Roasted soybeans and an estrogenic growth promoter affect growth hormone status and performance of beef steers.
This study investigated the effects of a roasted soybean (RSB)-supplemented diet and an estrogen implant (SYN; Synovex-S ear implant, 20 mg estradiol benzoate plus 200 mg progesterone) in young crossbred beef steers on their performance and plasma growth hormone (GH) response to challenge injections of thyrotropin-releasing hormone (TRH) + GH-releasing hormone (GHRH). Twenty individually fed steers (body weight 255 +/- 5 kg) were assigned to the following treatments: 1) no SYN and fed a soybean meal-supplemented diet, 2) no SYN and fed the RSB-supplemented diet, 3) plus SYN and soybean meal, and 4) plus SYN and RSB. Steers were fed 1.13 MJ metabolizable energy/kg metabolic body weight daily of an 18% protein diet. After a 5-wk growth period, all steers were challenged (intravenous injection) over a 3-wk period with three levels of a combination of TRH + GHRH (0.1 + 0.01, 1.0 + 0.1, 2.5 + 0.25 microg/kg body weight, respectively). After an additional 3 wk, steers were reimplanted and a second 5-wk growth period was followed by a single challenge of the 1.0 + 0.1 TRH + GHRH dose level. Plasma nonesterified fatty acid concentration was greater when steers were fed the RSB compared with soybean meal (265 vs. 205 micromol/L; P < 0.01; SEM = 9.5). Body weight gains for treatments 1, 2, 3 and 4 were 1.35, 1.21, 1.47 and 1.38 kg/d, respectively (RSB, P < 0.10; SYN, P < 0.07; SEM = 0.06). Gain/dry matter intake (g/kg) means were 184, 167, 197 and 184 (RSB, P< 0.04; SYN, P < 0.07; SEM = 7.5). Feeding roasted soybeans results in depressed area under the GH response curve [907, 555, 827 and 989 microg/(L*min) (SYN x RSB, P < 0.03; SEM = 117)] and depressed peak response (37.2, 26.6, 33.5 and 41.1 microg/L [SYN x RSB, P < 0.05; SEM = 4.5]), an effect alleviated by estrogen for young growing steers (Period 1) but not for heavier steers (Period 2).
Rumsey
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Livestock and Poultry Sciences Institute, ARS, USDA, Beltsville, MD 20705-2350, USA.
Elsasser
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Kahl
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D000818:Animals; D001835:Body Weight / Q000502:physiology; D002417:Cattle / Q000097:blood* / Q000254:growth & development* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004343:Drug Implants; D004967:Estrogens / Q000008:administration & dosage / Q000494:pharmacology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D006133:Growth Substances / Q000008:administration & dosage / Q000494:pharmacology*; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D013025:Glycine max; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D004343:Drug Implants; D004967:Estrogens; D005230:Fatty Acids, Nonesterified; D006133:Growth Substances; D013973:Thyrotropin-Releasing Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone