The immune system during the periparturient period is impaired. At this time the most important factor causing immune-suppression in highly productive cows is metabolic stress resulting from hormonal and metabolic fluctuations, a negative energy balance, shortage of proteins, minerals and vitamins which are required to meet the demands of the fetus as well as the onset of lactation. This stress can activate the hypothalamic-pituitary-adrenocortical axis (HPA), which results in increase plasma corticosteroids. As a result, the cortisol concentration during the periparturient period increases by several folds particularly on the day of calving. Cortisol is a powerful immune-suppressive agent. During stress, this hormone causes depression of the leukocyte proliferation and their functions. Decreased phagocytosis of neutrophils, decreased cytotoxic ability of lymphocytes, as well as depressed activity of their cytokines, make it impossible for the normal, efficient maternal immune recognition and rejection of fetal membranes (as a foreign, allogeneic tissue expressed fetal antigens—MHC class I proteins by trophoblast cells) and finally results in their retention in cows. The metabolic periparturient stress also activates production of catecholamines, especially adrenalin. Adrenalin activates adrenoreceptors of the myometrium and then causes hypotony or atony of the uterus. Thus, cortisol and adrenalin inhibit rejection and expulsion of fetal membranes and cause their retention. These mechanisms of retained placenta (RP) often have a metabolic etiology and occur in herds, where important infectious diseases causing placentitis are absent or prevented. The aim of this article is to show the fundamental mechanisms occurring during periparturient stress and the accompanied immune-suppression in cows, as well as their consequences in relation to RP. The paper also gives examples of the symptomatic prevention of RP in cows caused by metabolic and immune suppressive factors. The prevention of RP was carried out using drugs which inhibit the activity of cortisol or adrenalin in dairy cows during calving.

The time around calving in highly productive dairy cows is a critical period in terms of their metabolism, which is connected with high demands of the foetus as well as with the onset of lactation. Retained placenta in cows may have multifactorial aetiology, but in herds which are free from infectious diseases, the most important reasons are; periparturient metabolic changes and disturbances to the internal balance and stress. During the periparturient period, the most important factor causing immune suppression and hypotony of uterus in cows is metabolic stress due to hormonal and nutritional factors, including metabolic fluctuations, negative energy balance, as well as shortage of proteins, minerals, vitamins and antioxidants. This metabolic stress as a result of an imbalance in the internal metabolic homeostasis activates the hypothalamic-pituitary-adrenocortical axis (HPA) and increases serum corticosterid (cortisol) concentration, especially on the day of calving. Cortisol is a powerful immune suppressive factor that causes depression of leukocyte proliferation and their functions. The periparturient metabolic stress may also stimulate the production of catecholamines, especially adrenalin. Elevated levels of adrenalin activate adrenoreceptors of the myometrium, which in turn cause hypotony or atony of the uterus at calving in cows. Elevated levels of cortisol and adrenalin may significantly inhibit the rejection and expulsion of foetal membranes in cows, resulting in an increased incidence of their retention. These important mechanisms for placental retention in highly productive dairy cows often have primary nutritional metabolic aetiology, but they also occur during secondary metabolic disturbances and metabolic stress during calving. This metabolic and immunological aetiology and pathogenesis of retained placenta usually occur in highly productive periparturient cows on dairy farms in the absence of bovine infectious diseases, which can couse placentitis, stillbirth and the infectious origin of foetal membrane retention. The paper presents the most important metabolic, mineral and immunological disturbances as conditions for retained placenta in dairy cows. It also shows different methods of herd monitoring, important examples of clinical and laboratory diagnostics, and methods of nutritional and veterinary prevention of this health problem in dairy cows.

BackgroundThere is some controversy about the extent of changes in different sperm cell features in stored boar semen, especially regarding the potential role of the DNA fragmentation assay for assessment of sperm fertilizing ability. The aim of this study was to assess the effect of time of storage and the dynamic changes in sperm cell characteristics in normospermic boar semen stored in long-term extender, in order to determine the susceptibility to damage of particular structures of spermatozoa during cooling and storage at 17 °C for 240 h post collection. The study included five ejaculates from each of seven boars of the Polish Large White breed (n = 35 ejaculates). The sperm characteristics were assessed using a flow cytometer and a computer assisted sperm analyzer on samples at 0, 48, 96, 168 and 240 h post collection.ResultsThe sperm chromatin structure assay (SCSA) showed a significant abrupt increase (P < 0.01) in the DNA fragmentation index (%DFI) after 48 h of semen storage with only subtle changes thereafter, not exceeding 5% on average after 240 h of storage. The use of a combination of SYBR-14/PI stains did not reveal any significant changes in the percentage of live sperm cells up to 168 h of semen storage. A significant (P < 0.01) decrease in the percentage of live spermatozoa with intact acrosomes was observed after prolonged semen storage (168 h). A significant and progressive decrease in sperm motility was recorded during the whole period of semen storage.ConclusionsStorage of boar semen extended in long-term diluent at 17 °C for 48 h initially induced a decrease in the integrity of sperm DNA. This suggests that the structure of boar sperm DNA is susceptible to damage, especially during semen extension and at the beginning of sperm storage. These findings support the opinion that the SCSA test has only a low potential for routine assessment of boar semen preserved in the liquid state and for assessment of sperm quality changes during 10 days of semen preservation. Remarkably, the integrity of acrosomes and plasma membranes remained nearly unchanged for 7 days.

The knowledge of the existing levels and the interrelationships between various blood and milk parameters is very useful for the analysis and monitoring of homeostasis high-yielding dairy cows. The aim of the study was to evaluate these values and correlations for selected blood markers of liver function aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), bilirubin, albumin, glucose, cholesterol) and selected milk parameters: somatic cell count (SCC), colony-forming units (CFU), fat, protein, lactose, dry matter (DM), fat-free dry matter (FDM), and milk production in cows during late lactation period. At the same time blood and milk samples were collected from 11 clinically healthy milking cows in later lactation period. The 11 selected cows were examined once a day for 3 days resulting in 33 sets of blood and milk samples for laboratory and statistical analysis. Significant positive correlations were observed between: ALT and albumin, ALT and cholesterol, GGT and glucose, albumin and cholesterol, CFU and fat, CFU and DM, SCC and protein, fat and DM, protein and FDM, lactose and FDM, GPT and FDM, albumin and protein, albumin and FDM, glucose and fat, as well as significant negative correlations between: AST and ALT, AST and GGT, AST and albumin, CFU and lactose, fat and lactose, fat and FDM, lactose and DM, DM and FDM, AST and SCC, AST and protein, AST and FDM, ALT and fat, ALT and DM, glucose and DM, cholesterol and CFU. The results obtained may be important for detecting of different biochemical pathways and helpful in estimating, predicting or determining trends, the direction of changes in liver functions and assessing the risk of alert levels for liver blood markers, when only daily results of milk parameters are available.

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