Rapid improvement of immunity to Teladorsagia circumcincta is achieved through a reduction in the demand for protein in lactating ewes J.G.M. Houdijk a, * , F. Jackson b , R.L. Coop b , I. Kyriazakis a,c a Animal Nutrition and Health Department, Scottish Agricultural College, Kings Buildings, Edinburgh EH9 3JG, UK b Moredun Research Institute, Pentland Science Park, Bush Loan, Penicuik EH26 0PZ, UK c Veterinary Faculty, University of Thessaly, P.O. Box 199, 43100 Karditsa, Greece Received 17 May 2005; received in revised form 26 September 2005; accepted 27 September 2005 Abstract Protein supplementation can improve the resistance to parasites of periparturient ewes, as indicated by reduced nematode egg excretion and worm burdens. However, the rate at which this improvement can occur is largely unknown. We investigated the rate of improvement by assessing temporal changes in faecal egg counts after we experimentally reduced nutrient demand. Three groups of nine pregnant ewes each were trickle infected with Teladorsagia circumcincta from day K70 to day 16 (parturition is day 0 ). Two groups of twin-rearing ewes were fed at 0.8 (L22) or 1.2 (H22) times their assumed metabolizable protein requirements, and a third group was fed the same daily food allowances as L22 ewes, but one of their lambs was removed on day 10 (L21). Ewes were slaughtered on day 21 to assess worm burdens, in vitro larval establishment on abomasal explants, and mucosal inflammatory cells. Faecal egg counts of L22 ewes were higher than H22 ewes throughout lactation. After the removal of one lamb, faecal egg counts of L21 ewes decreased within 5 days to levels similar to H22 ewes. Relative to L22 ewes, L21 and H22 ewes had lower worm burdens, parasite per capita fecundity and in vitro establishment rates of both T. circumcincta and Haemonchus contortus. Mucosal mast cell and eosinophil counts were similar for all ewes, but H22 ewes had higher globule leukocyte counts than L22 and L21 ewes. The data suggest that a reduction in protein demand can rapidly improve periparturient immunity to T. circumcincta. This may be associated with increased parasite expulsion, reduced fecundity and non-parasite specific reduction of in vitro larval establishment. q 2005 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Sheep; Lactation; Protein nutrition; Immunity; Teladorsagia circumcincta; Larval establishment; Tissue explants 1. Introduction The periparturient breakdown of immunity to parasites may be due to a lower priority of scarce metabolizable protein (MP) allocation given to immune rather than to reproductive functions (Coop and Kyriazakis, 1999; 2001). Consequently, at times of MP scarcity, immune functions may be penalized. Conversely, an increase in MP supply and/or a reduction in MP demand can be expected to restore periparturient immunity to parasites, as indicated by reduced nematode egg excretion and worm burdens. Indeed, protein supplementation to periparturi- ent ewes has decreased faecal egg counts (FEC) and worm burdens (Donaldson et al., 2001; Houdijk et al., 2003; Kahn et al., 2003), whilst single-rearing ewes usually have lower FEC and smaller worm burdens than twin-rearing ewes (Romjali et al., 1997; Donaldson et al., 1998; Houdijk et al., 2001a; Kahn et al., 2003). The main objective of this experiment was to assess the rate at which an improvement in MP nutrition can reduce the degree of the periparturient breakdown of immunity. This was evaluated by assessing changes in FEC over time after a reduction in MP demand, achieved through a reduction in litter size. This rate of improvement is largely unknown, but can be considered an important parameter for assessing the viability and acceptability of protein supplementation as a non-chemical parasite control strategy. We assessed this rate through a reduction in MP demand rather than through an increase in MP supply. This was expected to avoid the potential confounding effects of any dietary influences on gastrointestinal environ- ment that can affect directly parasite survival (Petkevicius et al., 2003). We hypothesized that a reduction in MP demand would reduce FEC to the same level achieved by MP supplementation. A reduction in FEC may be the result of International Journal for Parasitology 36 (2006) 219–227 www.elsevier.com/locate/ijpara 0020-7519/$30.00 q 2005 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpara.2005.09.014 * Corresponding author. Tel.: C44 131 535 3245; fax: C44 131 535 3121. E-mail address: jos.houdijk@sac.ac.uk (J.G.M. Houdijk).