APPLICATION OF GNRH-TEST IN CANDIDATES OF BEEF-TYPE BREEDING BULLS

Reproductive biological state of 12 to 14 month old Hungarian red-spot ted (n = 17) and limousine (n = 5) genotype beef-breed breeding bulls, under farm progeny test (OPT), as well as Hungarian red-spotted (n = 24), charolais (n = 8) and hereford (n = 6) genotype beef-breed breedi ng bulls, under central OPT, was evaluated on the basis of their testi s circumference and results of their testosterone response to exogenic GnRH-treatment. Circumference of the testis of bulls was measured acc ording to the proposals of Taylor (1984), as well as Bourdon and Brink s (1986). The GnRH-treatment was carried out by the im. application of 100 mug Ovurelin (Reanal, Budapest). Testosterone content of blood se rum was determined by I-125 radioimmuno-assay before and 120 min after GnRH-treatment. The following conclusions have been reached: High var iance in the testosterone content of blood serum before GnRH-treatment - except for the hereford genotype - indicated significant individual differences (Table 1). Close positive correlation was found between t he testosterone level and value of the change of testosterone level in the blood serum following GnRH-treatment (n = 85, r = 0.7, P < 0.001, Table 2). Based on these findings, the GnRH-test can be simplified (t he blood collection before treatment could be neglected). The testoste rone response following GnRH-treatment, the circumference of testis, t estosterone values measured following GnRH-treatment could be predicte d in different extents (R2 = 0.3-0.9) and with varying statistical rel iability with knowledge of the age and body-mass in the investigated p opulations (Tables 3 and 4). However, definite stand-point can only be formed for that after investigations carried out in hundreds of indiv iduals in different populations of a breed.