Journal Article


R J Dewhurst
G R Edwards
M McGee
N M Wheadon



animals chemistry nitrogen female body weight animals inbred strains cattle weight gain nitrogen isotopes growth development blood mass spectrometry poaceae silage algorithms energy intake models biological reproducibility of results ireland crosses genetic

Plasma nitrogen isotopic fractionation and feed efficiency in growing beef heifers. (2014)

Abstract Fractionation of N isotopes occurs in many metabolic reactions which causes tissue proteins to become enriched in ¹⁵N while urea (urine) is depleted in ¹⁵N relative to the diet. We investigated ¹⁵N enrichment of whole plasma and its relationship with feed conversion efficiency (FCE) in growing beef heifers (n 84) offered 2 kg/d of concentrates with grass silage ad libitum. Heifers were on average 299 (SD 48·3) d old and weighed 311 (SD 48·8) kg. Plasma was obtained on day 79 (n 84) of the experiment and from a subset of animals (n 20) on four occasions between days 16 and 79. Silage DM intake (DMI) averaged 4·1 (SD 0·74) kg/d and concentrate DMI was 1·72 kg/d. Mean mid-test live weight was 333 (SD 47·6) kg, daily gain was 0·53 (SD 0·183) kg, FCE (g live-weight gain/g DMI) was 0·09 (SD 0·028) and residual feed intake (RFI) was 0 (SD 0·428). N isotopic fractionation (Δ¹⁵N; plasma δ¹⁵N - diet δ¹⁵N) averaged 3·58 ‰ on day 79 (n 84) and 3·90 ‰ for the subset of heifers. There was no relationship between Δ¹⁵N and RFI. Plasma δ¹⁵N and Δ¹⁵N were related to both FCE (negative) and animal weight (positive) for the whole population, and repeatable for the subset of animals over four time points. These relationships of Δ¹⁵N with FCE and animal weight are consistent with the anticipated negative relationship with N-use efficiency. There is potential to use Δ¹⁵N to provide rapid, low-cost estimates of FCE in cattle.
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Full list of authors on original publication

R J Dewhurst, G R Edwards, M McGee, N M Wheadon

Experts in our system

Mark McGee
Total Publications: 81