Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 12, 1996
Publication Date: N/A
Interpretive Summary: The use of oilseeds in the diet is an important option for producers to increase the energy density of cattle diets in addition to supplying dietary protein. However, the literature suggests that certain dietary fats may not support performance at a level as great as that suggested by the estimated energy content of that fat. More specifically, dietary oils have been shown in the human, rat, and pig to reduce growth hormone release consistent with a negative effect on growth. This study investigated the effect in both nonimplanted and estrogen-implanted young beef steers of feeding a diet supplemented with roasted soybeans vs. soybean meal on performance and on the sensitivity of growth hormone release following a challenge injection of thyrotropin releasing hormone+growth hormone releasing hormone. Feeding roasted soybeans reduced performance and the release of growth hormone. Implanting steers with an estrogenic growth promoter appeared to alleviate the negative effect of roasted soybeans. The negative effect of oilseeds may not be observed in feedlots that utilize estrogenic growth promoters, but the growth regulatory effects of oilseeds via influences on growth hormone in cattle warrant further investigation.
Technical Abstract: This study investigated the effect of feeding a roasted soybean supplemented diet to either nonimplanted or estrogen implanted 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 (initial BW 255 plus-minus 5 kg) were used in a 2 x 2 factorial of - or + dietary roasted soybeans (RSB) and - or + Synovex-S ear implant (SYN, 200 mg progesterone and 20 mg estradiol benzoate). After a 35-d growth period, all steers were challenged (iv injection) over a 3-wk period with three levels of a combination of TRH+GHRH (.1+.01, 1.0+.1, 2.5+.25 ug/kg BW, respectively). After 3 wk, steers were reimplanted and a second 5-wk growth period was conducted followed by a single challenge of the 1.0+.1 TRH+GHRH dose. Plasma NEFA concentrations were increased by the RSB diet (205 vs 265 Equivalents/L; P < .01; SEM=9.5). Mean BW gains for -SYN-RSB, -SYN+RSB, +SYN-RSB, and +SYN+RSB were 1.35, 1.21, 1.47, and 1.38 kg/d, respectively (RSB, P < .10; SYN, P < .07; SEM=.06). Gain:DMI (g/kg) means were 184, 167, 197, and 184 (RSB, P < .04; SYN, P < .07; SEM=7.5). For Period 1, area under the GH response curve was 907, 555, 827, and 989 [ng/mL]*min (SYN x RSB, P < .03; SEM=117) and peak response was 37.2, 26.6, 33.5, and 41.1 ng/mL (SYN x RSB, P < .05; SEM=4.5). For the second period, response curve area (P < .05) and peak (P < .10) were affected only by SYN. It is concluded from these data that feeding roasted soybeans results in depressed responsiveness to TRH+GHRH challenge which is alleviated by estrogen implant in young growing beef steers.