Growth, carcass and meat quality attributes of dairy-beef bulls and steers slaughtered at eleven months of age : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science, Massey University, Palmerston North, New Zealand
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2021
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Massey University
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Abstract
New Zealand dairy industry produces approximately 4.2 million calves annually but around half of these are processed within two weeks of birth as “bobby” calves. Bull calves retained for rearing for beef undergo a physical form of castration (usually using a rubber ring) and are raised as steers. Castration is painful and steers typically grow slower than bulls. The practice of processing bobby calves at a young age raises animal welfare concerns which threaten the dairy and beef industries’ social license to operate and has potential to impinge on New Zealand’s international market reputation and conceivably become a non-tariff barrier to trade. An alternative to early-life processing is to utilize the surplus calves in an accelerated beef production system with slaughter as a yearling. The objective of the study was to compare the growth, carcass and meat-quality attributes of Hereford x Friesian-Jersey bulls and steers slaughtered at 11 months of age. The study aimed to identify if there is need to castrate bulls in the yearling beef production system to optimize their growth, carcass and meat quality and whether proteolytic aging of the meat will affect meat quality attributes. Hereford-sired bulls (n=17) and steers (n=16) born to dairy cows (Friesian and Friesian x Jersey) were raised on pasture as a single group until slaughter at 11 months and processed at Venison Packers Feilding Ltd in June 2019. There was no difference in the growth rate of bulls compared to steers, with an average daily gain of 0.9 kg/day. The final live weight did not differ between bulls and steers at 306±7.1 and 303±6.9 kg respectively (P=0.773). There was no difference in carcass characteristics of bulls and steers (P>0.05), except that the top side weight was greater for bulls than steers (P=0.022) while intramuscular fat was greater for steers than bulls (P<0.001). Although the ultimate pH was greater in bulls than steers (5.68±0.04, 5.55±0.04; P=0.036), both values were within normal range (pH between 5.4 and 5.7). There was no difference between bulls and steers for meat colour, shear force and myofibrillar fragmentation index (P>0.05). However, drip loss after 24 and 48 hours was greater in bulls than steers (P<0.05). Aging did not influence meat tenderness (P=0.682) with both aged and unaged samples having shear force values less than 6 kgF. The low shear force values, usual beef colour values, and ultimate pH values in the ideal range indicates that meat from bulls and steers processed at 11 months of age will be acceptable for consumers of beef. The similarities in meat quality and carcass attributes for bulls and steers at 11 months of age indicates that they could be one category in a classification scheme.