Repeatability estimates and selection flock effects for faecal nematode
egg counts in Romney breeding ewes
C.A. Morris, T.G. Watson, R.L. Baker, A.P. Hurford, B.C. Hosking
AgResearch, Ruakura Agriculture Centre, Private Bag 3123, Hamilton,
New Zealand
Proceedings of the New Zealand Society of Animal Production. 1993,
53: 227-230
A selection experiment to breed for high (H), control (C) or low (L)
faecal egg count (FEC) levels in weaned Romney lambs was established in
1985, being maintained at Rotomahana (until weaning 1988) and at Tokanui
thereafter. In winter 1990, pregnant ewes (aged 2 to 6 years) were drafted
into grazing groups according to expected lambing date ('early' and 'late'
ewes), in order to study periparturient FEC. Non- pregnant ewes and
unmated yearling females were also recorded. Faecal samples for FEC were
taken from all females (n=253) before and after the pregnant ewes lambed
(median lambing dates for early and late ewes being 19 August and 31
August), and then in October and in November. Lambs were also faecal
sampled at 3-month weaning. A mixed model was fitted to log e (FEC +
100), with fixed effects for selection flock, group (early ewes, late ewes, non-
pregnant ewes, yearlings), sample day and the interaction of group and day,
and with 'animal' as a random effect. The repeatability was 0.50 ± 0.04 and
selection flock means (transformed from the log scale) were: H, 349; C, 160
and L, 140 eggs/g, with significant differences (P<0.001) between and H and
C or L flocks. Over all flocks, the means were highest immediately after
lambing (292 eggs/g) and lowest in November (135 eggs/g). Ewes which
were early, late or non-pregnant and yearling females had means of 325, 259,
154 and 119 eggs/g respectively (P<0.01). Regressions of the lamb's log FEC
on the dam's mean log FEC, with or without adjustment for selection flock,
showed that a 10% increase in the dam's FEC was associated with a 2.3% or
4.7% increase in the lamb's FEC, respectively.
Keywords: NZSAPAB;
Internal parasites; selection; faecal egg count; ewes; repeatability.
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Last Updated 25-01-1997
