Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2004
Publication Date: 12/1/2004
Citation: Aiken, G.E., Tabler, S.F. Influence of fasting time on body weight shrinkage and average daily gain. Professional Animal Scientist. 20(2004):524-527. Interpretive Summary: Average daily weight gain is the most effective measure for testing differences between treatments in grazing experiments. Unfortunately, precision in weighing cattle is low due to variations in gut fill. Grazing researchers typically have reduced variation in gut fill by fasting cattle from feed and water before weighing, but there are animal welfare concerns for fasting cattle in hot and humid conditions and for those exhibiting toxicosis from grazing endophyte-infected tall fescue. Yearling steers were pastured and weighed on three different dates (May 13, April 11, June 17) to determine the influence of fasting time (0, 2, 4, 6 8, 10, and 12 h) on percent body weight shrinkage and on the precision of measuring average daily gain between fasted and non-fasted cattle. Trends in percent body weight shrinkage differed among the three dates as fasting time increased. Average daily gains were inconsistent across 0 to 12 fasting times when cattle were weighed following 29 d, but were stable after 67 days on test. Unshrunk body weights are as effective as shrunk body weights in measuring ADG if duration between initial and final body weight is sufficient in length. Results of this experiment will provide support to grazing research being conducted with environmental conditions that restrict the use of fasted body weights for determining average daily gain.
Technical Abstract: A grazing experiment was conducted to determine differences in rate of body weight shrink among weigh days and to compare accuracy and precision in measuring average daily weight gain between unshrunk and shrunk body weight. Twenty-four yearling steers were grazed on a predominately tall fescue (Festuca arundinacea Schreb.) pasture and moved 2 days 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 11 April and 17 June (6 fasting times), and for 14 h on 13 May (7 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 body weight and shrinkage for each fasting time on 11 April and 17 June, but not for 13 May. Average daily gains were inconsistent across unshrunk and shrunk body weights on 13 May (29 d on test) but were stable among body weight measures on 17 June (67 days on test). Unshrunk body weights are as effective as shrunk body weights in measuring ADG if duration between initial and final body weights is sufficient in length to reduce variation in body weight attributed to gut fill.