Productive, physiological and biochemical changes in imported and locally born Friesian and Holstein lactating cows under hot summer conditions of Egypt.

Twenty each of healthy lactating Friesian and Holstein cows were studied. They were of similar age and body weight, nonpregnant in their third lactation and 80-100 days post partum. The investigation was carried out for 8 weeks on two farms at the same time during the hot summer season in Egypt. The first farm was in Demietta (North east of the Nile Delta, 31 degrees 40' N) on 20 Friesian cows and the second was in Fakous (East of the Nile Delta, 30 degrees 40' N) on 20 Holstein cows. On each of the two farms, 10 cows were newly imported and 10 were born in Egypt. The average daily milk yield and total milk production in the third lactation of the newly imported cows were significantly higher than those of the locally born cows for both Friesians and Holsteins. At the same time, the T4, T3, urea-N, haematological values and AST enzyme activity in the newly imported cows were significantly lower than those in the locally born ones in both breeds, while the locally born cows showed significantly lower values for rectal temperature and respiration rate, as well as for AST and Alk-P enzyme activities, than the newly imported cows of either breed. Holstein cows surpassed the Friesians in milk production, as well as thyroid hormone secretion and cholesterol, haemoglobin, packed cell volume and erythrocyte count values. The opposite was found for serum total protein, urea-N and creatinine concentrations, leukocyte count and AST, ALT and Alk-P enzyme activities.