The influence of repeated treatment with a hormonal growth promotant on tenderness and intramuscular fat in tropical beef cattle

Abstract

The effect of reimplantation with a hormonal growth promotant (HGP) on meat tenderness was investigated using steers generated from the northern crossbreeding program of the Cooperative Research Centre for the Cattle and Beef Quality. For the 1996 and 1997 calf crops, straightbred Brahman and F1 Brahman cross steers were allocated to finish at pasture or in a feedlot, to target slaughter liveweights of 400 (Domestic Market), 520 (Korean Market) or 640kg (Japanese Market) and remained either untreated (Control) or treated every 100 days with 20mg Oestradiol-17 (Compudose 100). The average age at first implantation was 14.2 months for the 1996 calf crop and 12.3 months for the 1997 calf crop. A least-squares analysis of the tenderness scores of the m. longissimus dorsi indicated that the taste panelist could detect a small reduction (P<0.05) in tenderness from the aggressive strategy (up to 725 days exposure to HGP) of implantation with an oestrogen. The effect of HGP treatment for the Pasture-finished group was 6.3 units (P<0.05) and from the Feedlot-finished group was 4.9 units (P<0.05). The reduction was greater in straightbred Brahman (13.4 units) than the F1 Brahman cross (average of the F1's, 3.9 units). The positive linear relationship between taste panel tenderness and intramuscular fat was significant for Pasture finish (P<0.05) and tended to significance (P<0.10) for Feedlot finish. An aggressive sustained growth promotion strategy has been shown to increase the toughness of beef, however it is unlikely that such an implant strategy will be used in commercial practice.