Experimental Procedures
General Management
Mature cull cows previously adapted to the feedlot were used to determine the effects of trainer animals on performance and health of newly arrived feedlot steers. The trainer cows were allowed a 3-week pen and diet adaptation period prior to arrival of the newly weaned calves. During the adaptation period, the trainer animals were fed a 60% corn silage, 16% CP feedlot receiving diet (Table 1). Cows were culls from the Coshocton Branch of the Ohio Agricultural Research and Development Center (OARDC). Cows were culled based on poor production or because they were not pregnant. Cows were transported to the OARDC Feedlot 1 week after weaning and began the adaptation period immediately upon arrival. Nonpregnant cows were implanted with Synchromate-B (Upjohn Co., Kalamazoo, MI) and given an injection of prostaglandin 3 days before the experiment began to prevent them from coming into heat when they were serving as trainers of the experimental animals. Cows were reimplanted 10 days later. Trainer cows were weighed at the beginning and end of the adaptation period and individual feed intakes were recorded.
The experimental animals were crossbred beef steer calves originating from three locations; a Virginia sale barn, and newly weaned calves from the Coshocton Branch of OARDC, or the Ohio State University herd in Columbus. Calves were transported approximately 520, 40, and 95 miles (respectively) to the OARDC feedlot and all calves (within a trial) arrived on the same day. Upon arrival, calves were given a 2 hour rest period during which they had access to hay and water prior to being weighed, ear-tagged, and dewormed with Ivomec (Merck, Rahway, NJ). The purpose of the rest period was to allow the calves an opportunity to eat some hay and drink their fill of water prior to being weighed so as not to have an arbitrarily low starting weight. Calves were vaccinated against IBR, PI3, 7-way Clostridial bacterin, Haemophilus somnus, and Pasteurella upon arrival. Initial and final weights were determined using the average of weights measured on two consecutive days. Interim weights were taken every 7 days, immediately before feeding, to determine weekly performance. Both trials were 28 days in duration. After processing, newly arrived steers were allotted to 15 X 15 ft pens with eight or nine steers per pen. Procedures for use of the trainer animals and experimental design will be described later for each trial. For both trials, trainer animals were present with the experimental animals for the first 14 days of the trial and were then removed from the pens. Pens were constructed of metal gates, cables, and concrete slatted floors and were located in an open sided barn. Steers were fed once daily (0900 hours) and ad libitum intake of each pen was recorded. Cattle were fed using a conveyor belt and a plow that purged feed into the individual bunks for each pen. Feed bunks were 15 feet long. Mixing and delivery of feed took approximately 5 minutes for each pen. Experimental animals were fed the same diet used during adaptation of the trainer animals (Table 1).
Health status of the animals was determined by visual analysis and rectal temperature. Any steers visibly anorexic, showing nasal mucous discharge, coughing, or breathing rapidly were removed from their pen, and their rectal temperatures were determined using a manually read veterinary thermometer. Any animal with a rectal temperature greater than 103oF was treated with antibiotics. Animals were returned to their pen of origin immediately after their rectal temperature was determined, and any needed antibiotic treatments were administered. Animal care procedures were according to accepted standards (Consortium, 1988).
Trial 1. Twelve mature Simmental X Angus cows (BW, 1279 ± 26 lb) were penned individually and used as trainer animals in a completely randomized design experiment. After processing, 216 newly received calves were allotted by weight to 24 pens with nine calves per pen. Twelve of these pens each contained a previously adapted trainer cow. Calves in pens without a trainer cow were housed so they were not in visual contact with calves in pens containing trainer cows.
Eating behavior of experimental animals was determined using a point in time assessment. At four points in time (5, 15, 30, and 60 minutes) after feed delivery to a pen, the number of calves in the pen that were eating was recorded. Feed delivery to the pens was staggered at 5 minute intervals due to mixing and delivery time constraints; this facilitated data collection. Point in time assessments of eating behavior were conducted on days 1, 2 and 4 after arrival of the calves. Data were analyzed using the GLM repeated measures procedures of SAS (1988) for a completely randomized design experiment. The model contained effects due to trainer cow status, and repeated measures over time. Time and interactions with time were tested using residual mean square as the error term. Pen served as the experimental unit.
Trial 2. Twelve mature Simmental X Angus cows (BW, 1274 ± 79 lb) were penned individually and used as trainer animals in a completely randomized design experiment. After processing, 207 newly received calves were allotted by weight to 24 pens with eight or nine calves per pen. All procedures were as described for Trial 1, except point in time assessment of eating behavior was conducted on days 1, 2, 4, 8, 13 and 15. Day 15 represented eating behavior the first day after trainer cows were removed from the pens.