The study, published in the July Journal of Dairy Science, featured 850 Holstein cows from 13 commercial dairy herds that were assigned to either a 35-day (short) or a 60-day (conventional) dry period, based on milk yield, number of calves and estimated calving interval. Lower incidence of metabolic disorders for second lactation, compared to third or later lactation cows in both groups. â¢ Cases of mild ketosis were lower for cows in the shortened dry period group. â¢ Occurrence of retained placenta was higher for second and later lactation cows in the short dry period.