Objective: Energy requirements for maintenance (MEm; kJ/BW0.75) and growth (MEg; kJ/g) of growing fat-tailed Afshari lambs were estimated using Relative Growth Index (RGI) method. Method: Thirty healthy fat-tailed Afshari male lambs (40±1.5 kg, age: 170± 10 days) that were individually housed were used. Lambs were randomly assigned to three plane of nutrition in a completely randomized design The lambs were fed either ad libitum (ADL, n=10), or restricted to 80% (R80, n=10) and 60% (R60, n=10) intake of ADL. The RGI was calculated by dividing metabolic body weight (BW0.75) to average daily gain (ADG; g). Then, the MEm (kJ/BW0.75) and MEg (kJ/g) were extrapolated from the intercept and slop of a linear regression between RGI and metabolizable energy intake (MEI) per unit of gain. The observed daily gain values of Afshari lambs were compared to the predicted value of daily gains from CNCPS-S. Results: Estimated MEm was 440 kJ/BW0.75 [ME (kJ/g ADG) = 440 RGI (BW0.75) + 24.2 (kJ/g ADG), R2=0.85]. The calculated MEm for a male Afshari lamb with 45 kg body weight and qm=0.64 and 250 g gain was 13.7 MJ per day based on RGI equation (440×17.37 + 24.2×250 = 7645(MEm) + 6050 (MEg)). The predicted ADG of fat-tailed Afshari lambs by the CNCPS-S model was markedly affected by feed intake level. Conclusions: This study suggests that RGI method is suitable to predict energy requirement of fat-tailed sheep and that a single recommendation (e.g. NRC) for all sheep breeds under diverse management conditions cannot be feasible.
Bayat, M. , Kiani, A. and Azizi, A. (2025). Estimation of energy requirements for maintenance and growth of male Afshari lambs from 40 to 50-kilogram using Relative Growth Index method. Iranian Journal of animal Science, (), -. doi: 10.22059/ijas.2025.396786.654081
MLA
Bayat, M. , , Kiani, A. , and Azizi, A. . "Estimation of energy requirements for maintenance and growth of male Afshari lambs from 40 to 50-kilogram using Relative Growth Index method", Iranian Journal of animal Science, , , 2025, -. doi: 10.22059/ijas.2025.396786.654081
HARVARD
Bayat, M., Kiani, A., Azizi, A. (2025). 'Estimation of energy requirements for maintenance and growth of male Afshari lambs from 40 to 50-kilogram using Relative Growth Index method', Iranian Journal of animal Science, (), pp. -. doi: 10.22059/ijas.2025.396786.654081
CHICAGO
M. Bayat , A. Kiani and A. Azizi, "Estimation of energy requirements for maintenance and growth of male Afshari lambs from 40 to 50-kilogram using Relative Growth Index method," Iranian Journal of animal Science, (2025): -, doi: 10.22059/ijas.2025.396786.654081
VANCOUVER
Bayat, M., Kiani, A., Azizi, A. Estimation of energy requirements for maintenance and growth of male Afshari lambs from 40 to 50-kilogram using Relative Growth Index method. Iranian Journal of animal Science, 2025; (): -. doi: 10.22059/ijas.2025.396786.654081
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