Genetic and phenotypic parameters of Australian Large White and Landrace boars performance-tested when offered food ad libitum

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Abstract
Genetic analyses were carried out on 935 Large White and 767 Land-race boars performance-tested from 25 kg to 80 kg live weight under individual andad libitumfeeding conditions. Traits analysed were daily weight gain (GR), feed conversion ratio (FCR), daily feed intake (FI) and subcutaneous fat depth (F). Genetic parameters were estimated from sire components obtained by conventional hierarchical analyses of variance and covariance.Large White pigs grew faster, had higher intakes of feed and utilized it more efficiently than Landrace. There was no breed difference in fat depth. Heritabilities, pooled over both breeds, were 0·36 ± 0·10, 0·27±0·08, 0·62±0·13 and 0·47±0·11 for GR, FCR, FI and F respectively. Noteworthy among the correlation estimates were strong and positive correlations between FI and the other three traits. A positive genetic correlation between GR and FCR arose from a very high coefficient of genetic variation for FI.Selection indexes emphasising efficiency of lean growth were constructed using some or all of the 4 traits as measured variables. Their use is expected to reduce FI and GR on feeding ad libitum. The results indicate the need to select pigs on the same level of feeding as that used in production.