THE EFFECT OF AGE AND METHOD OF CASTRATION ON PLASMA-CORTISOL IN BEEF-CALVES

Plasma cortisol concentration (PCC) was measured at 0, 2 min, 3, 6, 12, 24 and 30 h in 36 calves castrated at 78 +/- 12 d of age or 167 +/- 14 d of age by either surgical or burdizzo methods or left as bulls (control). At 2 min, bull calves had greater (P < 0.05) PCC (22.2 +/- 4.5-mu-g L-1) than burdizzo castrates (10.4 +/- 3.0-mu-g L-1) while surgical castrates were intermediate and not different (P > 0.05) from either group (11.4 +/- 2.9-mu-g L-1). There were no further differences between groups until the 30 h postcastration bleed when PCC for bull calves (22.1 +/- 6.0-mu-g L-1) was greater (P < 0.05) than surgical (7.4 +/- 2.3-mu-g L-1) and burdizzo (9.5 +/- 2.4-mu-g L-1) castrates. At late castration, there was an immediate rise in PCC 2 min postcastration for burdizzo castrates (32.0 +/- 3.1-mu-g L-1) which was greater (P < 0.05) than surgical castrates (18.6 +/- 4.1-mu-g L-1), while bull calves (23.0 +/- 1.9-mu-g L-1) were intermediate and not different from either castration group. At 3 h, PCC of surgical (44.4 +/- 4.2-mu-g L-1) and burdizzo (38.6 +/- 8.3-mu-g L-1) castrates was greater (P < 0.05) than bull calves (24.1 +/- 8.5-mu-g L-1). At 6 h, surgical castrates had a greater (P < 0.05) PCC (27.5 +/- 5.4-mu-g L-1) than burdizzo castrates (15.3 +/- 0.41-mu-g L-1) but neither group was different (P > 0.05) from bull calves (17.2 +/- 2.7-mu-g L-1). There were no further differences between groups up to 30 h postcastration. It was concluded that castration at a young age caused no physiologically detectable stress while physiological stress was detectable in older calves but that, in older calves, burdizzo was less stressful than surgical castration. Average daily weight gain did not differ (P > 0.05) between castrated and bull calves.