The main goal of this paper was to investigate the influence of some additives included into high yielding dairy cows rations to overcome the problems in early lactation. These substances directly affect the productive performances of dairy cows as well as udder health. The commercial name of investigated preparation is 'YEASTURE' and it is composed of live yeast cultures selected from three strains Saccharomyces cerevisisiae in combination with probiotic bacteria and enzymes (Lactobacillus casei, Streptococcus faecium, Aspergillus oryzae, Lactobacillus acidophilus, 1,3-b and 1,6 D-Glucan, hemicellulase, Protease, Cellulase, Alpha amylase) which have the ability to modify the fermentation in rumen stimulating the development of ruminal bacteria and increasing the fibre digestion. Effects of this preparation have been investigated on 60 Holstein-Friesian cows divided into two groups. The diets were identical, and trial group received also 10 g of preparation Yeasture daily. Application of Yeasture started 15 days prior to calving and lasted until 60th day of lactation As a research result improved in vitro disappearance of diet dry matter from roughage (alfalfa hay, maize silage and ensiled sugar beet pulp) was established. Preparation Yeasture influenced quantity and composition of the milk. The difference between trial and control group was 2.57 kg 4%FCM or 8.70% (P<0.01) and 7.16% milk fat (P<0.05).Trial group supplemented with Yeasture showed lower somatic cells count by 7.3 percent points what indicated better health of cow's udder. Based on the presented results it can be concluded that inclusion of preparation Yeasture into diets for dairy cows in transition period can be recommended.

Causes for cow culling in a tie stall system were investigated on a sample of 3060 cows culled in 2011, on seven large dairy farms in the Belgrade region. The total level of culling was 34.58% of the average number of cows. The number of cows culled decreased with lactation order (from 981 cows in the first to 294 cows in the sixth and later lactations). The most dominant cause for culling were diseases of the legs and hooves (28.4%), as was expected, having in mind the tie stall system. If selection (low production) is abstracted as the reason for culling, what stands out by importance are metabolic diseases (15.7%) and problems of reproduction (reproductive diseases-8.6%, and difficult calvings and abortions 5.7%). With the increase of duration of the lactation during which cows were culled, reproductive diseases gained importance as the reason for culling, while the importance of metabolic diseases and diseases of the legs and hooves in this context decreased. When culled, on the average, cows were 5.2 years old, having on the average spent 1112 days in production, of which 978 days in milking. Their average milk production per day of milking was 22.00 kg, per day of life 10.6 kg, and per day of production 19.8 kg.

It is general knowledge that management influences results in cattle production to the highest extent, and that the culling of cows is a very good indicator of the success of farm management. A comparison of results of culling for first calving cows on farms with various levels of production in 2011 established differences both for the number of culled animals and the reasons for culling. On farms with higher levels of production, the share of first calving cows in overall culling was 25.9% or 4.5% less than on farms with a lower level of production, i.e. 4.8% less died, and 0.7% first calving cows had to be slaughtered, while 5.6% more first calving cows were culled for economic reasons. At both levels of production, dominant reasons for culling were diseases of the legs and hoofs, which can be linked to the tie stall system (more pronounced on farms with higher production) and metabolic disorders (more dominant on farms with lower production). Reproduction was a more considerable problem on farms with higher milk production, while culling due to selection was more pronounced on farms with lower production. In early lactation of first calving cows, regardless of the level of production, dominant reasons for culling on farms are leg and hoof problems and metabolic disorders (total: 55% i.e. 55.9%). When reasons for culling of first calving cows after 100 days of lactation are investigated, on farms with high production the significance of diseases of legs and hoofs remains almost unchanged, but culling due to reproduction grows to 28%. On farms with lower production, culling due to leg and hoof diseases is considerably reduced after 100 days of lactation, however culling due to selection is tripled (62%).

The objective of this paper was to study variability, heritability and correlation of the three production traits in 1409 first-calf heifers of Holstein-Friesian breed; including the determination of the quantity of milk during lactation (ML), the quantity of milk fat during lactation (MM) and the quantity of protein during lactation (PR). According to the obtained results it could be concluded that there were statistically significant differences (P&lt;0.01, P&lt;0.05, P&lt;0.001) between ML, MM and PR regarding the effect of season of the first calving and the length of the first lactation. In addition, there were also significant differences (P&lt;0.01, P&lt;0.001) between ML and PR with respect to the effect of farm on which animals were raised, while on MM variability the year and age at first calving had a significant effect (P&lt;0.05). A share of Holstein genes and the ration which animals were fed had no effect (P&gt;0.05) on variability of any of the examined traits, while the farm on which animals were raised had no effect (P&gt;0.05) on MM, and year and age at first calving did not demonstrate (P&gt;0.05) statistically significant effect on ML and PR. By applying the animal model, based on the use of kinship matrix which involved 3867 animals, by help of REML methodology following heritability coefficients were evaluated: ML h2= 0.25; MM h2= 0.40; PR h2= 0.37. Coefficients determined for genetic and phenotypic correlations indicated existence of complete and positive correlations between these traits the interval of values being from rg = 0.96 between ML and MM to rg = 1.00 between ML and PR.

Lifetime milk production is a key success factor in fulfilling the production potential of high-yielding cows. Lifetime milk production traits are pronouncedly variable. The life expectancy and the length of productive life of dairy cows are repeatedly limiting factors for improving lifetime milk production. Lifetime milk production is greatly depended on age at first calving and the number of lactations during productive life. Previous researches have implied there are real chances for improving the lifetime milk production of high-yielding cows. The goal of this research was to investigate the significance of key systematic factors on the lifetime production of high-yielding Black-and-White cows. The animals included in the sample had different share of Holstein genes. The researchers determined systematic factors that caused some significant phenotypic variations of the investigated trait. The average lifetime milk production was 25,002.66?7,755.39 kg. When observed by cow genotypes, the mean values of the lifetime milk production varied from 27,061.37 kg (<58% HF) and 24,761.26 kg (58-73% HF) to 23,185.36 kg (>73% HF). The differences in lifetime milk production determined among the animals were due to a highly significant (p?0.01) impact of the bulls ? the sires of the cows and the year of culling; the impact of the class of HF genes was significant (p?0.05), whereas the impact of the reason for culling was non-significant (p>0.05).