Fat accretion measurements strengthen the relationship between feed conversion efficiency and Nitrogen isotopic discrimination while rumen microbial genes contribute little

Abstract

The use of biomarkers for feed conversion efficiency (FCE), such as Nitrogen isotopic discrimination (Δ15N), facilitates easier measurement and may be useful in breeding strategies. However, we need to better understand the relationship between FCE and Δ15N, particularly the effects of differences in the composition of liveweight gain and rumen N metabolism. Alongside measurements of FCE and Δ15N, we estimated changes in body composition and used dietary treatments with and without nitrates, and rumen metagenomics to explore these effects. Nitrate fed steers had reduced FCE and higher Δ15N in plasma compared to steers offered non-nitrate containing diets. The negative relationship between FCE and Δ15N was strengthened with the inclusion of fat depth change at the 3rd lumbar vertebrae, but not with average daily gain. We identified 1,700 microbial genes with a relative abundance >0.01% of which, 26 were associated with Δ15N. These genes explained 69% of variation in Δ15N and showed clustering in two distinct functional networks. However, there was no clear relationship between their relative abundances and Δ15N, suggesting that rumen microbial genes contribute little to Δ15N. Conversely, we show that changes in the composition of gain (fat accretion) provide additional strength to the relationship between FCE and Δ15N.

Identifying cattle with superior growth feed efficiency through their natural 15 N abundance and plasma urea concentration: a meta-analysis.

“…Interestingly the response of FCE to Δ 15 Nanimal-diet variation at the individual level was almost identical with both statistical approaches used here (slope of -0.033 kg/kg [eq. 4; Table 2] and -0.034 kg/kg [Figure 4A]) and very close to the response of NUE to Δ 15 Nanimal-diet variations previously found by meta-analysis (-0.035 kg/kg; Cantalapiedra-Hijar et al, 2018).…”

Identification of Rumen Microbial Genes Involved in Pathways Linked to Appetite, Growth, and Feed Conversion Efficiency in Cattle

“…Ruminants live in a symbiotic relationship with their rumen microbiota (comprising bacteria, protozoa, fungi, and archaea), which produce enzymes able to digest their food by breaking down complex polysaccharides of the plant biomass into volatile fatty acids (VFA), microbial proteins, and vitamins (Russell and Hespell, 1981; Bergman, 1990; Van Soest, 1994). Thus, the rumen microbiota fermentation profile has a significant influence on the feed conversion efficiency of the host (Russell, 2001; Li et al, 2009; Hernandez-Sanabria et al, 2011; Jami et al, 2014; Sasson et al, 2017; Meale et al, 2018) and is accountable for up to 70% of the host’s daily energy requirements (Bergman, 1990).…”

Abstracts from the Proceedings of the 33rd Biennial Conference of the Australian Association of Animal Sciences

“…live weight gain/dry matter intake) in cattle and sheep (Wheadon et al 2014;Cheng et al 2015). Recent work indicated that fat measurements strengthen the relationship between cattle FCE and plasma Δ15N (Meale et al 2018). This study aimed to determine whether sheep body composition measurements can strengthen the relationship between FCE and plasma Δ15N.…”

“…Individually housed lambs were adapted to the trial diets for 14days. Wool growth was measured using the dye-band technique (Meale et al 2014), whereby a band of black commercial hair dye was applied to the mid-side of each lamb on Day 0. After an experimental period of 11weeks, wool was clipped from the dye-band site and analysed for wool yield and quality parameters.…”

“…Plasma nitrogen isotopic fractionation (plasma Δ15N) was identified as a biomarker for feed conversion efficiency (FCE; i.e. live weight gain/dry matter intake) in cattle and sheep (Wheadon et al 2014;Cheng et al 2015). Recent work indicated that fat measurements strengthen the relationship between cattle FCE and plasma Δ15N (Meale et al 2018).…”