Mirjana Joksimovic-Todorovic

Effect of heat stress on milk production in dairy cows

Heat stress in dairy cows is caused by a combination of environmental factors (temperature, relative humidity, solar radiation and air movement). Continual genetic selectin for greater performance results to increased sensitivity to heat stress. It was one of the reasons why lactation curve during summer has decreasing trend compared to spring in which lactation curve maintained within high levels. The trial was conducted in spring (April-May) and summer period (June-July) on total of 40 dairy cows of Holstein-Friesian breed in early lactation period (first 60 days of lactation). Milking capacity in cows and milk chemical ingredients (milk fat and proteins) were statistically significantly higher in the spring period compared to summer, while higher values of lactose were not statistically significant. Total average milk production per cow was significantly higher in spring period (42.74±4.98l) than in summer (39.60±5.09l) at the level of P 0.05).

THE EFFECT OF ANTIOXIDANTS ON PREVENTING THE RETAINED PLACENTA IN DAIRY COWS

Retaining of placenta is one of the most common ailments in dairy cows and it occurrs if placenta is not removed in the period of 12-14 hour after calving. The ailment is of multifactorial etiology and a primary cause is often unknown. During periparturient period in cows the metabolical, hormonal and biochemical changes are observed. Immunosuppression also characterizes this period and it is associated with endocrinal changes and decreased feed intake. Reduced function of neutrophiles before parturition is in correlation with increased frequency of incidence of postparturition ailments. Selenium and vitamin E are the most important antioxidants which have a positive effect on neutrophiles function protecting them from oxidative damage.

The effect of the extract of rhizome and root of hellebore (Helleborus odorus W. et K.) on parameters of white blood count and degree of phagocytosis in Wistar rats.

The objective of this research was to study the effects that the extract of rhizome and root of Helleborus odorus W. et K. (Ranunculaceae) can have on modifications in the parameter values of white blood cells count and degree of phagocytosis by peritoneal macrophages and neutrophil granulocytes in Wistar rats. The trial was conducted on 28 rats divided into 4 groups with 7 animals in each group. To the control group of rats sterile physiological solution in the quantity of 0.25 mL/100 g BW was applied intramuscularly. For the purpose of monitoring the effect of the extract of rhizome and root of hellebore (HE) during a time period, the HE was applied intramuscularly to rats in a dose of 10 mg/100 g BW, while the blood samples for analysis were taken after 24h, 48h and 72h. The consequence of intramuscular application of HE was an increased count of total leukocytes in all trial groups, the most expressed leukocytosis being registered 24h after application of HE. Statistically significant higher value in the count and percent of neutrophil granulocytes in the blood was recorded 24h after treatment in relation to the control and two other trial groups (p<0.001), among which a statistical significance was not established. The extract of hellebore rhizome and root has led to lymphopenia, resulting in the increase of the neutrophil/limphocyte index in the trial groups 24h and 48h after treatment. The application of HE had no significant effect on the count of monocytes in treated animals. The applied extract has caused a significant increase in the degree of phagocytosis by residing peritoneal macrophages and neutrophil granulocytes in blood.

The importance of antioxidants in the protection against mycotoxicoses in farm animals

Mycotoxins are biologically active substances that are synthesized by saprophytic and parasitic fungi, and which, when taken into organism by ingestion, can provoke intoxications known as mycotoxicoses. Farm animals show different susceptibility to mycotoxins depending on various factors: genetic (species and breeds), physiological (age and obesity) and environmental (hygienic and climatic). One of the mechanisms of mycotoxin activities is peroxidation of lipids brought about directly by the production of free radicals or by increased sensitivity of tissue to peroxidation. Peroxidation of lipids provoked by mycotoxins is caused by low level of natural antioxidants, so they have a crucial role in the protection against mycotoxins. Nutritive stress can influence negatively the relationship between antioxidants/pro-oxidants, and mycotoxins are nowadays regarded as leading factors of stress induced by nutrition. This optimal relationship can be regulated by the use of antioxidants in food (selenium, vitamin E, carotenoids, etc.) known to prevent tissue damages caused by free radicals. Selenium and vitamin E are essential nutrients which contribute to the preservation of animal health by realizing mutual biological activities in the organism. This paper presents the findings on mechanisms of the action of different species of mycotoxins and the importance of antioxidative protection in farm animals, as well as the results of our investigations of influence of mycotoxins on the occurrence of some reproductive disorders in pigs.

Physiological aspects of behaviour of sows and piglets during the lactation period.

Maternal ability represents complex interactions between different forms of behaviour and physiological characteristics. Behaviour and metabolic processes are partly under the control of endocrine and nervous systems. Sows are different from other mammals, in that sows bear a large number mature baby, capable immediately to suckling. Post partum anabolic processes become catabolic, giving priority to dairy gland in relation to other tissues. Maximum secretated milk takes place betwen 2. and 3. week. Sows lost in body mass and it is appeared the change in value of some bloods parameters. Haemotologic analyses have suggested the increase in total number of leukocytes and neutrophilic granulocytes and the decrease in the number of lymphocytes, monocytes and eosinophils on the first day postpartum. In the third and fourth week of lactation a statistically significant fall in the number of leukocytes and granulocytes in relation to the first day was observed, along with a significant increase in limphocytes, monocytes and eosinophils. Erythrocyte count, haemoglobin concentration and haematocrit value decreased during the lactation period. Level of glucose in plasma is low (it is decreasing for more than 50%), while the level of urea is high, due to huge proteins available. It can also be noticed that there is a high mobilisation of body fat an increasing level of NEFA (non-esterified fatty acid). Secretion of milk is under control prolactin and oxytocin. Oxytocin affects on maternal behaviour and prolactin is linked with timing of suck.