The climatic conditions in Croatia are deteriorating which significantly increases the frequency of heat stress. This creates a need for an adequate dairy farming strategy. The impact of heat stress can be reduced in many ways, but the best long-term solution includes the genetic evaluation and selection for heat stress resistance. In order to create the basis for genetic evaluation, this research determined the variation in daily milk yield (DMY) and somatic cell count (SCC) as well as the differences in resistance to heat stress due to production level (high, low) and breed (Holstein, Simmental) of dairy cattle breed in Croatia. For statistical analysis, 1,070,554 test-day records from 70,135 Holsteins reared on 5679 farms and 1,300,683 test-day records from 86,013 Simmentals reared on 8827 farms in Croatia provided by the Croatian Agricultural Agency were used. The results of this research indicate that the high-producing cows are much more susceptible to heat stress than low-producing especially Holsteins. Also, the results of this research indicate that Simmental breed, in terms of daily milk production and somatic cell count, could be more resistant to heat stress than Holstein. The following research should determine whether Simmentals are genetically more appropriate for the challenges that are in store for the future milk production in this region. Furthermore, could an adequate production level be achieved with Simmentals by maintaining the heat resistance?
Considering the rapid climate changes worldwide, with the purpose to reduce financial losses for dairy farmers and enable a more sustainable farming as well, there is an increasing necessity to implement breeding values for heat resistance in breeding strategies. The estimation of breeding values requires a determination of temperature-humidity index (THI) threshold value. Therefore, the objective of this study was to determine the temperature-humidity index (THI) threshold values for daily milk yield, daily fat and protein content of milk produced by Holsteins and dairy Simmentals in Croatian farms. With that purpose, 1.070,554 test-day records from 70.135 Holsteins reared on 5.679 farms and 1.300,683 test-day records from 86.013 Simmentals reared on 8.827 farms in Croatia were compared to records of ambient temperature and relative humidity collected in the barn, during regular milking recordings from January 2005 to December 2012. Accordingly the following conclusions could be drawn: threshold values for daily milk yield were highly dependant on the parity and breed (Holsteins: 68, 69 and 72 for 1 st , 2 nd , 3+ parity; Simmentals: 77 for 1 st ); daily fat and protein contents showed a highly significant decrease due to heat stress condition (THI in 66-80) in both, Holstein and Simmental cows, and in all parity classes; multiparous cows were more resistant to heat stress than primiparous; Simmental cows were more resistant to heat stress than Holsteins.
Original scientific paperIzvorni znanstveni članak seed quality and plantlets development. The highest average values for germination and seedling root and shoot lengths were obtained after the storage at -80°C, and the lowest after storage at room temperature. The highest average values for emergence, plantlet height and roots and shoots fresh weights were obtained after the storage at -20°C, while the root length was greatest after the storage at -80°C. Tetraploid cultivar Calibra had significantly greater average values than diploid Bartwingo for all the investigated traits except for germination and primary shoot length. SUMMARY The aim of this research was to investigate the seed quality of perennial ryegrass after 5-year storage treatments at various temperatures. The seeds of two cultivars of perennial ryegrass (diploid Bartwingo and tetraploid Calibra) were used, and the storage treatment temperatures were: room temperature (about 21°C), 10°C, -20°C and -80°C. Seed quality traits (germination and seedlings' root and shoot lengths) were determined before and after the storage treatments. Additionally, early development traits in mini-pots during the first two months of development (emergence, plantlet height, plantlet root length, fresh weight of roots and shoots) were tested. The research has shown significant effects of storage temperatures to all the investigated traits of
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