Year of Publication

2011

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Agriculture

Department

Animal Science

First Advisor

Dr. Kyle R. McLeod

Abstract

Processes that regulate site of fat deposition in beef cattle are poorly understood. For the producer to procure the greatest profit, it is ideal to maximize intramuscular fat. Furthermore, to understand the physiological mechanisms affecting fat depots, it is necessary to evaluate hormones involved in growth regulation. Using a 2 x 2 factorial design of treatments, four experiments were conducted to examine two adipogenic compounds, chlortetracycline and dexamethasone. Synovex-S® and Revalor-S® were used to investigate potential interactions between growth implants and adipogenic compound. Growth performance, carcass quality, organ and fat mass and plasma hormone concentrations were measured in these studies.

In Exp. 1, 24 steers received either 0 or 350mg chlortetracycline/d, with or without Synovex-S®. On d 30, 56 and 106, steers received a bolus injection of 1 ug/kg BW thyrotropin-releasing hormone and 0.1 ug/kg BW GH-releasing hormone and serial blood samples were collected. Synovex-S® increased (P ≤ 0.009) rate and efficiency of gain and decreased (P = 0.05) time to peak for GH concentrations. Chlortetracycline attenuated (P ≤ 0.05) the effects of implant on triiodothyronine release, slaughter weight and carcass quality. In Exp. 2, 96 steers received either 0 or 39.6 ppm chlortetracycline/d, with or without Revalor-S®. Implant increased (P < 0.0001) ADG; however, efficiency of gain was greater for implanted steers in the absence of chlortetracycline (interaction, P ≤ 0.03).

In Exp. 3, 144 steers received either 0 or 0.09 mg dexamethasone/kg BW on d 0, 28 or 56, with or without Revalor-S®. Average daily gain was lower (P = 0.0003) for implanted steers receiving dexamethasone compared to those receiving no

dexamethasone (interaction, P = 0.05). Omental fat mass was greater (P = 0.01) for non-implanted steers receiving dexamethasone compared to no dexamethasone (interaction, P = 0.006). In Exp. 4, 96 steers received either 0 or 0.09 mg dexamethasone/kg BW on d 0, 28, 56 or 84, with or without Revalor-S®. Average daily gain and efficiency of gain were both 13% greater (P ≤ 0.05) with implant. Conversely, DEX lowered ADG by 10% (P = 0.007). There were no effects of treatment on fat mass weights.

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