动物营养试验中，一般设计不同的日粮或营养素饲喂动物后，每隔几周采集一次样品或记录生产性能。统计数据时，一定要利用混合模型进行方差分析，模型参数如下供参考：

proc mixed;
class trt week cow;
model protein=trt week trt*week;
random cow(trt);
repeated week/type=ar(1) sub=cow(trt) r rcorr; * select type which produce the smallest AIC value
*repeated week/type=cs sub=cow(trt) r rcorr; * select type which produce the smallest AIC value
*repeated week/type=un sub=cow(trt) r rcorr; * select type which produce the smallest AIC value
*repeated week/type=ante sub=cow(trt) r rcorr; * select type which produce the smallest AIC value
lsmeans trt week trt*week/pdiff adj=tukey;
run;