7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France Session 11. Growth and meat quality Communication N° 11-46 BONE MINERALIZATION AND BODY COMPOSITION OF NEWBORN CROSSBRED AND PUREBRED CALVES USING DUAL ENERGY X-RAY ABSORPTIOMETRY (DXA) A. Scholz 2 , S. Nüske 2 , P. Soffner 1 and M. Förster 1 Ludwig-Maximilians-University Munich, Veterinary Faculty, 1 Institute of Animal Breeding, Veterinärstr. 13, 80539 Munich, Germany 2 Experimental Farm Oberschleißheim, Hubertusstr. 12, 85764 Oberschleißheim, Germany INTRODUCTION This study was performed in the context of a crossbreeding program with cattle of the dairy breed German Holsteins and the two-purpose breed (milk and meat) German Fleckvieh (Simmental) at the Experimental Farm Oberschleissheim of the University Munich. Since German Fleckvieh cows are more robust and have less health problems (udder and legs) than German Holsteins in an automatic milking system with free cow traffic (Scholz et al., 2001a, b), one question was, if already the newborn F1 crossbred calves of these two breeds would show an advantage in bone stability (and body composition for meat production) over their parent breeds. The data were acquired by using dual energy x-ray absorptiometry (DXA), which is a relatively new method for the measurement of bone mineralization and body composition in livestock (Mitchell and Scholz, 2001). The principle of DXA is based on the different x-ray attenuation of different body tissues. Thus, the whole body or body regions (claws: Nüske et al., 2002) can be analyzed for bone mineral content (BMC, g or %), bone mineral density (BMD, g/cm²), and for the content of fat tissue (DXA Fat, g or %) or lean tissue (DXA Lean, g or %). In this study the bone mineralization and composition of the whole body of female and male calves was compared among the four different breeding types: [German Holsteins -- DH], [German Holsteins | x German Fleckvieh ∼ -- DH-FV], [German Fleckvieh | x German Holsteins ∼ -- FV-DH], and [German Fleckvieh -- FV] during growth from birth (≥ 4 th day of life) until 50 th day of life. In addition, the study was aimed at the assessment of DXA for the measurement of early bone mineralization and body composition under the aspect of genetic evaluation of different breeding lines in cattle. MATERIAL AND METHODS Beginning at day 4 post partum, we performed three DXA scans using a GE LUNAR DPX- IQ  scanner (Fig. 1) with a three week interval. Totally, 31 male (m) and 32 female (w) calves from the two breeds DH and FV, and of the two F1 sublines DH|FV∼ or FV|DH∼ were analyzed under light sedation with Xylazin (Rompun  2 %) [1.5-2.5 ml/100 kg body weight -- BW, i.m.] (Tab. 1). The calves originate from the matings of 4 DH sires and 5 FV sires with totally 29 DH and 25 FV cows or heifers (1 st –6 th lactation; 1 FV cow with 1 calf in 4 th and twins in 5 th parity). Among all calves were 12 twins (from 6 twin births), and 3 calves originated from a triple birth. With exception of one twin birth, all multiple births originated from FV cows. Up to the 7 th day of life, all calves were fed individually colostrum (4 – 6 l) and