Liveweight gains, and carcass and meat characteristicsof entire, surgically spayed or immunologically spayed beef heifers

Abstract

Summary. Growth, carcass and meat characteristics, market suitability and economic return were compared in surgically spayed (SS), immunologically spayed (IS) and entire (E) heifers. Spaying had no effect on daily weight gains of heifers up to 8 weeks following spaying. Between spaying at 15 months of age, and slaughter at 30 months of age, growth was greater for E heifers (0.36 kg/day) than for SS heifers (0.32 kg/day) (P<0.01) and for IS heifers (0.33 kg/day) (P<0.05). There was no difference in growth between SS and IS heifers. Carcass weights at slaughter were: E, 246 kg; SS, 239 kg; IS 240 kg (P>0.05). Other carcass attributes (meat and fat colour, texture and marbling) were similar for the 3 treatments. Subcutaneous rump fat depth (P8 site) was similar for the 3 groups (E, 20 mm; SS, 21 mm; IS, 19 mm) and the percentages of carcasses that had rump fat depths between 6 and 22 mm were: E, 72%; SS, 66%; IS, 83% (P>0.05). All other carcasses had fat depths greater than 22 mm. Warner-Bratzler initial yield and peak force values of striploin (Longissimus dorsi) samples were lower (P<0.05) in the SS treatment than both E and IS treatments, whereas Instron compression values from the E striploin were lower (P<0.05) than for both the SS and IS treatments. There were no differences between treatments in any meat attributes measured from the eye round (Semitendinosus). Entire heifers ($A522) realised a higher (P<0.05) carcass value than SS heifers ($495) whilst IS heifers ($503) did not differ (P>0.05) from E and SS heifers. Direct costs of the spaying treatments (SS, $2.50 per head; IS, 4 vaccinations at $5.50 each) increased the difference relative to E heifers to $29.50 (SS) and $41 (IS) per head.