Effects of handling, shearing and previous exposure to shearing on cortisol and β-endorphin responses in ewes

The objectives of the study were to compare the effects of handling and shearing on plasma cortisol and β-endorphin levels of ewes and to determine if adaptation to annual shearing occurred. Plasma cortisol and β-endorphin concentrations were determined during either handling only or handling plus shearing in 12 ewes previously exposed to annual shearing (1–4 times) and in 12 naïve ewes. The handling process consisted of four steps: 1) moving ewes from their quarters into the shearing room; 2) moving them in groups of four into a holding pen; 3) moving them in pairs to a shearing platform where they were up-ended and restrained as in shearing; and 4) moving them into another holding pen in the shearing room. Half of the ewes were sheared during step 3 of the handling process. Handling and shearing elevated (P < 0.0001) plasma cortisol and β-endorphin concentrations, but the responses to the handling process and to the handling plus shearing process were similar (P > 0.1). Moving the ewes from their quarters to the shearing platform resulted in significantly higher plasma cortisol, which remained elevated for 60 min. Plasma β-endorphin was only transiently elevated after shearing was completed. Previous exposure to shearing enhanced the cortisol (P < 0.001) and β-endorphin (P < 0.05) responses to handling and shearing. Both responses were significantly greater and longer in the ewes sheared previously. The results indicate that the stress response to handling was equivalent to that of handling plus shearing, and that the stress response was much greater in ewes previously exposed to annual shearing. Key words: Cortisol, β-endorphin, negative adaptation, shearing, stress, ewes

THE EFFECT OF ASSISTANCE AT CALVING, INJECTIONS OF RECOMBINANT BOVINE SOMATOTROPIN AND JUGULAR CATHETERIZATION ON SERUM CORTISOL AND ITS INFLUENCE ON THE GnRH-INDUCED LH RESPONSE IN POSTPARTUM DAIRY COWS

Serum cortisol levels were determined in 18 cows administered 25 mg d−1 of recombinant bovine somatotropin or a placebo following jugular vein catheterization on day 14 postpartum. Cows that received assistance at calving had lower (P < 0.01) serum cortisol concentration postpartum. Restraint and catheterization caused an elevation (P < 0.1) of cortisol levels. Treatment with rbST did not effect postpartum cortisol levels. LH response to exogenous GnRH was not affected by the postpartum Cortisol level. Key words: Cortisol, somatotropin, ganadotropin-releasing hormone, luteinizing hormone, dairy cow, stress

EFFECT OF STAGE OF LACTATION AND OF DAILY INJECTIONS OF GRF AND TRF ON SERUM CORTISOL IN LACTATING SOWS

Two experiments were conducted with 51 primiparous sows to determine the effects of stage of lactation and treatment with growth hormone-releasing factor (GRF) and thyrotropin-releasing factor (TRF) on serum cortisol concentrations and pulse profiles. Animals were injected with either saline, GRF (20 μg kg−1 in both experiments), TRF (1 μg kg−1 and 9 μg kg−1 in exps. 1 and 2, respectively) or GRF-TRF (administered in combination at the levels mentioned above). Peptides were given subcutaneously twice daily between days 5 and 25 postpartum. In exp. 1, mean cortisol levels were higher on day 5 than on subsequent sampling days due to higher peak amplitudes. This result is discussed with respect to stress. Mean serum cortisol concentrations did not vary significantly between days 5, 15 and 25 of lactation in exp. 2. No evidence of a morning peak and late afternoon low was observed in cortisol secretion of sows during lactation. Finally, none of the hypothalamic factor treatments altered the basal serum concentrations or the peak amplitudes of cortisol. However, in exp. 2, the frequency of cortisol peaks was lower for the GRF- and TRF-treated sows than for the control and GRF-TRF sows. Key words: Cortisol, GRF, TRF, lactation, sows

GLUCOCORTICOID STATUS AND GROWTH MANIPULATION IN SHEEP

Concentrations of plasma total and plasma free cortisol and the extent of bonding of cortisol in the cytosol of skeletal muscle in sheep implanted with trenbolone, zeranol or receiving a restricted dietary intake were studied. No correlation between glucocorticoid status and growth was observed, although cytosolic binding was reduced with trenbolone treatment. Key words: Cortisol, muscle receptors, sheep, anabolics, growth