Responses of pregnant ewes and young lambs to ovalbumin immunization, antiovalbumin antibody transfer to lambs, and temporal changes in antiovalbumin antibody(,)(2)

Factors affecting the decay of maternally derived IgG and ability of neonatal lambs to produce protective amounts of their own IgG are not well understood. Thus, we conducted 3 experiments to quantify the 1) response of pregnant ewes to ovalbumin immunization, 2) antiovalbumin antibody (OV-IgG) transfer to lambs, 3) changes over time in OV-IgG in lambs, and 4) response of young lambs to ovalbumin immunization. In Exp. 1, ewes (n = 10/group) either received control (adjuvant + saline) or ovalbumin (ovalbumin + adjuvant + saline) injections at ≈ 42 and 14 d prepartum. Ovalbumin increased (P < 0.001) ewe serum and colostrum OV-IgG. Serum OV-IgG was greater (P < 0.0001) in lambs from ovalbumin-treated than in lambs from control ewes. In Exp. 2, lambs (n = 20/group), which were from ewes that had received ovalbumin prepartum, were given either control or ovalbumin injections on d 1 and 15 of age. From d 1 to 15, maternally derived OV-IgG was less (P < 0.04) in ovalbumin-treated than in control lambs. After d 15, OV-IgG was greater (P < 0.001) in ovalbumin-treated than in control lambs. In Exp. 3, lambs (n = 20/group), which were from ewes naïve to ovalbumin, received 1 of 4 treatments: 1) d-1 + d-15 control injections; 2) d-1 + d-15 ovalbumin; 3) d-28 + d-42 control; and 4) d-28 + d-42 ovalbumin. In d-1 + d-15 ovalbumin lambs, OV-IgG increased (P < 0.001) from d 7 to 21 after treatment and then decreased (P < 0.004) after d 28. In d-28 + d-42 ovalbumin lambs, OV-IgG increased (P < 0.001) steadily until d 21 after treatment and then stabilized after d 21. At ≈ 159 d of age, lambs in each group received injections consistent with their original type. After the d-159 treatment, ovalbumin injection increased (P < 0.0001) OV-IgG, and the injection type × time interaction was significant (P < 0.0001). In d-28 + d-42 ovalbumin lambs, OV-IgG just before the d-159 injections was greater (P < 0.006) than that in the other groups. In this study, late pregnant ewes produced OV-IgG after ovalbumin injections and then transferred OV-IgG to lambs via colostrum. Ovalbumin treatment of young lambs reduced circulating maternally derived OV-IgG, but it also induced an immune response in the lambs. Overall, our results support recommendations to vaccinate ewes against common pathogens during late pregnancy and to ensure that lambs receive adequate colostrum soon after birth.