Abstract: 【Objective】 This study aimed to maintain semen quality and insemination capacity, which were impaired in boars adversely affected by summer heat stress, by immunization against inhibin (IHN) and follistatin (FST). 【Method】 Twenty-one boars, which exhibited semen quality problems of decreased sperm motility in summer months, were selected and equally divided into 3 groups (n=6). Immunization procedures consisted of a primary injection (i.m.) of 2 mg recombinant IHN? α-subunit protein in 2 ml mineral oil adjuvant, and two booster immunizations with 1 mg IHN protein at 21-d intervals for Group A boars. Group B boars were similarly immunized as in Group A boars, but apart from IHN immunogen, also immunized against equal amount of FST protein on each occasion. Group C served as controls that received mineral oil adjuvant on the same occasions. In the 9-wk experimental period, blood samples were collected for measurements of antibody titres, plasma concentrations of FSH and testosterone. Semen was collected every week and examined for sperm motility and density. 【Result】 Immunization against IHN and FST significantly elevated plasma anti-IHN and anti-FST antibody titres, increased FSH and testosterone concentrations, maintained semen sperm motility and sperm density, which in the control boars decreased progressively during the experiment. 【Conclusion】Immunization against IHN and FST was capable of overcoming the adverse impact of heat stress, thus to increase FSH and testosterone secretions, and to maintain boar semen motility, density and reproductivity in hot summer months.

Key words: inhibin &alpha, subunit , follistatin , immunization , boar , hormones , semen quality