This research was conducted with the aim оf estimating genetic trend for a functional length of productive life (FLPL) in the population of Black and White cattle in Serbia. Research and bulls genetic evaluation for functional longevity were performed on a set of data provided by Agricultural Corporation Belgrade AD (PKB) which contained data on longevity and origin of 22109 cows out of which 26% records were right-censored. Functional length of productive life (FPLP) represents a time period from the first calving to culling or censoring corrected for milk production. Breeding values were estimated using Weibull method of proportional risks within survival analysis a genetic trend for FLPL was calculated using of a regression analysis. The cows included in the analysis were on average first calved in the age of 809 days and had an average share of 81.9% genes of Holstein Friesian breed. An average length of productive life was 1267 days (41.6 months). Distribution of bull standardised breeding values did not statistically significantly differ from normal distribution. An average standardised breeding value was 99. A slightly positive genetic trend was determined, that is, the length of functional productive life was by selection increased by 0.021 day at an annual level while a reliability of estimated breeding values showed a negative trend.

Group of secondary traits such as health, longevity, type and milkability represents some of very important factors for successful milk production. These traits have been given great importance in recent years. In order to realize productive life of dairy cows as long and successful as possible, special attention should be directed to traits of type and body constitution.Objective of the research was to establish heritability coefficients for 14 type traits of first calving Black and White cows, effect of genetic and paragenetic factors (bull sires, farm, year and season of calving, age at scoring and share of Holstein-Friesian [HF] genes) on type traits, so that these scores could be included in calculation of breeding value of the animal. Also, average values of milk traits have been established: milk yield and yield of 4 % fat corrected milk (FCM), content and quantity of milk fat.Evaluation was performed on a sample of 2 976 first calving Black and White cows. Evaluated cows were reared on 7 farms of the Agricultural Corporation Belgrade in Serbia.Analysis of discontinuous and continuous influences was done using the method of least squares. Investigation indicated that the value of linear type evaluation should be included in the total evaluation of the breeding value and in this way complete insight into genetic supremacy, especially of breeding bulls, would be obtained. Use of bull semen of proven supremacy in transmission of genes desirable from the aspect of body constitution, in the process of artificial insemination, would lead faster to production herds with animals which are uniform in type, of good conformation and longevity, which is of special significance in conditions of intensive rearing of dairy cattle.

In order to examine the biased milk production depending on the sex of calves, data on calving and milk yield characteristics of 15,181 Holstein type cows in PK Belgrade, Serbia were analyzed. A total of 30,362 lactations that were realized in the period from 1985 to 2017 were analyzed. Data were prepared and analyzed using the SAS software package (SAS Institute Inc. Software License 9.3, 2012). The expression and variability of investigated traits were determined using the PROC MEANS procedure, while the effect of individual factors on milk yield traits was analyzed using the PROC GLM procedure. Obtained results deviate from the views of the Trivers–Willard (TW) hypothesis. The results indicate that mothers invest more in female offspring by producing a higher milk and fat yield in the first and second lactation compared to male offspring. This is especially emphasized under better environmental conditions. The highest milk yield (7788 kg) and fat yield (271 kg) in the second lactation were achieved in the combination with two consecutive female calves in the group of higher-than-average milk production farms, and lowest in the combination of two consecutive male calves (6783 kg for the MY and 243 kg for the FY), respectively.

The aim of this study was to analyze the influence of farm conditions and season of birth on body mass, respiratory system diseases and diarrhea occurrence, and mortality during the first month of calves' life. The study was conducted on two tie-stall-system farms with intensive milk production and similar nutrition of dairy cows, but with differences in rearing conditions of calves in the first week of life. The calves were tied on lying area with straw as bedding material (farm A) or free in individual boxes with straw bedding (farm B). In the first consumption, they take 1-2 L of colostrum produced by their mother or by another cow (farm A), or 2.5-3 L of colostrum produced by their mother or by another cow or frozen colostrum (farm B). According to the results, average body mass of calves was significantly higher on farm B than of those on farm A at all ages (on birth, at 8 days, and 30 days). Mortality rate and diarrhea occurrence in calves were higher on farm B, while respiratory system diseases incidence was higher on farm A. All observed welfare indicators were very significantly (P < 0.01) influenced by farm conditions and birth season.

Data set including 10860 primiparous Holstein-Friesian breed cows first calved in the period from 2011 to 2015, was used in determining phenotypic variability and correlation between the traits of milk yield and linearly estimated traits of udder and angularity. The average values obtained for type traits (angularity, fore udder attachment, front teats placement, teats length, udder depth and rear udder height) were 6.47; 5.74; 4.96; 5.20; 5.99 and 6.25, respectively. The values obtained for phenotypic correlations between linear type traits and traits of milk yield ranged from -0.042 (udder depth and milk yield) to 0.335 (fore udder attachment and protein yield). Positive phenotypic correlation (0.293) was recorded also between fore udder attachment and milk yield which is deemed the most important trait of milk yield while the lowest correlation between milk yields was determined in relation to udder depth (-0.033). The results obtained indicate a possibility of applying direct and indirect multiple traits selection which should be conducted within a national progeny-testing programme on Holstein-Friesian bulls by using the method of selection indexes.