Effects of flax supplementation and a combined trenbolone acetate and estradiol implant on circulating insulin-like growth factor-I and muscle insulin-like growth factor-I messenger RNA levels in beef cattle1,2

Abstract

We evaluated effects of a 5% (dry matter basis) ground flaxseed supplement (flax) and a trenbolone acetate and estradiol-17beta implant, Revalor-S, on circulating IGF-I and muscle IGF-I messenger RNA (mRNA). Sixteen crossbred yearling steers (initial BW = 397 kg) were assigned randomly to one of four treatments: 1) flax/implant; 2) nonflax/implant; 3) flax/nonimplant; and 4) nonflax/nonimplant. Serum was harvested from blood collected on d 0 (before implant or flax addition), 14, and 28, and used in subsequent analyses of circulating IGF-I. Biopsy samples (0.5 g) were obtained from the longissimus muscle on d 0, 14, and 28. Total RNA was isolated from the muscle samples, and real-time quantitative-PCR was used to assess relative differences in IGF-I mRNA. Flax supplementation had no effect (P > 0.10) on circulating IGF-I concentrations. Following implantation, sera from implanted steers had 52 and 84% greater (P < 0.05) IGF-I concentrations than sera from nonimplanted steers on d 14 and 28, respectively. On d 28, local muscle IGF-I mRNA levels increased 2.4-fold (P < 0.01) in biopsy samples obtained from implanted compared with nonimplanted steers. Muscle biopsy samples from nonflax cattle had 4.4-fold higher (P < 0.01) levels of IGF-I mRNA than those from flax cattle on d 28. To determine whether a component of flax, alpha-linolenic acid (alphaLA), was directly responsible for IGF-I mRNA down-regulation, we incubated primary cultures of bovine satellite cells, from implanted and nonimplanted steers, in two concentrations of alphaLA (10 nM and 1 microM). An implant x dose interaction (P < 0.05) was observed for IGF-I mRNA concentrations in bovine satellite cells cultured for 72 h with alphaLA. Satellite cells from nonimplanted steers had similar (P > 0.10) IGF-I mRNA concentration regardless of the level of alphaLA exposure; however, satellite cells from implanted steers exposed to 10 nM and 1 microM alphaLA had 2.5- and 2.0-fold greater IGF-I mRNA levels, respectively, than cells from implanted steers that were not exposed to alphaLA (P < 0.05). Administration of a Revalor-S implant increased circulating IGF-I and local muscle IGF-I mRNA concentrations in finishing cattle. However, muscle IGF-I mRNA levels were decreased by flax supplementation. Muscle cell culture experiments suggested that alphaLA was not responsible for the IGF-I mRNA down-regulation.

Fecal and Urinary Lignans, Intrafollicular Estradiol, and Endometrial Receptors in Lactating Dairy Cows Fed Diets Supplemented with Hydrogenated Animal Fat, Flaxseed or Sunflower Seed

“…In the present study, a diet supplemented with flaxseed did not affect IGF concentration in either follicular fluid or plasma. In agreement with our findings, another study [36] also reported that plasma IGF-I concentrations in beef steers fed 5% ground flaxseed were not different from that of steers fed a control diet. Similarly, in lactating dairy cows fed a protected form of whole flaxseed, plasma IGF-I concentrations did not differ from that of cows fed a diet with no added fat [9].…”

Effects of growth-promoting agents and season on blood metabolites and body temperature in heifers1,2

“…After d 28, IGF-I concentrations returned to near d 0 (96.9 ng/mL) concentrations in the winter, but remained elevated above d 0 (60.6 ng/mL) concentrations during the summer, although mean IGF-I concentration from d 28 through d 84 were similar in winter (108.1 ng/mL) and summer (102.7 ng/mL). Dunn et al (2003) reported increases in sera IGF-I concentrations of 52 and 84% because of using growthpromoting implants in steers. In that study, the 28-d gain response to implanting ranged from 0.52 to 0.97 kg/d.…”

Effects of ovariectomy and anabolic steroid implantation on the somatotrophic axis in feedlot heifers

“…It should be noted, however, that the Pampusch et al (2003) study was a comparison within steer (i.e. d 0 to d 7) and the Dunn et al (2003) study compared implanted to non-implanted steers, which could explain differences in the final expression between studies. Pampusch et al (2003) observed that IGF-1 expression Dunn et al (2003) showed that, although IGF-1 in circulation increased as early as 14 d post-implantation, mRNA expression of IGF-1 in the muscle did not increase until d 28 and was 2.4 fold greater in implanted calves than non-implanted calves at that time.…”

“…d 0 to d 7) and the Dunn et al (2003) study compared implanted to non-implanted steers, which could explain differences in the final expression between studies. Pampusch et al (2003) observed that IGF-1 expression Dunn et al (2003) showed that, although IGF-1 in circulation increased as early as 14 d post-implantation, mRNA expression of IGF-1 in the muscle did not increase until d 28 and was 2.4 fold greater in implanted calves than non-implanted calves at that time. This latter study demonstrates that an increase in serum IGF-1 may be observed without an increase in hepatic IGF-1 expression, as noted in the present study.…”