Effects of increasing dosages of zeranol implants on lamb growth, carcass characteristics, blood hormones, and nitrogen metabolism

• Published in: Journal of animal science Vol. 91; no. 2; pp. 986 - 994
• Main Authors: Eckerman, S R, Lardy, G P, Thompson, M M, Van Emon, M L, Neville, B W, Berg, P T, Schauer, C S
• Format: Journal Article
• Language: English
• Published: United States 01.02.2013
• Subjects: Animals; Body Composition - drug effects; Dose-Response Relationship, Drug; Estrogens, Non-Steroidal - administration & dosage; Estrogens, Non-Steroidal - pharmacology; Female; Insulin-Like Growth Factor I - metabolism; Male; Nitrogen - metabolism; Sheep - blood; Sheep - growth & development; Sheep - physiology; Thyroid Hormones - blood; Zeranol - administration & dosage; Zeranol - pharmacology
• ISSN: 1525-3163
• DOI: 10.2527/jas.2011-4818

The objective of this research was to compare the growth performance, incidence of prolapse and mortality, carcass characteristics, blood hormone concentration, and N balance of lambs implanted with increasing dosages of zeranol. One hundred forty-four crossbred lambs (29.6 ± 4.9 kg) were used in a completely random design and placed into 16 feedlot pens (4 pens/treatment) for a 116 d finishing study. Lambs were fed an 84.7% corn and 15.3% market lamb pellet (DM basis) diet ad libitum. Treatments were 0, 12, 24, and 36 mg zeranol (Ralgro; Schering-Plough), and lambs were implanted in the ear according to treatment on d 0. Lambs were weighed. Thirty lambs (67.6 ± 3.4 kg) and 96 lambs (65.8 ± 5.1 kg) were harvested on d 84 and d 118, respectively. Carcass data were collected 24 h after chill. Blood samples were collected on d 0, 28, 56, 70, 82, 99, and 116 from 64 lambs (29.6 ± 2.1 kg) in the feedlot study (subsample of 4 lambs per pen) and analyzed for thyroxine, triiodothyronine, and IGF-I. A second study was conducted to compare effects of 0, 12, 24, or 36 mg zeranol on N balance in 16 crossbred lambs (34.8 ± 2.1 kg). There were no differences among treatments for BW, ADG, DMI, and G:F (P > 0.05) in the feedlot study. However, there was a linear increase for incidence of prolapse (P = 0.006; 2.78, 5.55, 24.98, and 27.75%, respectively) and mortality (P = 0.005; 0.00, 5.55, 11.10, and 13.88%, respectively) as zeranol dosage increased. Carcass characteristics, blood hormone concentrations, and N balance were not affected by treatment (P > 0.05). These results indicate zeranol increases incidence of prolapse and mortality without increasing growth performance.