The effects of age of castration on carcass characteristics, meat quality and fatty acid profile of finishing South African Mutton Merino lambs

Abstract

This study compared the effect of either keeping South African Mutton Merino (SAMM) ram lambs intact, or castrated with age applicable methods on their carcass characteristics, meat quality and fatty acid composition of subcutaneous fat (SCF) and intramuscular fat (IMF). Ten lambs per treatment were castrated early at one week of age (EAR) with an elastrator band (4.4 kg ± 0.78 kg: mean ± SD), another 10 lambs at eight weeks of age (late castration - LAT) with a burdizzo (23.6 kg ± 2.26 kg: mean ± SD), whereas another ten lambs were left intact (CON). The two castration methods used were based on cost, ethical prescriptions and to mimic commercial operations. The lambs were housed individually in 30 pens (1.404 m2) for the duration of the study. Animals were housed on an elevated slatted wooden floor in the same metabolic building with an extractor fan to promote ventilation. At the start of the feeding trial, the age of the lambs was on average two and a half months with a live weight of 24.3 kg ± 4.10 kg (mean ± SD). The lambs were fed a standard commercial finishing diet for 67 days and slaughtered when they reached approximately 44.2 kg ± 6.35 kg (mean ± SD) live weight. After slaughter, carcass characteristics (cold carcass) and meat quality were evaluated. The left 3-rib cut was dissected (9th through 11th rib) and the muscle percentage for CON lambs was higher compared to both EAR and LAT lambs. Therefore, CON lambs produced leaner carcasses compared to EAR and LAT lambs. Castration status had no effect on meat Warner-Bratzler shear force (WBSF), consumer sensory analysis nor colour. For proximate composition, CON lambs had higher moisture compared to LAT lambs while LAT had higher dry matter compared to CON lambs. Both, EAR and LAT lamb’s meat had higher organic matter compared to CON lamb’s meat, but these differences were negligible. For IMF in the longissimus thoracic et lumborum muscle, CON lambs’ meat had higher total PUFA, α-linolenic acid, total PUFA n-6, linoleic acid, PUFA:SFA ratio and PUFA:MUFA ratio than meat from both EAR and LAT lambs. Eicosapentaenoic acid (EPA) and total PUFA n-3 were both higher for meat from CON lambs than LAT lamb’s meat, while palmitic acid and conjugated linoleic acid (CLA) were higher for EAR lamb’s meat than CON lamb’s meat and EAR lambs than LAT lamb’s meat, respectively. For SCF, CON lambs had higher heptadecenoic acid and linolelaidic acid than LAT lambs. The calculated atherogenicity index (AI) of SCF was higher for LAT lambs compared to CON lambs. Limited effects of castration age on the possible health benefits of SAMM lamb meat were proven in the current study. It is however suggested that for a higher production response and carcass muscle content, to either keep SAMM rams intact or at least postpone castration for as long as possible.