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:

• Lower body condition scores

• Higher feed costs

• Reduced conception rates

• Weak calves

• Lighter calves

• Poor health

• Reduced milking ability

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