The test of supplementary feeds using "green oat hay plus animal nutrition blocks" was carried out on thirty pregnant cows of late pregnancy（after 153 days）.The results indicated that the difference of weight between treated groups and control group were not significant（P＞0.05） during whole experiment period.But the difference of the birth weight of yak calves（13.05 kg and 11.50 kg） were very significant（P＜0.01）.