15N as a marker for effed efficiency in beef cattle

Abstract

Line 38. Specify which percentage does “extreme animals” refer to [AU]: Sorry but this specification was already shown in the first version “the top 20% highest and lowest animals within-CG in terms of RFI and FCE (extreme animals)” Introduction Line 70. Suggest “ranking individual animals” [AU]: Done Line 77. I think there is a leap in the explanation regarding feed sorting. Consider expanding with one or two sentences to clarify the point [AU]: Done, thank you. Materials and Methods Lines 119-120. Did the authors try running the analyses both with and without Study #8, as 15N abundance was not measured in plasma urea but in muscle? [AU]: In a previous experiment from our team (Nasrollahi et al.2020) we obtained similar relationships between Δ15N and feed efficiency regardless the isotopic analysis was conducted on plasma or muscle. We did not try to remove study ID#8 because we consider that all animal proteins once the isotopic equilibrium is reached has similar isotopic signatures (excepting the case of hair where no turnover exist). We have added in L178-181 the following statement to justify it: According to previous results from our team (Nasrollahi et al., 2020) and to allow sufficient time to reach an isotopic equilibrium, Δ15Nanimal-diet