Nitrogen (N) plays a decisive role in the growth and yield of crops. Hence, a high maize grain yield depends upon substantial N inputs. In the present study, morphological traits and yield components, grain yield, rain use efficiency (RUE), and N partial factor productivity (NPFP) were analyzed in two maize hybrids (ZP666 and NS6030) for 2 yr using four N rates (0 (N0), 60 (N60), 120 (N120), and 180 (N180) kg N ha⁻¹). In a climatically more favorable year (2022), the studied traits and NPFP were higher, while RUE was lower. Hybrid ZP666 had higher values of morphological traits and yield component traits, except 1000-grain weight, grain yield, RUE, and NPFP, than hybrid NS6030. The highest values for morphological traits, yield components, grain yield (9383 and 9456 kg ha⁻¹), and RUE (27.1 and 27.2 kg ha⁻¹ mm⁻¹) were obtained at 120 and 180 kg N ha⁻¹. The NPFP decreased significantly with increasing N input, from 137.6 (control) to 52.5 kg grain per kg fertilizer N (180 kg N ha⁻¹). A suitable hybrid selection and the application of a moderate N fertilizer rate of 120 kg N ha⁻¹ could contribute to high yields and lower nitrogen losses to the environment and promote sustainable agriculture.

The research was performed on Holstein-Friesian and Black and White bull dams reared on five farms of Agricultural Corporation of Belgrade - PKB. The study included 575 lactations of cows selected as bull dams and their progeny calved in the period from 2007 - 2014 and represent progeny of 24 bulls. The following dairy traits were analysed in a standard lactation (305 days): milk yield (kg) - MY, milk fat content (%) - % MF, milk fat yield (kg) - MFY, protein content (%) - % PC and protein yield (kg) - PY. Holstein-Friesian bull dams and their progeny, in standard lactation, produced on average 9239.84 ? 1607.64 kg of milk, with a milk fat content of 3.44 ? 0.20 and protein content of 3.21 ? 0.12. The impact of bull - sire, year of birth, lactation order, farm, year and calving season was present at different levels of statistical significance on yield traits, while the genetic group had no influence on any of the milk traits. Bull - sire, year of birth, lactation order and calving season did not influence the variability of milk fat and protein content. Heritability of observed milk traits was medium to low. The content of milk fat and protein had the lowest values of heritability, 0.014, and 0.024, respectively. The heritability of milk yield, milk fat yield and protein yield was 0.293, 0.319 and 0.273, respectively.

The Simmental breed of cattle is mostly reared in the central part of the Republic of Serbia, where it makes up about 80% of all breeds. In areas of more intensive cattle production, populations of cattle with pronounced milk yield are reared. In more extensive, as well as hilly and mountainous areas, somewhat less productive animals are raised. The main goal of this study was to examine the variability of genetic correlations of milk and fertility traits on the farms of individual agricultural producers using modern methods, depending on the breeding area, i.e. the region in which they are bred and reared. This study included 2589 controlled Simmental heifers, with lactations concluded during one year. All first calving heifers were housed and reared on agricultural family farms in the area of Central Serbia. The paper examines genetic correlations between the following traits of milk yield and fertility: duration of lactation, milk yield in standard lactation, milk fat content in standard lactation, milk fat yield in standard lactation, yield of 4% FCM in standard lactation, age at first calving, duration of service period. The results of the study of genetic correlations were obtained using mixed LSMLMW models (Harvey 1990). The examined genetic correlations of milk yield and fertility traits in Simmental cows showed pronounced variability depending on the breeding area where the cows are reared.

In the last decades, there has been a trend present in the world to increase the size of dairy herds while increasing the yield of milk per head. In addition to environmental and economic benefits, this trend carries certain risks for the welfare of cows because in conditions of increased agglomeration of cattle the possibility of spreading of pathogens is also increased, there are less opportunities for adequate control and cows are exposed to greater selection and production stress. Research of the relationship between herd size and welfare quality parameters is still not sufficient to make relevant conclusions. Starting from that, the aim of this study, conducted in Serbia, is to examine the influence of herd size on parameters related to providing good feeding and housing conditions as important segments of the overall welfare of dairy cows. The assessment of given welfare parameters was done by Welfare Quality? Assessment Protocol for Cattle (2009) on 16 dairy farms of different herd sizes (large, medium and small) and housing management. The results indicate that there are significant variations in welfare indicators in each of the observed groups, which is why the size of the herd cannot be taken as a parameter that explicitly determines the quality of welfare. However, individual observation and comparison of welfare parameters between groups indicate that small herds in our production conditions could be identified as the greatest risks to the welfare of cows. In small herds, the highest share of cows of poor (4.62%) and fattened condition (8.76%) was found, as well as the lowest freedom of movement because cows on small farms are mostly reared in a tied system. Average values of indicators: lying down time (6.24s), frequency of collisions with equipment (13.25%) and high dirt contamination of cows (65.6-89.8%) further emphasize the issue of providing comfort in small herds.

The main goal of this research was to examine, using modern methods, the variability of phenotypic correlations of production performances and reproductive properties of Simmental cows reared on the farms of individual agricultural producers, in different breeding areas of the Republic of Serbia. The study of phenotypic correlations of milk performance and fertility properties in different regions of Serbia was carried out on a total of 3.056 primi parous Simmental heifers under control, with lactations completed within one year. The examined animals were reared on different individual farms, and mainly in very different conditions of housing and nutrition, depending on the breeding area. The study of phenotypic correlations included the following milk performance traits: milk yield, milk fat content, milk fat yield, yield of 4% corrected milk; and fertility properties: age at first calving and service period. The results of the study among other things indicate that although the phenotypic correlations between the fertility and milk performance properties show different degrees of variation, they should be taken into account in the final assessment of the breeding value of the animal, so that the breeding selection programs are more comprehensively designes.

The body weight of calves in the earliest period of their life (age from 0 to 7 days) is under the greatest influence of the farm and the season of birth. The farm manifests its influence most often through the conditions of nutrition and housing and the organization of the technological production process, while the influence of the birth season is manifested through microclimatic and nutritional conditions, as well. The most common deficiencies related to the nutrition of newborn calves are related to: inadequate colostrum supply in terms of quality, quantity and time of colostrum intake, which is closely related to the organization of the technological production process on the farm. Dietary deficiencies affect the body weight of calves at birth and at 8 days of age. In a study conducted over a year (4 seasons), the colostrum diet of newborn calves of the HF breed on two farms (A and B) with a tied housing system was analyzed. Calves were fed colostrum on both farms at intervals, usually up to 2 hours, less often up to 4 hours after birth. The colostrum consumed came from the mother, most often, and less often from the other cow, while on one of the farms it was also used frozen. However, the amount of colostrum consumed was deficient, it was 1-2 l on farm A, and 2.5 to 3 l on farm B. The occurence of a deficient diet or other deficiencies in the diet of calves was indicated by the average body weight, measured at birth and at the age of 8 days. On farm A, a lower average body weight of calves (37.95 and 39.68 kg) was recorded than on farm B (40.00 and 41.80 kg) by age categories, respectively. The average body weight of calves was statistically significantly (p <0.01) influenced by the farm and the season of birth, as well as their mutual interaction, but the effect of the farm was more pronounced.