Evaluation of the Captec controlled-release chromic oxide capsule for fecal output determination in sheep.

One pen feeding study was conducted with 24 wether lambs to compared fecal output (FO) determined by total fecal collection with FO estimated by dosing lambs with chromic oxide controlled-release capsules. Lambs (39 +/- 1.5 kg BW) were fed either alfalfa hay (ALF), Coastal bermudagrass hay (CBG), or a commercially available pelleted (PEL) sheep diet (eight lambs/diet). After dosing, rectal grab samples and total collection of feces were taken daily for 31 d. Constant fecal excretion of Cr was achieved approximately on d 8 (range = d 5 to 13) after dosing. Capsule expiration was accompanied by a sharp peak in Cr excretion approximately on d 27 (range = d 24 to 30). Complete excretion of Cr by d 31 occurred in only seven lambs. Agreement between actual and predicted FO was examined by linear regression from d 8 to 22. Best parameter estimates and highest R2 were observed when sampling a) every other day from d 11 to 19 (five samplings), b) daily from d 8 to 17, c) daily during the entire period, and d) daily from d 13 to 22. Sampling for 5 d chosen at random consistently gave poor results. Sampling every 3rd d gave the poorest results. Controlled-release capsules predicted FO very accurately in lambs fed ALF. Reliable estimates were obtained in 67% of cases investigated with CBG, whereas only 25% of estimates were reliable with PEL. The controlled-release capsules always overestimated FO of wethers fed CBG and PEL, implying that in those lambs the actual release rate of Cr was less than that specified by the manufacturer.