NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
INHERITANCE OF WOOL-CHARACTERS IN SHEEP
373
Standardized environmental conditions have been shown by many workers to
be essential in any experiment where wool-characters are involved, and this is of
such common knowledge that it requires no further emphasis. Spöttel (1929),
Knoblich (1926), Seholz (1927), and others have discussed the importance of environ
mental conditions at considerable length and may be consulted.
It will be desirable to review in brief such published results as have a bearing
on the inheritance of those wool-characters which have been studied. It will be
noted that there are in some instances opposite or different results reported by
different workers who deal with the same quality or characteristic. Apart from
experimental error, this may be taken to indicate divergent modes of inheritance in
different breeds or crosses. There is no reason, for example, why length of wool-fibre
should not behave as an incomplete dominant in one particular cross-breeding
experiment, whilst in another, where different breeds are used, it may exhibit the
characteristics of blended inheritance.
INHERITANCE OF WOOL FINENESS.
In a general way it has long been known that by crossing fine-wooled with
coarse-wooled sheep, the F 1 will exhibit one of two wool-types: (1) it will carry
markedly mixed wool in which fibres characteristic of each parent may be found
in varying proportions; or (2) the wool will be of a fineness intermediate between
parental types. "Where the cross is made between a fine-wooled breed and one with
a mixed hairy type of fleece, e.g. in the Merino × Scottish Blackface reported by
the British Research Association for the Woollen and Worsted Industries (1922,
et seq.), the F 1 shows a mixed type of fleece. Where the two parental breeds are
each possessed of fleeces without great variability in fineness, the progeny shows
intermediate characteristics.
Bailey (1914) reported intermediate inheritance in fineness in the Merino ♂ ×
Shropshire ♀♀ crosses, and Pazzini (1915) reported similar results in the crosses
of Tiber valley sheep by Rambouillet rams. F. R. Marshall (1916), Baur and
Kronacher (1919), studying Mele (Leicester ♂ × Merino ♀♀) flocks and crosses
between Merino ♂ × Mele ♀♀, and Cotswold ♂ × Merino ♀♀, conclude that fineness
is determined by polymeric genes. The parental breeds used showed considerable
genetic variability and in consequence there was variability in the first and second
final generations. In the opinion of the authors, the alternating mode of inheri
tance is invölved and the maintenance of type is determined by the trend of selec
tion. It is further pointed out that certain characters, in particular fineness of
wool and type of staple, are based on a single factor or are closely linked.
Adametz (1918, 1920), in Karakul × Rambouillet crosses, found that most of the
374 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
F 1 possessed the mixed fleece approaching the Karakul, and he concludes that pro
bably not more than two factors are involved. Spöttel and Tänzer (1922) point
out that Adametz did not pay sufficient attention to the variability of the parental
breeds. Kronacher (1924) analysed wool from a Mele flock of 75 head. Merino
wool is class AA ; Leicester wool is class C, D, E; 40 per cent. of Meles fell into
class A, 29 per cent. into class B, and 31 per cent. into class C. He found no
constant intermediate type, as had been postulated by Thilo (1922); rather is there
definite segregation, and a polymeric basis appears probable. Terho (1923) obtained
the following figures in analysing shoulder samples from parental breeds, Meles, etc.
—
Leicester
Merino
F 1 (Mele)
F 2
F 1 ×Merino ...
.....
F 1 ×Leicester
.......
Number
6
40
24
22
79
8
Mean fineness
in µ
40.0
22.7
31.0
30.0
26.4
31.3
Standard
deviation
..
2.08
3.51
4.38
2.49
..
The table shows that both F 1 and F 2 animals are intermediate, whilst each
back-cross shows a shift towards the characters of the original parental finer-woolled
type (Merino). By the application of Castle and Wright's formula Terho finds
that five or six pairs of genes are involved.
Tänzer and Spöttel (1922) observed intermediate-fineness characters in F 1
generations between crosses of Zackel sheep with Rambouillet and Electoral Merinos.
Hill (1923-24) records an intermediate F 1 in Hampshire ♂ × Ramboillet ♀♀, Daven
port and Ritzman (1926) on the other hand found in this same cross that the
F 1 had wool nearly as coarse as the Hampshire parent, indicating almost complete
dominance. Burn's (1925) and Scholz's (1927) results agree with those of Hill.
Spöttel in his book (1925) notes in crosses between Mouflon and various Merinos
(Electoral, Escurial, Negretti, and Rambouillet) that about 50 per cent. of the
F 1 animals showed fineness of fleece intermediate between the parents', whilst
the others approximated to either one or other of the parental types. In the
F 2 the distribution was similar, but the range of variability was greater. Among
the seven F 3 animals raised, all but one were of the Merino type. The Somali,
which resembles the Mouflon in wool-characters, gave similar results when crossed
to Merinos. Spöttel, on his results, assumes the action of seven polymeric genes
382 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
The determination of the number of wool-fibres growing upon a unit area of
skin has not yet been sufficiently studied to permit of definite conclusions being
drawn. Difficulties in securing accurate samples have been great, and until recently
there has not been available a technique free from serious objections. Burns and
Miller (1931) describe two methods which are calculated to overcome the more
serious objections raised against some of the earlier methods and which have given
satisfactory results up to date. There has not yet been time, however, to use these
extensively in experiments on the inheritance of fibre population-density.
Preliminary results, however, support the hypothesis that with certain excep-
tions (of which crosses involving Merino parents appear most important) number of
fibres per unit area is inherited in an intermediate manner.
INHERITANCE OF KEMP FIBRES.
During recent years the occurrence of kemp fibres in the wool of sheep has
formed the subject of numerous studies (Bliss, 1926; Duerden, 1926 ; Roberts,
1926; Blyth, 1926 ; and Hirst and King, 1926). The precise nature of the kemp
fibre can now be defined and it is important to differentiate between it and the
medullated coarser wool-fibre, such as is commonly found in Romney wool. Kemp
fibres, as they occur in domesticated sheep, represent a remnant of the coarse,
hairy, outer-coat of the primitive sheep. As typically encountered, the kemp fibre
is short, thick, rigid, and finer at tip and root than along the shaft; it possesses a
fairly regular wave or crimp in one plane only, is extremely brittle, has a ' dead
white' or chalky appearance, and is medullated except for the short fine tip and,
when shed naturally, for a portion of the proximal part of the shaft. In many
breeds, if not in all, kemp has the further characteristic that its period of growth
and the time of its shedding occur independently of the other constituent fibres in
the fleece. Some kemp fibres are cut off at shearing time; others may have
already been shed but are still entangled amongst the wool-fibres of the fleece ;
whilst some are shed and fall to the ground before the wool-fibres have grown long
enou gh to retain them.
Owing to its lack of elasticity and the difficulties met with in attempting to dye
it, the presence of kemp in wool for manufacturing purposes is a decided disadvan-
tage.
There have been strong reasons for considering that differing degrees of kempi¬
ness are inherited. Barker (1931) admirably summarizes these as follows :—
1. In the course of work on the Welsh Mountain Sheep it has been found that
there is a very close connexion between the type of birth-coat possessed by the
376 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
In a paper on Lincoln ♂ × Hissar ♀♀ crosses Belhov, Belehov, Dobrogorsky
and Zhitnikov (1932) give the following table of degrees of fineness observed;
Measurements in µ
Fine wool-fibres
Transition fibres....
Kemp.....
Dead hair
F 1
23.4
37.43
51.1
80.9
Hissar
23.05
35.89
..
158.79
Lincoln
..
47.12
..
..
The authors state that the uniformity of the fleece is unsatisfactory, and more
so in coloured animals than in white-fleeced ones.
Belehov (1932) discusses a Mouflon × Chuntuk cross in which seven F 1 animals
were raised. The following figures for fineness were obtained :
Measurements in µ
Fine wool-fibres
Kemp
Dead hair......
F1
16.8
65.9
122.45
Mouflon
13.1
..
169.8
Chuntuk
25.0
96.4
..
Zhitnikov (1932) reporting the results of crosses between Chushka ♂ × Karakul
ewes, states that the fleece in the F 1 generation possesses all the different types of
fibre found in the parental breeds, but that the number of transition fibres is greater,
the amount of kemp is smaller, whilst the proportions of fine woolfibre are
intermediate.
He gives the following figures —
Measurements in µ
Fine wool-fibres
Transition fibres
Kemp fibres......
F1
21.8
44.8
60.59
Karakul
26.5
49.7
62.7
Chushka
36.72
52.59
63.03
Nichols, in a paper not yet published on wool-characters in the Border Leicester
♂ × Cheviot ♀♀ (i.e., the Scottish half-bred sheep), discusses the data of mean fibre-
length, mean weight-length ratio, and mean fibre-volume of samples from the
parental, F 1 and F 2 generations. He shows that for length there is a tendency to
INHERITANCE OF WOOL-CHARACTERS IN SHEEP
377
a bimodal type of distribution of the figures for mean lengths in the long-wooled
breed (Border Leicester), with a more or less normal dispersion of frequencies in the
Cheviot. In the succeeding generations all parental types are found, but in the
F 1 a proportion of animals is encountered with a bimodal distribution similar to
the parental long-wool type. His conclusions support the findings of Davenport
and Ritzman, that wool-length and fineness are dependent in inheritance upon
multiple factors, rather than upon any simple Mendelian type of inheritance. His
results also tend to show that follicular activity is dominantly inherited in direct
ratio to the length of wool produced; this may be expressed by the statement
that long wool is incompletely dominant to short wool, the length depending upon
a multiple factor system.
In a series of observations carried out in this Institute, in crosses between ewes
of the Scottish Mountain Blackface breed, with rams of Derbyshire, Gritstone,
Cheviot, Border Leicester, Lincoln, Southdown, South African Merino, and Welsh
Mountain rams, we have found that the F 1 animals of both sexes, from the mating of
fine-wooled breeds (Merino and Southdown) to the Blackface, show very mixed
wool in which there is little uniformity in length or fineness, but in which the
character of fineness is generally intermediate between the parental types. Great
differences were shown between different F 1 animals although the parental ewes
were themselves fairly uniform and of the same wool-type.*
In back-crosses to Merino ♂ the progeny showed a fleece of fine wool generally
approximating the Merino, but with a few coarse hairy fibres scattered through it,
whilst in the opposite back-cross the wool was similar to Black-face wool with a
greater admixture of fine wool-fibres and a much greater density.
In crosses by breeds carrying wool of intermediate fineness (Cheviot, Derby-
shire, Gritstone, and Welsh Mountain) the half-bred progeny showed greater
uniformity of wool-type amongst themselves but carried fleeces of mixed fibres.
Kemp, which is a common constituent of the Blackface fleece (average about 8 per
cent. by weight), was reduced to negligible proportions, and the fine-wool content
of the fleece was greatly increased. Back-crosses yielded animals in which the
wool was almost indistinguishable in fineness from that of the pure breed used.
In crosses from Lincoln and Border Leicester rams, strictly uniform classes of
F 1 animals were raised. The wool was coarser than in the other crosses and was
still mixed in type. We concluded from the series that inheritance of fineness
depended upon a multiple factor system and was of the intermediate variety.
* There are three distinct types of Blackface wool—the soft, open finer wool of the west of Scotland
generally; the hard, dense, coarse wool from south central and east-central Scotland, and the interme-
diate type from north-central areas. Between these there are all gradations.
378 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
Where there is great divergency in fineness between parental types, little uniformi
ty could be expected, but the use of rams of the long, lustre-wool type gave a very
uniform generation. (Full results of this work will be published later.)
INHERITANCE OF LENGTH OF WOOL-FIBRE.
Mean length of wool-fibre in all breeds except those with a very even staple is
difficult to determine. In breeds where the fleece has a typically pointed staple,
which includes all the long-wool, lustre-wool, mixed-wool, and many of the inter
mediate types, the staple is composed of fibres of varying lengths, the tip being
formed by the longest fibres. In such a staple, when the fibres of which it is
composed are measured, it is found that typically they show a fairly normal
frequency-dispersion curve, with considerable variation between different staples.
When staple is considerably thicker at its base than at its tip, as in breeds which
have mixed wool, the frequency-dispersion curve is likely to be bimodal with a
tendency towards great irregularity, especially marked when measurements are
made during the course of active wool-growth. In the Down breeds and in wool
of the Merino types, where the staple is ' blocky' at the tip, mean fibre-length can be
more accurately determined, but care must be exercised in obtaining representative
samples.
In very general terms, wool-length in crosses is intermediate between the
parents'. Some authors have reported greater length to be mainly dominant to
shorter length, but, since other workers using the same breeds have failed to find
any evidence of dominance, it would appear that in the former cases there may
have been a failure to appreciate the differences in length between first year's
fleece and subsequent fleeces. Reference has already been made to this point.
Among the results recorded where the inheritance of wool-length was studied
in breeding experiments, the following are cited as typical examples. Thilo (1912)
found Leicester ♂ × Merino ♀♀ that the length of wool in the F 1 generation, was
intermediate between the parents'. Measurements recorded were; Leicester,
18 cm.; Merino, 6 cm.; F 1 12 cm. Baur and Kronacher (1919) confirmed these
findings. Macalik (1924) reports intermediate length in crosses, whilst F. R.
Marshall (1916) during an examination of hundreds of Corriedales, found that none
had wool as short as the longest Merino, and although the length of wool in the
Lincoln was approached by some Corriedales, it was never attained. In subsequent
generation wool-length remains intermediate, and the typical Corriedale breed has
wool of intermediate length; at the same time it should be remembered that the
modern Corriedale has been continuously selected for just this intermediate length,
and it is difficult to get information of the number of culls which were made in
early generations because of irregular length of wool. Ewart (1919) found the F
INHERITANCE OF WOOL-CHARACTERS IN SHEEP
379
animals of Southdown ♂ × Blackface ♀♀ crosses had wool of intermediate length;
measurements given being as follows: Southdown, 10.2 to 14 cm.; Blackface,
32.6 cm.; F 1 15.3 to 21.6 cm. Davenport and Ritzman (1926) find that in the
Southdown ♂ × Rambouillet ♀♀ cross the F 1 animals have a greater wool-length
than either of the parental breeds.; they find this to be even more pronounced in
the Hampshire ♂ × Rambouillet ♀♀, whilst in the Oxford ♂ × Rambouillet ♀♀,
the progeny has a wool-length approaching the length found in the Oxford. They
suggest that in the latter cross the greater length of wool in the Oxford is dominant
to the shorter length in the Rambouillet. Scholz (1927) found that in the Mutton-
Merino × Württemburg cross the wool-length in the F 1 was intermediate, but had a
tendency to approach the length of the Württemburg. Horlacher and Good (1922)
found that in the cross between Kentucky Mountain ♀♀ and Hampshire ♂ the wool-
length was almost as great as in the Kentucky ewe, whereas when the Southdown or
Rambouillet ram was used the length in the F 1 animals was intermediate. This
suggests that the greater length of wool in the Kentucky Mountain sheep is dominant
to the length in the Hampshire but not to that of the Southdown or Rambouillet.
Elpatjevsky (1929) reports upon crosses between the Merino and various coarse-
wooled breeds. Of these he states that the order of suitability for crossing with
Merinos is as follows: " The thin-tailed, long-tailed sheep, Kurduk (fat-tailed) sheep,
and Voloshian ". He reported that in the F 1 animals the length of fine wool-fibres
is greater than in the parental animals — an observation which suggests that first
year's fleeces only were considered (v. s.). He states that the factor for 100 per
cent. fine wool-fibres is epistatic to the factor for hairiness (' beard hairs').
Numerous other observers have described crosses between recognised breeds or
types of sheep and have found that the majority of the F 1 animals grow a length
of wool-fibre which is intermediate between the parental types, although with
certain crosses, especially those where the parents are widely divergent in wool-
characterization, the degree of variation in fibre-length in the F 1 generation may be
considerable.
INHERITANCE OF CRIMP.
It has recently been shown by Barker and Norris (1930), Norris (1931), Norris
and Claassens (1931), and Norris and van Rensburg (1930) that crimp can no longer
be considered a static characteristic of wool; rather it is an expression of a periodic
function of time, irrespective of the length of wool which may be produced during
that time. The authors prove that in a given animal the total number of crimps
per fibre, in the fibres of a lock of wool selected haphazard from any point of the
fleece, is independent of the length of the fibre. Fibre-lengths in the same lock
may vary by many centimetres, but the total numbers of crimps per fibre shows
G
380 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ III, IV.
a variation in no way related to this variation in fibre-length. Consequently, the
fibres which have the fastest rate of growth in a staple produce crimps which are
larger than those produced by the slower-growing fibres, and upon occasions (such
as during the spring flush of grass, or when body metabolism is most active) the
staple will show wider crimps than at other times. The earlier method of evaluat
ing crimping in wool by measuring the number of crimps per unit length of the
staple (cm. or in.) is consequently no longer valid. (For further information see S.
G. Barker, 1931.)
Various authors have made records of the inheritance of number of crimps per
unit length. These may be cited, although, in the light of the work mentioned
above, the data presented cannot be regarded as eminently useful.
Bailey (1914) in crosses of Shropshire ♂ × Merino ♂♂ found the number of
crimps per unit of fibre-length to be intermediate in the F 1 Pazzini (1915) ana
lysed the cross of sheep of the Tiber valley (land sheep X Bergamask breed) X
Rambouillet rams, and found the following numbers of crimps per cm.:
Native sheep, 1st shear .
„ „ 2nd shear .
Cross-bred, 1st shear .
„ 2nd shear .
.
.
.
.
...
...
...
...
. 6.8
. 8.1
. 10.9
. 12.3
In the F 2 there was still more crimping. Tänzer and Spöttel (1922) in the Zackel
X Somali cross found that the lambs at two months old exhibited crimpiness
which, owing to a more close fleece, was not so corkscrew-like and open as the
Zackel, but approached rather the Karakul type. The tendency towards crimp is
present in both parents, but very weak in the Somali. Thus, the crimp would be
transmitted by the Zackel, whilst the closeness is a Somali character. Terho (1923)
gives the following data :—
Leicester........
Merino..........
F1
F 2
F 1 × Leicester......
F 1 × Merino.......
No. of
animals
5
40
22
22
7
78
Mean
length of
crimp
12.3 mm.
1.66 mm.
2.64 mm.
2.45 mm.
4.00 mm.
2.31 mm.
INHERITANCE OF WOOL-CHARACTERS IN SHEEP
381
The small crimp of the merino appears to be incompletely dominant over the
large crimp of the Leicester. No crimps as large as 4.8 mm. occurred in F 1 though
they may be observed in F 2 and in back-crosses to Leicester. No suggestion is
made as to the number of genes, but polymery is probable. The British Research
Association for the Woollen and Worsted Industries (1925) observed in the Black-
face × Kerry Hill cross an F 1 of three types, viz., two parental and a third with
marked wavy wool.
INHERITANCE OF WEIGHT AND DENSITY OF FLEECE.
In searching the literature for records of experiments which have been con-
ducted in an endeavour to determine the mode of inheritance of weight of wool
produced and the density of wool fibres on a unit area of skin, a considerable
amount of general evidence can be produced; but there is a lack of adequate criti-
cal experimentation.
In most breeds of sheep there exists a degree of variation of gross fleece-
weights of the order of 20 per cent. This is due to variations in actual production
of clean wool occasioned by individual differences in age, size, sex, environment,
and genetic constitution, to different degrees of admixture of wool with débris, soil,
sand, dung, etc., and to variations in the contents of grease and moisture. Conse-
quently, by weighing fleeces as they are removed from the sheep, reliable results
are only obtained when large numbers are available. In most of the controlled
genetic experiments reported, the numbers of sheep have been small, and mean
weights for the breed or cross are not available for comparison: whilst individual
fleece-weights from breeders' flocks kept under commercial conditions are difficult
to obtain.
For strict genetic treatment, weights of clean, scoured fleece are desirable ; a
rapid means of determining the yield of clean scoured wool and a technique for
determining absolute dry weights (either by direct readings or by calculation from
suitable samples of conditioned wool) would be necessary. These determinations
entail a great expenditure of time and considerable labour, especially where large
numbers of sheep are dealt with, and the writer knows of no large-scale experi-
ments where they have been recorded.
From an examination of such results as have been published, from the experi-
ences of practical breeders, and from careful observations made at this Institute,
it is permissible to conclude that gross weights of fleece follow the general rules of
intermediate inheritance. This applies to observations made within a breed or flock
as well as to observations made in cross-breeding experiments in which gross fleece-
weights in the parents were widely different.