Abstract
Forty crossbred wether lambs (average initial weight = 30 kg) were used to determine the effects of zeranol on carcass composition and metabolite concentrations in blood when fed at two levels of feeding: Lambs were implanted with zeranol (12 mg) at 30-d intervals and fed at two levels of feed intake (restricted and ad libitum) in a 2 x 2 factorial arrangement of treatments. Restricted fed lambs were fed to gain 50% of body weight gained by lambs allowed ad libitum access to feed. Lambs with ad libitum and restricted access to feed were slaughtered after 98 and 154 d, respectively. Zeranol increased average daily gains (ADG) and gain to feed by 20 (P <.05) and 17% (P < .03), respectively. Carcass fat percentage tended to be reduced by 7.4% in implanted lambs, however, there was no difference in daily fat gain (g/d) in implanted vs non implanted lambs. Yet zeranol increased carcass protein by 33%(P<.10). Restricted feeding reduced (P <.05) daily fat gain (40%) and CP gain (32%) but increased (P < .06) feed to gain (45%), percentage carcass ash (12%), and dressing percentage (9%). Zeranol increased pituitary weight (P <.001), plasma glucose (P <.05), mean serum growth hormone (GH; P < .05), baseline GH (P < .05), GH pulse amplitude (P < .05), and insulin-like growth factor-I (IGF-1; P < .00 1) levels by 40%, 13 %, 42%, 7 1 %, 33%, and 53%, respectively. Restricted feeding reduced(P<.10)serum IGF-I by 16%. These results indicate that continuous administration of zeranol alters the GH-IGF-I axis regulation of growth and carcass composition in lambs.
Scott, Patricia Lynn (1995). Effects of zeranol on serum concentrations of growth hormone, IGF-I and metabolites and on carcass composition of lambs fed at two levels of intake. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -S365.