The effect of sire selection for helminth egg counts on progeny helminth egg counts and live weight.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 16 THE EFFECT OF SIRE SELECTION FOR HELMINTH EGG COUNTS ON PROGENY HELMINTH EGG COUNTS AND LIVE WEIGHT C.R. ESDALE*, R.D. LEUTTON**, P.K. O' ROURKE* * and T.H. RUDDER** SUMMARY Progeny of sires selected for compared. A parental selection difference of log 0.36 epg between vs 2.47 P<O.O05) which represents a no significant differences between low or high helminth egg counts (epg) differential of log 0.69 epg resulted the progeny of the two sire lines (log realized heritability of 0.52. There sires within selection lines. were in a 2.11 were Sire selection line had no significant effect on live weights at birth, weaning or 18 months of age. There was an effect of sire within the low (P=O.OOl) and high (P=O.O58) selection lines on 18 month live weights. These differences reflected the sire's own ranking for 18 month live weight. The results indicate that, at the level of epg counts recorded in this experiment, live weight and helminth resistance as measured by egg counts are not related. (Key words:sire selection, helminths, live weight.) INTRODUCTION The use of anthelmintics to alleviate the effects of endo-parasite burdens in yearling cattle is widely regarded as a necessary management practice. Seifert (1971b), Turner and Short (1972), Bryan (1976) and others showed that anthelmintic treatment improved liveweight change especially during periods of nutritional stress. The extent of mortality from helminth burdens is not well documented but deaths are known to occur (Seifert 1971b; Bryan Anthelmintic treatment is a recurring cost, and there is a danger of 1976). drug resistance developing in the helminth population (Kelly and Hall 1979). Genetic manipulation of cattle by choice of breed and by within breed selection can be used to control cattle tick (Seifert 1971a). However, less attention has been given to the genetics of helminth resistance. of helminth egg counts have been shown to be moderate to high Repeatabilities (Seifert 1971b), indicating reasonably consistent ranking of animals according to helminth egg count. Preliminary studies by Seifert (1977) also indicated moderate to high heritabilities for helminth egg counts. These studies imply that selection for helminth resistance may be a feasible alternative to anthelmintic treatment. Preliminary results from a single generation selection experiment in which sires were selected for high or low faecal egg counts are reported in this paper. MATERIALS AND METHODS The experimental animals were F2 et seq. generation Africander-Hereford cattle bred and reared at Brigalow Research Station (24050's 149Q48'E) approximately 190 km south-west from Rockhampton, Queensland. They were the \ progeny of three bulls selected for low and three bulls selected for high helminth faecal egg counts. These bulls were bred and reared at Mt Eugene, a * ** Queensland Department of Primary Industries, M.S. 586, Theodore QLD 4719 Queensland Department of Primary Industries, G.P.O. Box 46, Brisbane QLD 4001 199 Proc. Aust. Soc. Anim. Prod. Vol. I6 commercial breeding and fattening property located at 24OlO'S 150�25'E was based approximately 70 3am south of Rockhampton, Queensland. Selection counts between August 3 and December 10, 1981 when the on four epg Individual and group epg counts and 560 bulls were c. 8 to 13 months of age. day (18 month) live weights for the 'low' and 'high' bulls and for the complete group from which they were selected are shown in Table 1. Table 1 Helminth egg counts (epg) and 18 month live weights of the sires of the experimental animals and of the unselected group from which they were drawn. Helminth resistance, based on egg counts was unknown for 107 of the 128 dams of the experimental animals and these dams were allocated to the six sire Helminth egg groups at random within age and lactation status categories. counts from c. 8 to 13 months of age (August to December) were known for the remaining 21 dams and they were allocated to sire groups to give 1ow:low and The overall mean difference between the dams in high:high egg count joinings. By contrast, the the two sire lines was only log 0.12 epg (log 1.64 vs 1.76). selection differential between the two selected sire groups was log 1.25 epg This gives a parental selection differential of log 0.69 epg. Experimental procedures The egg the of The experimental animals were born on November 2 (+20 days SD) 1983. effect of sire selection for egg counts was based on the mean of four counts taken between August 20 and December 7, 1984 using a modification of 1948) and expressed as eggs per gram (epg) McMaster technique (Whitlock faeces. Live weight adjusted for age and epg transformed to log10 (count + 1) were analysed using a standard least squares method for unequal sub-class numbers. In addition to the factors shown in Table 2, dam age, sex of calf and the first None of order interactions were initially included in the analytical models. the interactions was significant and therefore, the final model contained only Correlations between mean log epg counts and the the four main effects. production indices were estimated after removal of the four main effects. Repeatability was estimated by intraclass correlation after removing the effects of selection line and sex. 20 0 Proc. Aust. Soc. Anim. Prod. Vol. 16 RESULTS AND DISCUSSION Table 2 Effect of sire selection on progeny egg counts and live weights to months of age 18 Selection line had a significant effect (P<O.OOS) on log epg but there was no effect of sire within line (Table 2). The lack of effect of sire within line is consistent with egg counts (Table 1). The repeatability of epg was significant (t=0.20 - 0.05 SE, P(O.01). + The difference between sire lines was log 0.36 from a parental selection differential of log 0.69 epg representing a realized heritability of 0.52. Preliminary studies by Seifert (1977) gave a heritabilty of 0.78 based on w3 epg counts from August to January for animals aged 12 to 18 months, while a heritability estimate of 0.4520.27 (from the mean of four egg counts) was obtained from paternal half-sib relationships in data from four earlier calf crops of Africander-Hereford heifers bred and reared at Brigalow Research Station (Rudder unpublished data). These estimates indicate that helminth egg counts can be reduced through sire selection. Selection line had or 18 months of age. the low (P=O.OOl) and the sire's own 18 month no significant effect on live weight at birth, weaning Differences in 18 month live weight between sires within high (P=O.O58) selection lines reflect the rankings of live weights. Helminth egg count was not correlated with either live weight at 18 months or liveweight gain from weaning to 18 months, (r = -0.05 and 0.10 P>O.O5, respectively). The relationships of parasitic burdens, as measured by egg counts, and liveweight gain have not been consistent. Turner and Short (1972) and Frisch and Vercoe (1982) found no significant relationship, but Seifert (1971b, 1977) found negative effects of epg counts on liveweight gain. Seifert (1971b) and Turner and Short (1972) indicated that when animals were gaining 201 Proc. Aust. Soc. Anim. Prod. Vol. 16 live weight, parasitic burdens had little or no effect, under nutritional stress. but became important These results indicate that egg counts can be reduced by selection but this effect may not result in change in live weight for-age. Seifert (1971b) and Turner and Short (1972) showed that reducing egg counts to approximately less than 100 epg by anthelmentic treatment resulted in increased liveweight gain. Perhaps, epg counts need to be reduced to a much lower level than achieved in this experiment before differences in live weight are realised. ACKNOWLEDGEMENTS The efforts of our colleagues who contributed to maintenance of experimental animals and collection of support by AMRC are gratefully acknowledged. REFERENCES BRYAN, R.P. (1976) experimental design, and financial data Aust. Vet. J. 52: 403. FRISCH, J.E. and VERCOE, J.E. (1982) World Congress on Genetics Applied to Livestock Production, 2nd, Madrid, 1982. Round Tables Section RT-E-4, 307. KELLY, J.D. and BALL, 1979'. PP. 19-3 1. SEIFERT, G.W. (1971 a) SEIFERT, G.W. SEIFERT, G.W. Oceania', (1971 C.A. (1979) 'New south Wales Veterinary Proceedings 22: 22: Soc. 159. 839. Aust. J. Agric. Res. Aust. J. Agric. Res. Congr. b) (1977) 'Third Int. Canberra 7-4-8. (1972) Adv. Breed. Res., Asia and TURNER, H-G. and SHORT, A.J. WHITLOCK, H.V. (1948) Aust. J. Agric. Res. 23: 177. J. coun. scient. ind. Res. Aust. 21: 177. 20 2