Effects of different dry period lengths on production and economy in the dairy herd estimated by stochastic simulation

A range of preplanned dry period lengths in a dairy herd was evaluated, at different culling strategies and feeding regimes, by means of a dynamic stochastic model simulating the production at herd level. Dry period lengths were studied in the range of 4 to 10 weeks. The culling strategies exhibited two different rates of voluntary culling for reproductive failure and milk production, and the feeding regimes consisted of grass silage ad lib. and either 8 or 12 kg of concentrates/day in the first 24 weeks of lactation. The economic result was studied under a herd size and a milk quota constraint, respectively. A dry period of seven weeks appeared to be preferable under most circumstances. The net revenue per unit of milk sold was less sensitive to dry period length than the net revenue per cow per year. No major interactions between dry period length and culling strategy or feeding regime were found. The conclusions were fairly insensitive to price changes, and to variation in the assumed effect on lactational performance of dry period lengths from 6 to 8 weeks.