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 during the transition period. 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 demand for amino acids (AA) increases near calving and after to support fetal growth, mammary development, and the onset of lactation.
The protein recommendation for mature dry cows is typically between 12 to 15% CP or approximately 800 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 since the demand for AA for fetal growth and mammary development is less. With the use of close-up diets that are low in fermentable carbohydrates, in particular starch, like the controlled energy, high forage diet, the diet may need to be supplemented with RUP ingredients to provide the appropriate amount of MP with the proper AA profile. Field observations support providing a greater supply of MP during the close-up period to account for intake variation within a pen of cows in the range of 80 to 100 g MP/kg dry matter (DM; 36 to 45 g MP/lb DM) ensuring that a greater proportion of cows are receiving adequate MP (≥1,100 g per day). Interestingly, controlled research studies during the close-up period that have increased MP supply have shown an inconsistent lactation response. This might be due to a lack of AA balancing, especially for lysine and methionine, in some studies and the supply of MP in the fresh diet. A meta-analysis of studies that changed prepartum MP supply showed a limited benefit other than milk protein yield when MP supply was 1200 g vs. 900 g/d.
Fresh cows should be fed a diet formulated to provide sufficient amounts of fermentable carbohydrates and rumen degradable protein to promote microbial growth as a source of protein while promoting intake. 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. Some studies have shown a positive lactation response to either infusing more protein or feeding to increase the MP supply. At Miner Institute we observed greater yields of energy-corrected milk and protein when we increase MP supply in early lactation following a higher supply of MP prepartum. It’s possible that the early lactation response to increased MP may be influenced by how the cow is fed protein during the dry period.
A recent study by Cornell University researchers, published in the Journal of Dairy Science, evaluated MP supply during both the close-up and fresh periods. They fed multiparous Holstein cows 1 of 4 treatments starting at 28 days before calving until 21 days after calving. Close-up cows were fed diets to supply either a control (85 g MP/kg DM; 39 g MP/lb DM) or higher amount of estimated MP (113 g MP/kg DM; 51 g MP/lb DM) with a similar amount of methionine (1.24 g/Mcal metabolizable energy (ME)) and lysine (3.84 g/Mcal ME). Fresh cows were fed diets to supply either a control (104 g MP/kg DM; 47 g MP/lb DM) or higher amount of estimated MP (131 g MP/kg DM; 60 g MP/lb DM) with a similar amount of methionine (1.15 g/Mcal ME) and lysine (3.16 g/Mcal ME). A common diet was fed to all cows from 22 to 42 days after calving. Feeding diets that increased supply of MP in either the fresh period or close-up and fresh period and had adequate amounts of methionine and lysine relative to ME increased lactation performance without affecting intake or subclinical ketosis. Changing the close-up and fresh period MP supply affected plasma AA concentrations, but did not affect indicators of protein/muscle mobilization, suggesting that increasing the MP supply positively affects nutrient partitioning towards the mammary gland.
— Heather Dann