A modelling study of once-bred heifer beef production

Sixteen cows were randomly allocated to he two treatment groups; one was given high digestibility hay (57% DMD and the other low digestibility hay (52% DMD). Hay was available to appetite during the daytime, while the cows grazed on a common pasture allowance (12 kg DM per cow) at night. Cows offered high digestibility hay ate more hay (P<0.01) but less pasture (P<0.05) than those on the low digestibility hay. Pasture intake was reduced by 0.2kg DM for each increase of 1 kg DM eaten as high digestibility hay. Cows offered the high digestibility hay ate more hay (P<0.01) but less pasture (P<0.05) than those on the low digestibility hay. Pasture intake was reduced by 0.2 kg DM for each increase of 1 kg DM eaten as high digestibility hay. Cows offered the high digestibility hay produced slightly more milk than those on the low digestibility hay. This difference averaged 1.3 L per cow daily, but was significant only in week 1. The composition of milk did not differ between the two groups. The cows offered the high digestibility and also gained significantly more liveweight. The data show that the quality of supplemental hay has an effect on milk production, but that the effect is smaller than might have been predicted because of the increased substitution of hay eaten instead of pasture by cows given the higher quality hay and because of increased liveweight gain by these cows. The probable economic value of high digestibility supplement is discussed briefly.