Body weight and ultrasound measurements over the finishing period in Iberian and F1 Large White x Landrace pigs raised intensively or in free-range conditions

Iberian (IB) pigs are often finished on grass and acorns, and they are known for their ability to deposit high amounts of fat. Live weight, body dimensions and backfat depth measured by ultrasounds in various layers and backfat depots, were collected in an experimental group (n = 117) of IB and crossbred Large White x Landrace pigs (F1), finished either intensively or in oak-tree forests in a factorial experiment. Weight and ultrasounds data were collected at the beginning, midpoint and end of the finishing period, which occurred at a mean live weight of approximately 85, 125 and 160 kg, respectively. Changes in live weight and fat depth over the finishing period were assessed and body dimensions and backfat depth measured by ultrasounds were used to predict carcass traits. Genetic groups differed considerably in growth rate (P < 0.01), with higher ADG in IB than in Fl pigs by about 200 and 80 g/d in the first and second stages of finishing, respectively. Finishing system also affected growth rate (P < 0.01), with faster growth in intensively finished pigs, by about 380 g/d in stage 1 and 220 g/d in stage 2 of finishing. The mean ADG was always higher in the first than in the second stage of finishing, particularly in IB pigs and those finished intensively. In all fat depots considered, the internal fat layer was thicker than the external layer. The major differences in backfat thickness were observed between genetic groups while differences between finishing systems were smaller and often not significant (P > 0.05). At the end of the finishing period, total backfat was about twice thicker in IB than in Fl pigs in the dorsal and P2 depots (P < 0.05), and nearly 50% thicker in rump backfat (P < 0.05). The correlations between dorsal and P2 backfat measurements obtained in carcasses at 24 h post mortem and the same measurement obtained by ultrasounds right before slaughter were near 0.85 for total and internal backfat layers (P < 0.05), but dropped to about 0.3 to 0.6 when estimated within genetic group. Stepwise regression equations estimated to predict various carcass and meat traits indicate that morphometric characteristics had a modest contribution for most carcass traits while the depth of the internal layer of P2 backfat was of major importance in many cases. The ability to predict dressing percentage and abdominal fat had modest accuracy, while ham tissue composition and intramuscular fat percentage could be accurately predicted based on in vivo indicators.