The objective of the present study was to determine the inhibitory effect of dietary rosemary diterpenes on the formation of the volatile organic compounds (VOCs) responsible for rancid flavour in raw lamb meat. The lamb diet was supplemented during the fattening stage with two levels (200 and 400 mg/kg feed) of a dietary rosemary extract (DRE) containing carnosic acid and carnosol (1 : 1, w/w). The formation of VOCs (determined by headspace solid-phase microextraction at 40°C and MS) and odour deterioration (assessed by quantitative descriptive analysis) were monitored in meat fillets (longissimus dorsi-lumborum muscle) packed in a 70/30 O2/CO2 protective atmosphere and kept at 2°C for up to 14 days. The raw meat odour deteriorated under pro-oxidizing conditions due to the development of an incipient rancidity caused by the formation of volatiles from lipid oxidation. A total of 46 volatile compounds were determined in lamb headspace: 18 aldehydes, seven alcohols, seven organic acids, six ketones, four furan compounds, two benzene compounds, one ester and one terpenoid. The use of DRE contributed to inhibit VOC formation and rancidity. Heptanal, octanal, nonanal and 2-pentyl-furan were the only VOCs affected (P<0.05) by the diet at any storage time. In general, VOC formation rate during storage was lower (P<0.05) in the meat from lambs that received a diet supplemented with 400 mg DRE/kg feed than in the meat from lambs receiving no dietary supplementation. VOC inhibition was less effective when the dose of DRE was reduced to 200 mg/DRE kg, although it depended on the VOC analysed. The intensity of rancid odour correlated (P<0.05) with the values of 43 of the 46 VOCs. The highest coefficients were obtained for octanol and octanal (R>0.75; P<0.001), although similar values were obtained for the coefficients of a large number of carbonyl, alcohols and furan compounds, among other volatiles, which can be considered molecular markers of rancidity in raw lamb meat. Principal component analysis confirmed that the differences in the VOC profile make it possible to identify whether or not samples have been reinforced with dietary rosemary diterpenes. Thus, VOC profiling can be regarded as a useful tool for assessing the dietary treatments used in sheep to improve the oxidative stability of lamb meat.

A simulation study, based on a closed sheepmeat breeding nucleus and incorporating marker-assisted selection (MAS), was used to evaluate response when different proportions of animals were marker typed. Two traits were included in the simulation: trait 1, a production trait where phenotypes were available prior to selection, and trait 2, a carcass trait where phenotypic information was not available on breeding animals. Selection on an index which comprised estimated breeding values (EBVs) for both traits was possible by calculating EBVs for trait 2 as the sum of EBVs for a polygenic component, obtained from a genetic regression, and EBVs for a major gene component, obtained by inferring genotypes at a major gene locus from a linked marker locus. Different marker typing strategies were evaluated. These differed in the criteria used to select progeny for typing, and in the proportion of male and female progeny selected. Typing progeny that were likely to be used as a breeding animal, but excluding those whose marker genotype could be predicted with reasonable certainty, was an efficient genotyping strategy. Close to maximum gain at the major gene locus was achieved when only a proportion of animals were marker typed (for example 90% of maximum response was achieved with a little over one-third of the selection candidates marker typed). This indicates the potential for substantial savings in relation to the cost of marker typing in commercial breeding flocks.