Summary Postpartum stress and the resumption of pituitary and ovarian functions were investigated in 29 dairy cows during the first month after calving. Adrenocorticotropic hormone (ACTH, 25 i.u., IM) challenge tests for adrenal function at 8 and 22 days postpartum and gonadotropin releasing hormone (GnRH, 50 μg, IM) challenge tests for pituitary function at 7 and 21 days postpartum were conducted. Ovarian function, particularly the interval to first ovulation, was evaluated through weekly rectal palpation and ultrasonographic examination, as well as thrice weekly milk progesterone levels. Elevated basal Cortisol levels were found in 24.1% and 20.7% of cows at 8 and 22 days postpartum, respectively. Adrenal response to ACTH was similar at 8 and 22 days postpartum with low, medium and high peak responses in 13.8%, 62.1% and 24.1% of cows, respectively. A moderate correlation was observed between basal and peak Cortisol levels. Peak pituitary luteinizing hormone (LH) response was low in 65.5%, medium in 27.6% and high in 6.9% of cows at 7 days postpartum. Pituitary responsiveness improved by day 21 with low in 34.5%, medium in 37.9% and high in 27.6% of cows. About a week after calving, a negative correlation between peak Cortisol and peak LH levels was observed. First ovulation occurred in 28%, 48% and 17% of postpartum cows during the second, third and fourth week, respectively. These results indicate a negative effect of peak Cortisol levels on pituitary responsiveness to GnRH stimulation during the first week, altered adrenal and pituitary function in a third of the cows until the third week and restoration of ovarian function in most cows (93%) a month after parturition.
ACTH challenge tests for the assessment of stress on the first and third week postpartum and bacteriologic examination of uterine swabs on the second and fourth week, were conducted in dairy cows following clinically normal (n=12) and abnormal (n=21) puerperium. Postpartum ovarian activity and uterine involution were also investigated. The basal plasma cortisol concentrations (mean ± S.E.) during the first and third week postpartum were 3.1 ± 0.9 ng/ml and 3.4 ± 1.1 ng/ml in normal cows, and 6.5 ± 1.9 ng/ml and 4.9 ± 1.2 ng/ml in abnormal cows, respectively. The mean basal plasma cortisol values of abnormal cows were elevated and significantly higher (P<0.05) during the first week postpartum. Bacterial organisms were isolated from the uterus of 33.3% of normal and 61.9% of abnormal cows during the second week postpartum and in 33.3% of normal and 23.8% of abnormal cows during the fourth week. Resumption of ovarian activity was neither affected by puerperal disorders nor uterine bacterial infection. Uterine involution at 4 weeks postpartum was completed in all cows with normal puerperium and delayed in 23.8% of abnormal cows. The results indicate that cows with abnormal puerperium had significantly higher basal cortisol levels, and had higher occurrence of uterine bacterial infection during the second week when compared with normal cows.
Effects of body condition at parturition, purperal complications, milk yield and parity on the sequential changes in postpartum adrenocortical and pituitary functions , ovarian activity and uterine involution were investigated in 44 high-producing Holstein Friesian cows. One half of the cows had normal adrenocortical function and the other half had either enhanced or depressed adrenocortical function 8 days postpartum. The adrenocortical function was found to be normal in all cows 22 days after calving. Pituitary gland response to GnRH was low in 68.2 % of cows 7 days after parturition and 31.8 % still had low response 21 days postpartum. A significant negative correlation (P<0.05) was observed between basal and ACTH-stimulated plasma cortisol levels and GnRH-stimulated plasma luteinizing-hormone levels 7 to 8 days after calving. Multifactorial analysis of variance showed that postpartum adrenocortical function was enhanced by poor body condition at calving, high milk yield, and increased parity. In association with enhanced adrenocortical function, pituitary function tended to be depressed 7 days postpartum in cases of poor body condition, high milk yield and increased parity. Among all the various factors examined, milk yield had the most significant effect on postpartum adrenocortical and pituitary functions. Uterine involution tended to be delayed in cows with poor body condition at calving, high milk yield and increased parity. It may be concluded that undernutrition, high milk yield and increased parity are predominant factors causing enhancement of adrenocortical function which is associated with depression of pituitary function.
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