall climates growth proceeds much more
slowly and the reproductive stage is reached only after many months of slow
vegetative growth. This might be interpreted as an effect of temperature on
carbon assimilation ; the rate of carbon assimilation, and hence the rate of growth
within certain limits increases with temperature. The amount of carbon assimi-
lated per unit leaf area need not, however, alter, unless there is an alteration in the
ratio of leaf area to total dry weight. The actual facts are as yet undetermined.
Another habitat factor that may affect the growth rate is the length of day.
It is known that short-day types of plants are found in tropical regions and long-
day types in polar and cold temperate regions (13), and Auchter and Harley (14)
have shown that in temperate regions the pasture plants are of a type that form
reproductive organs only during periods of long days. Moreover, Tincker (15) has
shown that the long-day types of plants may be kept in the vegetative stage by
exposing them to short-day conditions. While the length of day is known to have
a complex effect on the growth and development of the plant, we do not know the
precise relationship it bears to carbon assimilation in the pasture plants under
consideration.
We may turn now to the question of mineral uptake. This process is known
to follow a fundamentally different course from that of carbon assimilation. Thus,
Richardson, Trumble, and Shapter (2) have shown that in pasture plants in South
Australia, the rate of absorption of nitrogen and phosphoric acid, i.e., total amount
absorbed in unit time, is much greater in the early vegetative stages than the rate
of synthesis of organic matter; nitrogen and phosphoric acid are utilised in con-
siderable amount during the tillering and root establishment charaterising the
early phase of development. After this early tillering stage, the rate of absorption
falls rapidly.
On the other hand, the rate of carbon assimilation, i.e., the total amount of
carbon assimilation in unit time, is dependent, apart from temperature, light and
carbon dioxide supply, mainly upon the area of green leaf surface and as this
normally increases till the approach of flowering, the rate of carbon assimilation
correspondingly increases and attains a maximum shortly before this stage. Thus
the maximum rate of nitrogen and phosphorus absorption on the one hand, and
carbon assimilation on the other, occur at two different periods of the plant's deve¬
368 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
lopment. As a consequence, the percentage of nitrogen and phosphorus, expressed
in terms of dry matter, gradually falls from a maximum value in the earliest vege-
tative stage to a minimum value at maturity. The amount of nitrogen and phos-
phorus absorbed by a gramineous pasture plant is limited by the amount that can
be rendered available by the soil during the vegetative phase. If nitrogen is
available and soil moisture conditions are favourable tillering proceeds to the limit
of the available nitrogen supply and to a lesser extent to the limit of the available
phosphate supply.
In temperate regions and winter rainfall climates a long period of slow
vegetative growth precedes the reproductive phase, and it is probable that under
such conditions the normal pasture could secure the necessary nitrogen and minerals
from the soil at a sufficiently rapid rate to keep pace with the somewhat slow photo-
synthetic activity of the plant except on the poorest types of soil, and except during
late spring or early summer when the flush of growth occurs.
An application of nitrogen just prior to this stage normally increases both the
yield of dry matter and the protein content of the herbage in Britsh pastures.
In tropical and sub-tropical regions of summer rainfall and winter drought, growth
commences with the onset of the wet season towards midsummer, and is exceedingly
rapid from the outset on account of high temperatures and favourable soil humidity
and the demands of the pasture for nitrogen and phosphate are correspondingly
great.
Very little is known of the rate at which nitrification or denitrification proceeds
in pasture land under tropical conditions, or of the precise effects of. comparatively
heavy tropical rains and occasional periods of drought on the available nitrogen
and phosphate supply of the soil. It is possible that the demands of the rapidly
growing pasture for nitrogen and phosphorus may, for various reasons, exceed the
rate at which supplies are made available in the soil, in which case, the amount
of tillering will be adjusted to the available nitrogen supply.
Photosynthetic activity, however, on account of high temperature and favour-
able light conditions continues at a relatively high level under tropical and sub-
tropical conditions, with the final result that the nitrogen and phosphorus content,
and to a lesser extent the silica-free ash content, expressed in terms of dry matter
produced, will be relatively low.
It is possible, therefore, that the explanation may be found in terms of differ-
ence in the effect of the two contrasting types of climate on the uptake of nitrogen,
phosphorus and other minerals on the one hand and assimilation of carbon on the
other, the carbon-nitrogen ratio tending to be high in tropical and sub-tropical
climates, and low in the temperate and winter rainfall climates.
EFFECT OF CLIMATE ON COMPOSITION OF PASTURE PLANTS
369
REFERENCES.
1. Orr, J. B. Minerals in pastures and their relation to Animal Nutrition. (Lewis, London),
1929.
2. Richardson, A. E. V., Trumble, H. C. and Shapter, R. E. Factors affecting the mineral
content of pastures. Bull. 49, Council for Sci. & Ind. Research, Melbourne.
3. Godden, W. Journal of Agric. Sci., 1926,16, 78.
4. Aiyer, A. R. P. and Kayasth, R. N. Mineral composition of fodders of the Central Provin¬
ces and Berar. Agriculture and Livestock in India, 1931,1, 526-532.
5. Report of Sudan Government Chemist. Tropical Agriculture, Trinidad, 9, 11, p. 355.
6. Follett-Smith, R. R. Agricultural Journal, British Guiana, 1930, 3, 142-159;
7. Husband, A. D. and Taylor, A. P. Journal of Agriculture, Southern Rhodesia, 1931,
154-169.
8. Henrici, M. 16th Report of the Director of Veterinary Services, South Africa, pp. 435-499.
9. Brunnich, F. Annual Reports of Department of Agriculture & Stock, Queensland, 1927-
28; 1928-29.
10. Rowett Research Institute.—Private Communication.
11. Orr, J. B. Sixth Report of Committee on Mineral Content of Natural Pastures—Economic
Advisory Committee, 1931.
12. Woodman, H. E. Private Communication.
13. Maximov, N. A. Biol. Zentr., 49, 513-543.
14. Amchter and Harley. Am. Society Hort. Sc, 21,Annals of Botany199.
15. Tincker, M. A. Annals of Botany 39,1925, pp. 721-754.
A GENERAL REVIEW OF THE INHERITANCE OF WOOL
CHARACTERS IN SHEEP.*
BY
WILLIAM C. MILLER,
(Institute of Animal Genetics, Edinburgh).
INTRODUCTION.
It is very desirable in considering the inheritance of the physical characteris-
tics of wool to realize very clearly that wool-fibres as produced owe their characters
partly to the basic genetic constitution of the animal, whilst they are partly a
more or less accurate reflection of the environmental influences to which the sheep
have been subjected from birth to shearing, or between successive shearings. For
the full expression of the potentialities of the hereditary constitution of the sheep,
environmental influences must obviously operate. Different environments can,
within limits, modify the expression of the genetic constitution of sheep, for wool-
production, but genetic constitution, being fixed, cannot be changed by environ-
mental agencies. The Merino sheep, kept in the damp temperate conditions of a
British sheep farm, grows wool which still has certain Merino characteristics, but
it is widely different from the wool which the same sheep grows, for example, in
Australia or in the phosphorus-deficient areas of South Africa. The sheep upon a
deficient diet — irrespective of what the deficiency is — grows a finer, shorter,
less elastic fibre and a less dense fleece than does the same sheep when its ration is
adequate. The successive effects of severe drought and heavy rains, acting through
the herbage, are well known in tropical and sub-tropical sheep-rearing countries.
The influences of disease can be determined on the wool-fibre, just as they can
upon any other keratinized cutaneous structure—horn, hoof, or finger-nail.
Desiderata for genetic experiments.—A lively appreciation of the wide variations
which are encountered between breed and breed, between flocks within a breed,
between individuals, and actually between fibre and fibre, is therefore highly
necessary in any genetic approach made to determine the inheritance of wool-
characters.
The desiderata for a genetic experiment in which details of fleece and wool-
characterization are involved, may be defined in the following terms :—
1. The sheep should be typical examples of their breed or cross, and each
sex of the parental generation should be uniformly homozygous for
the particular characters involved.
* Reprinted from the Empire Journal of Experimental Agriculture, Volume I, No. 2, July, 1933.
( 370 )
INHERITANCE OF WOOL-CHARACTERS IN SHEEP
371
2. The females of the P 1 generation should be of the same age — prefer-
ably not primiparous, and the age of the male should not vary by
more than ±1 year from the age of the females.
3. Examination and analysis of fleece-characters in the parental generation
should be carried out on 12 months' growth of wool, or if this is not
possible, samples should be taken at the same time from all the sheep
so that comparable results may be obtained and variations reduced
to a minimum. Upon no account should samples be taken from the
first year's growth of wool in F 2 and subsequent generations unless
similar samples are available from the parental generations (vide
infra).
4. Not less than 20 females should be used for each mating, and not less
than 25 individuals of F 1 and subsequent generations should be
retained for observation and examination.
5. For some time prior to and during experiment the sheep of each genera-
tion should be kept under the same conditions of management.
6. A uniform method of sampling should be adopted in all generations
and duplicate or quadruplicate samples from each body area are
desirable. The same technique should be applied in the examination
of the samples.
7. Parental and all subsequent generations should be kept in the same
locality so that variations due to climatic influence may be reduced
to a minimum (vide infra).
That some criteria should be defined will become clear later, when it will be
shown that various workers have been unable to interpret their results at all
satisfactorily, chiefly because of the extreme variation in the parental types used.
In some experiments for degree of characterization the extremes of male and
female parental generations overlapped, and it obviously becomes difficult in such
cases to obtain significant figures in F 1 or subsequent generations. It is to be
feared that many of the results which are given later are useless from the point of
view of determining the genetic factors involved in the inheritance of fleece-
characters.
Since wool can be influenced in length, fineness, density, etc., by environment-
al agencies, standardized conditions are highly necessary for the experimental
flocks. The duration in time of wool-growth influences the ultimate length of
fibre in the sample. Since the first year's fleece may represent from 14 to 16
months' actual growth of wool (according to the relationship between the dates of
parturition and shearing), and since most lambs are born with a deciduous
birth-coat, which is replaced either partially or completely by the adult coat, and
372 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
since this transition is effected earlier in some individuals and breeds than in others,
it is highly necessary to make physical examinations upon a fleece which represents
growth between successive shearing-dates separated by 12 months. It is very
probable that many of the conflicting results recorded are due to a neglect of these
considerations—the first fleece (gimmer fleece) of the offspring being compared with
adult fleeces from the parents. In this way, since first fleeces are usually finer and
longer than adult fleeces, figures that are not strictly comparable have been recorded,
and there appears to be little general agreement between reported results.
The age of the parental generations is especially important in studies of the
inheritance of number of fibres per unit area of the skin (i.e. density), and in the
inheritance of defects in wool such as kemp, medullated fibres, and pigmented fibres.
It is common knowledge that fleeces from young ewes are denser than fleeces from
the same sheep grown in later life. According to May (1868), wool-fibres are
coarsest during the third year of life, whilst others, Kleine and Stricker (1924), and
Spöttel (1929), show that in some breeds the second year's growth is the coarsest.
The change probably takes place at different times in different breeds and in differ-
ent individuals, observations showing that when the sheep attains full physical
maturity and reaches the prime of life, it can be expected to grow its coarsest wool.
Old breeding ewes of some breeds have a notoriously thin covering of fine wool on
their bellies, withers, and along the backs—more particularly in the long-wool or
lustre-wool breeds.
In many genetic experiments it is possible to calculate the number of individuals
which should be raised by an examination of the uncontrollable variability in the
parents, but in genetic work with wool-characters it is not always possible or
convenient to make character determinations on the parental generation before the
actual matings are arranged. A knowledge of the average or expected lambing
percentage in a given flock, or with a given breed, enables an estimate to be made
with a fair degree of accuracy of the number of F 1 lambs which may be expected
from a given number of parents. The statement that not less than 20 ewes should
be used for each genetic experiment, where wool-characters are involved, is based
upon our experience in this Institute during past years. With all the improved
British low-ground breeds a minimum lambing ratio of at least 125 per 100 ewes
can be confidently expected, and given freedom from disease and suitable freeding
and management this proportion of lambs should be reared. In the majority of
cases, ewes of the British mountain breeds kept upon the low ground and subjected
to conditions which induce a rising metabolism before and during mating, will give
a yield of lambs which approximates to the same figure, but mountain ewes in their
natural habitat cannot be expected to rear more than 100 lambs per 100 ewes, and
in very many cases they will fall far short of this figure.