Previous studies have shown that using non-invasive techniques such as the measurement of the velocity of ultrasound (VOS) through live animals (Sim. 1983) can, in the body of the lactating dairy cow, provide reliable estimates of chemical composition and energy content (Ivings,Gibb,Dhanoa and Fisher.1993). In this study VOS was used to monitor the changes in body composition of dairy cows fed concentrates containing differing levels of crude protein (CP).

Fifty-five Holstein-Friesian cows were offered 5kg of fresh concentrate containing 156(L),245(M) or 338(H)g CP/kg dry matter (DM) together with grass silage (162g CP/kg DM,D value 0.723,ME 12.3 MJ/kg DM and pH 3.72) offered ad-libitum over weeks 4 to 21 of lactation. There were five treatments designated LL,LH,MM,HL, HH with a change of CP level where appropriate in week 13. Five cows were selected from each treatment and VOS measurements taken from two sites on the hindquarters (B and Bl) at weeks 12,15,18 and 21. Liveweights were also taken at this time.