Recombinant bovine somatotropin (rbST) increases size and proportion of fast-glycolytic muscle fibers in semitendinosus muscle of creep-fed steers.

The objective of this study was to determine the effect of recombinant bovine somatotropin (rbST) on muscle fiber histology and histochemistry in creep-fed beef steers. Crossbred steer calves were assigned to one of two treatment groups: control (sham-injected; n = 12) or rbST-injected (0.09 mg x kg(-1) x d(-1); n = 12). Calves were injected every 14 d starting at d 28 of age until weaning at 205 d of age. Biopsies of the semitendinosus muscle were performed on d 100, and slaughter samples of semitendinosus muscle were collected for muscle fiber analyses on d 206. The rbST-treated calves had larger (P = 0.045) fast-twitch-glycolytic (FG) fibers [2,564 +/- 10 vs 2,351 +/- 11 microm2 cross-sectional area, respectively] than controls. No differences (P = 0.36) between rbST-treated and control steers in cross-sectional area were detected for slow-twitch-oxidative (SO) [1,192 +/- 20 vs 1,148 +/- 22 microm2, respectively] or fast-twitch-oxidative-glycolytic (FOG) fibers [1,484 +/- 35 vs 1,403 +/- 38 microm2, respectively]. The percentage distribution for FOG fibers was greater for control calves than for the rbST-treated calves (38.4 vs 34.9 +/- 0.1%, respectively; P = 0.014), whereas the percentage distribution for FG fibers was greater in the rbST-treated calves than for control calves (53.5 vs 48.4 +/- 0.2%, respectively; P = 0.03). The percentage distribution for SO fibers tended to be greater for the control calves than for the rbST-treated calves (13.1 vs 11.7 +/- 0.1%, respectively; P = 0.07). The percentage of FG fibers increased with age (45.4 vs 56.6 +/- 0.8%, respectively; P = 0.001), whereas the percentage distribution of SO (14.3 vs 10.5 +/- 0.5%, respectively) and FOG fibers (40.3 vs 32.9 +/- 0.7%, respectively) decreased (P = 0.001) from d 100 to d 206. The increased longissimus muscle area and dissectable lean tissue in rbST-treated calves are associated with a greater percentage of FG fibers, which possess larger cross-sectional areas than the other fibers.

Effects of growth-promoting implants on morphology of Longissimus and Semitendinosus muscles in finishing steers.

Growth-promoting implants lead to increased muscle accretion in ruminants. To elucidate the effects at a cellular level, muscle fiber distribution and cross-sectional area (CSA) of longissimus (LM) and semitendinosus (ST) muscles were compared in implanted and control steers. Sixty-four Charolais steers were assigned to one of four treatments (16 steers/treatment): (1) no implant, (2) Synovex-S® (estradiol benzoate+progesterone), (3) Ralgro® (zeranol) or (4) Revalor-S® (trenbolone acetate+estradiol-17ß). The experiment was carried out using four slaughter groups (SGRP). Sixteen steers each were slaughtered after 48, 104, 160 and 175 days (four steers/treatment) on trial. Steers on an implant treatment were first implanted at 15 months of age (day 0) and re-implanted at 56 and 112 days. Muscle fibers in the LM and ST (for both live biopsy and post-mortem samples) were characterized as either slow-twitch oxidative (SO), fast-twitch oxidative-glycolytic (FOG) and fast-twitch glycolytic (FG) fibers. Fiber distribution was minimally affected by SGRP in these physiologically mature steers. Implantation with Synovex did not alter fiber distribution in either muscle compared with control steers. Both Synovex-implanted and control steers showed a decrease of FG and an increase of FOG fibers in the LM from day 0 to SGRP 2 followed by an increase of FG and a decrease of FOG fibers. Ralgro- and Revalor-implanted steers had an almost constant fiber distribution in the LM throughout the experiment resulting in higher precentages of FG fibers in SGRP 2 (P<0.05) than SYN or CON steers. Biopsy samples of the LM muscle which were excised 51 days (SGRP 1-3) or 65 days (SGRP 4) before slaughter proved to be suitable for the determination of fiber distribution in live animals. Fiber area increased in post-mortem samples of both muscles from SGRP 1-3 in all treatment groups followed by a plateau. Implantation with Revalor led to an additional increase in fiber area from SGRP 3 and 4 (P<0.05). Synovex did not affect fiber area compared with control steers whereas Ralgro and Revalor implants led to larger fibers in SGRP 3 and 4, respectively. It can be concluded that some growth-promoting implants result in noticeable differences in muscle hypertrophic responses which coincide with their different effectiveness to enhance lean mass accretion.

Lipid composition of carcass tissue from transgenic pigs expressing a bovine growth hormone gene.

Fatty acid profiles and cholesterol content of whole-carcass ground tissue were compared from 26 transgenic (T) pigs expressing a bovine growth hormone gene (bGH) to 26 sibling control (C) pigs. All pigs were fed a common diet and were slaughtered at five different live weights: 14, 28, 48, 68, and 92 kg. The left side of each intact carcass was ground and tissue samples were analyzed for lipid composition and cholesterol content. At 14-kg body weight, carcasses from bGH-T pigs contained 38% less fat, 44% less saturated fatty acids (SFA), 48% less monounsaturated fatty acids (MUFA), and 38% less polyunsaturated fatty acids (PUFA) than C pigs. At 28 kg, bGH-T pigs had 38% less total carcass fat, 42% less SFA, 46% less MUFA, and 24% less PUFA than C pigs. At 48-kg body weight, bGH-T pigs contained 48% less carcass fat, 55% less SFA, 59% less MUFA, and 22% less PUFA than C pigs. At 68 kg, bGH-T pigs had 78% less carcass fat, 78% less SFA, 79% less MUFA, and 53% less PUFA than C pigs. At 92 kg, carcasses from bGH-T pigs contained 85% less carcass fat, 85% less SFA, 91% less MUFA, and 66% less PUFA than those from C pigs. Cholesterol content was not different between bGH-T pigs and C pigs at any of the carcass weights. The trend was for cholesterol content to decrease from the 14- to 92-kg weight group. These results suggest a dilution effect of carcass fat and fatty acids in carcass tissue from bGH-T pigs with increasing live weight.