The effect of age on the response of Romney sheep to gastrointestinal nematodes during grazing.
Three groups of Romney sheep, reared worm-free in pens from birth until 4, 16 or 28 months of age, were permitted to graze nematode-infected pasture for 4 weeks after which they were returned to pens and slaughtered 4 weeks later. Three groups of three Romney sheep reared and maintained worm-free for similar periods served as uninfected control groups. Faecal egg counts (FECs) 8 weeks after grazing commenced were significantly greater in 4-month-old sheep than the 28-month-old animals. At slaughter, no difference in nematode burdens among these three age groups was found. Histological examination of the abomasal and small intestine mucosa, taken from sheep at slaughter, revealed significantly greater numbers of globule leukocytes/mucosal mast cells (GL/MMC) bur fewer connective tissue type mast cells (CTMC) in sheep aged 16 and 28 months than in those aged 4 months. The numbers of eosinophils in the gastrointestinal mucosal tissues of the three groups of infected sheep were not significantly different. In uninfected sheep the numbers of eosinophils, GL/MMC and CTMC in the mucosal tissues did not differ between the three age groups and the numbers of GL/MMC and CTMC were similar to those in 4-month-old infected sheep. Eosinophil numbers in the mucosal tissue of the infected groups were significantly higher than in the uninfected groups. In the infected groups, FECs but not worm burdens were significantly negatively correlated with GL/MMC numbers.(ABSTRACT TRUNCATED AT 250 WORDS)
Douch
P G
PG
Wallaceville Animal Research Centre, AgResearch, Upper Hutt, New Zealand.
Morum
P E
PE
D000018:Abomasum / Q000473:pathology; D000375:Aging / Q000276:immunology*; D000818:Animals; D005243:Feces / Q000469:parasitology; D005753:Gastric Mucosa / Q000473:pathology; D005767:Gastrointestinal Diseases / Q000662:veterinary*; D007113:Immunity, Innate; D007413:Intestinal Mucosa / Q000473:pathology; D007421:Intestine, Small / Q000473:pathology; D008415:Mastocytosis / Q000662:veterinary; D009349:Nematode Infections / Q000276:immunology*; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology*