Dairy Sheep Symposium - the Department of Animal Sciences ...

Percent
100
80
60
40
20
0
87
Effect of Light Treatment
Production Group 1999
30
62
Marked Lambed
20
Light Treatment
Natural
The discrepancy between ewes marked and ewes lambing is something we have noticed
every year, but the discrepancy does vary a bit from year to year. It could partially be influenced
by weather conditions, and partially because not all ewes conceive from the first breeding (this
holds true even in the normal breeding season). In the natural breeding season, ewes that don’t
conceive on the first breeding will usually cycle again but this is probably not the case with the
“out of season” breedings. It could be that some light control ewes don’t conceive the first time,
and then don’t cycle again. This is known to happen in ewes treated with hormones for out of
season breeding, and it may well apply to light control protocols as well.
This is also an area that merits further research, because if the number of successful Fall
lambing could be moved closer to the number of marks, it would greatly increase the efficacy of
the light control protocol.
In the Fall of 1998, before starting the formal light control protocol, we made a decision to
put our lactating ewes on a 20-hour light schedule. We did this primarily to see if we could
extend the lactations of the ewes that lambed in mid to late summer and in the Fall. We have
noticed over the years that Fall lactations have tended to be shorter and less productive than
Spring lactations, and that mid to late summer lambing ewes tended to sharply drop in milk
production as the days grew shorter.
While, subjectively, we believe that leaving the lights on in the milking barn has resulted in
more productive Fall lactations, it is hard to separate the effect of our ongoing selection program
from the effects of the light control. Fall lactations are no longer greatly less productive than
Spring lactations. However, we have experienced increasingly productive average lactations
every year since we began, so the more productive fall lactations may not be only a result of the
lights.
Leaving lights on in the milking barn did yield some surprising results. We quickly noticed a
significant percentage of ewes that ended their lactations in the Spring, after lactating for two to
five months under 20-hour days in the milking barn, quickly bred back after they were dried off.
This we can surely attribute to the lights, because the results of the two years since we started the
milking barn light treatment, 1999 and 2000 were so dramatically different than the two years,
1997 and 1998 before we started light treatment.