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FLEECEWEIGHT_-SELECTED AND CONTROL SHEEP
A thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University
JOHN F WILLIAMSON
1994
11
Abstract
Internal parasitism in sheep selected for increased wool production for 37
years ( FW) and in unselected controls (C) was studied. FW sheep were shown to consistently develop higher FECs than C sheep when grazing naturally infected pasture. Resistance to establishment of infective larvae of Haemonchus contortus and
Ostertagia circumcincta, but not Trichostrongylus colubriformis, was lower in artificially infected adult FW sheep.
Several parasitological and immunological parameters were compared between lines. Antiparasite antibody levels in grazing lambs and artificially infected adult sheep did not differ between lines. There was a typical strong inverse relationship between numbers of mucosal mast cells and numbers of parasites in FW sheep, whereas no relationship was evident in C sheep. Packed cell volume was lower in
FW sheep than C sheep and thymus weights were heavier in FW sheep. Blood gastrin levels tended to rise more in C sheep than FW sheep when infected.
Production loss associated with infection in each line was examined.
Albendazole controlled release capsules (CRC) were used to prevent infection in some sheep from each line while the remainder were allowed to become subclinically infected. Despite F\V sheep developing a larger burden than C sheep there was little evidence that this resulted in greater production loss in FW sheep.· Production loss was not found to be associated with decreased feed intake .
. Decreased resistance to internal parasites (of some species) following selection for increased wool production has been clearly demonstrated. This suggests that resistance traits and wool production are unfavourably genetically correlated, which
I
will slow selection responses when all traits need to be simultaneously improved.
Despite the effectiveness of CRC treatment in preventing establishment of an adult parasite burden, production in treated sheep, particularly rams, was lower than
in subclinically infected sheep at some stages of the trial. The cause of this effect is unknown.
The effect of CRC treatment of young sheep (aged 6 months) was examined 1 0 months later when sheep were artificially infected. Resistance to establishment of T. colubriformis larvae was lower in previously treated sheep, as were thymus weights. It appears that CRC treatment of sheep may have a detrimental long term effect on resistance to parasites.
In an unrelated study the effect of kiwifruit vinegar (8.2g/1 00rnl) on parasitological and production parameters in lambs and fertility in two-tooth ewes was investigated. There was a tendency (not significant) for FECs in vinegar treated lambs to be lower than in untreated lambs. Treatment had no effect on liveweight gain, wool growth, or wool colour, but caused a small reduction in wool yield. Pre
mating liveweight of two-tooth ewes and reproductive status 38 days after removal of the ram was not affected by vinegar treatment.
iv Acknowledgements
Several people deserve my thanks for their part in this study and for helping to make my time at Massey a highly enjoyable and interesting one.
My supervisors, Professors Hugh Blair and Dorian Garrick, for providing expert guidance while allowing a free hand to fully explore my thesis topic.
Bill Pomroy, Barbara Adlington and Shirley Caulder, for technical advice on things parasitological, and assistance with processing of samples.
Staff and post-graduate students of the Animal Science Department, who were always friendly and ready to lend a hand.
My friends, in particular the "Ferguson Street Crew" for the many good times spent together while taking time out from this Masterate.
Massey University Research Fund, C. Almer Baker Trust, and Nufarrn for financial assistance.
Title Page
Abstract 11
Acknowledgements IV
Table of Contents V
List of Tables vii
List of Figures Vlll
One Introduction . . . 1
Two Literature Review . . . 3
Section One: Parasitology and Immunology 1 . 1 Parasite biology . . . 3
1 . 1 . 1 Life cycle . . . 4
1 . 1 .2 Epidemiology . . . 4
1 .2 Control strategies . . . 5
1 .3 Effects of parasites . . . 6
· 1 .3 . 1 Pathology . . . 6
1 .3.2 Production depression . . . 6
1 .4 Anthelmintic resistance . . . 7
1 .5 Host responses to infection . . . 8
1 .5. 1 Basic immunology . . . 8
1 .5.2 Resistance mechanisms . . . 1 1 1 .6 Genetic control of host immune responses . . . 1 2 1 .7 Analysis of parasite data . . . 1 3 Section Two: Selection for Increased Resistance to Parasites 2. 1 Genetic variation in resistance . . . 1 4 2. 1 . 1 Between breeds . . . 14 2. 1 .2 Within flocks . . . 1 5 2. 1 .3 Major genes . . . 1 6
Table of Contents (Contd)
2.2 Selection criteria . . . . . . . . . . . . . . . . . . . . 1 6 2.2 . 1 Faecal egg count . . . . . . . . . . 1 6
2.2.2 Ovine lymphocyte antigens . . . . . . . . . . . . . . . . . 17
2.2.3 Immunological function . . . . . . . . . 1 7 2.2.4 Haemoglobin genotype . . . . . . . . . . . . 1 8 2.2.5 Gastrin level . . . . . . . . . . . . . . . . . 1 8 2.3 Parasite adaptation . . . . . . . . . . . . . . . . . 1 8 2.4 Specificity of resistance . . . . . . . . . . . . . . . . . 1 9 2 . 5 Stability o f resistance . . . . . . . . . . . . . . . . . . 20
2.6 Relationship between resistance and production . . . . . . . . 2 1 2.6. 1 Liveweight gain and wool growth . . . 2 1 2.6.2 Fertility . . . . . . . . 23
2.6.3 Dagginess . . . . . . . . . . . . . . . . . 24
2. 7 Resistance versus resilience . . . . . . . . . . . . . . 25
2.8 Vaccination . . . . . . . . . . . . . . . . . . . . . . . . 27
2.9 Immune function in genetically resistant sheep . . . 28
Three ' Parasitism and production in fleeceweight-selected and control sheep' . . . .. . . 30
Four ' Parasitological characteristics of fleeceweight-selected and control sheep' ... 43
Fbe Adilitional ma�rial . . . 6 1 Six Summary and conclusions . . . . . . . . . . . . . 67
Seven References . . . 70
Appendix 1 ' The evaluation of kiwifruit vinegar as a stock feed' . . . 84
Table 1 Production and serum gastrin levels in Fleeceweight-selected and Control sheep when subclinically infected and with infection controlled by CRC treatment . . . 37
2 Faecal egg counts in Fleeceweight-selected and Control sheep subclinically infected with internal parasites . . . . . . . 38
3 Parameters measured in Fleeceweight-selected and Control sheep at 16 months of age which received previous CRC treatment or were untreated at 6 months of age, when artificially infected with larvae
... 53
4 Parameters measured in Fleeceweight-selected and Control sheep at 16 months of age which received previous CRC treatment or were untreated at 6 months of age, when artificially infected with larvae, and in uninfected sheep . . . . . . . . . . . . . . . . 54
List of Figures
Figure 1
2
The general seasonal pattern of populations of infective larvae on sheep pastures . . . 5
The relationship between faecal egg count at day 27 and total worm count in FW and C sheep artificially infected with nematode larvae
... 49
3 The relationship between faecal egg count at day 27 and Total Pathogenic Index in FW and C sheep artificially infected with nematode larvae . . . 50
4 The relationship between mucosal mast cell count and worm count in FW and C sheep artificially infected with nematode larvae
... 5 1
5 Faecal egg counts of non-CRC FW and C ewes in 1992 (untransformed means and std errors) . . . 62
6 The effect of kiwifruit vinegar and anthelmintic capsules on liveweight gain and clean midside wool growth in ewe lambs . . . 88
7 The effect of kiwifruit vinegar on faecal egg count in non-capsule treated ewe lambs . . . 89
