Antibody responses of grazing alpacas (Lama pacos) in New Zealand to intestinal nematodes.

Alpaca (Lama pacos) were grazed for 10 months (October 1992-June 1993) on pasture with sheep or on pasture which had been recently grazed by sheep. The alpaca, of various age groups, totalled 94 at the beginning of the experiment and during the course of the experiment 32 progeny (cria) were born, 10 in spring 1992 and 22 in autumn 1993. Serum levels of specific antibodies to excretory/secretory antigens of the third larval stage (L3) of Cooperia curticei, Ostertagia circumcincta or Trichostrongylus colubriformis and somatic antigens from adult T. colubriformis were determined at monthly intervals by ELISA. Faecal egg count and live-weight were determined monthly and fleece-weight was measured at shearing. Three days after the birth of the cria, serum antibody levels ranged from 0.46-0.85 optical density units for the L3 antigens and averaged 0.22 for the adult T. colubriformis antigen. These levels declined to 0.1-0.24 and 0.06 respectively by 2-3 months of age. Subsequently, antibody levels increased steadily to reach maximal adult levels at approximately 23-26 months. Antibody levels were negatively correlated with FEC, but positively correlated with live-weight at 7 months although at 15 months antibodies and live-weight were negatively correlated. A positive correlation was found between weight and FEC. Fleece-weight showed no correlation with antibody level, a positive correlation with weight and a negative correlation with FEC. The relationships among antibody responses, FEC, live-weight and fleece-weight observed for alpaca in this experiment suggest that antibody responses might provide a useful indicator of alpaca immuno-responsiveness and has potential for use as a parameter for selection of alpaca with reduced FEC.