Adopting the cross design, 16 Holstein-Friesian cows of stable production performance were divided into group A and group B. The experiment was divided into two periods.

• 试验选取16头生产性能稳定的荷斯坦奶牛，采用交叉试验设计，设计两个处理组(A组和B组)，试验分为两个时期，两组在两期中互为对照。