The objective of this study was to compare different faecal sampling regimes (collected in the morning (am) or the afternoon (pm), or the weighted mean of both times) for determining the concentrations of faecal markers (the natural odd-chain n-alkanes (C27 – C35) contained in feed, the dosed (once daily in the morning) synthetic n-alkanes (C32 and C36) and titanium dioxide (TiO2)) and their accuracy for estimating dry matter digestibility (DMD) and faecal dry matter (DM) output from wethers (n = 30) fed cut ryegrasses. The concordance correlation coefficient (CCC) with measured faecal DM output was strong (CCC = 0.8) for faecal DM output predicted from the mean concentration of C32 in morning and afternoon faeces (am+pm), moderate (CCC = 0.6-0.7) when predicted from TiO2 am and am+pm, and weak when predicted from C36. The DMD predicted by C27 and C33 at either collection time, and by C29 and C31 for samples collected in the pm, were similar to measured DMD. The estimated DMD based on faecal C35 had a negligible CCC with measured DMD (CCC<0.1), while other natural n-alkanes had a low to moderate CCC (0.3-0.6) with measured DMD, especially for the samples collected pm and am+pm. For applications with grazing animals, where marker dosing and faecal sampling is often restricted to once daily in the morning for practical reasons, TiO2 was the most accurate marker to estimate faecal DM output and C31 or C33 were the most accurate and precise markers to estimate DMD.

A Jonker, and GP Cosgrove

Proceedings of the New Zealand Society of Animal Production, Volume 77, Rotorua, 43-48, 2017
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