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The objective of this work was to evaluate the ultrasound method as a tool for in-vivo breast and abdominal fat prediction on Campero-INTA broilers. Breast length (mm), width (mm), surface (mm2; ultrasound) and depth (mm; ultrasound), and abdominal fat depth (mm; ultrasound) were measured at 65-66 and 72-73 days of age on 96 males. At 79 days of age, the broilers were weighed and slaughtered. Breast and abdominal fat weights (g) were obtained. Multiple regression equations were fitted using live weight (g) and in-vivo measurements to predict breast and abdominal fat weights and proportions (g/g). The best model for each case was selected by the Stepwise procedure. Equations fitted were verified using another set of data. Breast weight prediction using live weight and breast length in the model was as accurate as using live weight and breast depth. The former is recommended for breeding work. Abdominal fat weight prediction using ultrasound measurements of fat was less accurate than breast weight prediction. Repeatabilities for ultrasound breast measurements were higher (0·72 to 0·73) than those for abdominal fat (0·51 to 0·52). Operator effect may be important when training levels are different.

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The association between body weight-age and egg weight-age patterns was studied in a segregating population of laying hens belonging to the F3 generation of a Rhode Island Red x White Leghorn reciprocal cross. Body weight and egg weight were expressed as a function of time using the model developed by Weatherup and Foster. Each hen was characterized in terms of its asymptotic body weight (ABW), maturing rate for body weight (MBW), asymptotic egg weight (AEW), and maturing rate for egg weight (MEW) values. Four groups of hens were distinguished by means of a principal component analysis. Birds belonging to Groups 1 and 3 were discriminated for their egg weight-age pattern. Group 1 included hens laying the heaviest eggs (AEW = 66.1 g) at the lowest maturing rate (MEW = 0.922), the inverse being true for birds in Group 3 (AEW = 55.7 g and MEW = 0.737). Birds belonging to Groups 2 and 4 were distinguished for their body weight-age pattern. Hens in Group 2 showed the lowest ABW (1,893 g) and MBW (0.764) whereas the heaviest (ABW = 2,802 g) and less mature (MBW = 0.929) birds were found in Group 4. The results confirm the partial pleiotropic basis of the body weight-egg weight correlation, evincing the feasibility of applying selective pressure not only on each character separately but also on maturing rate independently of asymptotic weight within each trait. This strategy could be implemented using a biological selection index based on principal component analysis equations.