Abstract :
The long-term benefit of suckling for the resistance and resilience of lambs to Teladorsagia
circumcincta infection was investigated in a 20-week after-lambing trial period; during
which time the immune response was anticipated to be strengthening. In a two by two factorial
arrangement, one factor was ‘suckling’ with one twin lamb from each of 34 pairs being
either weaned (W−) at 39 days of age or allowed to continue suckling (S−) until necropsy
at mean ages of either 84, 112 or 140 days. The second factor was ‘parasite infection’ with
lambs in each ‘suckling’ treatment group either artificially challenged with an equivalent
of 1000 L3 T. circumcincta larvae d−1 (−I) from day 42 of age until necropsy or not artificially
challenged (−N). All lambs and their dams grazed ryegrass pastures throughout the trial;
these were intended to be relatively parasite safe, although worm burdens of SN and WN
groups suggested there was a considerable parasite challenge from pasture from day 84
onwards. Despite this, suckled lambs consistently exhibited lower faecal egg counts (FECs;
P < 0.05) and worm burdens at slaughter on days 84 and 112 (P < 0.05 for both). Worms from
suckled lambs appeared to have reduced egg production indicating either a direct effect of
milk proteins on parasite fecundity or an indirect benefit of suckling through the provision
of nutrients for enhance immune capacity. Lamb growth rate was reduced by weaning
but not by artificial challenge (P > 0.05). It was concluded that while the enhanced protein
supply from suckling will facilitate greater growth rates in young lambs, weaning may not
necessarily be associated with reduced resilience to T. circumcincta infection. Furthermore,
suckling appears to assist in reducing worm burdens and parasite fecundity either through
a direct anti-parasitic effect or through hastening the acquisition of immunity when lambs
are exposed to larvae early in life.
