Predicting Feedlot Growth Performance over the Feeding Period Utilizing Steer Age and Body Weight

Typically, mean growth performance is known for the entire feeding period and is used to formulate feedlot finishing diets. A more accurate way for formulating diets would be to know performance (DMI and ADG) at the beginning of the feeding period when requirements are greatest. The objective of this pooled-analysis (2002-2015) of University of Nebraska-Lincoln research pen performance examined how steer age and feedlot entry BW affects growth performance over the finishing period. For data analysis, pens were divided into 3 subclasses when they started the finishing period, which included: 1) calf-fed (entering the feedlot at receiving), 2) short yearling (grazed during winter and entering the feedlot in May), and 3) long yearlings (grazed during the winter and summer and entering the feedlot in September). Furthermore, within each steer age class, pen means were grouped based upon initial BW (226.8 to 544.3 kg, in 45.4 kg increments) when starting the finishing diet. There were 1,002 pens of calf-feds, 1,114 pens of short yearlings, and 435 pens of long yearlings. As initial BW increased, DMO (kg/d) for the whole feeding period increased quadratically (P = 0.01) in calf-fed steers and averaged 10.4 kg/d. However, in short (11.7 kg/d) and long yearlings (12.9 kg/d), DMO increased linearly (P = 0.01) as initial BW increased. For all age groups and initial weight class of steers, calculating DMO as a percent of current BW was relatively constant over the entire feeding period with a range of 2.2 to 2.6%. Intake as a percent of current BW was greatest early (2.7%) in the finishing period and decreased linearly (P = 0.01) as days on feed increased (2.3%). A quadratic increase (P = 0.03) in ADG was observed in calf-feds as initial BW increased. No differences (P ≥ 0.60) in ADG were observed for short yearlings due to initial BW. However, ADG increased linearly (P = 0.01) as initial BW increased for long yearlings. As heavier cattle were placed within each age group, G:F decreased linearly (P = 0.01). Evaluating intake as a percent of current BW reduces variation due to steer age and BW; however, as days on feed increases, intake as a percent of current BW decreases. Predicting intake and growth performance over the entire feeding period is dependent upon steer age and initial weight when starting the finishing diet.

Key Words: cattle size, feedlot performance, intake