Ducháček J., Stádník L., Ptáček M., Beran J., Okrouhlá M., Čítek J., Stupka R. (2014): Effect of cow energy status on the hypercholesterolaemic fatty acid proportion in raw milk. Czech J. Food Sci., 32: 273-279.We evaluated the proportion of fatty acid groups, with an emphasis on hypercholesterolaemic fatty acids, in the milk of 25 Holstein cows during the 1 st period of lactation in relation to their negative energy balance (NEB). Sampling of each cow's milk started on the 7 th day after calving. Milk samples (n = 425) were collected at 7-day periods during the first 17 weeks of lactation. The proportion (%) of saturated (SFA), hypercholesterolaemic (HCFA), volatile (VFA), unsaturated (UFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fatty acids in the milk fat was determined. Body condition score and fat to protein ratio in milk were applied for precise determination of the NEB breakpoint during the observed period. The effects of parity, NEB, regression on lactation week and fat to protein ratio were evaluated using SAS 9.3. Milk contained a lower proportion of SFA as well as equally higher UFA (± 2.13%; P < 0.01) during the NEB period. The overcoming of NEB caused an increase in SFA, however, and simultaneously a significant decline in total HCFA (-1.86%; P < 0.01) as well as main MUFA (-1.81%, P < 0.05). The results document the necessity of increasing Holstein cow robustness to meet the production conditions in dairy farms in relation to the requirement of higher nutrient quality as well as the potential health benefits of cow's raw milk for consumers.

The aim of this study was to evaluate the relationships between milk fatty acid group contents and subsequent reproductive performance in Holstein cows. A total of 27 cows in the 1st to 4th lactations were included in the evaluation. Cows were divided into primiparous and multiparous groups. Daily milk yields increased in the first 8 weeks of lactation. Body condition score decreased until the third month of lactation. As the cows gradually recovered from the negative energy balance, the contents of saturated fatty acids (SFAs) increased, whereas the contents of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) decreased. The contents of SFAs and MUFAs were significantly (P < 0.01-0.05) correlated (r = -0.279 to r = 0.275) with all the reproductive traits evaluated (calving to first insemination interval, days open, and insemination index). PUFA was only correlated (P < 0.01) with calving to first insemination interval (r = -0.141). High milk SFA contents were associated with improved values of days open and insemination index, whereas opposite tendencies were observed for MUFA. It was concluded that the relationship was confirmed between the changes of different milk fatty acid group contents in early lactation, used as negative energy balance indicators, and subsequent reproduction results.