A series of 3 experiments were conducted to evaluate the use of microalgae as supplements for ruminants consuming low-CP tropical grasses. In Exp. 1, the chemical composition and in vitro protein degradability of 9 algae species and 4 protein supplements were determined. In Exp. 2, rumen function and microbial protein (MCP) production were determined in steers fed speargrass hay alone or supplemented with , , , or cottonseed meal (CSM). In Exp. 3, DMI and ADG were determined in steers fed speargrass hay alone or supplemented with increasing amounts of NPN (urea combined with ammonia sulfate), CSM, or . In Exp. 1, the CP content of and (675 and 580 g/kg DM) was highest among the algae species and higher than the other protein supplements evaluated, and sp. had the highest crude lipid (CL) content (198 g/kg DM). In Exp. 2, supplementation increased speargrass hay intake, the efficiency of MCP production, the fractional outflow rate of digesta from the rumen, the concentration of NHN, and the molar proportion of branched-chain fatty acids in the rumen fluid of steers above all other treatments. acceptance by steers was low and this resulted in no significant difference to unsupplemented steers for all parameters measured for this algae supplement. In Exp. 3, ADG linearly increased with increasing supplementary N intake from both and NPN, with no difference between the 2 supplements. In contrast, ADG quadratically increased with increasing supplementary N intake from CSM. It was concluded that and may potentially be used as protein sources for cattle grazing low-CP pastures.
The objective of this study was to compare the use of an external marker titanium dioxide (TiO₂) as an alternative to chromic oxide (Cr₂O₃) in dairy cows. Four dairy cows were allocated in individual pens and fed concentrate supplement and Pennisetum purpureum cv. Cameroon cut daily. Fecal excretion, forage and total dry matter (DM) intakes, and digestibility were measured and estimated with TiO₂ and Cr₂O₃. Chromic oxide overestimated and TiO₂ tended to overestimate fecal excretion compared with total fecal collection. Forage and total DM intakes were overestimated by Cr₂O₃. The apparent DM digestibility was underestimated by Cr₂O₃ and TiO₂. The organic matter (OM) digestibility was underestimated by both markers. There were greater mean bias, mean squared prediction error, and root of the mean squared prediction errors for all parameters estimated with Cr₂O₃. In conclusion, estimates using TiO₂ were more precise and accurate indicating that it can replace Cr₂O₃ as an external marker for grazing dairy cows.
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