Production and economic effects of shortening days dry for high producing dairy cows in Yazd province.

Days dry affects especially on milk production and reproduction. Persistency of high milk production cows increases income over feed cost per cow per day of calving interval. Also a shorter dry period reduces the frequency of diet change and facilitates nutrition management. Effect of length of days dry on productive performance of Holstein cows in Yazd province was studied by 1780 records of dairy herds of Yazd province. Strategy of shortening days dry from 60-d to 40-d increases 8% in income over feed cost per cow per day of calving interval in Yazd province. This result suggests increases in the efficiency of milk production especially in hot and dry areas.