When cows are MP deficient, they will break down muscle and other bodily protein sources. This is most severe in the first 10 days postpartum.
by Amanda Smith, Hoard's Dairyman Associate Editor
Over the years, tremendous attention and research dollars have been poured into studying cows' early lactation negative energy balance. But should we also be concerned with our fresh cows' protein balance? Generally, negative protein balance is not considered as big of an early lactation concern as negative energy balance. In the November Miner Institute Farm Report, Heather Dann delved a bit deeper into the protein drain our cows likely experience postcalving.
Cows struggle to consume sufficient amounts of protein to meet their amino acid needs in early lactation. Due to this, formulating diets to satisfy metabolizable protein (MP) requirements in early lactation is difficult.
When cows are MP deficient, they will break down muscle and other bodily protein sources. A high-producing cow can mobilize up to 2.2 pounds of tissue protein per day in the first week to 10 days after calving. This is the time period when protein balance is the most negative.
Over the first 5 to 6 weeks postpartum a high-producing cow can mobilize up to 46 pounds of protein reserves that are susceptible to change (labile). Many cows will return to a positive protein balance 3 to 6 weeks after calving.
Although protein mobilization contributes to insufficient protein and energy supplies, excessive use raises the risk of metabolic disorders and poor performance in lactation.
Many nutritionists formulate close-up diets to supply 1,100 to 1,300 grams of MP per day. This amount typically prevents protein mobilization before calving when intakes are lowest. This is critical as mobilization of protein reserves before calving reduces the amount available postpartum.
In lactation, the use of lower crude protein (CP) diets is becoming more popular as producers strive to reduce the environmental and economic consequences of feeding excess nitrogen. However, given the negative MP balance in early lactation, it is unclear if lower protein diets can be used successfully in early lactation, noted Dann.
Recently conducted work at Miner with diets varying in MP indicates that protein reserve mobilization was not affected by the dietary MP supply. Their results suggest that mobilization is regulated primarily by hormonal changes and is less responsive to moderate changes in MP supply in early lactation.
Early lactation diets can be formulated to contain less CP than traditionally fed by 1.5 units and successfully support lactation when adequate amounts of fermentable carbohydrates and rumen degradable protein are included to promote microbial growth.
The author is an associate editor and an animal science graduate of Cornell University. Smith covers feeding, milk quality and heads up the World Dairy Expo Supplement. She grew up on a Medina, N.Y., dairy, and interned at a 1,700-cow western New York dairy, a large New York calf and heifer farm, and studied in New Zealand for one semester.
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