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

esults, so an average pasture CP value of 23 % corresponds to 64.6 and 57.0 mg/dl MU,
respectively, or 30.1 and 26.6 mg/d MUN, respectively.
Figure 9: Relationship between milk urea nitrogen and test day pasture crude protein for
supplementation treatments.
Milk urea nitrogen (mg/dl)
35
33
31
29
27
25
23
21
19
17
15
Supplemented
R 2 = 0.27
Unsupplemented
R 2 = 0.61
17 19 21 23 25 27
Pasture crude protein (%)
69
Supplemented
Unsupplemented
These high MUN values in all treatments suggest that pasture protein content was
sufficient to meet the nutritional requirements of the ewes. Additional energy in the
supplemented treatment did not improve the utilization of pasture protein, due to the protein
content of the supplement. High MUN values have been associated with excess protein intake
and low reproductive efficiency in Italian dairy ewes and Cannas (2002) suggests that ammonia
detoxification may increase the energy requirements of ewes. In addition, providing
supplemental protein to grazing ewes is expensive and, if unnecessary, will reduce farm
profitability.
Summary and Conclusions
Total milk, fat, and protein production in grazing dairy ewes was higher for ewes in early
compared to late lactation. Supplementation had a similar positive effect on daily milk yield of
grazing ewes in both early and late lactation when compared to the unsupplemented treatment.
In the United States, sheep milk prices are currently based on milk quantity without regard to
milk composition. Based on an average increase in milk production of 19.7 kg valued at
$1.32/kg, and 0.82 kg of supplement provided for 82 days, as long as the supplement costs less
than $ 0.39/kg (or $ 0.18/lb.), supplementation is profitable. While test day milk fat and milk
protein percentages were significantly higher for unsupplemented ewes, the significant increase
in test day milk production of supplemented ewes resulted in greater total milk fat and milk
protein with supplementation. Pasture DMI was not significantly affected by stage of lactation
or supplementation, but early lactation and supplemented ewes did consume numerically higher
kg of pasture DM than late lactation and unsupplemented ewes, respectively, suggesting the
ability of ewes to regulate intake to meet production requirements. Milk urea nitrogen values
suggested that rotationally grazed, mixed grass-legume pastures provided excess protein to