Across flock (co)variance components for faecal worm egg count, live weight, and fleece traits for Australian merinos

Khusro, Mohammad; Werf, J. H. J. van der; Brown, D. J.; Ball, Alexander

doi:10.1016/j.livprodsci.2004.06.012

Cited by 24 publications

(52 citation statements)

References 12 publications

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“…Pertaining to the interaction between birth year and sex, the results obtained in this study are in accordance with those obtained by Khusro et al (2004), Cloete et al (2007) and Matebesi-Ranthimo et al (2014). In all three studies, the effects of birth year and sex were involved in a significant interaction.…”

Section: Discussionsupporting

confidence: 90%

“…Studies by Cloete et al (2007), Snyman (2007) and Matebesi-Ranthimo et al (2014) reported an individual variation for FWEC ranging from 0 to 13700, 0 to 87800 and 0 to 32700 epg wet faeces, respectively. In a study by Khusro et al (2004), means for FWEC were 736 for hoggets and 779 for yearling Merino sheep, while the individual variation for FWEC ranged from 0 to 50000 epg in both age groups. The transformations used in this study are commonly applied to improve the extreme variation in data of this nature.…”

Section: Discussionmentioning

confidence: 94%

“…In all three studies, the effects of birth year and sex were involved in a significant interaction. In a study by Khusro et al (2004), the direction of the magnitude of difference in FWEC varied between yearling animals and hoggets. In yearling animals, ewes excreted more eggs than rams, while the opposite was true of hoggets.…”

Section: Discussionmentioning

confidence: 98%

“…Faecal worm egg count is known to be exceedingly variable and skewed, needing transformation prior to analysis (Greeff et al, 1995;Khusro et al, 2004;Morris et al, 2005;Cloete et al, 2007). Commonly used transformations that are applied to FWEC data are the cube root transformation and the log transformation.…”

Section: Methodsmentioning

confidence: 99%

“…As a result, FWEC has been used widely to measure parasite resistance, following artificial or natural infestation (Mandonnet et al, 2001;Cloete et al, 2007;Matebesi-Ranthimo et al, 2014). Previous studies have reviewed genetic factors that affect FWEC at international level (Khusro et al, 2004;Safari et al, 2005;Morris, 2011;Pickering et al, 2012). However, in South Africa, these genetic factors have been limited to the works of Nieuwoudt et al (2002), Snyman (2007), Cloete et al (2007) and Matebesi-Ranthimo et al (2014), all reporting data of flocks under institutional control.…”

Section: Introductionmentioning

confidence: 99%

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Environmental and genetic factors affecting faecal worm egg counts in Merinos divergently selected for reproduction

Mpetile¹,

Cloete²,

A³

et al. 2016

SA J. An. Sci.

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Infestation with gastrointestinal nematodes is probably among the most pervasive problems in smallstock production worldwide. Faecal worm egg count (FWEC) has been reported as an indirect measure of parasite resistance in livestock production. Environmental and genetic factors of FWEC were assessed, using data from Merino sheep that were selected divergently for reproductive performance at Elsenburg Research Farm. Data consisted of animals born in 1995 -1996, 1999, and 2001 -2013. Two datasets were considered: 1869 FWEC records of animals born in the years provided above, and 851 records of the divergently selected lines and the reciprocal cross between them, born in 2003 -2008. Rectal faecal sample grabs were obtained from individual animals after drenching had been withheld for approximately 6 to 10 weeks, generally in April. Nematode eggs in these samples were counted using the McMaster technique, with a sensitivity of 100 eggs/g wet faeces. The fixed effect of birth year x sex interaction was significant, with rams showing higher mean values for FWEC than ewes in most years, but these results were not consistent. FWEC showed significant but low heritability, estimates ranging from 0.06 for untransformed data to 0.10 for log-transformed data, suggesting that selection for low FWEC could be slow. There was no hybrid vigour and compelling evidence of genetic change in log-transformed FWEC in either line, suggesting a negligible genetic correlation between FWEC and reproduction. In this experiment, the researchers studied animals that had been exposed to parasite challenge in autumn. Therefore, the results of this study cannot be applied directly to a situation in which faecal samples were collected in other seasons. Future work is needed to determine the effect of season on the heritability of parasite resistance in South African conditions. ______________________________________________________________________________________

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Section: Discussionsupporting

confidence: 90%