Chlortetracycline supplementation of yearling dairy heifers1,2

Abstract

Chlortetracycline is an antibiotic that is used to increase weight gain, efficiency of gain, carcass grade, and conception rates. The objective of this experiment was to evaluate the effects of supplementation of 350 mg/d of chlortetracycline on ADG, G:F, BCS, thyroxine, and systemic glucose concentrations in yearling dairy heifers. Forty 12-mo-old Holstein heifers (initial BW = 363 +/- 21 kg) were housed in a free-stall barn with ad libitum access to feed and water for 104 d. A transition period was begun 14 d before the age of 12 mo to acclimate the heifers to the diet. The chlortetracycline-fed group (n = 20) consumed 328 +/- 8.2 mg of chlortetracycline/heifer daily. Measurements for BW, withers and hip heights, BCS, and health score were recorded weekly. Dry matter intake was measured daily. Blood was sampled every 4 d to determine plasma thyroxine and glucose concentrations and every 2 d to determine progesterone concentrations. Heifers were artificially inseminated on the first observed standing heat after 13 mo of age. There were no effects of chlortetracycline on ADG, G:F, withers and hip heights, BCS, blood glucose concentrations, peak progesterone concentrations, health, or conception rate. There was an interaction between treatment and time for chlortetracycline on serum thyroxine concentration. In the beginning of the experiment, serum thyroxine concentration was lower in heifers supplemented with chlortetracycline. There was no difference between treatments in thyroxine concentration at the end of the experiment. Chlortetracycline supplementation was not beneficial for yearling dairy heifers.

Effects of lasalocid and intermittent feeding of chlortetracycline on the growth of prepubertal dairy heifers

“…In this study, thyroxine concentrations were not different among treatments, which may partially explain the lack of skeletal growth in reference to hip and withers height improvement associated with CTC. Similar to the results of this study, Reid et al (2006) did not observe an increase in growth in CTC-supplemented dairy heifers or a difference in mean sera thyroxine concentrations. In our study, thyroxine may not have been affected either because of the CTC feeding regimen used or a potential breed difference in this response between beef and dairy heifers.…”

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 Reid et al. ( 2014 ) a total of 40 Holstein heifers (BW 363 kg, 12‐month‐old) were allocated to one of two dietary treatments. The basal diet was either not supplemented (control) or supplemented with chlortetracycline (unspecified chemical form; Aureomycin 90, Alpharma Inc., Fort Lee, NJ, USA) at a concentration of 350 mg/head/day (corresponding to ca.…”