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

(Penning et al., 1988). Another study of lactating ewes grazing different pasture allowances (500
or 750 kg organic matter/ha) with three levels of cereal supplement (0, 0.48 or 0.96 kg organic
matter/d) found no effect of ewe supplementation on lamb growth. There was an effect of
herbage allowance on lamb growth; ewes grazing paddocks with high herbage allowance
supported faster growing lambs (Milne et al., 1981). Therefore, forage availability has an
important effect on animal intake and performance. This study was conducted to determine the
effect of supplementation on milk production and milk composition of grazing dairy ewes at
different stages of lactation. In addition, the study measured dry matter intake on pasture using
titanium dioxide as an external marker and estimated protein utilization by monitoring milk urea
nitrogen levels.
Materials and Methods
Ewes and pasture. The study was conducted at the University of Wisconsin-Madison,
Spooner Agricultural Research Station from May 25 to August 15, 2005. Twenty acres of
pasture were divided into 1.5 acre paddocks and they ranged in composition from a mixture of
approximately 60% kura clover (Trifolium ambiguum Bieb.) and 40% orchardgrass (Dactylis
glomerata L.) and perennial ryegrass (Lolium perenne L.) to 5% kura clover and 95%
orchardgrass, Kentucky bluegrass (Poa pratensis L.) and quackgrass (Agropyron repens L.).
Ewes were moved to a new paddock at two to four day intervals, depending on forage
availability. The interval between grazing events in each paddock was approximately three
weeks. After grazing, each paddock was clipped to a height of 7.5 cm to allow for consistent
regrowth.
Fifty-six three-yr-old ewes were arranged in a 2 x 2 factorial treatment design; in early or late
lactation and receiving 0 or 0.80 kg DM/d of supplement. All ewes were weaned from their
lambs at 36 to 48 h postpartum and machine milked twice per day in a double-twelve parlor from
weaning and fed 0.80 kg DM/d of supplement and 1.9 kg DM/d of alfalfa silage in drylot until
grazing began on May 25, when supplementation treatments were applied. The ingredient and
nutrient composition of the supplement is reported in Table 1. All ewes were on pasture together
for approximately 20 h/d and were milked twice daily at 0530 and 1700h. Ewes were provided
water in the pasture and a free choice mineral-salt mixture in the parlor holding area; no shade
was provided in the pasture.
In addition to the 56 three-yr-old ewes, there were 20 two-yr-old ewes and 19 four-yr-old
ewes in late lactation that were divided between the unsupplemented and supplemented
treatments. They were managed with the 56 three-yr-old ewes. The two- and four-yr-old ewes
were not included in the analysis of the milk production data because this would have resulted in
the confounding of the effects of ewe age and stage of lactation, but some of these ewes were
used in the collection of dry matter intake (DMI) and milk urea nitrogen (MUN) data.
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