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Serum anti-Ostertagia ostertagi and anti-Cooperia oncophora antibody responses were assessed in first season and second season calves grazing permanent paddocks. Calves without previous exposure to trichostrongyles were found to mount significant parasite-specific IgG1 antibody responses within two months of introduction to the pastures. A significant serum IgA response to O ostertagi and IgG2 responses to both O ostertagi and C oncophora antigens were also observed, but these responses were weaker. No consistent serum anti-trichostrongyle IgM responses were discernible in either age group. Second season grazing calves had significantly elevated IgG1, IgG2 and IgA antibody levels at turnout when compared to first season calves, but only IgA antibody levels against O ostertagi increased during the second grazing season. Comparison of serum antibody levels in first and second season calves grazed separately or together suggests that mixed grazing had no discernible effect on antigen priming.

An amplified capture enzyme-linked immunosorbent assay (ELISA) has been developed by the use of the biotin-avidin detection system, for the measurement of canine plasma immunoglobulins (Ig) A, G and M. Test responses of dilutions of both the Ig standards and test plasma samples were consistently linear (r >0·987) for the three Ig classes. The within-assay variation was 3·53 per cent IgG, 5·84 per cent for IgM and 6·34 per cent for IgA. The analytical recoveries were 95 per cent for IgA, 97 per cent for IgG and 98 per cent for IgM. The lower detection limits of the assay were 38·4 ng ml −1 for IgG, 20·3 ng ml −1 for IgM and 41·2 ng ml −1 for IgA. The results indicate that this ELISA has a much higher sensitivity than the single radial immunodiffusion assay or the non-amplified ELISA for measurements of canine Igs, but has a comparable specificity and precision.

Pregnant non-lactating cows were immunised by intramammary infusion with killed Streptococcus uberis into one quarter and ovalbumin into another, at one week (group 2) or one week and two weeks (group 1) before the expected date of parturition. A small IgG1 and IgG2 antibody response to ovalbumin was detected in the serum of these cows. There was also a small increase in IgG1 and IgA serum antibody activity to S uberis. In whey the response was restricted to IgA with activity to S uberis. The IgA antibody response to S uberis in group 1 was significantly greater in the quarter immunised with bacteria than that of the control quarters for up to two months after calving. In contrast, the serum IgA response was short or absent in a number of animals.

The normal level of serum IgA in Western Australian dogs was defined by single radial immunodiffusion using sera from 100 healthy randomly selected adult crossbred animals. Serum IgA values of 185 animals from six breeds were also determined. The mean and variance of serum IgA of these groups were similar to the crossbred dogs with the exception of German shepherd dogs where these values were statistically greater. In addition, 210 dogs with a range of chronic diseases (autoimmune, hypersensitivity, pyoderma, neoplasia, demodecosis, disseminated aspergillosis) were assayed and low values recorded in five cases. In all disease groups the mean serum IgA value was significantly greater than in the crossbred group and the variance significantly greater in most of these groups. The German shepherd group were the only normal dogs with a mean and variance similar to those of the clinical series suggesting that this breed may have a primary defect in IgA metabolism.

IgA immunoglobulin levels were measured in the sera of 29 pigs from birth to maturity and in their dams. Adult levels were reached by 18-21 weeks of age. The serum IgA concentration at 6 weeks of age was double that of the concentration at 3 weeks and it appears that the IgA synthesis in young colostrum-fed pigs already has reached a significant level by 6 weeks of age. IgA immunoglobulin levels were estimated in porcine mammary secretions during the first 35 days of lactation and in secretions of individual mammary glands of vaccinated and non-vaccinated sows during the first 7 days of lactation. It appears that a 3-week-old pig receives 1.6 g of IgA per day via the milk of the dam and that IgA quantitatively is a major immunoglobulin in sows’ milk. There are significant differences in the IgA concentrations in secretions from individual glands of a SOW and in the IgA concentrations from different SOWS. Intramammary vaccination with an E. coli vaccine had no apparent influence on the quantity of IgA in secretions from the vaccinated gland when compared to the concentrations in non-vaccinated glands from the same sow or to the concentration in secretions from non-vaccinated sows. The significance of mammary secretion IgA in relation to enteric diseases in suckling pigs is discussed.

Serum immunoglobulin concentrations in clinically healthy German shepherd dogs were compared with those in mongrel dogs and Irish setters. Serum IgA concentrations were significantly lower in the German shepherd dogs than in the other two groups, while there were no differences in the concentrations of IgM or IgG. These findings suggest that production of IgA by gut associated lymphoid tissue may be abnormally low in the German shepherd dog.