After freshening, cows must rapidly ramp up their feed intake to meet the demands of increasing milk production. But during those first few weeks, when intake does not meet that demand, cows mobilize body fat reserves and body protein to fuel milk production. New research indicates that feeding more metabolizable protein (MP) and balancing the amino acid (AA) profile of the fresh cow diet can increase dry matter intake, milk yield and help minimize weight loss during the first few weeks of lactation.
Researchers at The Ohio State University evaluated 4 dietary strategies to identify the best way to increase MP and balance AA in the fresh cow diet. Both concurrent and carryover responses were examined through the first 90 days in milk. A total of 40 primiparous and 40 multiparous cows were enrolled in the experiment. All cows received the same close up diet (11.5% CP, 55.8% NDF, 1.37 Mcal/kg NEL) starting 2 weeks before expected calving date. After calving, cows were randomly assigned to 1 of 4 diets fed until 25 days in milk. Then from 26 to 90 DIM cows were fed the same lactation diet with 17% CP. During the 3 week treatment period, the 4 diets fed were as follows:
- Deficient MP diet: MP is 20% less than needed by the cow (17% CP, 24% fNDF).
- Adequate MP diet: MP meets cows’ needs using primarily soybean meal for RUP (20% CP, 24% fNDF).
- Blend diet: MP meets cows’ needs but uses a blend of soy, canola, corn gluten meal and rumen protected AA (20% CP, 24% fNDF).
- Blend with less forage: The blend diet but substituting forage NDF with added RUP rather than non-forage NDF (20% CP, 19% fNDF).
The blend diet was formulated to have a RUP supply and AA profile similar to the essential amino acid profile of casein.
Previous research by Schei et al., (2005) has shown that cows have a greater capacity to mobilize body fat for energy than to mobilize body protein, explains Bill Weiss, professor of dairy cattle nutrition at The Ohio State University. During early lactation, protein, not energy, is generally the first limiting factor. A lot of recent work has focused on answering the questions of how much MP do fresh cows need, how to meet that need and keep amino acids in balance, and how to increase dry matter intake for optimal results. This experiment was designed to help answer those questions and identify the dietary strategy that works best for fresh cows.
For some of the responses measured, results for multiparous and primiparous cows were the same. For example, during the first 25 days in milk, feed intake increased by 2.4 lbs/cow/day for all cows fed the blended diets compared to cows fed the diet with adequate MP supplied from a single source. In addition, all cows fed diets with the higher level of MP increased milk production, milk yield, energy corrected milk (ECM) and milk components by 6 to 7% regardless of parity.
When the level of forage NDF in the diet was reduced, but MP remained high, multiparous and primiparous cows responded differently. Multiparous cows decreased their dry matter intake, but primiparous cows increased their DMI. In addition, multiparous cows produced less milk, but primiparous cows produced more milk when fed the blended diet with less forage NDF compared to cows fed the blended diet with more forage NDF, 19 vs. 24% forage NDF, respectively. This indicates that multiparous cows may have a higher forage NDF requirement than primiparous cows in early lactation.
During the carryover period, 26 to 50 days in milk, there were again differences between multiparous and primiparous cows. Multiparous cows had the highest DMI and produced the most milk when previously fed the blend diet. But primiparous cows had the greatest DMI and highest milk production when previously fed the blend diet with lower forage NDF. When researchers looked at cumulative milk yields through 92 DIM the difference in multiparous and primiparous cows’ response to forage NDF in the diet continued. The carryover period provides further evidence that multiparous cows have a higher forage NDF requirement than primiparous cows when fed high MP diets in early lactation.
In a second paper, also in the May 2021 Journal of Dairy Science, the researchers examined if the dietary strategies studied would affect the mobilization of protein or fat stores from the body, body composition or nutrient partitioning during early lactation. Using calculations for empty body composition researchers detected several interactions of treatment with parity.
Overall, feeding fresh cows a diet high in MP with a balanced AA profile increased DMI and reduced tissue mobilization. However, how the additional energy from increased DMI was partitioned differed by parity. Primiparous cows used the greater DMI to minimize fat mobilization. Multiparous cows used the greater DMI to increase milk production.
When forage NDF was reduced, but MP remained high, tissue mobilization tended to increase. But again, there was a difference by parity. Primiparous cows mobilized more body fat, and multiparous cows mobilized more body protein. Overall, results indicate that parity, AA profile and forage NDF concentration fed to fresh cows can influence concurrent and longer-term partitioning of nutrients to tissues and to milk production.
In primiparous cows fed the blend diet (blend of soy, canola, corn gluten meal and rumen protected AA) or blend with lower forage NDF, intake of metabolizable protein was 1,800-1,850 grams/day. In multiparous cows fed the blend diet intake of metabolizable protein was 2,500 grams/day. Use this latest information to tweak your fresh cow diets to get cows the nutrients they need to thrive in their next lactation.