1. ABSTRACT Two thousand three hundred and sixty-four high-risk calves were procured through sale barns by three order buyers in Arkansas, Mississippi, and Texas for participation in a 240 - day metaphylactic antimicrobial research trial. Of the 2,364 head, 1716 were heifers (mean arrival weight = 512 lb), 299 were steers (mean arrival weight = 523 lb), and 889 were intact males (mean arrival weight = 508 lb). In addition to evaluating treatment effects of the various antimicrobials, one additional objective of this study was to characterize and quantify the impact of castration on animal health, growth performance, and carcass characteristics in growing-finishing cattle. Individual data were collected on each calf including standard animal health parameters, growth performance, and carcass characteristics. Each intact male calf was non-surgically castrated by administering an elastrator band at processing, which occurred within 24 hours of arrival. The morbidity of the intact males (49%) was higher (P<0.01) than the individuals that were castrated prior to arrival (35%). The relative risk of undergoing one morbid episode was 1.42, or 42% greater for intact males than for the steers. Furthermore, 24% of the population’s morbidity can be attributed to being castrated on arrival. The mortality (4.91%) and study rejection (4.91%) of the steers were lower than the mortality (7.1%) and study rejection (8.01%) of intact males, yielding a cumulative rate of loss of 9.82% of steers versus 15.11% of intact males that did not reach a desirable harvest weight. The risk of mortality was 1.42 times greater in the intact male population relative to the steer population. Similarly to the impact on mortality, the intact male population had a relative risk of removal of 1.63, indicating an excess study rejection of 63% compared to the steers. Morbidity was negatively associated with average daily gain, yield grade, hot carcass weight, and quality grade in this study. Intact males had a lower average daily gain at the time of reimplant and at harvest relative to the steers, while the steers had a 33 lb heavier hot carcass weight. The impact of individuals identified to have a pneumonic lung lesion at harvest revealed a reduction in overall average daily gain (.14 lb), yield grade (.13), and hot carcass weight (23 lb) compared with those with no lesions. Lung lesions were identified in 42% of the animals harvested, however 57.4 % of them were never been pulled for treatment, thus illustrating the difficulty and lack of accuracy in detecting respiratory disease in commercial feedyards. Castration at arrival in to the feedlot had substantial negative impacts on morbidity rates, mortality rates, removal rates, average daily gain, yield grade, quality grade, and hot carcass weight. Materials and Methods The results reported herein represent data recorded as part of a metaphylactic study. 2,364 head of high-risk calves were placed between June 20, 2003 and June 27, 2003 in to Cactus Feedyard, Cactus, TX. Calves were penned by load as feasible; however, if pen space became limited, calves were penned by sex according to order buyer and day of arrival. Standard processing was performed and typically occurred within 24 hours of arrival. Pen (treatment) assignments were made for individual animals at processing according to a prepared randomization schedule. Calves were individually weighed with each calf uniquesly identified. If testicles were present, calves were castrated non-surgically by banding (Calicrate®). Horns were tipped if required. Cattle were re-implanted between October 8 and 11, 2002. The mean days on feed was 244 days for steers. At harvest, individual ear tag numbers were matched to the packing plant carcass identification numbers and lungs were scored for occurrence and severity of pneumonic lesions and classified based upon degree of lung field involvement: Score 0 = no lesions; Score 1 = 20% involvement. For all statistical analyses, probabilities of less that 5% (P <.05) were considered significant. Discrete variables (number of times pulled, mortality, removal, lung lesion status, dehorn status) were analyzed using Chi-square anlaysis (SAS Institute, Inc.). The Effect of Castration on Animal Health, Growth Performance, and Carcass Characteristics of Intact Male Calves Entering the Feedlot Daniel C. Renfro DVM 1, 2, R. Spencer Swingle Ph.D. ¹, Daniel U. Thomson DVM Ph.D.¹, Mark Branine Ph.D.¹, Guy Loneragan DVM Ph.D.² ¹Cactus Research, Ltd., Amarillo 2 Division of Agriculture, West Texas A&M University, Canyon RESULTS AND DISCUSSION Of the males placed, n=1188, 45% were treated for respiratory disease. The morbidity in intact males was 40% greater than steers (n=299) enrolled in the study. The relative risk of undergoing one morbid episode was 1.42 or 42% greater for the population of intact males compared to steers. The risk of mortality was 1.42 times greater in the intact male relative to the steers. 24% of the observed morbidity and mortality were attributable to castration during initial processing in the feedyard. Study rejection was 1.63 times greater for intact males compared to steers. Moreover, 31.8% of study rejections were attributed to castration at arrival. The impact of individuals identified to have a pneumonic lung lesion at harvest revealed a reduction in overall average daily gain (.14 lb), yield grade (.13), and hot carcass weight (23 lb) compared with those with no lesions. Lung lesions were identified in 42% of the animals harvested, however 57.4 % of them were never been pulled for treatment, thus illustrating the difficulty and lack of accuracy in detecting respiratory disease in commercial feedyards. Castrating calves at arrival in the feedyard is associated with adverse effects on morbidity, mortality, and removal rates as well as reductions in feeding performance and carcass characteristics in the intact male population relative to the steers. # of times treated 123SEM HCW (lbs.)3356.59017.7 YG0.41.55.15 QG.5701.17.35 The Effect of Morbidity on Carcass Characteristics (Table 1) a. Values represent the amount of reduction in the corresponding parameter relative to those that were not determined to be morbid through the duration of the study. b. The values shown above all had a Pr>F of <.0001 INTRODUCTION Optimizing the quality of the cattle while minimizing purchase price is recognized as an efficient way to maximize the profitability of cattle during the growing-finishing phase. Historically, intact male calves have been discounted in typical cattle procurement arenas. It is unclear how much discount is appropriate. The objective of this study was to characterize and quantify the impact of castration on animal health, growth performance, and carcass characteristics in intact males castrated at feedlot arrival compared to those castrated prior to arrival. (ADG_1 = ADG to reimplant, ADG_2 = ADG from reimplant to harvest, ADG_3 = overall ADG) Effects of morbid events (treated once, treated twice, or treated three times), castration status, and lung lesion status (present or not) on performance and carcass characteristics were analyzed using the Proc GLM procdure of SAS (SAS Institute, Inc.), using the individual animal as the experimental unit. SEM=.16 SEM=.12 SEM=.10