great lakes dairy sheep symposium - the Department of Animal ...

Figure 6: Mean concentration of plasma prolactin in SDPP and LDPP ewes.
Plasma prolactin (ng/ml)
200
160
120
80
40
0
-6 -5 -4 -3 -2 -1 0 1
Summary and Conclusions
Week relative to lambing
80
LDPP
SDPP
Dairy ewes exposed to SDPP for approximately 6 weeks prepartum produced more milk than
ewes exposed to LDPP. Short days prepartum resulted in a decrease in prepartum circulating
prolactin levels, which may have contributed to increased sensitivity of the mammary gland to
circulating prolactin and an increase in milk production in the subsequent lactation. This may
have implications for dairy sheep flocks, most of which lamb once per year. Dairy ewes in late
pregnancy during times of the year with shorter day length (i.e. winter) might be expected to
produce more milk than ewes in late pregnancy during times of the year with longer day length
(i.e. spring). Prepartum photoperiod may be one of the factors contributing to the increase in
milk production of the Spooner Agricultural Research Station flock from 1996 to 2004 (Berger,
2005).
References
* Least squares means within a test day are different (P < 0.05).
** Least squares means within a test day are different (P < 0.001).
Akers, R. M. 2002. Lactation and the mammary gland. Iowa State Press, Ames, IA.
Akers, R. M., D. E. Bauman, A. V. Capuco, G. T. Goodman, and H. A. Tucker. 1981a. Prolactin
regulation of milk secretion and biochemical differentiation of mammary epithelial-cells in
periparturient cows. Endocrinology. 109:23-30.
Auchtung, T. L., P. E. Kendall, J. L. Salak-Johnson, T. B. McFadden, and G. E. Dahl. 2003.
Photoperiod and bromacriptine treatment effects on expression of prolactin receptor mRNA
in bovine liver, mammary gland and peripheral blood lymphocytes. J. Endocrinol. 179:347-
356.
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