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ARS Home » Research » Publications at this Location » Publication #71735
Title: RELATIONSHIP BETWEEN SCROTAL INFRARED TEMPERATURE PATTERNS AND NATURAL-MATING FERTILITY IN BEEF BULLS

Author
item LUNSTRA, DONALD
item COULTER, GLENN - LETHBRIDGE ALBERTA CANADA

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: In cattle, adequate thermoregulation of the testes is essential for sperm production and male fertility. While considerable variation in scrotal thermoregulatory efficiency exists among bulls producing semen of acceptable quality, the relationship between these thermoregulatory differences and bull fertility is unknown. To study this relationship, the einfrared temperature (IRT) pattern of the scrotal surface was recorded in 73 yearling beef bulls. Thirty bulls with acceptable testis size and semen quality were fertility tested by natural mating to females. Pregnancy rate was 15 to 17 percent lower for bulls with abnormal scrotal temperature patterns than for bulls with normal or questionable temperature patterns. In addition, pregnancy rate was negatively related to all three primary scrotal temperatures recorded; i.e. higher scrotal temperatures were reflected in lower pregnancy rates. Thus, bulls with abnormal scrotal temperature patterns produced spermatozoa that appeared to be normal, but these bulls exhibited a reduced ability to maintain an effective thermal gradient from top to bottom of the testes and achieved reduced pregnancy rates. Therefore, evaluation of scrotal temperature patterns shows promise as a tool for improving natural-mating fertility in beef bulls by identifying sires exhibiting impaired testicular thermoregulation and reduced fertility.

Technical Abstract: The infrared temperature (IRT) pattern of the scrotal surface, average scrotal surface temperature (STA), temperature at the top (STT) and bottom (STB) of the scrotum, scrotal temperature gradient (STG), and thermal class (TC = normal, questionable or abnormal scrotal surface thermal pattern) were recorded for 73 yearling beef bulls (14 mo of age). Among these bulls, 37 exhibited a normal temperature pattern (51%), 20 a questionable pattern (27%), and 16 an abnormal temperature pattern (22%). Bulls exhibiting abnormal scrotal temperature patterns had lower percentages of sperm exhibiting normal head (P=.03) and tail morphology (P=.03) than did bulls with normal or questionable thermogram patterns. Thirty of these 73 bulls were selected for natural mating and exposed single-sire to approximately 18 heifers/bull during a 45-d pasture breeding period. Based on testis size and semen quality, all bulls used for mating achieved a satisfactory score on the standard breeding soundness examination. Pregnancy rate was lower (P<.01) for bulls with abnormal scrotal temperature patterns (68+/-4%, n=8) than for bulls with normal (83+/-4%, n=13) and questionable temperature patterns (85+/- 4%, n=9), and pregnancy rate was related significantly to all four major characteristics (STA, SST, STB and STG) of scrotal thermograms. These data indicate that bulls with abnormal scrotal temperature patterns exhibit a reduced ability to maintain an effective thermal gradient from top to bottom of the testes and achieve reduced pregnancy rates when used for natural mating. Thus, IRT thermography of the scrotum shows promise in the beef bull as a tool for improving natural-mating fertility by identifying sires exhibiting impaired testicular thermoregulation and reduced fertility.