For profitable production of milk, a nonlactating or dry period is established between lactations of dairy cow. There has been substantial recent interest in shortening dry periods. Physiological studies show that the changes the udder goes through to prepare for the next lactation take about three weeks, and yet current advice is that the most appropriate dry period for a modern dairy cow is 45 to 60 days. More recent studies show good reason to question that advice, and suggest dry periods of 30 to 35 days have no detrimental effect on production, but information relating the effects of dry period to subsequent reproductive performance of lactating cows is sparse (Grummer, 2007). Also, the effect of this management change on follicular dynamic has not been adequately evaluated. Therefore, the objective of the present study was to determine the effects of dry period length on follicular dynamics in early lactating Holstein cows

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