title: Effects of feed intake and genetics on tissue nitrogen-15 enrichment and feed conversion efficiency in sheep.
abstract: This study investigated the effects of sheep genetics and feed intake on nitrogen isotopic fractionation (ΔN) and feed conversion efficiency (FCE; live weight gain/DMI), using a 2 × 2 factorial design, with 2 levels of genetic merit for growth (high vs. low) and 2 levels of feed intake (110 vs. 170% of ME for maintenance [MEm]). No effect of genetic merit was detected for live weight gain ( = 0.64), FCE ( = 0.46), plasma urea nitrogen ( = 0.52), plasma glucose ( = 0.78), and ΔN of wool ( = 0.45), blood ( = 0.09), and plasma ( = 0.51). Sheep receiving 170% of MEm had 175% higher live weight gain ( < 0.001) and 77% higher FCE ( < 0.001) than sheep receiving 110% of MEm. There was no difference among treatments at the beginning of the study for either blood or plasma ∆N, but the treatment groups started to diverge in blood and plasma ∆N at 21 and 7 d, respectively. Blood, plasma, and wool samples were enriched in N compared with feed. There was a higher blood, plasma, and wool ∆N for the low feed intake group than the high feed intake group ( < 0.001 in all cases). Across the 4 treatment groups, higher FCE in sheep was associated with lower ∆N for plasma, blood, and wool. Overall, the results are consistent with the potential of ∆N as a rapid, low-cost biomarker of FCE in sheep, despite there being no effects of genetic treatment on FCE and ∆N.
authors.forename: L
authors.initials: L
authors.lastname: Cheng
authors.forename: C M
authors.initials: CM
authors.lastname: Logan
authors.forename: R J
authors.initials: RJ
authors.lastname: Dewhurst
authors.forename: S
authors.initials: S
authors.lastname: Hodge
authors.forename: H
authors.initials: H
authors.lastname: Zhou
authors.forename: G R
authors.initials: GR
authors.lastname: Edwards
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D001786:Blood Glucose / Q000032:analysis; D001806:Blood Urea Nitrogen; D004435:Eating / Q000502:physiology*; D009584:Nitrogen / Q000097:blood; D009587:Nitrogen Isotopes / Q000097:blood / Q000378:metabolism*; D034561:Sheep, Domestic / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D015430:Weight Gain / Q000235:genetics / Q000502:physiology*; D014935:Wool / Q000737:chemistry
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D009587:Nitrogen Isotopes; D009584:Nitrogen