Over a two-year period, crossbred mature beef cows ( n = 178, Year 1; n = 148, Year 2) and young females (n = 43 nulliparous heifers, Year 1; n = 37 primiparous cows, Year 2) grazing in eastern Colorado were used to evaluate the effects of Cu, Zn, and Mn supplementation and source on reproduction, mineral status, immunity, and cow and calf performance. Cow treatments included: 1) control (no supplemental Cu, Zn, or Mn); 2) organic (50% organic and 50% inorganic Cu, Zn, and Mn); and 3) inorganic (100% inorganic CuSO4, ZnSO4, and MnSO4) trace minerals. Heifer treatments included: 1) organic, or 2) inorganic trace minerals. Free-choice mineral feeders were used to provide current NRC-recommended concentrations of Cu, Zn, and Mn from 54 and 82 d (Year 1, heifers and cows, respectively) and 81 d (Year 2) prior to the average calving date of the herd through 110 and 119 d (Year 1, cows and heifers, respectively) and 135 d (Year 2) post-calving. Terminal steer and heifer calves from each year's calf crop were maintained on their appropriate pasture trace mineral treatments and had exclusive access to mineral treatments via creep feeders from approximately 95 d of age until weaning. After weaning, calves were grown and finished in a feedlot on the same pre-weaning trace mineral treatments. Performance, immune response, mortality, morbidity, mineral status, carcass traits, and longissimus dorsi fatty acid profiles were evaluated. In the grazing portion of the experiment, results indicate that trace mineral supplementation in cows and source in cows and heifers affected trace mineral status. Reproductive results were variable in heifers; however, in cows trace mineral supplementation improved pregnancy rate to AI compared to cows not supplemented with Cu, Zn, or Mn for more than 1 yr. Calf performance was greater in non-supplemented control calves vs. supplemented calves in both years, while source also affected calf performance but not consistently in both years. Trace mineral source did not affect calf performance in young grazing females. During the feedlot phase in Year 1, gain to feed ratio was greater in Inorganic vs. Organic calves in both the growing and finishing phases and greater in non-supplemented control calves vs. supplemented calves only during the finishing phase; however, gain to feed ratios were not affected by either supplementation or source in Year 2. Liver Cu and Mn concentrations were affected by supplementation, however immune response, morbidity, carcass traits, and longissimus dorsi fatty acid profiles were not different across treatments. Based on the reduced reproductive performance in non-supplemented cows, as well as literature indicating that Cu affects luteinizing hormone (LH) release, the effect of Cu status, supplementation and source on pituitary responsiveness to gonadotropin releasing hormone (GnRH) were evaluated using 12 multiparous, non-pregnant, non-suckling, ovariectomized Angus cows. After receiving 5 mg Mo/kg diet and 0.3% S during a 216-d Cu depletion phase, nine cows were… Advisors/Committee Members: Engle, Terry E. (advisor), Burns, Patrick D. (advisor), Seidel, George E. (committee member), Whittier, Jack C. (committee member), Field, Thomas G. (committee member).

For the primary emphasis of this dissertation, twenty-three ranches were selected from ranch cooperators in a large scale Nebraska-based cattle system to establish baseline measurements for liver concentrations of trace minerals, disease titers, parasite load, percent morbidity and gain performance. Upon arrival at the feedlot blood, liver, and fecal samples were collected from approximately 10% of each ranch group. After all yr 1 cattle were harvested an 11 ranch subset of the original 23 ranches was selected based on ranch weaning practice for a second yr survey. In yr 2 all ranches shipped calves to the feedlot on the day of weaning and all fed a standardized free choice mineral containing organic trace mineral complexes (OTM) to cow calf pairs 45 d prior to weaning. Comparing yr 1 and 2 for the 1 ranches, percent 1st pulls decreased from yr 1 to yr 2. Carcass quality was decreased from yr 1 to yr 2. Liver Cu concentrations of calves at weaning increased from yr 1 to a yr 2 and Zn and Mn liver concentrations were similar across years. Across both years, higher liver Cu concentration was correlated with decreasing total pulls and increasing ADG and mortality tended to decrease as Cu concentration increased. Higher liver Mn concentrations tended to be correlated with lower total pulls. There was no correlation between liver Zn concentration and animal and health performance. In conclusion, allowing cow-calf pairs access to free-choice mineral containing OTM prior to weaning improved some aspects of feedlot health and performance. For a second paper feedlot performance records from the U.S. Meat Animal Research Center feedlot for 1993 through 2000, were analyzed to evaluate the impact of footrot on ADG and total days on feed. Records from the original pool of 36,755 bull, steer and heifer calves were sorted so that only steers that had a single footrot incidence and those with no other morbidities were included in the data set (7,100 steers). To roughly pattern these data to industry production practices, time of footrot insult during feeding was divided into three production periods; starting (0-60 d), growing (61-120 d) and finishing (121d - harvest). Records were evaluated to determine which limb was more likely to be affected with footrot. A total of 459 (6.5%) steers were treated for a single footrot incident. ADG for cattle experiencing a single footrot incident was decreased compared to non effected cattle. The production period of footrot onset impacted both ADG and total days on feed. Mean days on feed for the non-affected cattle was 262 d while mean days on feed for footrot affected cattle was 267 d (P<0.01). The impact of footrot on days on feed for the starting, growing and finishing periods was -9.9 d, +2.2 d and +14.3 d. Advisors/Committee Members: Whittier, Jack C. (advisor), Engle, Terry E. (advisor), Field, Thomas G. (committee member), Mortimer, Robert George (committee member).