Physical meat quality and chemical composition of the Longissimus thoracis of entire and immunocastrated pigs fed varying dietary protein levels with and without ractopamine hydrochloride

•Immunocastrates and entire male pigs were fed RAC with varying dietary proteins.•Immunocastration and feeding a medium protein diet decreased cooking loss.•RAC increased WBSF and decreased a* and b* values.•Sex-protein interactions were observed for muscle protein content, L* values and WBSF.•Differences observed were minor thus effects on meat quality are possibly negligible.

Physical and chemical attributes of the Longissimus thoracis (LT) of 96 PIC© entire (E) and immunocastrated (C) pigs were evaluated. The study followed a 2 × 2 × 3 factorial design where three diets of low, medium and high proteins (7.50, 9.79 and 12.07 g digestible lysine/kg) were fed either with (10 mg/kg) or without ractopamine (RAC) for the last 28 days of growth. Vaccination of C occurred at 16 and 20 weeks and slaughtering at 24 weeks of age. The LTs were analysed for moisture, protein, fat and ash contents as well as CIE L*, a*, b* colour, drip loss, cooking loss and Warner-Bratzler shear force (WBSF). Various sex and protein interactions were observed for LT protein content, L* values and WBSF. Cooking loss was decreased in C and by the medium protein diet. Feeding RAC increased WBSF values, whilst decreasing a* and b* values. However, the differences observed are minor and might be considered negligible when evaluated by a consumer.