Submitted to: Rangelands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2019
Publication Date: 6/17/2016
Citation: Derner, J.D., Reeves, J.L., Mortenson, M.C., West, M.S. 2016. Estimating overnight weight loss of corralled yearling steers in semiarid rangeland. Rangelands. 38(3):101-104.
Interpretive Summary: For grazing studies evaluating livestock weight gains, one of the common practices is to confine animals overnight without food or water in order to reduce fluctuations in gut fill (urine and feces). However, this practices results in weight loss for these animals that may take several days to weeks to recover. As such, there is a need to determine estimates of the amount of this overnight shrink to reduce the stress of shrinking and regaining weight for the grazing animals each time they are weighed. We determined shrink losses for crossbred yearling steers grazing shortgrass steppe in Colorado at of four weigh dates (June, July, August, September) in the 2009-2012 summer grazing seasons (total of 16 weighings). Overnight shrink in yearling steers was not influenced by environmental variables (air temperature and relative humidity). “Pencil shrink” percentages can be used for grazing studies and land managers (8.8-9.0% shrink values for June, July and August, and 7.1% for September) in semiarid rangelands with benefits of removing stress of yearling steers of losing the weight overnight and regaining this lost weight for each weigh date.
Technical Abstract: Free-ranging livestock grazing native vegetation on rangelands are frequently gathered and confined overnight in a corral (sensu drylot) prior to weighing to determine periodic weight gains for grazing studies. Quantification of this overnight percent shrink across the grazing season could provide temporal weight gain data without the logistical difficulties in gathering and holding animals, and will decrease associated animal stress from shrinking and regaining weight multiple times. We determined percent shrink losses for 20 individual crossbred yearling steers stocked at moderate grazing levels (0.65 Animal Unit Months, AUM/ha) on shortgrass steppe at the Central Plains Experimental Range (Nunn, Colorado, USA) for each of four trials (Trial 1: June; Trial 2: July; Trial 3: August; Trial 4: September) in the 2009-2012 summer grazing seasons (n= 16 weighings). Average relative humidity and average air temperatures, determined by adding hourly average values for the entire 17 hour shrink period (1400 h of the pre-shrunk day to 0800 h of the next day) were evaluated for influencing percent shrink losses. Overnight percent shrink in yearlings was insensitive to pre-shrunk weight of yearling steers (P=0.7685), relative humidity (P=0.2238) and average air temperatures (P=0.2913) across the 16 trials. Mean percent shrink was 8.4% ± 1.6 (SD) across all trials, with similar values for Trial 1 (8.7% ± 1.3 SD), Trial 2 (8.7% ± 1.7 SD), and Trial 3 (9.0% ± 1.0 SD), although lower values for Trial 4 (7.1 ± 1.3 SD). These shrink values can be used to accurately estimate temporal weight gain data within a grazing season in semiarid rangelands. Furthermore, use of these shrink percentage estimates removes the need for overnight holding of livestock thereby eliminating the stress of losing/regaining weight.