Environment discomfort and ability to sustain the performance level during life time under the sub-tropical conditions in imported Holstein Friesian young cows

In the present study, the Holstein Friesians were imported from Germany to the sub-tropical environment in Jordan as pregnant (between 5 and 7 months) heifers. The study included some performance traits as affected by season of the year, parity and classes of each of milk yield, lactation period and days open. The results indicated that the animals were exposed to severe heat stress during summer and to mild climate (without heat stress) during autumn and winter. Days open, lactation period and calving interval values were higher (P < 0.05) in summer than in autumn The estimated average deviations percentage occurred as a result to the inadequate conditions was 37.8 for imported young cows, when considering that the optimum comfort environmental temperature for Holstein cattle as 10 degrees C. Effects of parity were significant (P < 0.001 or 0.01) on days open, number of inseminations per conception, milk yield and calving interval. The estimated values were higher (P < 0.05) in the second parity than in the other parities. Average deviations in the traits in different parities, relatively to the values of the same traits in the first parity, was estimated as 10.33\%. When studying the effects of some trait classes, it was found that days open and number of services per conception increased (P < 0.001) with the increase in classes of milk yield, dry period and calving interval also increased (P < 0.001) with the increase in classes of lactation period, and lactation increased (P < 0.001) with the increase in classes of days open. The results may indicate that deterioration of the newly imported Holstein cow traits under the sub-tropical environment, a state of reversal to origin.