271 ACTA UNIVERSITATIS AGRICULTURAE ET SILVICULTURAE MENDELIANAE BRUNENSIS Volume LIX 35 Number 6, 2011 EFFECT OF BARN AIRSPACE TEMPERATURE ON COMPOSITION AND TECHNOLOGICAL PARAMETERS OF BULK MILK PRODUCED BY DAIRY COWS OF CZECH FLECKVIEH AND HOLSTEIN BREEDS O. Polák, D. Falta, O. Hanuš, G. Chládek Received: August 31, 2011 Abstract POLÁK, O., FALTA, D., HANUŠ, O., CHLÁDEK, G.: Effect of barn airspace temperature on composition and technological parameters of bulk milk produced by dairy cows of Czech Fleckvieh and Holstein breeds. Acta univ. agric. et silvic. Mendel. Brun., 2011, LIX, No. 6, pp. 271–280 On two farms (A and B), samples of bulk milk produced by dairy cows of the Holstein (H) and Czech Fleckvieh (CF) breeds were collected every week on the same day within the time interval of 36 weeks. The aim of this sampling was to determine the effect of barn airspace temperature on milk compositon and its technological parameters. The following average values of all bulk milk samples (n = 72) were recorded: barn airspace temperature (BAT) 12.08 °C; rennet coagulation time (RCT) 211 sec.; curd quality class (CQC) 1.53; titratable acidity (TA) 7.16 °SH; protein content (P) 3.46 %; fat content (F) 4.09 %; lactose content (L) 4.79 %; and solids non fat (SNF) 8.86 %. As compared with H, dairy cows of CF breed produced milk with statistically significantly higher (P < 0.01) contents of P (+0.27 %) and SNF (+0.26 %). The remaining differences were statistically insignificant (P > 0.05): BAT (−2 °C); RCT (−4 sec.); CQC (0 class); TA (+0.11 °SH); F (+0.05 %) and L (−0.03 %). As far as the effect of temperature was concerned, calculated correlation coefficients and plotted graphs indicated a marked effect of BAT on RCT; F and P. This effect was in all cases markedly negative: at lower BAT, F and P values were higher and RCT longer while at higher temperatures they were lower and shorter. These trends were similar in both breeds regardless to differences in average values of aforementioned parameters. barn airspace temperature, milk, composition, technological parameters, Holstein, Czech Fleckvieh Although the milk cattle shows a high adaptability to a wide scale of climatic conditions, its performance can be influenced by great temperature fluctuations occurring within the year. Nowadays, effects of the heat stress represents a tropical problem also in Eastern and Central Europe. Summer climate causes the heat stress of dairy cows and the heat stress results in am depression in milk production. The heat stress occurs in situations when the ambient temperature is higher than that of the animal’s thermal neutral zone (Novák et al., 2009). According to Vokřálková and Novák (2005), the thermoneutral zone of dairy cows ranges from −5 to +24 °C. Other authors reminded that in high-yielding (i.e. > 6,500 kg) and, especially, older cows, the thermal stress developed at temperatures > 21 °C (Novák et al., 2009; Vokřálková and Novák, 2005). The heat stress problem is getting worse as production levels continue to rise (Mitlöhner et al., 2002; Beatty et al., 2006). The summer depression in production of milk causes significant economical losses in the dairy industry. The basic condition of dairy farm management depends on the knowledge of and understanding to factors affecting milk production at most, i.e. not only nutrition and health status of dairy cows but also the parity and calving season,