Researchers at the College of Agriculture and Animal Husbandry of Qinghai University, working at the Black Tibetan Sheep Breeding Centre in Guinan County, randomly assigned 60 two-month-old male lambs weighing 13 to 14 kilograms to two groups. One group was castrated after weaning, while the other remained intact. Both groups were housed in separate pens but managed and fed identically, and after a one-week acclimatisation period the formal feeding trial ran for 120 days. At the end of the trial, six animals from each group were humanely slaughtered under animal welfare protocols following a 12-hour fast, and muscle samples were collected bilaterally between the ninth and eleventh ribs, flash-frozen on dry ice, and stored at minus 80 degrees Celsius until analysis. The work was approved by the Animal Ethics Committee of Qinghai University under approval number QUA-2020-0709.

The team then subjected the meat to an unusually rigorous battery of tests combining classical meat-science measurements with modern metabolomics. Conventional quality indicators included pH at 24 hours post-mortem, cooking loss, drip loss, Warner-Bratzler shear force, cooked meat percentage, and texture profile parameters such as hardness, elasticity, chewiness, cohesiveness, and resilience. Nutritional composition, namely crude protein, moisture, and crude fat, was determined using accepted AOAC methods. To peer into the molecular machinery underlying these traits, the scientists deployed untargeted metabolomics on an Agilent 1290 Infinity ultrahigh-performance liquid chromatography system coupled to an AB Triple TOF 6600 mass spectrometer operated in both positive and negative ionisation modes, alongside targeted amino acid quantification using UPLC-ion mobility separation with multiple reaction monitoring on a 5500 QTRAP instrument, and fatty acid profiling by gas chromatography-mass spectrometry after methyl esterification.

The physical results were striking. Meat from the castrated group, designated BTC, showed significantly lower drip loss than meat from intact rams, designated BTN, indicating better water retention during storage, a trait consumers associate with juicier, more tender products. At the same time, cooking loss, elasticity, chewiness, and cohesiveness were all significantly higher in the castrated group, changes the authors attribute to shifts in muscle fibre type and structure that they plan to characterise in future work. The pH values of both groups fell within the normal fresh-meat range of roughly 5.67 to 6.28 at 24 hours, although the castrated animals trended lower, and there were no significant differences in cooked meat percentage, hardness, or resilience. Crucially, castration did not alter the crude composition of the meat: moisture, protein, and fat contents were statistically indistinguishable between the groups, meaning the animal’s fundamental nutritional payload remained intact.

The metabolomics told a richer story. Principal component analysis clearly separated castrated from non-castrated samples, and supervised PLS-DA and OPLS-DA models, with high explained variance and predictive statistics, confirmed significant metabolic segregation between the groups. In the negative ion mode alone the team identified 586 metabolites, dominated by lipids and lipid-like molecules at about 31 percent of the total, followed by organic acids and their derivatives at nearly 24 percent. Applying strict criteria of variable importance in projection greater than 1 and a P value below 0.05, the researchers pinpointed 34 differentially abundant metabolites, 15 of them upregulated and 13 downregulated in castrated sheep. Notable upregulated compounds included uric acid, vitamin C, malate, glutamine, oleic acid, and ammelide, while compounds such as L-malic acid, maltotriose, D-lactose, inosine 5′-monophosphate, and several phospholipid species were reduced.

Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes illuminated the biological circuits most affected by castration. Purine metabolism, general metabolic pathways, bile secretion, the phosphotransferase system, glyoxylate and dicarboxylate metabolism, pyrimidine metabolism, and ABC transporters emerged as the key pathways distinguishing the two groups. The authors propose that DL-2-phosphoglycerate, upregulated in castrated muscle, feeds into glycolysis where it is converted by enolase to phosphoenolpyruvate and then by pyruvate kinase to pyruvate, ultimately contributing to lactate formation and the slight decline in muscle pH observed 24 hours after slaughter. ABC transporters, one of the most extensively studied protein families in biology, may in turn shuttle metabolites across membranes, modulating the amino acid content of muscle tissue in concert with the phosphotransferase system and glyoxylate and dicarboxylate metabolism.

Targeted metabolomics added nutritional depth. Of 31 amino acids and derivatives detected, 11 were significantly elevated in castrated sheep, and the totals for non-essential amino acids, umami amino acids, and overall amino acid content were all significantly higher than in intact rams. Umami compounds such as aspartate and glutamate are central to the savoury taste that makes lamb so prized, and the finding mirrors earlier reports that castrated boars carry more umami amino acids than females. Meanwhile, fatty acid profiling identified 40 fatty acids, 23 of which differed significantly between groups. Levels of saturated, monounsaturated, and polyunsaturated fatty acids were all significantly higher in castrated animals, the n-6 to n-3 ratio shifted significantly, and oleic acid, the dominant monounsaturated fatty acid, was upregulated, consistent with previous castration studies in goats, cattle, and pigs.

Correlation analysis wove these threads together. Drip loss was negatively correlated with uric acid, suggesting that the castration-driven rise in this purine metabolite, routed through purine metabolism, bile secretion, and general metabolic pathways, may help the muscle hold onto its water. Total and non-essential amino acid scores correlated positively with vitamin C, malate, glutamine, oleic acid, and ammelide, all of which were elevated in castrated sheep, while elasticity showed a strong positive relationship with oleic acid and ammelide. The researchers note that prior work links purine metabolism to enhanced umami flavour and that guanine content correlates positively with savoury intensity in pork, lending plausibility to the idea that castration subtly tunes flavour chemistry as well as texture in Tibetan mutton.

The study is not without limits. Given cost and animal ethics considerations, only six castrated and six intact sheep were analysed, and the authors acknowledge that additional quality-relevant metabolites may await discovery in larger cohorts. Still, the practical implications are considerable. Castration improved several eating-quality traits and boosted amino acid and fatty acid levels while reducing drip loss, but it also raised cooking loss and saturated fatty acid content. The team suggests that future feed formulation for castrated flocks, for example incorporating flaxseed to push the fatty acid profile toward beneficial n-3 species, could amplify the benefits while offsetting the drawbacks. For the herders of the Qinghai-Tibet Plateau, and for a growing global market that prizes distinctive, high-quality lamb, an ancient pastoral custom now rests on a firm molecular foundation.

Subject of Research: Effects of castration on meat quality and muscle metabolites in Black Tibetan sheep on the Qinghai-Tibet Plateau

Article Title: The effects of castration on the quality of black Tibetan sheep meat and muscle metabolites

Article References: Xu, X., Han, L., Yue, Q., Hou, S., Luo, Z., Gui, L., Yang, B., Wang, Z., Yuan, Z., & Sun, S. (2026). The effects of castration on the quality of black Tibetan sheep meat and muscle metabolites. Food Science of Animal Resources, 46(1), Article 91. https://doi.org/10.1007/s44463-026-00067-8

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00067-8

Keywords: castration, Black Tibetan sheep, meat quality, metabolomics, amino acids, fatty acids, drip loss, oleic acid, purine metabolism, ABC transporters, Qinghai-Tibet Plateau, lamb meat