The role of nutrition and genetics in milk protein concentration this spring
Ruminant Nutrition Specialist, Aisling Claffey takes a closer look at the factors influencing milk protein concentration this spring, and identifies ways in which farmers can limit the drop.
Milk protein concentration will be at its lowest as the cow approaches peak milk production. This will result in a decline throughout late-February into March on most farms, depending on calving pattern.
Milk protein curves are strongly influenced by herd genetics for milk protein with approximately 70% of the variation both between individual cows and between herds being explained by genetics or the Predicted Transmitting Ability (PTA) for milk protein %.
Pasture digestibility accounts for a further 30% of the herd level variation. Concentrate feeding rate has a relatively minor effect on milk protein content and will not compensate for poor forage quality or low genetic merit for protein content.
Figure 1 outlines the typical milk protein concentration curves for three given annual milk protein concentrations ranging from 3.4 to 3.7%. Typically milk protein % drops to 0.3-0.4% below the annual average at this time point.
Figure 1: Expected weekly milk protein profiles for three levels of annual milk protein ranging from 3.4-3.7%
A more rapid drop in milk protein concentration and/or milk protein concentrations below 3.20% in herds with high genetic merit for protein % can indicate that fermentable energy is limiting in the diet. This will often occur where cows are rehoused due to poor weather conditions on poorer quality forage, as the energy density of the diet and digestibility of the forage is lower than that of grazed grass (1.0-1.1 UFL/kg DM for spring grass vs 0.8 UFL/kg DM for 70 DMD grass silage).
Figure 2 illustrates this effect at a national level in spring 2024. This dietary driven drop in milk protein also occurs in low protein genetic merit herds, however, for such herds the effect can often be to reduce milk protein to below 3.0%. This captures the importance of trying to maintain some level of grass in the diet during periods of challenging weather through the use of on-off grazing and improving grazing infrastructure on farm.
Figure 2: Annual milk protein % profiles across 2020-2024 period
It is important therefore to consider genetics and diet in tandem when assessing bulk tank solids content. Altering diet to improve milk solids content in the short term is very much limited in comparison to the potential gains from changing breeding targets. Consult your EBI report within ICBF to determine your current PTA for fat and protein % within your herd and read Dairy Specialist, James Dunne’s advice here on making more intensive genetic gain within your herd by paying greater detail to dam selection, in addition to bull selection.
The current base cow, or a PTA of 0.0 % for milk protein %, will deliver an annual milk protein % of 3.36. Every 0.05 % PTA above this will result in a 0.2% increase approximately, provided the herd gets appropriate management and nutrition.
This piece is part of a wider Spring Nutrition Q+A series which explains aspects of feeding the early lactation dairy cow at grass in more detail, please follow the below link: