RELATIONSHIPS BETWEEN VELOCITY OF ULTRASOUND IN LIVE LACTATING DAIRY-COWS AND SOME POST-SLAUGHTER MEASUREMENTS OF BODY-COMPOSITION

During an experiment to measure changes in body composition of lactating Holstein-Friesian dairy cows, the velocity of ultrasound (VOS) through two hindquarter sites and a shoulder site was measured. Fifty-four cows were offered grass silage ad libitum with 3, 6 or 9 kg dry matter (DM) per day of concentrates. Six cows were slaughtered 2 to 4 days post partum (week 0) and two from each diet at 2, 5, 8, 11, 14, 19, 24 and 29 weeks post partum. After slaughter the right half-carcass and organs were frozen and minced before chemical analysis and the left half-carcass from 15 animals was jointed and fully dissected into bone, muscle, subcutaneous and intermuscular fat and other tissues. The relationships between the VOS measurements, together with live weight (LW) and the proportions of dissected fat and muscle tissues in the half carcass were examined and found to be comparable with published data for beef cattle. The relationships of the VOS measurements and LW to chemically determined fat and crude protein (CP) and derived estimates of energy were examined for the carcass and for the whole empty body, and found to account for proportionately 0.66 to 0.87 of the variance. The use of this non-invasive technique to monitor changes in body composition of dairy cows during lactation is therefore suggested as a useful and reliable technique. Dissection of a small inexpensive abdominal sample joint to estimate the fat : muscle ratio of the carcass was found to account for 0.85 of the variance. Finally, the relationship between dissected fat and muscle tissue weights in the half carcass and chemical fat and CP weights in the carcass and empty body were examined and found to be highly correlated.