Factors affecting the longissimus dorsi muscle depth and backfat thickness measured by ultrasound technique in lambs

study was conducted to estimate the effect of systematic factors on characteristics of meatiness and fattiness scanned by ultrasound in live lamb. The second aim of the study was to compare two statistical models (with and without regression on lamb liveweight) for analysis of variance in muscle depth and backfat thickness. Ultrasonic measurements collected in field conditions during the years 1999-2005 were available for 6270 purebred Suffolk (SF), 4191 Charollais (CH), 1320 Texel (T) and 2093 Romney (RM) lambs. Lambs were scanned at the age of 80-120 days by 5MHz linear probe behind the last rib vertebra after wool combing. The averages for muscle depth were 25.54, 23.56, 24.04 and 24.29 mm and for backfat thickness with skin 3.22, 2.83, 2.88 and 3.69 mm for SF, CH, T and RM lambs. According to Akaike criterion the statistical model with regression on lamb liveweight better fits the analysed data both for muscle depth and backfat thickness. Including the lamb liveweight effect into model equation caused decrease of influence of dams age and type of birth effects on the variability of both examined traits. On the contrary, effect of sex increased. After adjustment with the same liveweight the female lambs had significantly higher muscle depth and backfat thickness compared to male lambs. This fact is probably caused by different body proportions of males and females. Rams have their body mass concentrated rather in the chest and rack area than in the scanned part of the body.