Characteristics of Lacha and Rasa Aragonesa lambs slaughtered at three live weights.

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.