Selection for economic characters in Merino sheep

137 Pages·014.98 MB·English

by  Morley, Frederick Harold William

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u a m i m *» bcoiomic Q m m m m s m
M2KIH0 O P
by
frederick Barold Willim Jforley
A Dissertation Submitted to the
§taAmt# Faculty in Partial fulfillment of
The Requirements for the Degree of
DOCTOR Of PHILOSOPHY
Major Subject®: Animal Breeding
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Iona State College
1950
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UMI Number: DP13383
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II, mt moBim.............. .............. §
in. t m w m « i mnosAM. .................. a
A, fhe S n v i r o n m o n t , . 8
3.t9fc» Sheep...... 11
6. She Characters Observed.............. 13
If. »SfI«A*Ii 'or VUtm&lQ RAMWfSBS,... . . . . . *
A. Phenotypic Meaae, fariaaees sad @#«rela»
tioBs....................................... 26
1. source of lata*..................... 36
2. Besulte............................. 26
B. BepeataMllty. ..... 34
1. definition. ....... 34
2. lata used and Methods of analysis... 3?
3. Results.... 40
4. Comparison with published estimates. 44
0. leiatire Kconoiaic Values.................... 47
v. r a of M in a si
A. HerttaMllty....... 51
1. Definition......... 51
2. Methods and results............... 52
B. tenetic Correlations Between Various
Characters...... 63
1. Definition............ 63
2. Methods .... 63
3. Results 65
VI. CALOULAf I0M OF A SBLiSC'HOli IMDSX. ....... 68
VII. ®180tfSSl«,...... 83
A. General Restrictions........................ 83
1. fbenetypiG Statisiiee.*..,.................. 84
C. Genetic Statistics....... 88
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The Australian Merino sheet 1* probably one of the h»st demonstra­
tions of the power of selection to Improve production in a domestic
animal. Becords of average wool production from Balgety1 s Animal
leview (ltd®) show an increase la average fleece weight from 4.9
pounds for the five year# eating 1981 to 8.2 pounds for the five year*
ending 1948 (fig. 1), tome of this increase has probably resulted from
improved husbandry, including nutrition, disease control and control of
external ant internal parasites. Some may also he accounted for by dis­
continuation of the practice| common ever §8 years ago, of washing
sheep before 'shearing.
the following considerations suggest that genetie change has been
responsible for some of the improvement, firstly, the majority of sheep
la Australia are grated In semi-arid regions in which nutrition is gen­
erally beyond the control of the pastoralist, except Insofar as stocking
rats Is controlled. Apart, from brief periods of submaintenance feeding
during severe droughts, sheep seldom receive supplementary feed end are
wholly dependent on pasture. While pasture improvement has increased
production considerably on seas properties (Gluniee loss et al. 1987),
its offset on the general average wist be rather unimportant when one
considers that only a small proportion of sheep are graced on improved
pastures.
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the rapid improvement fit*® during the early part of
the period appears to h^y# become slower during the last three decades.
Many of'th® important advances 1m nutrition, disease centre! and
parasite control took'.place during the lSi@*s and 1930*s, whereas the
greatest increase In fleece weight occurred prior to 1920, a-period
when centre!' of internal parasites each as the stomach worm (laeaonehua
contortus) 'and intestinal worms (f richestrongylid spp.), as well' as
sheep blowfly (hacilia cuprina Sc.), was relatively crude sued Inadequate.
these reasons for considering genetic factors as having teas
important receive substantial support from' observations on a museum
flock at Camden Park, lew tenth Wales, which has hem maintained relative*
ly free from selection and without introduction of breeding stock, these
sheep as® an altogether different type from the majority of stud Merino
sheep seen today, having smaller frame, smoother shine and cutting
much lighter fleeces of finer wool.
While there is thus considerable cause for breeders* satisfaction
'With the progress achieved, there 'are some indications that selectlea
may -have reached a point of diminishing returns, the Increase la fleece
weight ever the Inst'19 years has not beta substantial when one considers
that some of the greatest improvements la husbandry 'have occurred during
this period. Shifting emphasis from wool production to other characters
may 'have retarded improvement in fleece weight,
Changing economic and ecological circumstances have necessarily
directed selection from fleece weight towards other characteristics.
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for example the blowfly menace tea compelled breeders to practice selec­
tion .against fold®, end a rapidly lavoicping f»t-laifi» industry haa
demanded eeloetioa for * ior§#-ft»«e4 sheep suitable for use as a anther
of crossbred lambs. Such attention toother ehansciere haa caused the
problem of eoleetleit to become .tamMiad? complex, a situation only
to bo expected in a ^rural sad industrial economy undergoing rapid
expansion sad dtversification. • fh* develop*®!*! of synthetic toxtiloe
servos to emphasise the relative lasfo-ytiince of the attributes of wool
which compete with or t#»i&««»e»t those of man-made fibers, that, develop­
ment may shift attention rapidly t© ■fharscterlstlce of wool not previous­
ly considered important.
With these considerations in mini* the present study was undertaken
I® explore- and clarify sows-, of the problems confronting the breeder
under existing circumstances, and -if possible, to euggest measures
which might improve efficiency of selection.
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