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The Norwegian College of Veterinary Medicine, Oslo
Abstract
In the selection of bulls for breeding purposes growth rate is an important characteristic. In this study 411 bulls, 5 to 11 mo of age were subjected to a human chorionic gonadotropin (hCG) stimulation test. Plasma testosterone 7 h postinjection of hCG was related to monthly weight gain in the month of blood sampling and to daily gain from 3 to 11 mo of age. The bulls were divided into two groups according to plasma testosterone concentrations; those with values above and those with values below the average for each age group. Overall ages (5 to 11 mo), the bulls in the high testosterone group had higher monthly (P>.001) and daily (P>.025) weight gain than those in the low testosterone group. However, when split into two groups according to age (5 to 7 and 8 to 11 mo), only the older animals showed the relationship described above. The results indicate that determination of plasma testosterone might supplement other criteria in the selection of breeding bulls for beef production. Eight to 11 mo of age, when differences between high and low levels of testosterone were greatest, would appear to be the most suitable period for sampling.
1 We would like to thank the staff at Oyer and Klepp bull testing stations for valuable help. We would also like to thank Dr. Karl Halse for his valuable help in the analyses of data. The expert technical assistance of laboratory engineer Randi Løes Skogstad is gratefully acknowledged. This investigation was financially supported by the Agricultural Research Council of Norway, Project No. 18.801.24.
2 Dept. of Physiol., P.O. Box 8146 Dep., Oslo 1, Norway.
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