Shearing influences the milk fatty acid profile of dairy ewes

In Mediterranean areas shearing is commonly performed during late spring and, therefore, ewes
may be exposed to cold stress especially during the night. Short-term periods of cold exposure can increase
hepatic glucose production, decrease insulin secretion and increase fat catabolism and plasma
non-esterified free fatty acids (NEFA) concentration. These metabolic adaptations to cold exposure can
increase the mammary uptake of long-chain fatty acid from plasma. The present study aimed to investigate
the metabolic response of dairy ewes to shearing by monitoring their milk fatty acid (FA) profile.
Twelve 2-4-year-old Sarda ewes, in mid-late lactation, were used. The trial lasted from 30thMay to 9thJune 2006. The pre-experimental period (pre-shearing, PrS) was from 30thMay to 5thJune (shearing
day), being followed by the experimental period (post-shearing, PoS) until 9thJune. On shearing day,
the flock was divided in two groups (6 ewes each) which were then managed differently: non-confined
group (NCG) and confined group (CG) which was kept in a sheepfold during the night. Four samplings
during PrS and other four during PoS periods were performed. During the trial, ewes were fed concentrate
at 1000g/d per head, during the two daily milking, and hayad libitum, and grazed on green
clover (3h/day). Daily milk production was recorded and daily milk samples were collected for analysis
of fat content and FA profile. Shearing did not influence milk yield but increased significantly milk
fat content (6.37vs.6.94% for PrS and PoS, respectively;P<0.01). Ewes confinement during the night
did not affect milk yield and its fat content. Shearing modified significantly the FA profile of milk. The
concentration of C8, C10, C12 and C16 increased significantly from PrS to PoS. On the other hand,
the content of long-chain FA (>C18:0) did not change between PrS and PoS (46.26 vs. 46.40mg/100g
of FAME, respectively). These results suggest that the increase of milk fat after shearing was related
to the increase of the main FA synthesized by the mammary gland. However, the unexpected increase
in the synthesis of short- and medium-chain FA after shearing suggests that these animals were not
subjected to cold stress. Therefore, the mechanism involved in the modification of the FA profile caused
by shearing in dairy ewes should be elucidated.