Farm Ireland

Tuesday 21 November 2017

Some simple rules to boost fat and protein levels in your milk


Mary Kinston

Good grass growth throughout July has provided the constant challenge of maintaining grass quality. Many have taken the opportunity to remove surpluses and improve pasture quality by removing the noticeable seed heads that have become apparent and the clumps of grass that cows have rejected.

Alongside these grassland management challenges many farmers have expressed concern for their milk composition at this time of year. Milk-fat percentage has cropped up as a point for discussion at many groups. While reasonable to very good levels of 3.8-4.4pc have been common, some farmers have experienced milk-fat falls to levels of 3.5-3.7pc in July and are wondering why. Milk protein concentration has also been questioned by a few. Milk protein has held at reasonable levels and tests of greater than 3.3-3.7pc have been presented at a number of my discussion groups. However, there are some who have had poor milk protein levels and levels as low as 3.1-3.2pc are causing concern. As a facilitator, I get asked the question of why such occurrences happen. Obviously, maintaining high concentrations of fat and protein in milk when milk price schedules are component-based is important. In addition, reasonable contents and consistent levels indicate good herd nutrition.

So while there is a risk of getting over complicated and missing the big picture, there is also an opportunity to look at factors which influence milk-fat and protein concentrations and let farmers come to their own conclusions about what needs to change at a management level.

You should always focus on the areas you can simply control, rather than getting bogged down in the detail by chasing the last 20pc, and compromising the system overall.

Milk-solids concentrations vary with breed, genetics within the breed and the stage of lactation. After calving, both fat and protein fall to reach a low at around 2-3 months of lactation, and then increase to the end of lactation. So in July a spring-calving herd should expect milk constituents to start to rise.

Milk fat is substantially affected by the level of effective fibre in the diet. This is why fibre-based supplements, such as grass silage or hay, generally increase milk-fat concentration.

Chewing is an important element of the process of rumination as it stimulates the production of saliva, which acts as a buffer in rumen to prevent a drop in rumen pH, and influences the ratio of volatile fatty acids (VFA) produced.

Milk-fat depression is due to a change in VFA proportions and changes in rumen bio-hydrogenation process. Unfortunately, this is where understanding what's going on gets complicated and at a farm level its application is difficult. However, there is a way to measure the fibre content of a feed by determining its neutral detergent fibre (NDF) level. As a general rule, the fibre content of the diet should be a minimum of 35pc to 40pc of diet dry-matter.

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Considering that grass is the sole or main feed source for most dairy cows at this time of year and the fact that high fibre seed heads are evident in many pastures, low milk-fat readings are unexpected. However, the addition of silage ground with soft leafy covers could potentially have low NDF content. Therefore, sending off a herbage sample to determine NDF may give you some answers.

The introduction of hay or molasses (soluble carbohydrate) can also be used to stimulate milk fat. However, hay can potentially reduce the cow's total intake and molasses is an undesirable expense when grass is plentiful and milk quota limiting. Therefore, unless your cows have signs of acidosis or the milk fat percentage is more than 0.2pc below the same time last year, it is likely that milk fat content will recover with no change in management strategy as the grazing rotation extends over the coming month.

Make sure your magnesium supplementation is adequate, as research has shown that supplements of magnesium oxide given to hypomagnesaemic cows have produced increases in milk-fat yield of 3-11pc.

Energy intake is the most important factor influencing milk protein. If energy intake is depressed through poor-quality or insufficient pasture, forage or by heat stress milk protein content will be depressed.

Therefore, maintaining pasture quality in mid-lactation is an essential driver of milk protein content. Generally, unless the amino acid supply is deficient relative to dietary energy, additional protein in the diet has little effect on milk composition, even if it does boost total milk and protein yields.

I have always found it rather odd that when farmers buy a load of ration they ask for the protein percentage and rarely get quoted for its energy content! As a rough rule of thumb, minimum crude protein contents should be 18, 16, and 14pc of diet dry-matter for early, mid, and late-lactation respectively. A crude protein level of 12pc is adequate for dry cows.

Mary Kinston is a farm consultant based in Kerry. Email:

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