Reduced Ostertagia circumcincta burdens in milk-fed lambs

Aims: To compare the susceptibility to parasitism by Ostertagia circumcinct a of lambs fed entirely with bovine milk or weaned on to solid feed at 3 we eks of age. In addition, the effect of a single daily feed of milk on worm burdens was assessed. Methods: Eight lambs were assigned to each of the 3 diets: milli (M), milk plus solid feed (cereal-based pellets and lucerne chaff) (MS), or solid fee d only (S). Those to be fed solid feed were converted from complete milk fe eding to the designated diet during their third week of life. From 3 weeks of age, all lambs were infected with 1000 O. circumcincta larvae twice week ly for 6 weeks; 4 lambs from each diet group were given normal sheathed L3 and another 4 were infected with exsheathed larvae. Faecal egg counts (FEC) and serum gastrin and pepsinogen concentrations were monitored from Day 17 after first infection, and worm burdens and abomasal pH and morphology wer e determined at necropsy. Results: Total worm burdens and FEC were significantly lower in the M than MS and S groups, whereas there was no significant difference between those receiving sheathed and exsheathed larvae. The milk-fed lambs had a smaller reticulo-rumen and omasum and a more acidic abomasal pH. Serum gastrin and pepsinogen were increased in all groups, irrespective of diet or type of la rvae used for infection. Conclusions: The cause of the lower worm establishment in lambs fed only mi lk was probably not failure to exsheath in the immature gastro-intestinal t ract, as there were similar worm burdens in lambs whether sheathed or exshe athed larvae were administered. The lower pH of the abomasal contents of th e preruminant lambs may have been a factor, as the parasites have previousl y been shown to die more rapidly in vitro at low pH. Alternatively, the mil k itself had adverse effects on the parasites, but was ineffective when com bined with solid feed. There was no benefit from feeding a milk plus solid diet over a solid diet.