This paper reviews the application of intraruminal chromium controlled release capsules (CRC, Captec (NZ) Ltd, Auckland) to the measurement of herbage intake in ruminants. The capsules are designed to provide for the linear release of Cr2O3 over c. 25 days in sheep and c. 20 days in cattle. Uniform release of Cr2O3 is achieved 2 to 3 days after oral administration of the CRC but steady state levels of Cr2O3 in the faeces are usually not achieved until day 7 or 8 in sheep and day 5 or 6 in cattle. Where cross-over or multiple feeding level experimental designs are applied, time should be allowed for Cr2O3 to adjust to a new steady state in the faeces before sampling for each new treatment. The period of time required varies from 3 to more than 5 days depending on the size of feed intake change. The continuous mode of marker release in the rumen reduces diurnal variation of Cr2O3 in the faeces and this allows rectal sampling regimens to be applied at different times of each sampling day. Sward sampling of faeces reduced disturbance of animal grazing to a minimal level since Cr2O3 is delivered by a single CRC application. The effects of level of feed intake and feed type on the rate of Cr2O3 release are usually small, but release rates may be up to 13% lower in rumen-fistulated than in non-fistulated animals and may differ for capsules of the same time applied to different ruminant species. Reduced animal handling, flexible faecal sampling times and lower labour requirements with CRC technology, compared to daily drenching of Cr2O3, enable the number of experimental animals to be increased. This improves the likelihood of detecting differences in mean intake between groups. Intakes of individual animals will not be reliably estimated with chromic oxide CRC until the digestibility of herbage consumed by individual animals can be measured more accurately.
Proceedings of the New Zealand Society of Animal Production, Volume 50, , 397-402, 1990
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