Doctor of Philosophy / Department of Animal Sciences and Industry / Twig T. Marston / The primary study investigated the use of ractopamine HCl and implants in cull beef cows. Thirty-two cull cows were used to determine the effects of feeding ractopamine HCl and/or implanting on feedlot performance and carcass composition. Cows were individually fed a high concentrate diet for 60 days. Carcass data were collected and carcasses were fabricated. Implanted cows had greater dressing percentages and tended to have heavier hot carcass weights than non-implanted cows. Cows that had been treated with implant and ractopamine HCl tended to be fatter than those not treated. Ractopamine HCl fed cows had more marbling than their contemporaries. The data also indicated that younger cows (< 6 years of age) had greater feedlot performance than the older cows. An experiment was conducted to determine if corn and grain sorghum dried distillers grains could be effective protein supplements for growing cattle. Crossbred heifers (n = 78) were individually fed 2.72 kg·head·-1d·-1 of supplements containing corn, soybean meal, and grain sorghum; or cracked corn and corn distillers grains with solubles; or cracked corn, sorghum distillers grains with solubles, and ground grain sorghum (all formulated to equal 20% CP). Heifers grazed native-grass and were fed smooth broom hay. A digestion trial was done during the last week of the trial. No differences were noted in weight gain or total diet digestibility, however, DMI was less for heifers receiving either distiller’s based supplement. Ninety-six pregnant, mature, spring-calving cows grazing native grass pasture were used to determine if early weaning calves reduced subsequent winter supplementation cost. Previous to the feeding trial, calves had been weaned at 115 or 212 d of age. Cows were fed either 1.4 kg·hd-1·d-1 or 1.27 kg·hd-1·d-1 of a common 45% CP supplement. Cows were supplemented for an average of 110 d of pregnancy. Earlyweaned cows were heavier and had greater body condition scores than contemporaries at the commencement of supplementation. At calving the early-weaned cows fed the lesser supplemental amount had similar body weight and body condition scores as later-weaned cows fed the greater amount of supplement, thus, the early weaning routine allowed a 30% savings of winter protein supplement.

Doctor of Philosophy / Department of Animal Sciences and Industry / Michael E. Dikeman / Sixty cull cows were utilized to investigate the effects of feeding a single or sequence of β-adrenergic agonists (β-AA) on performance, mRNA expression, carcass traits, economics, meat palatability, and ground beef color. Treatments included: 1) concentrate fed for 74 d (C); 2) concentrate fed for 49 d then supplemented with ractopamine-HCl for 25 d (RH); 3) concentrate fed for 51 d then supplemented with zilpaterol-HCl for 20 d (ZH); 4), concentrate fed for 26 d then supplemented with RH for 25 d followed by ZH for 20 d (RH + ZH). No differences existed among treatments for performance or carcass characteristics. However, cows supplemented with ZH (ZH and RH + ZH treatments) had increased LM areas (P = 0.18) compared to control and RH cows. Sequential feeding of RH followed by ZH had no influence on β2-adrenergic receptor (AR) mRNA expression. However, β2-AR mRNA was increased (P < 0.05) in the RH and ZH treatments when RH or ZH was supplemented during the last 20 to 25 d of feeding. Myosin heavy chain (MHC) Type IIa mRNA decreased (P < 0.05) from d 24 to 51 in all cows, while MHC-IIx increased (P < 0.05) in the ZH and RH + ZH treatments during ZH supplementation. No differences were observed in ground beef color shelf-life among treatments. Effects of β-AA supplementation on meat palatability varied among muscles. Infraspinatus steaks had improved (P < 0.05) WBSF values with β-AA supplementation. Psoas major steaks from the RH + ZH treatment were rated as more tender than steaks from all other treatments. Non-enhanced LM steaks from ZH supplemented cows had higher (P = 0.12) WBSF values along with decreased (P < 0.0001) percentages of degraded desmin compared to control and RH cows. Collagen solubility of the LM was increased with ZH supplementation compared to RH and control cows. Enhancement of steaks with 0.1 M calcium lactate improved LM tenderness of β-AA supplemented cows. Implanting and feeding cull cows for 74 d, regardless of β-AA supplementation, added value by transiting cows from a “cull” cow to “white” cow market.