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Diet selection by steers using microhistological and stable carbon isotope ratio analyses
L L Bennett1, A C Hammond, M J Williams
1University of Florida, Gainesville 32611-0910, USA.
Journal of Animal Science
|August 26, 1999
Summary
Microhistological analysis is more informative than carbon ratio analysis for determining cattle diet composition in tropical pastures, especially when forbs are present. This helps understand grazing selection in complex swards.
Area of Science:
- Animal Science
- Nutritional Ecology
- Forage Science
Background:
- Determining diet botanical composition is crucial for understanding grazing animal nutrition and pasture management.
- Microhistological (MH) and stable carbon isotope ratio (CR) analyses are common methods, but their effectiveness can vary with pasture complexity.
Purpose of the Study:
- To compare the accuracy of microhistological (MH) and stable carbon isotope ratio (CR) analyses in determining the botanical composition of steer diets.
- To assess the reliability of these methods for analyzing ingesta and fecal samples from cattle grazing mixed tropical grass and rhizoma peanut pastures.
Main Methods:
- Two grazing seasons (1992, 1993) in Brooksville, FL, using steers on rhizoma peanut-mixed tropical grass pastures.
- Forage availability and composition were assessed using a weighted-disc double-sampling technique.
- Ingesta and fecal samples from cannulated and non-cannulated steers were analyzed using MH (rhizoma peanut, grass, forb) and CR (C3, C4 plants) methods.
Main Results:
- Both MH and CR analyses showed significant interactions with year and sampling date, indicating dynamic forage availability.
- MH analysis revealed strong positive correlations between ingesta and fecal samples for rhizoma peanut (r = .73-.92) and forb (r = .86-.98).
- CR analysis showed a positive correlation for C3 plants (r = .62), but MH analysis provided more distinct differentiation when forbs were a significant dietary component.
Conclusions:
- Microhistological analysis is more informative than carbon ratio analysis for estimating diet selection by cattle grazing complex tropical pastures, particularly when forbs are present.
- The accuracy of CR analysis can be limited by the grouping of diverse plant types (e.g., rhizoma peanut and forb) into a single C3 component.
- Accurate diet composition analysis is vital for effective pasture and animal management strategies.