PSXIV-3 - Effect of Pen Mud Accumulation on the Growth Performance Growing-finishing Calf-fed Holstein Steers in the Feedlot During Summer in Southern California

Abstract: Objectives were to evaluate the relationship between pen mud accumulation and growth performance of calf-fed Holstein steers during the extreme heat characteristic of the months of August and September in the Southern California desert region. Holstein steers (n = 105; initial BW = 443 ±17 kg) were utilized in 28-d experiment (August 17 – September 14, 2021). Steers were blocked by initial shrunk weight (220 d before the initiation of the experiment) and randomly assigned to 21 pens (5 steers per pen). Pens were 62 m² with 25 m² overhead shade, automatic waterers and 2.4 m fence-line feed bunks. All steers were fed a steam-flaked corn-based growing-finishing diet. A bolus measuring temperature activity (smaXtec Basic, Smaxtec Animal Care GmbH, Austria) was placed in the rumen of each steer 55 d before the initiation of the experiment (June 22, 2021). Mud scores were recorded weekly by visual inspection. Mud score was determined as the percentage of pens surface area covered with mud. Scores were determined as follows: 1 – 0 to 20% of pen covered by mud; 2 – 21 to 40% of pen covered by mud; 3 – 41 to 60% of pen covered by mud; 4 – 61 to 80% of pen covered by mud; 5 – 81 to 100% of pen covered by mud. Ambient temperature averaged 33.2 ±2.3° C for the experimental period. Temperature of dry pen surfaces was greater than that of muddy surfaces (50.3 vs 20.4° C, respectively, P < 0.01). The relationship between ruminal temperature and pen mud score was not appreciable (P = 0.56). However, ADG was greater with a pen mud score of 2. Average daily gain decreased as pen mud score increased (r² = 0.55). Similarly, feed efficiency was greatest in pens with a pen mud score of 2. Greater pen mud scores resulted in decreased feed efficiency (r² = 0.56).