Document Type

Thesis - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science


Experiments were conducted to quantify the rate and extent of intramucular fat (IMF) development in nonimplanted steers (Exp. 1) and how this is affected by of anabolic growth promotants (Exp. 2). Angus steers of known age and parentage were used in a two year study (year 1, n = 40, year 2, n = 45). Five harvest groups were targeted over the course of the feeding periods to achieve hot carcass weights (HCW) of 204,250, 295, 340, and 386 kg. Regression equations were developed to quantify the changes in carcass characteristics over harvest groups. Harvest group affected the degree of marbling linearly (P < .01). Carcasses expressed Small degrees of marbling at 266 kg HCW and obtained an USDA Yield Grade of 3.0 at 291 kg HCW. Greatest advances in marbling relative to total carcass fatness occurred at HCW less than 300 kg. In experiment 2 Angus and Angus x Limousin steers (n=182; initial BW=309 ± 27.8 kg) were used to evaluate the influence of an estradiol (24mg) - trenbolone acetate (120 mg) implant on production and carcass traits. Treatments (TRT) were as follows: NI) No Implant, control; EI) Early Implant, d 1, BW=309 kg; or DI) Delayed Implant, d 57, BW=385 kg. Days on feed were constant across treatments. Cumulative ADG and G/F: were improved by implants. Implants (I) increased dressing percent (DP), HCW and longissimus muscle area (LMA). Ribfat (RF) and kidney, pelvic and heart fat (KPH) were unaffected by TRT. Implants advanced (P<.01) maturity scores (A51 vs. A59 for NI vs. n. Marbling scores were reduced (P<.05) by EI and were unaffected by DI (NI=Sma1165, EI=Small21, and DI=Small35). The IMF content of the L. dorsi was reduced (P<.10) by EI and was unaffected by DI (NI=5.1, EI=4.0, and DI=4.8%). Treatment affected (P<.10) the proportion of carcasses with marbling scores greater than Modest0 (NI=23.6, EI=7.8, and DI=22.6 %). Management practices administered during early periods of growth influenced final quality grade. Compensatory IMF content development did not occur.

Library of Congress Subject Headings

Beef cattle Adipose tissues -- Growth Anabolic steroids in animal nutrition Growth factors



Number of Pages



South Dakota State University