Plasma natural 15N abundance may predict both feed conversion efficiency and residual feed intake in beef cattle across different dietary conditions

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Guarnido Lopez, Pablo | Nasrollahi, Sayyed Mahmoud | Chantelauze, Céline | Renand, Gilles | Fossaert, Clément | Ortigues Marty, Isabelle | Cantalapiedra-Hijar, Gonzalo

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Cheap and rapid methods to predict between-animal variability of feed efficiency (FE) areneeded. We evaluated, by using a large dataset on beef cattle (n = 355) fed contrasting diets(grass vs corn based diets), the potential of plasma natural 15N abundance (δ15N) as abiomarker of between-animal variation in FE, measured either as feed conversion efficiency(FCE) or residual feed intake (RFI). Data were analyzed by mixed models, with diet and δ15Nas a fixed effect and experimental farm, batch and pen as random effects. A negative andsignificant correlation was found between FCE and δ15N within each contemporary group,with a lower response (slope) however in grass vs corn diets (δ15N × diet interaction; P =0.002). Likewise, we found a significant but positive relationship between δ15N and RFI, butwithout the influence of diet or any tested random effect. Our results indicate that δ15N is apromising biomarker of between-animal variation of feed efficiency (FCE and RFI) ingrowing beef cattle.

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