Contents This article reviews some of the recent advances in veterinary research regarding the causes, prevalence and clinical forms of pathological anoestrus in dairy cows. It is one of the few components responsible for occurrence of postpartum infertility in cattle, expressed in four clinical forms: silent heat, cystic ovarian disease, ovarian afunction and corpus luteum pseudograviditatis. The prevalence of these four forms in different herds is dependent on the managerial, environmental and nutritional status of the farm. Anything, regardless of its nature, that impedes the physiological mechanism involved in oestrus expression is liable to cause anoestrus. Nutrition (energy deficiency), interacted with other factors, is the major cause of this phenomenon (anoestrus). It has direct control of the postpartum anoestrus by negatively affecting the endocrine pathways responsible for proper functioning of the reproductive system through the blockage of pulsatile release of gonadotropin‐releasing hormone in the hypothalamus. Lack of proper training by the stockman substantially contributes to silent heat occurrence. Numerous attempts have been made to prevent or treat pathological anoestrus with exogenous hormones, or nonhormonal remedies like uterine palpation and infusion of Lugol's solution, all of which have produced variable but positive results. Specific treatment for each one of the four clinical forms is briefly outlined.

The investigations were carried out on a total of 70 cows with puerperal endometritis. In addition to intrauterine antibiotic treatment, 30 experimental animals were administered 20 microg GnRH analogue, buserelin, between days 10 and 12 post-partum followed by 500 microg PGF2alpha analogue, cloprostenol, 10 days later. Forty control cows were treated only with intrauterine antibiotics. Blood samples for progesterone determination were collected from the tail vein twice weekly until day 70 post-partum. The first rise in progesterone level above 3.18 nmol/l occurred significantly earlier in the experimental than in control cows (21.6 +/- 9.2 versus 27.8 +/- 12.3 days; p < or = 0.05). The duration of the first cycle post-partum was 15.0 +/- 4.3 days in experimental and 19.7 +/- 7.3 days in control animals (p < or = 0.05). However, no significant differences were observed in the occurrence of first oestrus post-partum. The involution of the uterus was improved after hormone treatment. At day 42 post-partum, completion of uterine involution was found in 93.3% of hormone-treated cows and in 82.5% of those treated with antibiotic only (p < or = 0.05). Clinical recovery was 96.6% in the experimental and 82.5% in the control group (p < or = 0.05). First service pregnancy rate was significantly better in hormone-treated than control cows (51.7 versus 36.4%; p < or = 0.05). Total pregnancy rate and insemination index values were not significantly improved following GnRH and PGF2alpha treatment. The average service period was 89.8 +/- 21.2 days in cows after hormone treatment, and 112.6 +/- 24.5 days in control cows. The difference was statistically significant (p < or = 0.05). These results indicate, that the sequential GnRH and PGF2alpha application in cows with puerperal endometritis positively affected ovarian function and uterine involution, resulting in improved fertility performance.

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Contents Concentration of estradiol‐17β in the milk and tail vein were determined by radio‐immunoassay in 40 dairy cows from day 20 prepartum to day 4 postpartum. The animals were divided into two groups according to their milk production in the previous lactation: group 1 (n = 20)‐high‐yielding cows (6500 kg milk per lactation), group 2 (n = 20) low yielding cows (3700 kg milk per lactation). The levels of estradiol‐17β were higher (p 0.01) in the milk vein than in the tail vein from about day 12 prepartum to parturition. In comparison with low‐yielding cows the high‐yielding cows had significantly higher (p 0.01) estradiol‐17β values in the mammary venous plasma, but not in peripheral plasma. In an in vitro experiment, homogenates of bovine mammary tissue collected on day 7 prepartum from two cows were incubated with 3H‐androstendione. After incubation the samples were extracted and 3H‐estradiol‐17β was separated by high‐performance liquid chromatography. Radioactivity of fractions containing 3H‐estradiol‐17β was determined and calculated as a percentage of total radioactivity. Androstendione was metabolized into estradiol‐17β to the extent of 37%. These results indicate that the mammary secretion of estradiol‐17β starts about day 12 prepartum and is associated with milk yield. Furthermore, the results of a preliminary in vitro study with a limited number of animals suggest that the bovine mammary tissue is able to synthesize estradiol‐17β near term.

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