| The effect of nutritional and hormonal factors on restricted and compensatory growth was studied in rats, lambs and steers. Three experiments were conducted to study the effect of bovine growth hormone (bGH) (150 ug/rat/day for experiments 1 and 2; 90 ug/rat/day for experiment 3), dietary energy and protein on restricted and compensatory growth of rats. In experiment 1 (30 days), bGH levels were these: (1) no bGH; (2) bGH days 16-30; (3) bGH days 1-30. Diets fed were these: I 3.6 Mcal/kg of feed (normal energy), 20% CP (normal protein); II 3.6 Mcal/kg of feed, 10% CP (low protein); III was diet I fed at 50% ad libitum; IV used a diet of 3.6 Mcal/kg of feed and 40% CP fed to 50% of ad libitum. In experiment 2 (16 days), rats received diets of experiment 1 for days 1-8 (restriction), then diet I ad libitum (days 9-16; recovery). Levels of bGH were these: (1) no bGH; (2) bGH days 1-4; (3) bGH days 4-8; (4) bGH days 1-8. In experiment 3 (16 days), rats received diet I either ad libitum or restricted to 50% of ad libitum for days 1-8 (restriction), and then all ad libitum (days 9-16; recovery). Levels of bGH were these: (1) no bGH; (2) bGH days 9-12; (3) bGH days 13-16; (4) bGH days 9-16.;Two trials were conducted to study the effect of zeranol on restricted and compensatory growth in growing-finishing lambs and in finishing cattle. The lambs were individually fed a pelleted diet (74.4% corn grain; 25.0% dehydrated alfalfa) either ad libitum or restricted to 50% ad libitum for days 1-57 (restriction), then all ad libitum during 51 or 83 days (recovery). Zeranol implants (12 mg) were these: (1) 2, one on day 1, one on day 57; (2) one on day 1; (3) one on day 57; (4) none. In the cattle trial, half of one group (previously restricted) and half of another (continuously full fed) were implanted with 36 mg of zeranol on days 1 and 63 of the trial. The steers were pen fed (79.3% high moisture corn and 10% corn silage) during 181 days.;During restriction in the lamb trial, intake level decreased (P < .0001) ADG and DDMI. Restricted lambs showed compensatory growth during recovery, but needed more (P = .0002) time than those full fed to reach FW. During recovery, previously restricted lambs had higher ADG (P = .0994) and DDMI (P = .0509) when implanted, compared to those not implanted. PFE, most carcass characteristics, moisture, EE, and CP were not affected by intake level nor by zeranol. In the cattle trial, previously restricted steers showed compensatory growth. Zeranol increased FW in full fed steers (P < .05) and in steers showing compensatory growth (P < .10). Carcass grade was not changed, except rib eye area which was larger (P < .05) for full fed implanted steers.;Bovine GH did not change performance, body ether extract (EE) or body crude protein (CP) in any of the experiments. In experiment 1, normal energy increased (P < .0001) final body weight (FW), average daily gain (ADG), daily dry matter intake (DDMI) and EE, but decreased CP. Normal protein increased FW (P = .0004), ADG (P = .0004), and CP (P < .0001), but decreased (P < .0001) EE. Partial feed efficiency (PFE) was not different among treatments. In experiments 2 and 3 rats showed significant compensatory growth during recovery. In experiment 2, low energy (P < .0001) and low protein (P = .0011) increased ADG during recovery, but overall PFE was relatively better for rats fed normal energy and protein diets. In experiment 3, previously restricted rats had higher (P = .0424) ADG during recovery, and a relatively larger overall PFE. |
