This study compared: (1) Freund's complete adjuvant and CpG oligodeoxynucleotide (ODN) 2006 in water-in-oil emulsion as adjuvants; and (2) increasing doses of a recombinant ovalbumin-LHRH (ova-LHRH) fusion protein as an antigen for a contraceptive vaccine. Treatment groups (n = 8 heifers/group) were: one untreated control group; five groups receiving CpG ODN with different doses of ova-LHRH (1.5; 2.3; 3.4; 5.1; and 7.6 mg); and one group receiving 3.4 mg ova-LHRH in Freund's. Heifers were immunized at weeks 0 and 14. Ail vaccine treatments caused gonadal regression and estrus suppression. CpG ODN is a suitable replacement for Freund's for LHRH immunization. (c) 2007 Elsevier Ltd. All rights reserved.