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Since the change in climate is unquestionable if we plan to have sustainable milk production we need to implement a long-term mitigation method. A precondition for the genetic evaluation and selection of genetically heat resistant animals is the measurement and analysis of the variability of microclimate parameters. Therefore, this research aimed to show the variability of microclimate parameters in a selected dairy cattle farm. The records of ambient temperature and relative humidity in the selected farm were measured using a Datalogger. The conducted research and data analysis indicate noticeable variability of observed microclimate parameters (ambient temperature, relative humidity and temperature- humidity index) in regard to the measurement days. Determined daily THI values indicate a high probability of the occurrence of heat stress in the observed period. Furthermore, daily monitoring of microclimate parameters enables timely reaction and prevention of more serious consequences of heat stress on dairy cows.

The study aimed to determine the effect of different fixed factors (breed, region, calving year, calving season, parity and lactation stage) on daily milk production (yield and content) of four dairy cattle breeds under the heat stress conditions (THI≥72). The research was conducted on a set of test-day records of four dairy cattle breeds (Simmental, Holstein-Friesian, Red Holstein and Brown Swiss) reared in the Republic of Serbia (Region of Mačva, Podunavlje and Šumadija). The statistical analysis included test-day records collected in the period from the beginning of the year 2012 to the end of the year 2019. Based on the performed analysis, it could be demonstrated that all the effects included in the statistical model (breed, region, calving year, calving season, parity and lactation stage) statistically highly significant (p

With the aim of determining the effect of response to heat stress, parity, breed and breeding region on somatic cell count (SCC) in dairy cattle, the individual test-day records of dairy cows collected from 2005 to 2012 in regular milk recording (AT4 / BT4 method) in Croatia were used. The proportional differences in log somatic cell count, and logSCC (in %) in subsequent milk recordings (1st, and 2nd) were determined in cows with a significant decrease in daily milk yield at a set temperature-humidity index, THI threshold (68, 72, and 76). The results indicate high variability in somatic cell count due to the animal’s response to heat stress (heat stressed at THI in 68, 72, and 76), parity (1, 2, and 3+), breed (Holstein, and Simmental) and breeding region (Central, and Eastern Croatia). Also, it could be pointed out that Holsteins, especially cows in higher parities (2, 3+) reared in Eastern Croatia were shown to be more sensitive to environmental stress, even in the period after heat stress (1st, and 2nd subsequent milk recording). Since SCC is not only an indicator for mastitis, but also reflects a cow’s immune response to general stress situations, the high variability determined may be explained by the individual adaptation capabilities of these two breeds to breeding conditions in the analysed regions.

Aiming determination of the persistency of heat stress effect in first parity Holstein cows regarding the region of breeding test-day records provided by the Croatian Agricultural Agency were analysed. Only cows with detected statistically significant decrease in daily milk yield at set temperature-humidity index (THI) threshold value (65, 70 and 75) were included in the further analyses. The persistency of heat stress effect regarding the daily milk traits was determined as a absolute drop in the subsequent milk recordings (1st and 2nd). The results of this research indicate significant difference in cows’ response to heat stress effect due to region of breeding and animal’s susceptibility to heat stress. The negative effect of heat stress was more pronounced and more persistent in cows bred in Mediterranean and Eastern Croatia. Also, the negative effect of heat stress was more pronounced and more persistent in cows that were more susceptible to heat stress (heat stressed at the lower THI threshold values).

Aiming determination of the variability in persistency of heat stress effect in dairy cattle regarding the breed and region test-day records provided by the Croatian Agricultural Agency were analysed. Only cows with detected statistically significant decrease in daily milk yield at set temperature-humidity index (THI) threshold value (68, and 72) were included in the further analyses. The persistency of heat stress effect was determined as absolute drop in daily milk yield in the subsequent milk recordings (1st and 2nd). The results of this research indicate high variability in persistency of heat stress effect in dairy cattle due to breed (Simmental, and Holstein), breeding region (Eastern, Central and Mediterranean Croatia), and individual’s susceptibility to heat stress (animals heat stressed at lower or higher THI (68 / 72) value. Since the genetic evaluation and selection of animals that are more resistant to heat stress is only long-term method to mitigate the impact of climate change, these factors should be taken into account in the models for genetic evaluation.

Heat stress has significant effects on milk production and composition as well as on cattle welfare. Cows with high production capacity have a faster metabolism, produce more heat in the body and more easily tolerate lower temperatures, while high temperatures can easily cause heat stress. Heat stress is state of an organism exposed to external or internal thermal factors whereby the homeopathic systems of the body are unable to resist their harmful effects. Heat stress directly or indirectly affects the physiology, reproduction, health, feeding, production and behaviour of animals and it can cause even death. Negative effects of heat stress on animal welfare can be observed in changes in animal behaviour. Affected animals are also passive, spend less time in social interactions and less time eating. These factors will certainly lead to drop in production. Therefore, it is necessary to study the welfare of the animal through the mental state of the animal, such as frustration or absence of pain, not just through physiological measures. The aim of this study was to review the connection between the heat stress environment and dairy cows’ welfare.

In order to determine the persistency of heat stress effect in dairy Simmentals in Eastern Croatia in accordance to the parity and susceptibility to heat stress, over 0.5 million of test-day records were analysed. Only cows with detected statistically significant decrease in daily milk yield were included in the further analyses. The persistency of heat stress effect in the subsequent milk recordings (1st and 2nd) was determined in cows that had significant decrease of daily milk yield at different temperature-humidity index (THI) threshold value (68 and 72). The obtained results indicate that cows heat stressed at lower THI threshold value had higher drop of daily milk yield in subsequent milk recordings. Also, primiparous experience higher drop than multiparous cows. The negative effect of heat stress on daily milk contents that existed in all cows was more pronounced in the 2nd subsequent milk recording. Finally, the lower THI threshold value, the stronger and more persistent was heat stress effect. Having in mind the quite probable increase of the frequency of heat stress days, it is necessary to develop an adequate strategy for dairy farming. Further research on genetic evaluation on heat stress should provide necessary informations.

Forecasts indicate that the world population will increase from current 7.2 billion to 9.6 billion till 2050. The combination of population growth, growing incomes and urbanization imposed enormous challenges on food and agriculture systems. On the other hand, the natural resources necessary to support global food and non-food production and agricultural services provision will not grow. Agriculture plays an important role in global environmental issues, such as climate change, land degradation, water pollution and biodiversity loss, therefore the future growth in production must be accommodated within the growing insufficiency of natural resources, including land, water and nutrients. Also, waste and greenhouse gasses (GHG) emissions must be reduced. The global livestock sector, with total GHG emissions estimated at 7.1 giga tones of CO2- eq/year (year 2005) which represent 14.5% of all anthropogenic emissions, significantly affects the environment. In terms of species, cattle are the main contributor to the sector’s emissions (65%), while in terms of commodity, beef is the main contributor with 2.9 giga tones of CO2-eq, or 41% of total sector emissions. The cattle sector, especially dairy cattle, although significantly contributing to the total GHG emissions, on the other hand, suffers significant losses due to induced climate change. Under heat stress conditions, lactating cows tend to decrease milk production as well as to increase prevalence of mastitis and fertility disorders. In many dairy- producing areas of the world heat stress conditions represent a significant financial burden (for instance $ 900 – $ 1, 500 million/year in the USA). Since dairy cattle are the contributor and the victim of ongoing climate change, application of adequate mitigation techniques is necessary to ensure the future of dairy cattle farms. There are many methods to decrease the impact of heat stress on cattle, for example shading, cooling and nutrition. Furthermore, selection of heat stress resistance could be an effective, long- term method. The other problem is sector’s GHG emission. The GHG emission intensities vary greatly among producers due to different agro- ecological conditions, farming practices and supply chain management. This variability gives opportunity to finding the adequate mitigation option. The reduction of the GHG emission could be achieved by: reducing production and consumption ; lowering the emission intensity of production ; or by combining the above mentioned. The adoption and application of mitigation techniques by majority of the world’s producers can result in significant reductions of emissions in interval from 14 to 41% depending of the selected specie, production system and world’s region. Since climate change is a global issue and livestock supply chains are increasingly internationally connected, effective mitigation actions could be achieved only by global approach. To conclude: the future of cattle breeding lies in a sustainable production system that provides an effective production of high quality meat and milk with animals selected to high heat tolerance as well as to low GHG emission per kg of product.

Sve brže i izraženije klimatske promjene u cijelom svijetu rezultiraju sve nepogodnijim uvjetima za stočarsku proizvodnju. U intenzivnoj proizvodnji moraju biti osigurani optimalni mikroklimatski uvjeti. Uvjeti toplinskog stresa dovode do smanjenja konzumacije suhe tvari, mliječnosti, promjene u sastavu mlijeka, porast broja somatskih stanica i pojavnosti mastitisa, narušavaju reprodukciju te dovode do značajnih financijskih gubitaka. Metode smanjivanja utjecaja toplinskog stresa podrazumijevaju optimizaciju hranidbe te primjenu različitih sustava hlađenja (kratkoročne), selekciju mliječnih goveda na otpornost na toplinski stres (dugoročna). Obzirom na nužnost razvoja i implementacije okolišno i ekonomski održivih proizvodnih sustava, glavni cilj istraživanja bio je utvrđivanje fenotipske i genetske varijabilnosti proizvodnih karakteristika mliječnih goveda uslijed toplinskog stresa te, razvoj metodologije genetske evaluacije mliječnih goveda na svojstvo rezistentnosti na toplinski stres. Za statističku analizu korištena je baza podataka kontrole mliječnosti (01/2005. - 12/2013) s približno 3 milijuna rekorda (HAPIH). Za statističku analizu korišten je statistički paket SAS te program VCE-6. Temeljem istraživanja utvrđen je negativan utjecaj povećanja parametara mikroklime na dnevnu proizvodnost, dok je analiza genetskih parametara indicirala visoke genetske korelacije između dnevne proizvodnje mlijeka u normalnim i uvjetima toplinskog stresa, kao i visoke korelacije između UV-ima u normalnim uvjetima i uvjetima toplinskog stresa. Utvrđeno indicira da će visoko produktivne krave održati jednaku razinu proizvodnje i u uvjetima toplinskog stresa. U cilju pojednostavljenja selekcije mliječnih grla na rezistentnost na toplinski stres, dnevna proizvodnja mlijeka je analizirana kao bivarijantna varijabla (u normalnim i u uvjetima toplinskog stresa), što znači da se za svako grlo procjenjuju dvije uzgojne vrijednosti (UV) (pri selekciji se uvažava UV sukladna uvjetima na farmi)., Increasingly faster and more pronounced climate change worldwide results in increasingly unfavourable conditions for livestock production. Optimal microclimatic conditions must be ensured in intensive production. Heat stress conditions induce a decrease in dry matter consumption, milk yield, changes in milk composition, an increase in the number of somatic cells and the incidence of mastitis, reproductive disorders, and significant financial losses. Methods of reducing the impact of heat stress include optimization of nutrition and the application of different cooling systems (short-term), and selection of dairy cattle for resistance to heat stress (long-term). Given the need to develop and implement environmentally and economically sustainable production systems, the main goal of the study was to determine the phenotypic and genetic variability of production traits of dairy cattle due to heat stress and to develop a methodology for genetic evaluation of dairy cattle for heat stress resistance. For statistical analysis, the milk recording database (01/2005 - 12/2013) with almost 3 million records (HAPIH) was used. The SAS statistical package and the VCE-6 program were used for analysis. Based on the research, the negative effect of increasing microclimate parameters on daily productivity was determined, while the analysis of genetic parameters indicated high genetic correlations between daily milk production under normal and heat stress conditions, as well as high correlations between BVs under normal and heat stress conditions. This indicate that highly productive cows will maintain the same level of production under conditions of heat stress. To simplify the selection of dairy cattle for resistance to heat stress, daily milk production was analyzed as a bivariate variable (under normal and under heat stress) which means that two breeding values (BV) are estimated for each animal (for the selection, BVs following the conditions on the farm should be considered).

Pod sezonske promjene u proizvodnje mlijeka spada veliki broj čimbenika od kojih smo najvaţniji spomenuli u ovom radu. Većina sezonskih promjena povezana je direktno ili indirektno s temperaturom zraka i vlaţnosti zraka zato smo tim čimbenicima posvetili najviše vremena. Tako se i promjene u hranidbi tijekom različitih perioda mogu povezati s promjenama u temperaturi, iz razloga što ţivotinja pokušava odrţati normalnu tjelesnu temperaturu pa se energija koja se inače koristi u metaboličke svrhe iskorištava u svrhu termoregulacije, što se odraţava na smanjenje konzumacije hrane. Zato se prilikom različitih perioda mijenja sastav obroka mliječnih krava u cilju osiguravanja dovoljne količine energije za što lakše odrţavanje normalne tjelesne temperature uz odrţavanje što veće dnevne proizvodnje mlijeka. U radu su napravljena istraţivanja direktnog utjecaja temperaturno humidnog indeksa odnosno toplinskog stresa na dnevnu količinu proizvodnje mlijeka, broj somatskih stanica u mlijeku, postotni udio mliječne masti u mlijeku i udio suhe tvari bez masti u mlijeku krava na farmi Grube d.o.o. Potnjani. Spomenuti su i utjecaji toplinskog stresa i na mnoge druge fiziološke čimbenike. Analiziran je utjecaj sezone u kojoj se krava teli koja prema mnogim istraţivanja ima značajan utjecaj na proizvodnju mlijeku. Na kraju rada spomenuti su načini zaštite kojima se mogu smanjiti utjecaji sezonskih promjena u svrhu odrţavanja kvantiteta i kvalitete proizvodnje mlijeka na visokoj razini., Under seasonal change in milk production we can find large number of factors of which the most important are mentioned in this article. Most of the seasonal changes are associated directly or indirectly with the temperature and humidity and that is why we devoted most of the time to these factors. Thus, the changes in feeding during different periods can be correlated with changes in temperature, because animals tries to maintain a normal body temperature, so the energy that is normaly used in metabolic purposes now is exploited for the purpose of thermoregulation, which is reflected in the reduction of food intake. That is why in different periods we alter the composition of servings of dairy cows in order to ensure sufficient energy supplies to more easily maintain normal body temperature while maintaining the highest possible daily milk production. In this work we have done research of the direct influence of temperature humidity index and thermal stress on the daily quantity of milk production, somatic cells in milk, percentages of milk fat and total dry matter without fat in the milk of dairy cows on the farm Grube d.o.o. Potnjani. We also mentioned the influences of heat stress on many other physiological factors. We also analyzed the influence of the season in which the cows calved, which according to many research has a significant impact on the production of milk. At the end of the work we mention the ways of protection which can reduce the effects of seasonal changes in order to maintain the quantity and quality of milk production at a high level.