Polyethylene glycol compared with ytterbium oxide as a total faecal output marker to predict organic matter intake of dairy ewes fed indoors or at pasture

Abstract

Several external markers can be used for estimating total faecal output in view of assessing ruminant intake at pasture. Among them, ytterbium (Yb) has been used for many years in various conditions. Polyethylene glycol (PEG) is a promising external marker because it can be rapidly determined using near-infrared spectroscopy (NIRS). The study consisted of 24 adult lactating dairy ewes over three periods (P1, P2 and P3), fed with three different diets: P1, total mixed ration (TMR); P2, Italian ryegrass (IRG); and P3, pasture. After an adaptation period, the ewes were administered a daily dose of ytterbium oxide (0.35 g/day) and PEG (20 g/day) for 2 weeks. During the last week, the daily organic matter intake (OMI OBS ) was measured. Faecal samples were collected at milking time (0800 and 1600 h) to determine marker content, using only samples collected in the morning (PEG m ) or by averaging samples (Yb, PEG ma ). Faecal marker content made it possible to assess total faecal output, either using the two recovery rates for PEG (0.98 or 0.87) or not. The OMI OBS was assessed on the basis of total faeces estimated with Yb (OMI Yb ) or PEG (OMI PEG ), and the digestibility was calculated on the basis of feed analysis. With total TMR (P1), the OMI PEG , corrected with recovery rate (OMI PEGm98 ) or not corrected (OMI PEGm ) was 2.40 kg/day and 2.50 kg/day, respectively, and was not different ( P > 0.05) from OMI OBS (2.51 kg/day), whereas OMI Yb was lower (2.14 kg/day) ( P < 0.001). With IRG (P2), OMI PEGm98 (1.67 kg/day), OMI PEGm87 (1.51 kg/day) and OMI Yb (1.59 kg/day) were not different ( P > 0.05) from OMI OBS (1.57 kg/day). With pasture (P3), the OMI PEGm (1.54 kg/day) and OMI PEGm98 (1.48 kg/day) were not different ( P > 0.05) from the OMI assessed from the biomass measurement (1.52 kg/day). The OMI Yb (1.36 kg/day) was lower ( P < 0.05) but not different from OMI PEGm98 and OMI PEGm87 . Spearman's rank correlation between OMI OBS and other OMIs (predicted with Yb or PEG P1 and P2) showed that it is possible to rank animals using PEG when there is a sufficiently wide range of OMI OBS (1.65 to 2.8 kg/day in P1) but not within a narrower range (1.47 to 1.72 kg/day in P2). In conclusion, the present study confirms that PEG is a valuable external faecal marker, easy to prepare (solution), administer and determine (NIRS). It can be used to assess intake with numerous animals at pasture, but only for groups, and not to quantitatively estimate individual OMI.

Polyethylene glycol marker measured with NIRS gives a reliable estimate of the rangeland intake of grazing sheep

“…Few experiments have been conducted indoors with fresh forage (Andueza et al, 2013;Hassoun et al, 2013 and or at pasture (Caja et al, 2009;Hassoun et al, 2014). † E-mail: philippe.hassoun@supagro.inra.fr The present experiment aimed to measure the usefulness of PEG as external faecal marker to assess dry matter intake (DMI) of sheep grazing rangeland pasture.…”

“…Few experiments have been conducted indoors with fresh forage (Andueza et al, 2013;Hassoun et al, 2013 and or at pasture (Caja et al, 2009;Hassoun et al, 2014).…”