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Genetic analyses of nematode egg counts in Hereford and crossbred Hereford cattle in the subtropics of New South Wales
Livestock Production Science, 12 (1985) 79--84 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
79
Short Communication G E N E T I C A N A L Y S E S O F N E M A T O D E E G G C O U N T S IN H E R E F O R D A N D C R O S S B R E D H E R E F O R D C A T T L E IN T H E S U B T R O P I C S O F NEW S O U T H W A L E S
ROGER BARLOW N.S. W. Department o f Agriculture, Agricultural Research and Advisory Station, Grafton, N.S.W. 2460 (Australia)
LAURIE R. PIPER C.S.I.R.O., Division o f Animal Production, Armidale, N.S.W. 2350 (Australia)
(Accepted 5 July 1984)
ABSTRACT Barlow, R. and Piper, L.R., 1985. Genetic analyses of nematode egg counts in Hereford and crossbred Hereford cattle in the subtropics of New South Wales. Livest. Prod. Sci., 12: 79--84. A total of 438 calves was produced by 123 sires of Hereford, Simmental, Friesian and Brahman breeds when mated to Hereford cows. Faecal egg counts and larval differentiation of nematode species were undertaken on one or two occasions prior to weaning at 7 to 8 months. Significant breed of sire and sire within breed effects were observed, but heritabilities, repeatabilities and phenotypic correlations were generally low to moderate.
INTRODUCTION
As y e t t h e r e have b e e n no definitive r e p o r t s o f resistance a m o n g nemat o d e s infecting cattle in Australia, b u t if w i d e s p r e a d resistance t o anthelmintics does d e v e l o p , cattle p r o d u c e r s will n e e d t o r e s o r t t o alternative control m e t h o d s . T h e possibility o f c o n t r o l t h r o u g h m a n i p u l a t i o n o f the h o s t g e n o t y p e is indicated b y evidence o f b o t h b e t w e e n - b r e e d (Seifert, 1 9 7 1 ; T u r n e r and S h o r t , 1 9 7 2 ) and between-sire variation (Albers, 1 9 8 1 ; Kloosterm a n et al., 1 9 7 8 ; Seifert, 1 9 7 7 ) f o r resistance t o n e m a t o d e s . In this paper, we e x a m i n e b r e e d o f sire and sire w i t h i n b r e e d effects using an indirect m e a s u r e o f n e m a t o d e i n f e s t a t i o n - - faecal egg c o u n t s . MATERIALS AND METHODS T h e e n v i r o n m e n t , t h e cattle a n d their m a n a g e m e n t were described b y Barlow and O'Neill ( 1 9 7 8 , 1 9 8 0 ) . Briefly, calves were grazed o n alluvial pastures
0301-6226/85/$03.30 © 1985 Elsevier Science Publishers B.V.
80
in the subtropics of N.S.W. and weaned at 7 to 8 months of age in early a u t u m n (March) of 1976, 1977 and 1978. There were no anthelmintics used over this period. Simmental, Friesian, Hereford and Brahman breeds, represented by 32, 31, 30 and 31 sires respectively, produced a total o f 438 calves with complete records (for this study), out of Hereford and Poll Hereford females. Sires were chosen at random, and replaced annually. Faeces samples were taken from all calves one m o n t h prior to weaning (except in 1976) and again at weaning in each year. Worm egg counts in faeces and larval cultures were carried out by the m e t h o d of Roberts and O'Sullivan (1950). The criteria of Keith (1953) were used for larval differentiation. Least-squares analyses of variance were undertaken to determine the factors significantly affecting the count of each nematode species separately, and of all species combined, for the samples taken at weaning in all years. Counts were transformed to log (count +1). A c o m m o n model was fitted initially as given by Barlow and O'Neill (1978), but the final model contained only significant effects and the terms, breed of sire, and sires nested within breeds and years. Estimates of the effects of breeds and sires on counts, and of heritabilities and correlations between counts, were obtained from these analyses. The estimates of parameters obtained from these analyses are quite valid as t h e y contain no dominance effects. The effects of breeds and years were tested using the between-sire variance as the error term, while other effects, including sires, were tested against the residual. A further set of analyses was undertaken to determine the repeatability of counts using the data collected in 1977 and 1978. RESULTS
Breed of sire, year, management group within year and sire within year X breed subclass were the only effects retained in the final model. Collectively, these variables accounted for between 29.3 and 39.7% of the total variation in faecal egg counts (EPG) for individual nematode species and for 28.2% of the combined count. Faecal egg counts o f all species except Haemonchus spp. varied significantly between years and management groups, but large burdens were not indicated for any species (Table I). Cooperia spp., Haernonchus spp. and Oesophagostomum spp. contributed most to the combined count in all years. Significant breed of sire effects were observed in the case of Oesophagostomum spp. only (Table I), but there was a general tendency for lower EPG among Brahman-sired calves across all nematode species. There was no significant sire effect on the EPG of any species when pooled over all sire breeds and years. Within breeds pooled over years, Friesian sires varied significantly for combined EPG, Haemonchus spp., Trichostrongylus spp. and Cooperia spp., while Simmental sires varied
0.04 (0.18) 0.31
Heritability
Repeatability
(0.6) (0.05) (0.06) (0.05)
2.36 2.30 2.34 2.22
Means within b r e e d of sire Simmental 113 Friesian 116 Hereford 96 Brahman 113
All species
2.30 (0.03) [499]
N u m b e r of animals
Overall m e a n s 438 [values u n t r a n s f o r m e d ]
I n d e p e n d e n t variable
(0.06) (0.05) (0.06) (0.06)
0.30
0 . 2 9 (0.19)
1.74 1.74 1.57 1.69
1.69 ( 0 . 0 3 ) [139]
Haemonchus
(0.05) (0.04) (0.05) (0.05)
0.II
0.19 (0.18)
0.51 0.53 0.55 0.42
0.50 (0.02) [6]
Trichostrongylus
(0.05) (0.05) (0.05) (0.05)
---0.01
0 . 2 6 (0.19)
0.78 0.60 0.75 0.59
0.68 (0.03) [11]
Ostertagia
(0.07) (0.06) (0.07) (0.06)
0.31
- 0.04 (0.17)
1.87 1.81 1.94 1.79
1 . 8 5 (0.03) [261]
Cooperia
(0.07) (0.06) (0.07) (0.07)
0.25
---0.22 ( 0 . 1 6 )
1.34 1.42 1.50 1.17
1,36 (0.04) [97]
(0.03) (0.03) (0.03) (0.03)
---0.04
...
0.26 (0.19)
0.17 0.17 0.18 0.09
0.16 (0.02) [2]
Oesophagostornum Bu n o s to r n u m
Least-square m e a n s , p a t e r n a l half-sib e s t i m a t e s o f heritabilities, r e p e a t a h i l i t i e s a n d s t a n d a r d e r r o r s o f log faecal egg c o u n t s f o r e a c h species
TABLE I
00
82
significantly for Ostertagia spp. A large proportion of the variation between Friesian sires was accounted for by variation between sires in one year. The heritabilities of single estimates of EPG were fairly low for individual species, and for the combined count, (Table I) although large standard errors were attached to these estimates. Repeatabilities were of a similar order of magnitude, indicating that repeat measurements should increase the precision of estimation considerably. A test of this, using the 1976 and 1977 data, was inconclusive because of the small numbers involved. Phenotypic correlations between the EPG for individual species and for combined counts over all species essentially reflected the part--whole nature o f the relationships, with higher values for the species contributing most to the total. Correlations among the EPG of individual species were small to moderate. The highest value of 0.48 was between two species with the highest mean counts, Haemonchus spp. and Cooperia spp., while the lowest correlations involved Bunostomum spp. {0.02 to 0.20). Scale effects could be affecting these relationships. Genetic correlations were rather meaningless because of large standard errors. DISCUSSION
Brahman-sired calves had significantly lower egg counts of Oesophagostomum spp., and non-significantly lower counts of all species combined. By contrast, in two separate studies involving Zebu X Hereford-Shorthorn and Hereford X Shorthorn cattle, no differences were observed between breeds for faecal egg counts, although Africander X Hereford-Shorthorn and Hereford X Shorthorn crosses showed greater responses to treatment with anthelmintics (Seifert, 1971; Turner and Short, 1972). The apparent conflict may support the view that egg counts are not reliable indicators o f worm burdens but equally could indicate differences between breeds in their tolerance of the effects of parasites. While there was evidence o f significant between-sire variation in some instances in the present study, the design was not sufficiently powerful to detect this variation with adequate precision. The optimum number of progeny per sire is given approximately b y the ratio of 4/h 2, and for a heritability of 0.25, 16 progeny would have been desirable. In this study the average number of offspring per sire was 3.4. Seifert (1977) reported very high estimates of heritability of egg counts for Haemonchus spp. (0.94), Cooperia spp. (0.60), Oesophagostomum spp. (0.93) and total species (0.78), and strong positive correlations among these counts. No standard errors were reported b u t only 14 sires with three to five progeny per sire were involved. Further, the estimates of egg counts were based on the mean of three observations, and this would have had the affect of reducing the environmental variance, and so increasing the heritabilities. However, even adjusting for this, using a repeatability of 0.30, Seifert's (1977) estimates were still much larger than those obtained in the present study.
83 ACKNOWLEDGEMENTS
Many people deserve mention, in particular Dr Peter Mylrea and his staff at the Regional Veterinary Laboratory, Wollongbar.
REFERENCES Albers, G.A.A., 1981. Genetic resistance to experimental Cooperia oncophora infections in calves. Meded. Landbouwhogesch. Wageningen, 81(1): 118 pp. Barlow, R. and O'Neill, G.H., 1978. Performance of Hereford and crossbred Hereford cattle in the subtropics of New South Wales: growth of first-cross calves to weaning. Aust. J. Agric. Res., 29: 1313--1324. Barlow, R. and O'Neill, G.H., 1980. Performance of Hereford and crossbred Hereford cattle in the subtropics of New South Wales: genetic analyses of preweaning performance of first-cross calves. Aust. J. Agric. Res., 31: 417--427. Keith, R.K., 1953. The differentiation of the infective larvae of some common nematode parasites of cattle. Aust. J. Zool., 1: 223--235. Kloosterman, A., Albers, G.A.A. and Van Den Brink, R., 1978. Genetic variation among calves in resistance to nematode parasites. Vet. Parasit., 4: 353--368. Roberts, F.H.S. and O'Sullivan, P.J., 1950. Methods for egg counts and larval cultures for strongyles infecting the gastro-intestinal tract of cattle. Aust. J. Agric. Res., 1: 99-102. Seifert, G.W., 1971. Ecto- and endoparasitic effects on the growth rates of Zebu crossbred and British cattle in the field. Aust. J. Agric. Res., 22: 839--850. Seifert, G.W., 1977. The genetics of helminth resistance in cattle. Proceedings of the Third International Congress on Advances in Breeding Research in Asia and Oceanea~ Canberra, Australia, pp. 7-4--7-8. Turner, H.G. and Short, A.J., 1972. Effects of field infestations of gastrointestinal helminths and of the cattle tick (Boophilus microplus) on growth of three breeds of cattle. Aust. J. Agric. Res., 23: 177--193.
RESUME
Barlow, R. et Piper, R.L., 1985. Diffdrences gdn~tiques dans le nombre d'oeufs de n~matodes chez les bovins Hereford et crois~s Hereford dans les milieux subtropicaux des N e w South Wales. Livest. Prod. Sci., 12:79--84 (en anglais). Sur 438 veaux issus de 123 taureaux Hereford, Simmenthal, Frisons et Brahman, accouples fi des vaches Hereford, on a effectu~ des comptages d'oeufs et de larves de n~matodes, une ou deux fois avant le sevrage ~ l'~ge de 7 ~ 8 mois. On a observ~ des differences significatives entre races de p~res et entre taureaux intra-races, mais les valeurs de l'h~ritabilit~, de la r~p~tabilit~ et des correlations ph~notypiques ont ~t~ en g~n~ral faibles moyennes.
84 KURZFASSUNG Barlow, R. und Piper, L.R., 1985. Genetische Analyse yon Nematodeneierz~hlungen bei reinen und gekreuzten Herefordrindern im subtropischen New South Wales. Livest. Prod. Sci., 1 2 : 7 9 - - 8 4 (auf englisch). Aus Anpaarungen von 123 Bullen der Rassen Hereford, Simmental, Friesen und Brahman an Herefordkiihe entstanden 438 K~ilber. Vor dem Absetzen mit 7 bis 8 Monaten wurden ein- oder zweimal Kotproben auf Eier yon Nematoden untersucht und anhand der Larven die Spezies festgestellt. Es wurden signifikante Unterschiede zwischen den Rasse der Vatertiere und zwischen Bullen innerhalb einer Rasse beobachtet, w~ihrend die Heritabilit~iten, Wiederholbarkeiten und ph~inotypische Korrelationen allgemein niedrig bis mittelm~issig ausfielen.
79
Short Communication G E N E T I C A N A L Y S E S O F N E M A T O D E E G G C O U N T S IN H E R E F O R D A N D C R O S S B R E D H E R E F O R D C A T T L E IN T H E S U B T R O P I C S O F NEW S O U T H W A L E S
ROGER BARLOW N.S. W. Department o f Agriculture, Agricultural Research and Advisory Station, Grafton, N.S.W. 2460 (Australia)
LAURIE R. PIPER C.S.I.R.O., Division o f Animal Production, Armidale, N.S.W. 2350 (Australia)
(Accepted 5 July 1984)
ABSTRACT Barlow, R. and Piper, L.R., 1985. Genetic analyses of nematode egg counts in Hereford and crossbred Hereford cattle in the subtropics of New South Wales. Livest. Prod. Sci., 12: 79--84. A total of 438 calves was produced by 123 sires of Hereford, Simmental, Friesian and Brahman breeds when mated to Hereford cows. Faecal egg counts and larval differentiation of nematode species were undertaken on one or two occasions prior to weaning at 7 to 8 months. Significant breed of sire and sire within breed effects were observed, but heritabilities, repeatabilities and phenotypic correlations were generally low to moderate.
INTRODUCTION
As y e t t h e r e have b e e n no definitive r e p o r t s o f resistance a m o n g nemat o d e s infecting cattle in Australia, b u t if w i d e s p r e a d resistance t o anthelmintics does d e v e l o p , cattle p r o d u c e r s will n e e d t o r e s o r t t o alternative control m e t h o d s . T h e possibility o f c o n t r o l t h r o u g h m a n i p u l a t i o n o f the h o s t g e n o t y p e is indicated b y evidence o f b o t h b e t w e e n - b r e e d (Seifert, 1 9 7 1 ; T u r n e r and S h o r t , 1 9 7 2 ) and between-sire variation (Albers, 1 9 8 1 ; Kloosterm a n et al., 1 9 7 8 ; Seifert, 1 9 7 7 ) f o r resistance t o n e m a t o d e s . In this paper, we e x a m i n e b r e e d o f sire and sire w i t h i n b r e e d effects using an indirect m e a s u r e o f n e m a t o d e i n f e s t a t i o n - - faecal egg c o u n t s . MATERIALS AND METHODS T h e e n v i r o n m e n t , t h e cattle a n d their m a n a g e m e n t were described b y Barlow and O'Neill ( 1 9 7 8 , 1 9 8 0 ) . Briefly, calves were grazed o n alluvial pastures
0301-6226/85/$03.30 © 1985 Elsevier Science Publishers B.V.
80
in the subtropics of N.S.W. and weaned at 7 to 8 months of age in early a u t u m n (March) of 1976, 1977 and 1978. There were no anthelmintics used over this period. Simmental, Friesian, Hereford and Brahman breeds, represented by 32, 31, 30 and 31 sires respectively, produced a total o f 438 calves with complete records (for this study), out of Hereford and Poll Hereford females. Sires were chosen at random, and replaced annually. Faeces samples were taken from all calves one m o n t h prior to weaning (except in 1976) and again at weaning in each year. Worm egg counts in faeces and larval cultures were carried out by the m e t h o d of Roberts and O'Sullivan (1950). The criteria of Keith (1953) were used for larval differentiation. Least-squares analyses of variance were undertaken to determine the factors significantly affecting the count of each nematode species separately, and of all species combined, for the samples taken at weaning in all years. Counts were transformed to log (count +1). A c o m m o n model was fitted initially as given by Barlow and O'Neill (1978), but the final model contained only significant effects and the terms, breed of sire, and sires nested within breeds and years. Estimates of the effects of breeds and sires on counts, and of heritabilities and correlations between counts, were obtained from these analyses. The estimates of parameters obtained from these analyses are quite valid as t h e y contain no dominance effects. The effects of breeds and years were tested using the between-sire variance as the error term, while other effects, including sires, were tested against the residual. A further set of analyses was undertaken to determine the repeatability of counts using the data collected in 1977 and 1978. RESULTS
Breed of sire, year, management group within year and sire within year X breed subclass were the only effects retained in the final model. Collectively, these variables accounted for between 29.3 and 39.7% of the total variation in faecal egg counts (EPG) for individual nematode species and for 28.2% of the combined count. Faecal egg counts o f all species except Haemonchus spp. varied significantly between years and management groups, but large burdens were not indicated for any species (Table I). Cooperia spp., Haernonchus spp. and Oesophagostomum spp. contributed most to the combined count in all years. Significant breed of sire effects were observed in the case of Oesophagostomum spp. only (Table I), but there was a general tendency for lower EPG among Brahman-sired calves across all nematode species. There was no significant sire effect on the EPG of any species when pooled over all sire breeds and years. Within breeds pooled over years, Friesian sires varied significantly for combined EPG, Haemonchus spp., Trichostrongylus spp. and Cooperia spp., while Simmental sires varied
0.04 (0.18) 0.31
Heritability
Repeatability
(0.6) (0.05) (0.06) (0.05)
2.36 2.30 2.34 2.22
Means within b r e e d of sire Simmental 113 Friesian 116 Hereford 96 Brahman 113
All species
2.30 (0.03) [499]
N u m b e r of animals
Overall m e a n s 438 [values u n t r a n s f o r m e d ]
I n d e p e n d e n t variable
(0.06) (0.05) (0.06) (0.06)
0.30
0 . 2 9 (0.19)
1.74 1.74 1.57 1.69
1.69 ( 0 . 0 3 ) [139]
Haemonchus
(0.05) (0.04) (0.05) (0.05)
0.II
0.19 (0.18)
0.51 0.53 0.55 0.42
0.50 (0.02) [6]
Trichostrongylus
(0.05) (0.05) (0.05) (0.05)
---0.01
0 . 2 6 (0.19)
0.78 0.60 0.75 0.59
0.68 (0.03) [11]
Ostertagia
(0.07) (0.06) (0.07) (0.06)
0.31
- 0.04 (0.17)
1.87 1.81 1.94 1.79
1 . 8 5 (0.03) [261]
Cooperia
(0.07) (0.06) (0.07) (0.07)
0.25
---0.22 ( 0 . 1 6 )
1.34 1.42 1.50 1.17
1,36 (0.04) [97]
(0.03) (0.03) (0.03) (0.03)
---0.04
...
0.26 (0.19)
0.17 0.17 0.18 0.09
0.16 (0.02) [2]
Oesophagostornum Bu n o s to r n u m
Least-square m e a n s , p a t e r n a l half-sib e s t i m a t e s o f heritabilities, r e p e a t a h i l i t i e s a n d s t a n d a r d e r r o r s o f log faecal egg c o u n t s f o r e a c h species
TABLE I
00
82
significantly for Ostertagia spp. A large proportion of the variation between Friesian sires was accounted for by variation between sires in one year. The heritabilities of single estimates of EPG were fairly low for individual species, and for the combined count, (Table I) although large standard errors were attached to these estimates. Repeatabilities were of a similar order of magnitude, indicating that repeat measurements should increase the precision of estimation considerably. A test of this, using the 1976 and 1977 data, was inconclusive because of the small numbers involved. Phenotypic correlations between the EPG for individual species and for combined counts over all species essentially reflected the part--whole nature o f the relationships, with higher values for the species contributing most to the total. Correlations among the EPG of individual species were small to moderate. The highest value of 0.48 was between two species with the highest mean counts, Haemonchus spp. and Cooperia spp., while the lowest correlations involved Bunostomum spp. {0.02 to 0.20). Scale effects could be affecting these relationships. Genetic correlations were rather meaningless because of large standard errors. DISCUSSION
Brahman-sired calves had significantly lower egg counts of Oesophagostomum spp., and non-significantly lower counts of all species combined. By contrast, in two separate studies involving Zebu X Hereford-Shorthorn and Hereford X Shorthorn cattle, no differences were observed between breeds for faecal egg counts, although Africander X Hereford-Shorthorn and Hereford X Shorthorn crosses showed greater responses to treatment with anthelmintics (Seifert, 1971; Turner and Short, 1972). The apparent conflict may support the view that egg counts are not reliable indicators o f worm burdens but equally could indicate differences between breeds in their tolerance of the effects of parasites. While there was evidence o f significant between-sire variation in some instances in the present study, the design was not sufficiently powerful to detect this variation with adequate precision. The optimum number of progeny per sire is given approximately b y the ratio of 4/h 2, and for a heritability of 0.25, 16 progeny would have been desirable. In this study the average number of offspring per sire was 3.4. Seifert (1977) reported very high estimates of heritability of egg counts for Haemonchus spp. (0.94), Cooperia spp. (0.60), Oesophagostomum spp. (0.93) and total species (0.78), and strong positive correlations among these counts. No standard errors were reported b u t only 14 sires with three to five progeny per sire were involved. Further, the estimates of egg counts were based on the mean of three observations, and this would have had the affect of reducing the environmental variance, and so increasing the heritabilities. However, even adjusting for this, using a repeatability of 0.30, Seifert's (1977) estimates were still much larger than those obtained in the present study.
83 ACKNOWLEDGEMENTS
Many people deserve mention, in particular Dr Peter Mylrea and his staff at the Regional Veterinary Laboratory, Wollongbar.
REFERENCES Albers, G.A.A., 1981. Genetic resistance to experimental Cooperia oncophora infections in calves. Meded. Landbouwhogesch. Wageningen, 81(1): 118 pp. Barlow, R. and O'Neill, G.H., 1978. Performance of Hereford and crossbred Hereford cattle in the subtropics of New South Wales: growth of first-cross calves to weaning. Aust. J. Agric. Res., 29: 1313--1324. Barlow, R. and O'Neill, G.H., 1980. Performance of Hereford and crossbred Hereford cattle in the subtropics of New South Wales: genetic analyses of preweaning performance of first-cross calves. Aust. J. Agric. Res., 31: 417--427. Keith, R.K., 1953. The differentiation of the infective larvae of some common nematode parasites of cattle. Aust. J. Zool., 1: 223--235. Kloosterman, A., Albers, G.A.A. and Van Den Brink, R., 1978. Genetic variation among calves in resistance to nematode parasites. Vet. Parasit., 4: 353--368. Roberts, F.H.S. and O'Sullivan, P.J., 1950. Methods for egg counts and larval cultures for strongyles infecting the gastro-intestinal tract of cattle. Aust. J. Agric. Res., 1: 99-102. Seifert, G.W., 1971. Ecto- and endoparasitic effects on the growth rates of Zebu crossbred and British cattle in the field. Aust. J. Agric. Res., 22: 839--850. Seifert, G.W., 1977. The genetics of helminth resistance in cattle. Proceedings of the Third International Congress on Advances in Breeding Research in Asia and Oceanea~ Canberra, Australia, pp. 7-4--7-8. Turner, H.G. and Short, A.J., 1972. Effects of field infestations of gastrointestinal helminths and of the cattle tick (Boophilus microplus) on growth of three breeds of cattle. Aust. J. Agric. Res., 23: 177--193.
RESUME
Barlow, R. et Piper, R.L., 1985. Diffdrences gdn~tiques dans le nombre d'oeufs de n~matodes chez les bovins Hereford et crois~s Hereford dans les milieux subtropicaux des N e w South Wales. Livest. Prod. Sci., 12:79--84 (en anglais). Sur 438 veaux issus de 123 taureaux Hereford, Simmenthal, Frisons et Brahman, accouples fi des vaches Hereford, on a effectu~ des comptages d'oeufs et de larves de n~matodes, une ou deux fois avant le sevrage ~ l'~ge de 7 ~ 8 mois. On a observ~ des differences significatives entre races de p~res et entre taureaux intra-races, mais les valeurs de l'h~ritabilit~, de la r~p~tabilit~ et des correlations ph~notypiques ont ~t~ en g~n~ral faibles moyennes.
84 KURZFASSUNG Barlow, R. und Piper, L.R., 1985. Genetische Analyse yon Nematodeneierz~hlungen bei reinen und gekreuzten Herefordrindern im subtropischen New South Wales. Livest. Prod. Sci., 1 2 : 7 9 - - 8 4 (auf englisch). Aus Anpaarungen von 123 Bullen der Rassen Hereford, Simmental, Friesen und Brahman an Herefordkiihe entstanden 438 K~ilber. Vor dem Absetzen mit 7 bis 8 Monaten wurden ein- oder zweimal Kotproben auf Eier yon Nematoden untersucht und anhand der Larven die Spezies festgestellt. Es wurden signifikante Unterschiede zwischen den Rasse der Vatertiere und zwischen Bullen innerhalb einer Rasse beobachtet, w~ihrend die Heritabilit~iten, Wiederholbarkeiten und ph~inotypische Korrelationen allgemein niedrig bis mittelm~issig ausfielen.