Research Information System
23 th European Poultry Congress, France, 1 - 04 August 2010, pp.892, (Full Text)
Alternative poultry production has increased substantially as a result of the greater demand for the so-called natural products. In this study, a slow-growing genotype (SG) and a commercial fast-growing genotype (FG) were raised in semi-extensive free range system. The birds had free access to pasture at 28 days of age. The age at slaughter was 63 days old. Birds were weighted weekly to determine individual body weight. Repeated measures term is used for multiple responses of a trait on the same animal over time such as weekly live weight measurements. Measures on the same animal close in time tend to be more highly correlated than measures far apart in time. Also, variances of repeated measures often change with time. Therefore different variance-covariance structures exist. The objective of this paper is to choose the best model to estimate weekly live weight by considering different covariance structures. The models were compared by using Akaike’s Information Criteria (AIC). “Unstructured” was chosen as the best covariance structure and the estimates of weekly live weights from hatch to 63 days of age were 44.95, 154.38, 365.89, 654.08, 1040.91, 1471.16, 2001.19, 2552, 3006.42 and 3424.75 g for FG and 42.23, 118.80, 258.61, 436.49, 660.39, 969.14, 1290.64, 1619.85, 1962.34 and 2302.78 g for SG.
Keywords: Free range system, Repeated measures, Covariance structure