Effects of ractopamine and sex on serum metabolites and skeletal muscle gene expression in finishing steers and heifers

Abstract

We evaluated growth-related responses to ractopamine in steers and heifers. Sixteen Angus steers (512 kg) and 16 Angus heifers (473 kg) housed in individual pens were used in a complete block design. At 90 to 97 d before the experiment, steers were implanted with 120 mg of trenbolone acetate and 24 mg of estradiol-17beta (Component TE-S) and heifers were implanted with 140 mg of trenbolone acetate and 14 mg of estradiol-17beta (Component TE-H). Treatments were arranged as a 2 x 2 factorial and included sex (steer vs. heifer) and ractopamine-HCl (0 or 200 mg/d). Cattle were fed a diet based on steam-flaked corn once daily. Blood and LM and biceps femoris (BF) biopsy samples were collected on d 0 (before ractopamine feeding) and after 14 and 28 d of ractopamine feeding. Serum insulin concentrations were not affected by ractopamine or sex. Serum IGF-I concentrations were greater in steers than heifers (P < 0.001), and steers demonstrated greater IGF-I mRNA expression in BF than heifers (P = 0.05). Ractopamine decreased serum IGF-I concentrations in heifers on d 14, but increased serum IGF-I concentrations in steers on d 28 (sex x ractopamine x day interaction; P = 0.03). Ractopamine did not affect (P >or= 0.19) mRNA expression of IGF-I, IGFBP-3, or calpastatin in BF or LM. However, ractopamine led to increases in LM expression of IGFBP-5 in heifers, but to decreases in expression in steers (ractopamine x sex interaction; P = 0.04). Ractopamine decreased myosin heavy chain IIA mRNA expression in BF (P = 0.04) but not in LM (P = 0.99). Ractopamine decreased beta(2)-receptor mRNA expression in LM of steers on d 14, but not on d 28; in contrast, expression of beta(2)-receptor mRNA in LM of heifers was not affected by ractopamine (sex x ractopamine x day interaction; P = 0.03). Although there were a few criteria for which ractopamine led to differences in response between steers and heifers, there were no striking disparities to suggest that the effectiveness of ractopamine would markedly differ between sexes.

Zilpaterol hydrochloride improves growth performance and carcass traits without affecting wholesale cut yields of hair sheep finished in feedlot

“…Also, Macías-Cruz et al (2010) observed greater yield of ribs, hindquarter and legs, but lower yield of forequarter, neck and shoulder in ewe lambs fed ZH during a warm season. It should be mentioned that there is no precise explanation for our results obtained, as previous studies in beef cattle have reported that ZH improved the development of type II muscle fibre, and consequently, muscle growth (Mersmann 1998;Walker et al 2010). Based on the above, we expected a greater yield of some wholesale cuts, mainly in those cuts with high amount of type II muscle fibre (i.e.…”

Feedlot performance and carcass traits of hairbreed ewe lambs in response to zilpaterol hydrochloride and soybean oil supplementation

“…Conversely, this experiment reported that wholesale cut yields were not affected by addition of ZH in the finishing diet of ewe lambs. Previous studies indicated that the effects of ZH on wholesale cuts depend on the presence and amount of type II muscle fibers located in each cut, given that β2-adrenergic receptors are mainly located in these fibers (Mersmann, 1998;Walker et al, 2010). However, the reason for the lack of ZH effects herein on cuts with high abundance of type II muscle fiber (legs, shoulders, and loin) is unclear.…”

The effects of gender and muscle type on the mRNA levels of the calpain proteolytic system and beef tenderness during post-mortem aging

“…According to Walker et al (2010), steers, when compared to heifers, had a tendency to have higher levels of β2-adrenergic receptor mRNA in the LT compared to the…”