Heterologous antibody-based immunity in cattle naturally infected with Ostertagia ostertagi and Haemonchus sp.

Heterologous antibody‑mediated immunity was evaluated in cattle naturally infected with Ostertagia ostertagi (Oo) and Haemonchus sp. (Hp). Antibody responses were assessed using ovalbumin (OVA) as unrelated model antigen in three groups of eight heifers, matched for eggs per gram of feces (EPG) and allocated to independent, nematode‑free pastures. Anti‑OVA titers were determined in serum by ELISA. EPG counts and nematode genera were determined in feces using the modified McMaster technique and pooled cultures, respectively. All variables were analyzed using mixed models. One group was previously dewormed and considered the control (C) group. A second group was designated HO (90.4% Hp and 7.8% Oo). A third group was designated OH (19.6% Oo and 78.8% Hp). EPGs were absent in the C group, and no EPG differences were observed between the parasitized groups throughout the study. The OH group exhibited a lower anti‑OVA titer peak compared with the C (p = 0.015) and HO (p = 0.024) groups. Moderate prevalences of Oo may reduce heterologous antibody peaks without affecting the overall curve, whereas high prevalences of Hp may not alter heterologous antibody-based responses in cattle.