EVALUATION OF THE CAPTEC CHROME CONTROLLED-RELEASE DEVICE FOR THE ESTIMATION OF FECAL OUTPUT BY GRAZING SHEEP

Three grazing experiments were conducted to compare actual fecal output [FO] by sheep, determined with fecal collection bags, to fecal output predicted using Captec chromic oxide [Cr2O3] controlled-release capsules. In Exp. 1, 14 crossbred wethers dosed with controlled-release Cr2O3 capsules rotationally grazed four paddocks of alfalfa [Medicago sativa L.] for 18 d. Total fecal collection and grab samples were taken daily from each animal; feces were dried and assayed for Cr. From d 5 to 12 after dosing, mean actual FO [429 +/- 9.6 g of DM/d] differed [P < .001] from FO predicted by the capsule [463 +/- 12.8 g of DM/d]. The correlation between actual and predicted FO was r = .59. When data were averaged by day, the correlation increased to .82. In Exp. 2, Tifton 44 bermudagrass [Cynodon dactylon [L.] Pers.] was strip-grazed for 30 d by the same 14 wethers used in Exp. 1. Mean actual FO [369 +/- 5.1 g of DM/d] differed [P < .0001] from predicted FO [415 +/- 9.3 g of DM/d], with a correlation of .60. In Exp. 3, 72 crossbred lambs were blocked by weight [light and heavy] and assigned to six groups of eight wethers] [four with fecal bags] and four ewes, allotted randomly to three stocking rates [74, 99, and 148 sheep/ha]. Sampling occurred from d 6 to 10 after dosing [Period 1] and d 20 to 24 after dosing [Period 2]. The correlation between actual and predicted FO in Period 1 was better [r = .63] than that in Period 2 [r = .46]; using means improved the results only for Period 1 [r = .77]. Although correlations were significant between predicted and actual FO, the controlled-release Cr capsule did not adequately predict total FO by wether lambs.