Predicting the metabolizable energy intake of ruminants using digestibility, ruminal methane production and fermentation data

Abstract

SUMMARYObtaining accurate estimates of the metabolizable energy (ME) intake (MEI; MJ/day) of individual grazing ruminants is an important requirement for effective nutritional management and genetic selection of energy efficient ruminants. Diet digestibility and the daily methane production rate (MPR; MJ/day) of ruminants can be closely linked with their MEI, so published data were examined to determine whether MEI could be accurately estimated from digestibility, MPR and other parameters able to be measured on grazing animals. Four modelling approaches were assessed or developed to estimate MEI: (i) a published fixed proportional relationship between the non-metabolizable losses of MPR and urinary energy (UE; MJ/day); (ii) the proportion of energy digestibility (EngDig); (iii) MPR and the ruminal factors that influence the stoichiometric relationships between MPR and MEI; and (iv) the calculated ME arising from rumen fermentation (MEf; MJ/day). Data to develop the models (n=61) were collected across three publications (Paper) where the Paper effect was treated as a random-effect variable. Each of the models (1–4) was challenged with an independent data set (n=19). The inclusion of MEf (P=0·01) to predict MEI [MEI=0·18 (2·03)+3·42 (0·36)×sqrt(MEf) (d.f.=57; residual log likelihood=173·6)] had the lowest mean square error of prediction (MSEP) when challenged with the independent data set; mean bias of −0·42 MJ/day (P<0·05), MSEP=0·68 MJ/day and the bias, slope and random components of the MSEP were, as a proportion, 0·26, 0·13 and 0·61, respectively. None of the models estimated MEI with sufficient accuracy to be useful for identifying individual animals with above average energetic efficiency. A critical limit to any model seeking to estimate MEI from MPR and fermentation traits appears to be the variation between animals and between diets, in the proportion of digested energy which is fermented relative to that which is made available by mammalian digestion, and this is evaluated.

Animal board invited review: genetic possibilities to reduce enteric methane emissions from ruminants

“…There were correlations of 0.40 with MY and CH 4 emission intensity, but correlations with gross CH 4 production were almost zero. Other studies (Robinson et al , 2010 ), suggest that VFA concentration has limited utility in predicting CH 4 emissions, although VFA production rate may be useful (McPhee and Hegarty, 2008 ). This contrasting evidence indicates considerable work is still required before the utility of VFA as an indicator of CH 4 emissions can be realised.…”

Applicability of short-term emission measurements for on-farm quantification of enteric methane

“…This would require measurement of CO 2 and methane concentration in the PAC and/or sampling of ruminal VFA by rumen intubation after the animals are removed from the PAC. Initial investigations into combining rumen stoichiometry and methane emission to calculate energy expenditure showed the benefit of including VFA data (McPhee and Hegarty, 2008).…”

Models for estimating feed intake in small ruminants

“…Nevertheless, this difficulty can be overcome by the implementation of the fecal NIRS technique, as suggested by Landau et al (2006) or by regression equations (e.g., Peripolli et al, 2011). McPhee & Hegarty (2008) have recently published a model aimed at estimating DMI, energy intake or OM intake in grazing herbivores, including sheep and goats, on the basis of forage composition and rumen parameters. However, none of the tested inputs was sufficiently accurate to estimate metabolizable energy Each point (n = 132) is the mean of 3 sheep data (elaborated from Molle et al, 2008b).…”