Possible differences between composition of raw milk due to dairy farming system (organic vs conventional) as well as seasonal variations were investigated. The samples were analysed during one year. A total of 6.782 samples of raw milk were collected (4.496 from organic farming). Dairy farms were located in the northern part of Republic of Serbia (Province of Vojvodina). The principle of analysis of raw milk samples was in accordance with the methodology by midinfrared spectrometry and flow cytometry. The fixed effect of system of farming and season (winter, spring, summer and fall) have shown a high statistical significance (P < 0.01) on all examined milk parameters except fat, total solids and somatic cell count, where the impact was slightly lower (P < 0.05). Significant difference wasn't found in number of bacterial colonies (P > 0.05). Composition of milk is also affected by a number of other factors, therefore it is recommended to involve factors such as nutrition of dairy cows, breed and farm management.

The purpose of this study was to examine possible relationship between milk urea and fertility of dairy cows using field data. This study also evaluated the influence of environmental factors on milk urea (MU) and the relationship between MU and daily milk yield, milk fat and protein percentage. The data were collected at 11 dairy farms in the Vojvodina region. Reproductive data and MU measurements were obtained from cows that calved between June 2013 and October 2015 and had a successful conception after calving. Statistical data processing was carried out by applying General Linear Model procedure, Statistics 13. Parity, calving season, season of milk control and farm were included in the models as fixed effects. Significant differences in MU concentrations were observed between farms (P<0.

The aim of this research was to determine the influence of lactation number and parity on milk yield of Saanen goat’s breed. It has been concluded that milk yield was higher for goats that had given birth to twins and three kids than for goats that had given birth to a single kid (P<0.05). The longevity has a great positive impact on production, given that goats in the fifth lactation produced more milk than goats in first or second lactation (P<0.05), while goats in the sixth lactation still produced more milk than goats in first lactation (P<0.05). During the period from 2014- 2019, the research was conducted on a farm of multiparous Saanen goats in Vojvodina (northern part of Serbia). In the observed period, the farm had between 350 and 400 goats per milking, and the research included a total of 1,628 concluded lactations, within which the first lactations were the most 484, then the second 381. According to the number of lactations, goats were grouped into classes from one to seven and from one to three for parity. By comparing each individual lactation, it was determined that in first lactation goats produced significantly lower milk than goats in the rest lactations(P<0.05), except the seventh. Research has shown that lactation number has a significant influence on milk yield (P=0.00). Increasing the fertility of goats significantly affects the production capacity of dairy goats, since does with a larger number of kids in the litter had a significantly higher milk production (P<0.05). Due to the larger number of kids in the litter, milk production also increases. Likewise, it is assumed that the increase in milk yield of goats with two and three kids is a consequence of a larger placenta, i.e. stronger lactogenic activity during pregnancy.

The effect of age at first calving (AFC) and various non-genetic factors i.e. season of calving, farm and system of housing on longevity and production traits were investigated. Longevity traits were studied using total lifetime (TL), length of productive life (LPL) and number of lactations (NL) while production was researched using lifetime milk yield (LMY). Data of 2037 Holstein dairy cows were provided by the main breeding organizations at the Faculty of Agriculture, University of Novi Sad. The average values and variability of examined traits as well as the effect of factors on longevity and production traits were investigated using fixed effect model by general linear model (GLM) procedure in software package Statistica 13. Results showed highly significant effect of the AFC, calving season and farm, on all studied longevity traits (P less than 0.01), while non- significant effect was expressed on lifetime milk yield (P greater than 0.05). The mean of AFC, TL, LPL, NL and LMY for Holstein cows were 27.3, 67.5, 40.2 months, 2.45 and 18798.0 kg, respectively. The maximum values of LPL, NL and LMY were noticed for cows with age at first calving before 23 months of age. The LPL ranged from 47.88 (AFC less than 23 m) to 35.84 m (AFC>29 m) and declined progressively when the AFC is increased, particularly in cows calving at more than 29 m.

The aim of this study was to determine the urea level in Saanen goat milk and examine the relationship between milk urea (MU) level and daily milk yield (DMY), milk fat, protein, lactose and solids non-fat (SNF) percentage in dairy goats. The observation was made on 1492 samples of milk control of Saanen goats in the period from March to November 2019. The samples were categorized into four groups based on MU level: I Group 10-20 mg/dl, II group 20.01-30.00 mg/dl, III group 30.01-40.00 mg/dl, IV group >40.01mg/dl. Analyses of raw milk samples were carried out on the FOSS instruments MilcoScan in Laboratory for Milk Quality Control, at the Faculty of Agriculture, Department of Animal Science. Descriptive statistic was done using program Statistica 13.5. The goats on the observed farm were reared in a closed system with balanced diet throughout the whole year. The study showed statistically highly significant differences (P<0.01) among MU groups for all milk parameters. The MU concentration was positively correlated (P<0.01) with fat (%), protein (%), lactose (%) and SNF (%), while it was negatively correlated only with DMY (kg).