LIVEWEIGHT GAINS, AND CARCASS AND MEAT CHARACTERISTICS OF ENTIRE, SURGICALLY SPAYED OR IMMUNOLOGICALLY SPAYED BEEF HEIFERS

Growth, carcass and meat characteristics, market suitability and econo mic return were compared in surgically spayed (SS), immunologically sp ayed (IS) and entire (E) heifers. Spaying had no effect on daily weigh t 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 great er 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 wer e: 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 tr eatments. 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 carcass es 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 tha n both E and IS treatments, whereas Instron compression values from th e E striploin were lower (P<0.05) than for both the SS and IS treatmen ts. There were no differences between treatments in any meat attribute s 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. Dire ct costs of the spaying treatments (SS, $2.50 per head; IS, 4 vaccinat ions at $5.50 each) increased the difference relative to E heifers to $29.50 (SS) and $41 (IS) per head.