leptin and Trichostrongylosis

A pen experiment was conducted to investigate the interaction of early-weaning and nutrient supply on the periparturient relaxation of immunity to the gastrointestinal nematode (GIN) Trichostrongylus colubriformis in Merino ewes. Mixed-age pregnant and non-pregnant (dry) ewes were infected with 8,000 T. colubriformis L(3)/week, and fed either a high or low quality diet. Following parturition, lambs were either removed from their mothers at 2 days of age or allowed to continue suckling. Systemic immunity began to wane during late pregnancy with circulating eosinophils and plasma total antibody (Ab) levels declining from day -37 (relative to the midpoint of lambing) and day -24, respectively. Pregnant ewes fed the low quality diet exhibited an increasing faecal worm egg count (WEC) from day -24 and had higher intestinal worm burdens on day 13, whereas ewes fed the high quality diet had a delayed transient rise in WEC of lower magnitude. Dry and early-weaned ewes remained highly resistant to T. colubriformis at all times. In the post-lambing/lactation period, ewes fed the high quality diet had higher levels of local total Ab and numbers of goblet cells (GC) in the small intestine on days 13 and 41. Lactating/suckled ewes had a lower anti-parasite local immune response as indicated by reduced titres of total Ab, IgG(1), IgM and IgA and lower numbers of mucosal mast cells (MMC), globule leukocytes (GL) and GC in small intestinal tissue compared to their dry and early-weaned counterparts. Early-weaning resulted in rapid recovery of blood eosinophils and total Ab. On day 13 post-lambing, titres of total Ab, IgG(1), IgM, IgA and IgE, and numbers of MMC and GL were greater than those measured in dry and suckled ewes. When fed the high quality diet, ewes had a higher dry matter (DM) intake, maternal weight, fat score, greater fat depth and eye muscle depth, birthed heavier lambs that had higher growth rates, and produced more milk. The physiological status of pregnancy resulted in a higher DM intake but lower measures of fat depth and eye muscle depth, and suckling led to an increase in DM intake but a reduction in body weight and fat score through mobilisation of fat and muscle reserves. Despite the marked effect of diet quality on production traits, some inconsistencies were observed between body composition and apparent parasite resistance, measured by WEC and worm counts, suggesting that the nutritional influence was not necessarily always mediated through chan

Topics: Animals; Antibodies, Helminth; Blood Cell Count; Body Composition; Body Weight; Diet; Feces; Female; Lactation; Leptin; Parasite Egg Count; Peripartum Period; Pregnancy; Random Allocation; Reproduction; Sheep; Sheep Diseases; Trichostrongylosis; Trichostrongylus

The hypothesis that increases in the concentration of the anorectic peptide leptin may be responsible for the immune-mediated reduction in feed intake (FI) during gastrointestinal parasitism in sheep was investigated. In a 2 x 2 x 2 factorial design, the first factor was age at the start of infection (5 months old v. 17 months old). The second factor was parasite infection (no infection v. administration of eighty L3 infective Trichostrongylus colubriformis larvae/kg live weight (LW) per d three times per week for 77 d). The third factor was immunosuppressive therapy with a corticosteroid (no therapy or weekly intramuscular injection of 40 mg methylprednisolone acetate/30 kg LW). Relative to their uninfected counterparts, a 20 % reduction in FI per unit LW (FI/LW; g DM/kg LW) was observed in infected non-suppressed 5-month-old lambs from 21 to 63 d post-infection (P < 0.001) but not in comparable17-month-old ewes or in corticosteroid-treated lambs or ewes (P>0.05 for all), allowing the suggestion that the anorexia was a consequence of the developing immune response. The reduction in FI/LW in 5-month-old lambs was not associated with an increase in plasma leptin concentration. Furthermore, plasma leptin concentrations were greater in corticosteroid-treated animals (P < 0.001) and in 17-month-old animals (P < 0.001), none of which displayed an infection-induced reduction in FI/LW. Plasma leptin was positively correlated with carcass fat percentage in both 5-month-old (P = 0.016) and 17-month-old (P < 0.001) animals and did not appear to provide a direct feedback mechanism that restricted energy intake. The results do not support the hypothesis that an increase in circulating leptin is directly responsible for the immune-mediated anorexia in lambs during T. colubriformis infection.

Topics: Adipose Tissue; Animals; Anorexia; Eating; Feces; Female; Glucocorticoids; Leptin; Parasite Egg Count; Sheep; Sheep Diseases; Trichostrongylosis