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PROTEIN NUTRITION FOR YOUR TRANSITION COWS

It’s widely recognized that protein nutrition during the dry and fresh periods affects lactation performance and health. The quality of the crude protein (CP) sources and the availability of fermentable carbohydrates in the diet for microbial growth in the rumen will impact the dietary protein needs. The supply of metabolizable protein (MP) provided from rumen undegradable protein (RUP) and microbial protein can be estimated by diet formulation models, such as CNCPS.

The protein recommendation for mature dry cows is typically between 12 to 15% CP or approximately 1,000 to 1,300 g of MP per day. Far-off cows are usually fed less protein than close-up cows when a two-group dry cow management strategy is used. Field observations suggest that providing a greater supply of MP during the dry period is benefi cial. This may be due to an underestimate of MP required in formulation models, providing a limiting amino acid (AA), providing AA for immune function under higher stress housing conditions, or accounting for intake variation within a pen of cows. A concentration of 40 to 45 g of MP per pound of dry matter intake was recommended recently by Van Saun and Sniffen at the Western Canadian Dairy Seminar to ensure that a greater proportion of close-up cows that are group fed receive adequate MP (≥1,100 g per day). Dry cow diets that are low in fermentable carbohydrates, in particular starch, like the controlled energy, high forage diet, may need to be supplemented with RUP ingredients to provide the appropriate amount of MP with the proper AA profile.

Fresh cows should be fed diets formulated to provide sufficient amounts of fermentable carbohydrates and rumen degradable protein to promote microbial growth as a source of protein. In addition, the diet should provide high quality RUP sources and include rumen-protected AA as needed to optimize the AA profile. Even with the best formulated diet, fresh cows will still experience a negative MP balance for 1 to 2 months after calving. In response to the negative MP balance, fresh cows will mobilize muscle and other protein sources in the body to support lactation through contributions of AA and energy. The key to controlling the severity and duration of the negative MP balance is to promote a rapid increase in dry matter intake during the fresh period.

In general, AA balancing and inclusion of rumen protected AA when needed is justified for transition cows. Lysine (Lys) and methionine (Met) are typically the limiting AA in MP during lactation and are assumed to be limiting during the transition period also.  There are a few studies that have evaluated supplementing rumen protected Met, Lys, or both during the transition period suggesting that balancing AA starting before calving and continuing into lactation can increase milk yield, milk components, or both although the responses were not always consistent across studies. It appears that the responses are dependent on dietary CP, supply of MP, and intestinal digestibility of the RUP supplements. It is recommended to provide ~75 g of Lys per day and ~25 g of Met per day to maximize the milk protein response. However, given the multitude of uses for AA, it is not clear if the current recommendations for Lys and Met optimize immune function, although use of rumen protected Met has been shown to improve immune function.