Influence of Fasting Time on Body Weight Shrinkage and Average Daily Gain1

Abstract

A grazing experiment was conducted to determine differences in rate of BW shrink among weigh days and to compare accuracy and precision in measuring ADG between unshrunk and shrunk BW. Twenty-four yearling steers were grazed on a predominately tall fescue (Festuca arundinacea Schreb.) pasture and moved 2 d prior to weighing to a 2-ha mixture of tall fescue-orchardgrass (Dactylis glomerata L.)-white clover (Trifolium repens L.). Steers were weighed unshrunk, penned with feed and water withheld, and then weighed at 2-h intervals for 12 h on April 11 and June 17 (six fasting times) and for 14 h on May 13 (seven fasting times). Percent shrink increased quadratically (P<0.001) with time, and the linear coefficient differed (P<0.05) among the three weigh dates (P<0.05). There were negative correlations (P<0.10) between BW and shrinkage for each fasting time on April 11 and June 17, but not for May 13. Average daily gains were inconsistent across unshrunk and shrunk BW on May 13 (29 d on test) but were stable among BW measures on June 17 (67 d on test). Unshrunk BW are as effective as shrunk BW in measuring ADG if duration between initial and final BW is sufficient in length to reduce variation in BW attributed to gut fill.