Effects of chlortetracycline and Synovex-S^® on growth rate and on plasma growth hormone and thyroid hormone concentrations following administration of thyrotropin-releasing hormone and GH-releasing hormone in beef steers

Abstract

. 2007. Effects of chlortetracycline and Synovex-S ® on growth rate and on plasma growth hormone and thyroid hormone concentrations following administration of thyrotropin-releasing hormone and GH-releasing hormone in beef steers. Can. J. Anim. Sci. 87: 327-341. Twenty-four Angus steers (365 kg ± 4) were assigned randomly to a 2 × 2 factorial arrangement of treatments of either 0 or 350 mg chlortetracycline d -1 , with or without Synovex-S to test the effects of chlortetracycline (CTC) and estrogenic implant on release of growth hormone (GH) and thyroid hormones. Steers received ad libitum a concentrate-forage diet over a 112-d feeding study, and growth and carcass characteristics were determined. On days 30, 56, and 106, steers received an injection, via jugular catheter, of 1.0 µg kg -1 BW thyrotropin-releasing hormone (TRH) + 0.1 µg kg -1 BW GH-releasing hormone (GHRH) and blood was collected from -30 to 360 min post-injection. Overall, compared with non-implanted steers, Synovex-S increased (P ≤ 0.009) rate and efficiency of gain, decreased (P = 0.05) time to peak for GH concentrations, whereas baseline concentrations of thyroid-stimulating hormone (TSH) were increased (P = 0.03). Additionally, the TSH response curve (P ≤ 0.05) and magnitude of triiodothyronine (T 3 ; P = 0.01) response were greater following TRH + GHRH challenge for implanted versus nonimplanted steers. There were no main effects of CTC; however, CTC attenuated (P ≤ 0.05) the effects of implant on T 3 release, slaughter weight, and carcass composition. In conclusion, Synovex-S alone increased BW gain and enhanced the response of GH, TSH, and T 3 to a TRH + GHRH challenge, whereas CTC alone did not affect rate and composition of gain or release of pituitary and thyroid hormones. However, CTC appeared to mitigate the effects of implant on T 3 release and carcass composition.

Maximum levels of cross‐contamination for 24 antimicrobial active substances in non‐target feed. Part 12: Tetracyclines: tetracycline, chlortetracycline, oxytetracycline, and doxycycline

“…In eight studies in fattening cattle, only two studies including a dietary chlortetracycline supplementation at 35 mg chlortetracycline/kg DM (Beacom et al., 1988 ; Baldwin et al., 2000 ) showed growth‐promoting effects. On the contrary, in other four studies, a dietary chlortetracycline supplementation at the same range of concentration in feed did not affect animal performance: 11 and 36–39 mg chlortetracycline/kg DM (Stanford et al., 2015 ); 38 mg chlortetracycline/kg DM (Kitts et al., 2007 ); 40 mg chlortetracycline/kg DM (Kitts et al., 2006 ; Reid et al., 2014 ). Equally, no effects on growth performance were observed when chlortetracycline was supplemented at 9 mg chlortetracycline/kg DM (Brown et al., 1975 ) or 589 mg chlortetracycline/kg DM (Cabral et al., 2013 ).…”

“…In the study of Kitts et al. ( 2007 ) a total of 24 crossbred steers of ca. 365 kg BW (Simmental‐Angus) were distributed in 24 individual pens and allocated to four dietary treatments (under a 2 × 2‐factorial design).…”