Effect of dietary protein and estradiol-17 beta on growth and insulin-like growth factor I in cattle during realimentation.
Forty-eight medium-framed, crossbred steers (average BW = 268 +/- 20 kg) were limit-fed a 35% concentrate diet to gain approximately .10 kg/d during a 66-d restriction (REST) period. This was followed by a 98-d realimentation (REAL) period in which steers were allotted to a 3 x 2 factorial arrangement of treatments. Treatments were 80% concentrate diets containing 9, 12, or 15% CP, and implantation of one-half of the steers with 24 mg/steer of estradiol-17 beta (E2; Compudose). The allotted steers were distributed across four pens (12 steers/pen) with each pen containing two replicates of each treatment combination. Individual feed intakes were monitored using a Calan gate system. Each steer had ad libitum access to its respective diet. Longissimus muscle area and fat thickness at the 12th rib were measured using real-time ultrasound. Dry matter intake was not affected by CP or E2 through d 56. Steers fed 9% CP weighed less (quadratic, P < .05) after d 14 than steers fed 12 or 15% CP due to slower (quadratic, P < .05) gains during this initial period. Implantation increased (P < .05) ADG from d 15 to 56 resulting in heavier BW (P < .05) on d 56 and 98. Increasing concentrations of dietary CP resulted in linear (P < .05) increases in longissimus muscle area on d 28 and 56, and fat thickness on d 98. Serum IGF-I concentrations were lowest on d -21 of REST and highest on d 28 of REAL (quadratic, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)
Hays
C L
CL
Department of Animal and Dairy Sciences, Alabama Agricultural Experiment Station, Auburn University 36849-5415, USA.
Davenport
G M
GM
Osborn
T G
TG
Mulvaney
D R
DR
D000818:Animals; D001806:Blood Urea Nitrogen; D001823:Body Composition / Q000187:drug effects / Q000502:physiology; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D004343:Drug Implants; D004435:Eating / Q000502:physiology*; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology; D011897:Random Allocation
D004044:Dietary Proteins; D004343:Drug Implants; D004958:Estradiol; D007334:Insulin-Like Growth Factor I