N-alkanes v. ytterbium/faecal index as two methods for estimating herbage intake of dairy cows fed on diets differing in the herbage : maize silage ratio and feeding level

Abstract

The aim of this study was to compare the n-alkanes and the ytterbium (Yb)/faecal index techniques as two methods for estimating the herbage intake of dairy cows fed indoors on different herbage : supplement ratios and feeding levels. The supplement was a mixture of maize silage and soyabean meal (ratio of 87 : 13 on a dry matter (DM) basis). In all, four treatments were studied. The herbage : supplement ratio in the diet was 25 : 75, 50 : 50, 75 : 25 and 50 : 50 for treatments 1, 2, 3 and 4, respectively. Animals were offered for treatments 1, 2 and 3, 100% of ad libitum intake measured before the experiment and 70% of ad libitum intake for treatment 4. Cows were fed herbage in the morning and supplement in the evening. A total of six lactating Holstein dairy cows were used in a 4 3 4 Latin square with four 14-day periods. Herbage and supplement intakes, faecal output (FO), in vivo organic matter (OM) digestibility and faecal recovery of markers were measured on the last 5 days of each period. Intake was estimated with the two methods and from two faecal sampling techniques, that is, total faecal collection v. grab sampling during milking. Mean herbage intake as fed, or estimated from n-alkanes or from the Yb/faecal index was 7.7, 8.1 and 10.2 kg DM, respectively. The mean prediction error, expressed as a fraction of actual herbage intake, was 0.10 and 0.50 for the n-alkanes and Yb/faecal index methods, respectively. The n-alkanes method clearly showed much better accuracy than the Yb/faecal index method for estimating intake, irrespective of the faecal sampling method, herbage : silage proportion or feeding level. For the nalkanes method, herbage intake was slightly overestimated (7%) when herbage proportion in the diet was high, due to a ratio of faecal C 33 : C 32 recovery .1. The high bias for the Yb/faecal index was due to the cumulative effect of overestimation of FO (mean recovery of Yb 5 0.92) and underestimation of the diet indigestible fraction (28%). Between-treatment variations of FO were on average well estimated by Yb. Between-treatment variations of OM digestibility estimated using the faecal index technique were lower than those observed in vivo. It is concluded that intake of grazing dairy cows receiving high levels of maize silage supplement should be estimated using the n-alkanes method.

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

“…On the contrary, OMI Yb was lower (−15%), suggesting that recovery rate would not be of 1.00 but 1.17 instead. Such a recovery rate is higher than the values (0.89 to 0.99) reported with beef cows (Prigge et al, 1981) and lambs dosed once daily (Krysl et al, 1988) or dairy cows dosed twice daily (Delagarde et al, 2010;Perez-Ramirez et al, 2012) and fed with different diets (hays, TMR or maize silage, and concentrate). However, similar results (1.07 to 1.19) were observed when beef cows were dosed twice daily (Prigge et al, 1981), and with lambs dosed once daily and fed hay supplemented with sorghum grain (Krysl et al, 1988).…”

Herbage dry matter intake estimation of grazing dairy cows based on animal, behavioral, environmental, and feed variables

“…No exact reference for the daily HDMI for individual animals exists under grazing conditions; thus, a genuine validation of the n-alkane method is not possible. Nevertheless, the n-alkane method is commonly suggested as one of the best available techniques for individual HDMI estimation of grazing animals (Smit et al, 2005;Decruyenaere et al, 2009;Pérez-Ramírez et al, 2012). However, there are weak points that may impede an accurate HDMI estimation.…”

Pasture intake and milk production of dairy cows rotationally grazing on multi-species swards

“…Methods of laboratory chemical analyses for ash, nitrogen, fibre and ytterbium have been described by Pérez-Ramírez et al (2012). PCd was determined following the Aufrère and Michalet-Doreau (1988) method.…”