Does milk supply have long-term benefits for resistance and resilience to nematode parasites in sheep?

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.