Summary Seven mature boars and 8 peripubertal boars were used to study the effects of elevated testicular temperature. The scrotum of the boars was covered by a textile‐aluminium foil insulation device for 100 hours. Insulation of the scrotum in the peripubertal boars took place at an age of 100 days. Pronounced changes in sperm characteristics, e.g. decreased sperm motility and high numbers of proximal cytoplasmic droplets, abnormal sperm head shapes and abnormal acrosomes, were seen during week 3 to 5 after scrotal insulation in the mature boars. An “immature” semen picture, i. e. low sperm motility, low total sperm count and high numbers of proximal cytoplasmic droplets and abnormal sperm head shapes, was seen in the first ejaculates in the peripubertal experimental boars. The semen picture was normal in the control boars. A maturation of the semen picture over time was seen in the experimental boars. However, remaining abnormalities in the sperm morphology together with the testicular histology indicate lasting pathological changes in the testes. Zusammenfassung Experimentell induzierte Hodenveränderungen beim Eber Morphologische Veränderungen bei adulten und peripubertären Ebern An 7 adulten und 8 peripubertären Ebern wurden Effekte einer erhöhten Hodentemperatur untersucht. Dabei wurde das Skrotum der Eber 100 Stunden lang mit einer Stoff‐ und Aluminiumfolie bedeckt. Diese Isolierung des Skrotums wurde bei den peripubertären Ebern im Alter von 100 Tagen vorgenommen. 3–5 Wochen nach der Skrotum‐Isolierung wurden bei den adulten Ebern ausgeprägte Veränderungen in den Spermien‐Merkmalen, wie z. B. verringerte Motilität, niedrige Gesamt‐Spermien‐Zahl sowie zahlreiche proximale Cytoplasmatropfen und abnorme Spermienköpfe beobachtet. Ein “unreifes” Bild der Spermien, wie z. B. geringe Motilität, niedrige Gesamt‐Spermien‐Zahl sowie zahlreiche proximale Cytoplasma‐Tropfen und abnorme Spermienköpfe ergab sich für die ersten Ejakulate der peripubertalen Versuchseber. Bei den Kontrollebern war das Spermienbild normal. Eine Verbesserung des Spermienbildes wurde bei den Versuchsebern in Abhängigkeit von der Zeit beobachtet. Jedoch deuten bleibende morphologische Abnormitäten der Spermien zusammen mit histologischen Befunden an den Hoden auf bleibende pathologische Veränderungen in den Hoden hin.

Summary The aim of this study was to investigate the effect of gonadotrophin‐releasing hormone (GnRH) immunisation on mature stallions that had been used for breeding. Four Standardbred stallions were used in the study: 3 experimental animals and 1 control animal. Semen was collected regularly, i.e. twice/week, during the 4 months prior to the experimental period. The stallions were immunised against GnRH with a GnRH‐BSA conjugate. Equimune was used as the adjuvant. The stallions were immunised on 5 occasions, 4 at 2 week intervals, and the fifth 4 weeks after the fourth. Blood samples were taken once a week for analysis of GnRH antibody titre and every third week for testosterone and oestrone sulphate analyses. Semen was collected once a week, and libido and sexual behaviour were observed. Ejaculate volume, sperm concentration, total number of sperm in the ejaculate, sperm motility and sperm morphology were evaluated. Testicular size was measured once a week. At the end of the study, the stallions were castrated, and a histological examination of the testes performed. All immunised stallions produced antibodies against GnRH, and plasma testosterone concentration decreased. However, the effect of immunisation varied between stallions. In 2 of the stallions, high levels of antibodies were found, while in the third, the level was moderate. Four weeks after the first immunisation, a decrease in libido was observed. Two months after the first immunisation, marked changes in semen quality were observed in the 2 stallions with high antibody titres. Fourteen weeks after the first immunisation, the total number of sperm/ejaculate had decreased from >8.6×109 to<2.7×109, sperm motility from >59 to<10% and the frequency of morphological normal spermatozoa had decreased from >60 to<14%. The dominating abnormalities were abnormal head shapes, proximal cytoplasmic droplets and detached heads. In the third stallion, only slight changes in semen quality were found. No changes were observed in the control stallion. Decreases in testicular size were noted in all of the experimental stallions. Pronounced histological alterations in the testes were observed in 2 of the stallions. It is concluded that the vaccine was effective in stimulating production of GnRH antibodies and in suppressing testicular function and androgen secretion. However, there was an individual variation in the responses among the stallions and, further, libido was not totally suppressed.

The aim of the present study was to investigate the effect of active immunization against GnRH in mature Standardbred mares (three experimental and one control mare) on antibody titres, ovarian function, hormonal levels and oestrous behaviour. The mares were individually teased with a stallion once each day. During the first part of the experiment (period I: late April until November), blood was sampled every third day during the first 3 months, thereafter once per week. In the second part of the experiment (period II: December until August), sampling was carried out every second week. Progesterone, oestradiol-17beta and LH were analysed. Rectal gynaecological examination was made with the same intervals as the blood samplings and included palpation of the genital organs and ultrasonography. The experimental mares were immunized against GnRH with a GnRH-BSA conjugate. Equimune (Vetrepharm, Bracetown, Business Park, Clonee, Co. Meath, Republic of Ireland) was used as adjuvant. The mares were immunized on four occasions (20-30 day intervals) and GnRH antibody titre was determined. All immunized mares produced antibodies against GnRH but the maximum titres as well as the duration of a greater than 10% binding capacity varied between the mares (1 : 1600 to 1 : 50 000; 5 to 12 months, respectively). After the first injection, all mares showed one oestrus and ovulated at the regular time. In two of the mares, the immunization resulted in ovarian atrophy. Their hormone levels of progesterone, oestradiol- 17beta and progesterone decreased to basal levels and the cyclical hormone pattern was interrupted from approximately 30 days onwards. They continued to show oestrous signs but with irregular durations and intervals. The third mare showed ovarian suppression only for short periods and not in both ovaries at the same time; the hormone levels were basal for only about 20 days (days 50-70) and the mare ovulated on day 75 after start of immunization. The other mares ovulated after 13.5 and 15 months, respectively. It is concluded that the effect of immunization against GnRH in mature mares was individual concerning antibody titre response and the suppression of ovarian activity and hormone levels. Mares with totally inactive ovaries continued to show oestrous signs but with irregular intervals and durations.

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