EFFECTS OF DIET, LITTER, AND SEX TYPE ON THE PERFORMANCE (FROM 22 TO 90 kg LIVEWEIGHT) AND CARCASS MEASUREMENTS OF CROSSBRED PIGS

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Abstract
Thirty-one Hampshire × (Landrace × Yorkshire) litters provided 48 littermate trios (boar + castrate + gilt). Each subgroup of 24 pigs (eight trios with similar liveweight) was assigned to six pens, a pair for each sex type. Subsequently, from 22 to 90 kg average liveweight, pigs were self fed either a Test Station diet (ROP; 16.3% crude protein and 12.83 MJ digestible energy/kg) or one representative of commercial practice (COM; 15.2% crude protein and 12.59 MJ DE/kg). The diets were allocated at random within each pair of pens and each subgroup represented a 2 × 3 factorial design. Sixty of the pigs (derived from 10 litters which contributed a trio to each diet) provided data on physical composition of the ham and chemical composition of a sample of the longissimus dorsi, in addition to routine live and carcass measurements from all pigs marketed. In comparison to COM-fed pigs, those consuming the ROP diet were superior only for growth rate (824 vs. 788 g/day, P < 0.01), liveweight gain per kilogram feed (383 vs. 358 g, P < 0.01) and carcass grade (Value Index of 105.2 vs. 104.2, P < 0.05). Sex-type comparisons revealed that castrates had the highest (P < 0.05) rates of feed intake and growth but boars were most efficient at feed conversion (P < 0.05) and tended to produce the leanest carcasses. Gilts were usually intermediate to boars and castrates in live and carcass performance. These differences in carcass merit were reflected in the relative proportions of fat and lean in the ham from each sex type but the bone content was highest (P < 0.05) for boars and the skin content was lower (P < 0.05) for gilts compared to males. Significant (P < 0.05) litter effects were found for growth and carcass measurements, for bone and skin contents of the ham and for N content of the 1. dorsi. Rank correlations for two standard selection criteria (age and backfat at 90 kg liveweight) between boars fed the ROP diet and their COM-fed littermate castrates and gilts were not significant (P < 0.05). The apparent economic benefit (returns less feed costs) was not reduced by feeding the less-expensive COM diet ($153 vs. $175/tonne) but favored the gilts over the castrates by at least $4 per pig. Key words: Pigs, diet, sex-type, litter origin, growth, carcass

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