It is well know that the physiological processes of all organisms are affected by the circadian rhythm, namely the alternation of day and night. Even the metabolism can change with this variable. A Chinese study has exanimated the difference on the composition of daily milk and night milk in the dairies.
All the vital parameters, of the organisms, highlight changes connected to this alternation.
In addition, the melatonin values (MLT) in the milk and in the blood of cows show an alternation, that favors a night rhythm. Actually many people claim that night milk has a better quality in comparison to the daily one.
Anyway, the differences on the fat included in the milk, protein, lactose, lipid compound and carbohydrate between daily and night milk have been rarely pointed out.
Higher concentrations of N-acetyl-d-glucosamine, cis-aconitated and d-sorbitol has been observed in daily milk. Instead, the other 33 metabolites identified, like carbohydrate, lipid, amino acid and aromatic compound are present in smaller concentrations in daily milk in comparison to the night one.
So the results of this research show, that the composition of night milk is considerably different from the one of daily milk and that considerable changes in the circadian rhythm modify the milk composition too.
Reference: https://www.ruminantia.it/giorno-e-notte-cosa-cambia-nella-composizione-del-latte-bovino/