Dry-off facilitator cabergoline hastened the GLUT-1 decrease and lactoferrin increase in the mammary tissue during drying-off in dairy cows
Résumé
In ruminants, the early phase of drying-off is a period of mammary gland
involution where lactose secretion is inhibited and lactoferrin is stimulated.
GLUT-1 is a glucose transporter that has a key role in supplying
substrate for lactose synthesis. The analysis of the changes in lactose
and lactoferrin contents in mammary secretions and in GLUT-1 and
lactoferrin contents in the udder can provide valuable information about
the speed of the mammary involution. To assess the effect of prolactin
inhibition by cabergoline on udder involution, 14 Holstein dairy cows
were injected with a single i.m. administration of 5.6 mg cabergoline (n
= 7) or placebo (n = 7) within 4 h after the last milking the day of drying
off (D0). After D0, hay and water ad libitum was supplied to the cows
for 10 d. Mammary secretion samples, collected during lactation (D-6)
and at D1, D2, D3, D4, D8 and D14 after the drying-off, were used for
lactose and lactoferrin analysis. Mammary biopsy samples, collected at
D-6, D1 and D8, were used for GLUT-1 mRNA and lactoferrin analyses.
Lactose content of mammary secretions progressively decreased during
involution, whereas their lactoferrin content increased. The change in
lactose content was associated with paralleled change in GLUT-1 mRNA
level in the udder. These decreases were faster in cabergoline treated
cows compared with controls with lower lactose content in cabergoline
treated cows already by D1 than in controls (P < 0.05) and significant
decrease in GLUT-1 mRNA levels at D1 and D8 respectively for cabergoline
and control treatments compared with D-6 (P ≤ 0.05). The rise
of lactoferrin content in mammary secretions was significant starting at
D4 in the cabergoline treated cows (P ≤ 0.05) whereas it only happened
at D8 in controls (P < 0.05). Overall, cabergoline treatment decreased
GLUT-1 mRNA level (P < 0.05) and increased lactoferrin content (P =
0.10). Similarly, lactoferrin immunostaining intensity in the mammary
tissue was higher at D1 than at D-6 in cabergoline treated cows (P ≤
0.05), whereas it tended to be higher only at D8 in controls (P < 0.10).
Our results indicate that cabergoline treatment was efficient to hasten
the udder involution and therefore facilitates the dry-off.
Domaines
Sciences du Vivant [q-bio]
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