Time of feeding and growth promotant effects on the winter growth performance and carcass traits of steers

Abstract

The effects of time of day of feeding and estrogenic growth promotant on growth performance and carcass traits were determined in three experiments conducted over 3 yr (winters 1998–1999, 1999–2000, 2000–2001). Crossbred steers (year 1, n = 144, year 2, n = 128, year 3, n = 144) were assigned at fall weaning on the basis of sire, age (190 ± 21 d, mean ± SD), and body weight (244 ± 34 kg) to one of eight pens in an outdoor lot at the Brandon Research Centre (49°54′N). In years 1 and 2, pens were assigned to either morning-fed (MF, 0900) or evening-fed (EF, 2000) treatments, and steers within pen were assigned to either Synovex Plus® (TAE) or Synovex S® (PE) growth promotants. In year 3, pens were assigned to either TAE or PE treatments and all were evening-fed. Beginning on Nov. 09 (0 d), steers were given a 20% hay, 80% concentrate (79.2% barley, 0.8% premix) mixed ration (88.6% dry matter, 13.7 MJ kg-1 digestible energy, 124 g kg-1 crude protein, 33.6 mg kg-1 lasalocid). Diets were fed, once daily, in amounts that were consumed before the next feeding, until steers were marketed. Growth promotants were administered at 0 and 84 d. The winter of year 2 was warmer (P < 0.05) than, and years 1 and 3 similar (P > 0.05) to, the 30-yr average ambient temperature (-8.8°C and -12.9°C, respectively). Evening feeding increased (P < 0.05) gain in body weight, especially in year 2 and backfat, especially in year 1, and this was reflected in heavier (P < 0.05) carcass weight in year 2, and whiter (P < 0.05) fat and greater (P < 0.05) rib eye moisture in year 1 and overall reduced (P < 0.05) feed cost of gain in winter. In all 3 yr TAE, relative to PE, produced greater (P < 0.05) body weight gain, and heavier, leaner carcasses with greater (P < 0.05) rib eye area, coarser (P < 0.05) meat texture and greater (P < 0.05) shear force, and reduced (P < 0.05) the feed cost of gain. Time of feeding and choice of growth promotant have significant potential to reduce the business risk of feeding steers in winter. Key words: Beef steer, growth implant, feeding strategy, growth promotant, carcass trait