SPONSORED BY CANOLA COUNCIL OF CANADA

By BRITTANY DYCK, CARSON CALLUM and ESSI EVANS*

*Brittany Dyck ([email protected]) and Carson Callum ([email protected]) are employed by the Canola Council of Canada in Winnipeg, Man. Essi Evans ([email protected]) is employed by Technical Advisory Services Inc. in Bowmanville, Ont.

Figure 1. Comparison of feed protein conversion to food protein by various agricultural enterprises (Flanders and Gillespie, 2015)

UNDER typical feeding conditions, approximately 25% of the total protein consumed by dairy cows is converted to milk. When comparing the efficiency of protein use for milk with other animal proteins, as in the Figure, the protein use in milk production is relatively efficient. However, the data show that a great part of the protein consumed by dairy cows is still lost as waste products.

With the nutrition formulation tools available, it is possible to greatly improve upon this number for more efficient protein conversion — and it is certainly economically and environmentally desirable to do so. Protein efficiency is often in the range of 25-35% (Sinclair et al., 2014), and one study found that protein efficiency could routinely be improved to reach 30-31% in New York dairy herds with correct ration balancing (Higgs et al., 2012).

There are a number of ways that the protein captured in milk can be increased:

1. Strive for high levels of milk and milk protein production. Higher-producing cows are more efficient than low-producing cows. The maintenance level of protein required is based on body size, and is theoretically independent of the level of production. Therefore, maintenance becomes a larger portion of the total protein used in low-producing cows, which are less efficient than high-yielding cows.

2. Feed according to level of production. Lower-producing cows, such as those in later lactation, have lower requirements for protein and amino acids. If grouping cows by production level or stage of lactation is possible, the nutrient formulation should be adjusted to reduce protein and amino acids for the groups producing less milk to improve overall efficiency.

3. Optimize microbial protein. Non-protein nitrogen from ruminally degraded proteins, as well as from urea that is transferred back into the rumen, is used to support microbial growth. Energy is more likely to limit microbial production than nitrogen, due to the cow's ability to regulate nitrogen entry into the rumen as needed (Reynolds and Kristensen, 2008).

4. Balance diets for essential amino acids. Research has been helping us determine the amino acid needs of dairy cattle. A 2007 study provided an "ideal" amino acid profile as a portion of the intestinally available protein derived from feed and microbial sources (Rulquin et al., 2007). Balancing for amino acids allows us to specifically target the exact protein requirements of dairy cows without feeding in excess.

The amino acid profile shown in Table 1 was developed to provide for optimum efficiency of milk protein production.

5. Be aware of rumen undegraded protein (RUP) levels. Previously, it was assumed that all soluble protein was degraded in the rumen. More recent research results now clearly show that the soluble fraction is degraded at variable rates, depending on the ingredient. As Table 2 shows, for some ingredients, like canola meal and linseed meal, an average of almost half of the soluble protein escapes degradation in the rumen. Therefore, some ingredients, previously regarded as "too soluble" to use in dairy rations, can actually support efficient milk production (Table 3), and may provide more RUP than ingredients with higher levels of protein, resulting in less waste.

6. Choose ingredients that best meet cows' needs. The amino acid profile of RUP is important to determine how "efficiently" each protein source will be used. An ingredient with a poor amino acid profile will not efficiently contribute to the total needs of a cow.

Table 4 shows the amino acid profiles of several proteins, relative to the ideal protein proposed by Rulquin et al. (2007). If that particular protein was the only source of intestinally available protein, then the lowest ratio between the content of amino acids and the ideal value would be the efficiency value. Rumen microbes have the most desirable profile, followed closely by canola meal. If RUP from canola meal was the only protein available, then only a 31% overage would be required to meet all essential amino acids. Canola as the only vegetable protein source would provide the highest level of efficiency. Soybean meal, if paired with a rumen-protected source of methionine, could likewise be used to a similar extent, but might be a more costly option. However, if only corn gluten meal were available, then a 330% overage would be needed, and formulation would be much more difficult.

7. Ensure that a wide selection of ingredients is available. The first limiting amino acid is not the same for all proteins, so a more efficient diet can be achieved by mixing protein ingredients. For example, according to the calculations in Table 4, canola meal's first limiting amino acid is leucine. However, corn distillers grains have an exceptionally good supply. A recent study revealed that, compared to distillers grains alone, milk production and milk protein yields were higher (Table 5) when cows were provided with a blend of canola meal and high-protein corn distillers grain (Swanepoel et al., 2014).

Milk protein production is a relatively efficient process. Nonetheless, there is considerable room for improvement. With a better understanding of calculating RUP and an improved ability to formulate diets on the basis of amino acids, ingredient selections can be made to reduce protein overages and reduce nitrogen lost to the environment, providing dairy producers with efficiencies that can support their profit margins.

References

Flanders, F., and J. Gillespie. 2015. Domestication and importance of livestock. In: "Modern Livestock & Poultry Production." Ninth edition. Cengage Learning.

Hedqvist, H., and P. Uden. 2006. Measurement of soluble protein degradation in the rumen. Anim. Feed Sci. Technol. 126:1-21.

Higgs, R.J., L.E. Chase and M.E. Van Amburgh. 2012. Case study: Application and evaluation of the Cornell Net Carbohydrate & Protein System as a tool to improve nitrogen utilization in commercial dairy herds. Prof. Anim. Sci. 28:370-378.

NRC.2001. Nutrient Requirements of Dairy Cattle. National Research Council, Washington. D.C.

Reynolds, C.K., and N.B. Kristensen. 2008. Nitrogen recycling through the gut and the nitrogen economy of ruminants: An asynchronous symbiosis. J. Anim. Sci. 86 (14 Suppl.):E293-E305.

Rulquin, H., G. Raggio, H. Lapierre and S. Lemosquet. 2007. Relationship between intestinal supply of essential amino acids and their mammary metabolism in the lactating dairy cow. In: "Energy & Protein Metabolism & Nutrition." EAAP publication No. 124. Ed. by I. Ortigues-Marty. p. 587-588.

Sinclair, K.D., P.C. Garnsworthy, G.E. Mann and L.A. Sinclair. 2014. Reducing dietary protein in dairy cow diets: Implications for nitrogen utilization, milk production, welfare and fertility. Animal 8:262-274.

Swanepoel, N., P.H. Robinson and L.J. Erasmus. 2014. Determination of the optimum ratio of canola meal and high protein dried distillers grains in diets of high producing dairy cows. Anim. Feed Sci Technol. 189: 41-53.