Effect of day length and exogenous melatonin on chemical composition of sheep milk

摘要

Changes in day length are a major factor in the productivity of farm animals showingreproductive seasonality. Parameters of milk production in sheep and goats are dependenton melatonin and prolactin concentrations. Changes in the prolactin secretion in lactatingsheep have an effect on the amount of milk produced, synthesis of milk proteins, fat andimmunoglobulins (i.e. milk composition). In the end the quality and commercial valueof milk is determined as well. The aim of this study was therefore to find out the effect ofday length and exogenous melatonin on the chemical composition of milk and the level offatty acids. Subjects were 60 Polish Longwool Sheep. Animals were randomly assigned tothree groups, Group I (n=20) – ewes raised under natural day length; Group II (n=20) ewesraised under natural day length and were implanted with melatonin; Group III (n=20) – ewesexposed to an artificially short photoperiod (16D:8L). Sheep were milked twice daily usingthe Alfa Laval Agri milking machine. Composite milk samples were collected every 28 days todetermine chemical composition and fatty acid content. The results obtained showed thatthe administration of exogenous melatonin and the simulation of a short-day photoperiodduring the summer period had significant effects on the milk levels of solids, protein, fat andlactose, and on the fatty acid content of sheep milk.