Protein requirements during mid-late lactation
As a rule of thumb, protein requirements for a mid-lactation cow are 14-16% crude protein. However, there are several factors that affect this requirement.
Energy status of the cow
Cows losing condition require more dietary protein to maximise milk production than cows gaining condition.
Milk production level
The greater the milk production the greater the demand for dietary protein.
Energy content of the feed (MJ ME/kg DM)
Cows offered high ME feeds require greater levels of dietary protein and in particular, rumen degradable protein.
Amino acid profile of the diet
Some supplements may be deficient in specific amino acids, even if they meet crude protein requirements.
Heat stressed cows reduce DMI, and expend energy trying to cool, therefore energy is generally limiting milk production and not protein.
Cows that walk further distances expend energy on activity and are less likely to require additional protein.
High rainfall / irrigated regions
In regions that have a high rainfall or are irrigated, summer pasture should meet protein requirements. However, in summer-dry, non-irrigated regions, the crude protein content of ryegrass and kikuyu can fall below this level.
Supplements that are incorporated into the diet of grazing cows through this period (and into late lactation) are also sometimes low in protein.
The protein in summer pasture is approximately 70 – 90% degradable in the rumen. If protein is limiting production in a pasture-based system, supplements high in undegradable dietary protein (UDP) are required to generate a milksolids response. Feeding supplements that are high in rumen degradable protein (RDP) or non protein nitrogen (NPN) will not improve production.
When considering protein supplementation in summer, always consider the economics of feeding the supplements first.
Over summer, some farmers share concerns intakes might be limited due to the high fibre content of pasture & other feeds, particularly during drought conditions.
Although there are minimum requirements on fibre, well managed pastures over spring will provide good energy intakes during summer and has a greater effect on summer pasture quality than the climate.
If large amounts of supplement low in effective fibre (e.g. fodder beet, maize grain, PKE) are being fed during a dry summer, there is a risk that fibre requirements may not be met. If you have concerns that you fall into this category, we recommend using the DairyNZ FeedChecker to calculate the fibre content of your diet before seeking further advice.