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A study was made of differences in the quality of meat from Lacha (L) and Rasa Aragonesa (RA) lambs slaughtered at 12, 24, or 36 kg live weight. Lambs from both breeds were weaned at 25 to 57 d, approximately 11.5 to 18.5 kg live weight, and fed concentrate and barley straw until slaughter at 24 and 36 kg live weight. Hot carcass weight, cold carcass weight, conformation, color, firmness, and thickness of backfat and color of rectus abdominis muscle were recorded on the carcass. Final pH (pHu), instrumental color (L*, a*, b*), myoglobin concentration, chemical composition, and water-holding capacity (WHC) of the longissimus muscle, shear force of the biceps femoris muscle, and iodine values and fatty acid composition of the i.m. and s.c. fat depots were determined. The percentage of fat in the longissimus muscle increased with live weight, and values for RA lambs were higher than those for L lambs. The WHC of meat from RA lambs was lower at 24 kg than at 12 or 36 kg slaughter weight. Live weight and breed had no effect on the shear force of the biceps femoris muscle. There was an increase in myoglobin concentration in the longissimus muscle with increased live weight in both breeds. The fatty acid content of s.c. and i.m. fat, which was not affected by breed, declined with the increase in slaughter weight. The polyunsaturated fatty acid content of the s.c. fat depot increased, whereas that of the i.m. fat depot decreased, with the increase in slaughter weight in both breeds. Subcutaneous fat had a higher content of heptadecanoic acid (17:0) than i.m. fat, and this increased with the increase in slaughter weight. In both depots, there was an increase in oleic acid (18:1) at 12 kg in RA lambs and at 24 kg in L lambs. In the s.c. fat depot, there was a progressive increase in linoleic acid (18:2) content with the increase in live weight in both breeds. There was a higher degree of unsaturation in the s.c. fat of RA lambs than in that of L lambs, which was reflected in the iodine value.

The influence of sex on the meat quality of Lacha (L) and Rasa Aragonesa (RA) lambs was studied. Male and female L lambs were given ewes' milk and were slaughtered at 25 and 24 days of age corresponding to 11·4 and 10·9 kg live weight (LW), respectively. Male and female RA lambs were weaned at 58 days (16·0 kg LW) and then given concentrate and barley straw until slaughter at 89 and 91 days of age, corresponding to 24·5 and 23·1 kg LW, respectively. The parameters measured on the carcasses were: hot carcass weight, cold carcass weight, conformation, colour, firmness and thickness of dorsal fat and colour of muscle rectus abdominis. Parameters measured on longissimus dorsi muscle were: ultimate pH (pHu), instrumental colour (L*, a*, b*), myoglobin concentration, ash, crude protein, fat, moisture and water-holding capacity (WHC). Iodine value and fatty acid composition were studied in the intramuscular (IM), intermuscular (IN) and subcutaneous (SC) fat depots. Females of both breeds had higher amount of IM fat (P < 0·001 and P < 0·05 for L and RA breeds, respectively) and firmer SC fat than males (P < 0·05). There were no differences between sexes in pHu, myoglobin concentration, WHC and the L*, a* and b* colour parameters. No significant differences between sexes were observed in the total saturated fatty acids, total unsaturated fatty acids and in the iodine value in the three fat depots studied in both breeds. However, the females of the breed had significantly higher proportions offatty acids with 15 carbon atoms (pentadecanoic (C15:0)) and with 16 carbon atoms (palmitic (C16:0)and palmitoleic (C16:1)) than the males in the three depots. The females of Rasa Aragonesa breed had a higher proportion of palmitoleic acid (C16:1)in the IM depot (P < 0·001) and of palmitic acid (C16:0)in the SC depot (P < 0·05) than the males. The absence of significant differences in the unsaturated fatty acid content between males and females showed that at the low slaughter weight, sex had no effect on the nature and composition of fat.

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