Discipline: Genetic parameters/QTL’s;
With climate change, thermal stress is expected to progressively pose more challenges to dairy production systems. This will be more pertinent inland than near the coast where the influence will be moderate. Heat stress is severely negatively correlated with production and reproduction before adaptation, but also moderately over the acclimatization period as the stress induced leads to a variety of genetic expressions, including regulation of cellular functions, ecosystem adaptation and acclimatization mechanisms which digress nutrients and certain metabolic functions from production and reproduction supporting functions. The identification of genes associated with these mechanisms will give us a deeper perception of the impacts of heat stress within the normal cell metabolism and can participate in mitigating reduced dairy productivity problems faced by producers.
In milk production, the acclimatization process is done through genetically induced systemic metabolic changes affecting in particular the udder, with acute and chronic phases including endocrine and genetic control. The adaptation process includes hereditable characteristics. Previous research has identified QTL’s in chromosome 11 that are associated with heat stress tolerance, such as hair length and sweating index. Thus, there are genetic markers that could be used as tools for heat tolerance. Tropical breeds such as Bos indicus types are expected to have more equipped genetic markers than traditional dairy breeds, such as Holstein, and which can be considered for crossbreeding in adverse environments.
The study referenced below aimed at examining the expression of genes on the udder, corresponding to various levels of adaptation or acclimatization to environmental stress. The authors utilized 18 cows from three genetic groups, Holstein, Gyr and Gyrolando, which is the Gyr – Holstein cross, all in the same stage of lactation, and subjected them to the same management conditions. Blood was collected to determine the hormonal profile and blood chemistry. Udder tissue was used for genomic studies, the isolations being called transcripts.
The hormones Prolactin and growth hormone were higher in the Holsteins, which is expected because of the higher milk production. There were no differences in indicator hormones associated with other major metabolic functions, such as IGF-1 and T3. From the 4608 transcripts in the databank that were used in this experiment, 105 specifically expressed genes were identified in at least one of the groups. Among these, 14 genes were related to the structure of the udder, to the response to thermal stress and to milk protein. The Holsteins, in comparison with the Gyr - Holsteins and Gyr groups, presented transcripts associated with epithelium cellular differentiation and proliferation in the udder, milk productivity and decreased heat stress tolerance. Gyr animals presented transcripts associated with cellular defence and increased tolerance to heat stress. The Gyr - Holstein group showed intermediary results compared with the other two groups, suggesting an ongoing tropical environment acclimatization process while maintaining dairy productivity.
Bottom line: Whereas crossbreeding in dairy operations is normally considered for beef production from culled cows or to utilize heterosis to control particular negative traits or outcomes, it can also be considered to mitigate the effects of climatic stress where the environment cannot be controlled such as with indoor systems.
D. Wetzel-Gastal, F. Feitor, S. van Harten, M. Sebastiana, L.M.R. Sousa & L.A. Cardoso, 2016. Genomic study of the mammary gland in bovines acclimated to a tropical environment. S.A J. Anim. Sci. 46, 1-13.