A method for non-destructively identifying a characteristic of a Gallus Gallus domesticus embryo in ovo, the method comprising: (a) obtaining a sample of material associated with an egg comprising the embryo, and (b) measuring a score value for the presence of, and concentration of at least a first biomarker in the sample indicative of the characteristic of the embryo, and (c) applying a threshold to the score value and concentration obtained in (b) to identify the characteristic for the embryo associated with the presence and concentration of the first biomarker, wherein the first biomarker comprises an amino compound having a molecular weight in the range of from 150 to 170 g/mole; wherein step (c) further comprises: (i) correlating each relevant biomarker signal with a reference biomarker by matching the spectrum of each correlating signal with the expected spectrum of the correlating reference biomarker using a similarity measure, to define at least one positively correlating signal; (ii) measuring the intensity of each positively correlating signal and scoring its absolute and/or relative signal intensity; and (iii) applying a threshold to the score value obtained from a similarity function to determine the correlated embryo characteristic; wherein the first biomarker is 3-[(2-aminoethyl)sulfanyl]butanoic acid, and a concentration of the first biomarker in an amount of 50 ng/ml or more in allantoic fluid of the embryo on day 7, 8 or 9 correlates to a female embryo, while a presence of the first biomarker present in less than 50 ng/ml correlates to a male embryo. (a) obtaining a sample of material associated with an egg comprising the embryo, and (b) measuring a score value for the presence of, and concentration of at least a first biomarker in the sample indicative of the characteristic of the embryo, and (c) applying a threshold to the score value and concentration obtained in (b) to identify the characteristic for the embryo associated with the presence and concentration of the first biomarker, wherein the first biomarker comprises an amino compound having a molecular weight in the range of from 150 to 170 g/mole; wherein step (c) further comprises: (i) correlating each relevant biomarker signal with a reference biomarker by matching the spectrum of each correlating signal with the expected spectrum of the correlating reference biomarker using a similarity measure, to define at least one positively correlating signal; (ii) measuring the intensity of each positively correlating signal and scoring its absolute and/or relative signal intensity; and (iii) applying a threshold to the score value obtained from a similarity function to determine the correlated embryo characteristic; wherein the first biomarker is 3-[(2-aminoethyl)sulfanyl]butanoic acid, and a concentration of the first biomarker in an amount of 50 ng/ml or more in allantoic fluid of the embryo on day 7, 8 or 9 correlates to a female embryo, while a presence of the first biomarker present in less than 50 ng/ml correlates to a male embryo. (i) correlating each relevant biomarker signal with a reference biomarker by matching the spectrum of each correlating signal with the expected spectrum of the correlating reference biomarker using a similarity measure, to define at least one positively correlating signal; (ii) measuring the intensity of each positively correlating signal and scoring its absolute and/or relative signal intensity; and (iii) applying a threshold to the score value obtained from a similarity function to determine the correlated embryo characteristic;