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

EFFECT OF PREPARTUM PHOTOPERIOD ON PROLACTIN
AND MILK PRODUCTION OF DAIRY EWES
Claire M. Mikolayunas 1 , David L. Thomas 1 , Yves M. Berger 2 , T. F. Gressley 3 , and
G. E. Dahl 3
Summary
1 Department of Animal Sciences, 2 Spooner Agricultural Research Station,
University of Wisconsin-Madison, Madison, Wisconsin, USA
3 Department of Animal Science, University of Illinois, Urbana, Illinois, USA
Increased photoperiod during lactation increases milk production in dairy cattle (Peters et al.,
1978) and dairy ewes (Bocquier et al., 1997), but decreased prepartum photoperiod has a positive
effect on subsequent milk production in dairy cattle (Auchtung et al., 2005). The objective of this
study was to determine the effect of prepartum photoperiod on milk production, milk
composition, and prolactin levels of 22 multiparous dairy ewes. Ewes exposed to short-day
photoperiods (8 h light; SDPP) for approximately six weeks prepartum produced an average of
0.12 kg/d more milk (P < 0.10) on each test day over the first eight weeks of lactation than ewes
exposed to long-day photoperiods (16 h light; LDPP). Average daily milk fat percentage was
higher (P < 0.0001) in SDPP ewes than LDPP ewes (6.02 vs. 5.44 %, respectively). Average
daily milk protein percentage was higher (P < 0.10) in SDPP ewes than LDPP ewes (4.55 vs.
4.44 %, respectively). Due to both more daily milk and higher milk fat and milk protein
percentages, SDPP ewes produced more 6.5 % fat corrected milk (FCM; + 0.21 kg/d; P < 0.05),
and 6.5 % fat and 5.8 % protein corrected milk (FPCM; + 0.20 kg/d; P < 0.05) than LDPP ewes.
Over approximately 121 days in milk, SDPP ewes produced more test day milk (P < 0.01) than
LDPP ewes (1.68 vs. 1.48 kg/d, respectively), but there were no differences in milk fat or protein
percentages. Both treatments experienced a prolactin surge at lambing, but SDPP ewes had
lower circulating prolactin (P < 0.05) than LDPP ewes from 7 d before to 0.5 d after lambing.
Previous studies in dairy cattle also found that prepartum prolactin levels were inversely related
to subsequent milk production. Decreased prepartum photoperiod may be important in increasing
milk production in dairy ewes.
Background
Annual milk production of dairy ewes at the Spooner Agricultural Research Station increased
from 1996 to 2004 (Berger, 2005). In an analysis of factors contributing to this progress, Berger
noted effects of dairy genetics, breed composition and weaning system, findings supported by
previous authors (Bencini and Pulina, 1997; McCusick et al., 2001). Some of the increase in
milk production was attributed to lengthening lactation due to lambing month. Lambing has
gradually moved closer to January, and dry off has remained in early fall, increasing the number
of days ewes are lactating. In addition, ewes are milking during the increasing daylengths of
spring and summer and are likely responding to the known positive effects of increasing
photoperiod during lactation on milk production (Bocquier et al., 1997). Lactating ewes exposed
to long day photoperiods (16 h light; LDPP) for the first 5 months of lactation produced 25%
more total milk than ewes exposed to short day photoperiods (8 h light; SDPP). At the end of the
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