Protein
Supplementation
Protein is necessary for
growth and to replace the daily break down of body tissues,
including muscle, blood, hair, and hooves. Protein is usually the
first limiting nutrient for cattle fed low-quality forages.
Protein is necessary for rumen microbes to digest fiber and other
feedstuff components.
Providing sufficient protein to cattle on pasture improves forage
digestion. Insufficient dietary protein can lead to:
Supplemental protein should be fed to
grazing cattle when forages fail to provide enough protein to meet
their nutrient needs. Forage protein levels also fluctuate greatly
during the grazing season as evidenced in Figure 4. When protein
from forage is inadequate in meeting the animal and rumen
microbial requirements, body condition score will decline.
Supplemental protein for range cattle
can be provided from natural protein sources, co-products, or from
non-protein nitrogen sources, such as biuret or urea. Natural
sources of protein provide an excellent source of protein, but can
be cost prohibitive at times. Because rumen microbes convert
non-protein nitrogen into protein, non-protein nitrogen sources
also work well when fed in the proper balance. Feeding high levels
of urea (greater than 25% of the supplemental crude protein) with
high-forage diets is not as cost-effective because much of the
urea is not utilized due to the rapid ammonia release rate of
urea. This rapid release of ammonia from urea can exceed the rumen
microbe’s ability to use the ammonia and results in more ammonia
being converted back into urea by the liver and excreted. Rapid
ammonia release can also cause ammonia toxicity, which can lead to
death. Biuret is a very safe source of non-protein nitrogen and
has an ammonia release curve very similar to soybean meal (Figure
5). Biuret can be utilized at very high levels with forage-based
diets and is more cost-effective than feeding natural source
proteins or high levels of urea.
Figure 5.
Ammonia Release Rates for Biuret, Urea, and Soybean Meal
Feeding supplemental protein can also
increase the amount of forage consumed by cattle. Table 2
estimates the daily dry matter intake for dry and lactating cows
with or without protein supplementation. Protein supplementation
(digestible intake protein or DIP) will increase the intake of
digestible dry matter of low- and medium-quality forages. Protein
supplementation of forages containing more than 9% crude protein
will have little effect on digestibility and intake in cattle.
Table 2 Estimated Intake of Forage
With and Without Supplementation
|
|
Forage
Intake (% BW, DM Basis) of Brood Cows |
|
|
Dry, Bred
Cow |
Lactating
Cow |
|
Low-Quality
Forage (<7% CP) |
|
|
|
No
supplement |
1.5 |
2.0 |
|
Protein
Supplement |
1.8 |
2.2 |
|
Average-Quality Forage (7-9% CP) |
|
|
|
No
supplement |
2.0 |
2.3 |
|
Protein
Supplement |
2.2 |
2.5 |
|
High-Quality Forage (>9% CP) |
|
|
|
No
supplement |
2.5 |
2.7 |
|
Protein
Supplement |
2.5 |
2.7 |
Source: C.A.
Hibbard and T.A. Thrift, Oklahoma
Feeding supplemental protein improves
the amount of forage cattle can consume, plus it can improve the
digestibility (Figure 6) of the forages consumed. This improvement
in forage utilization can lead to improved body condition scores,
which can in turn lead to improved profit potential of a cattle
operation.
Figure 6 Effect of Supplemental Digestible Intake Protein on
Digestion of Forage NDF
