Production performance and meat quality characteristics of sheep comprising four sex-types over a range of slaughter weights produced following commercial practice

Eighty four lambs comprising four sex-types (entire rams, castrated rams, vasectomised rams and entire ewes) were distributed equally into seven target slaughter weights (32, 36, 40, 44, 48, 52 and 56 kg). All lambs were born in early spring. Dams and lambs were out on pasture until late September when they were housed and fed concentrate and hay. At birth, ram lambs were heavier than ewe lambs (P < 0.01) and gained weight faster (P < 0.05). The three male sex-types were similar in birth weight, growth rate and dressing out percentage (P > 0.05), and were significantly lower than ewes in dressing out percentage (P < 0.001). The m. longissimus dorsi (LD) from all sex-types were similar in initial pH, ultimate pH and sarcomere length (P > 0.05) but differed in cooking loss and shear force (P < 0.05). The LD from ewes were lower in cooking loss than those from the male sex-types (P < 0.05), and recorded smaller shear force values (P < 0.05). The average a^* values (redness) of the LD was highest in ewes and differed only from that of vasectomised rams (P < 0.05). Ewes were also highest in oxymyoglobin proportion (P < 0.05). Although correlations between most meat quality parameters and slaughter weight were highly significant (P < 0.001) the correlation coefficients (r) were generally small.