Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 18, 1998
Publication Date: N/A
Interpretive Summary: Estrogenic growth promoters increase growth rate in growing beef cattle by up to 15% under conditions of adequate nutrition. On the basis of this study, protein as opposed to energy was determined to be the primary nutrient necessary for achieving this response. With moderate and greater DM intake, optimum response to estrogenic growth promoters is dependent on adequate dietary CP. Furthermore, increasing energy intake does not result in improved performance with Synovex-SR under conditions of inadequate dietary protein.
Technical Abstract: This study investigated the influence of intake and CP levels and the growth promoter Synovex-S on performance and N retention of young beef steers (avg BW 296 kg). In Exp. 1, four implanted Angus steers (20 mg estradiol benzoate plus 200 mg progesterone) and four steers that were not implanted were assigned to concurrent 4x4 Latin squares. Each square consisted of moderate and moderately high DM intake (4 or 6 kg/d) and low and adequate CP (450 or 600 g/d) intakes in a 2 x 2 factorial arrangement of intake treatments. Experiment 2 consisted of two replicates of 32 Hereford steers each (avg BW 324 kg). Each replicate was a factorial design in which steers were individually fed for 63 d ad libitum amounts of a 60% corn-based concentrate diet containing either 7.9, 10.0, 12.1, or 14.6% CP (dry matter basis) and either implanted or not implanted. Experiment 3 was the same design as Exp. 2 except that all steers (avg BW 315 kg) received a low protein diet (7.6% crude protein) with calculated energy densities of either 1.86, 2.04, 2.22, or 2.42 Mcal ME/kg DM. In Experiment 1 implant response was greater (P < .01) when adequate compared to low CP was fed. For Exp. 2, Synovex-S was less effective in improving efficiency for the lowest protein diet than for the other diets (11.7 vs 20.2%). During Exp. 3, neither Synovex-S nor dietary energy level influenced gain or efficiency of gain. Adequate dietary protein is necessary to optimize the response to estrogenic growth promoters.