Nutritional Guidance for the Milking Herd
21 May 2024Thanks for subscribing! Please check your email for further instructions.
Nutrition in dairy cattle is a complex area, and many farmers rely on their nutritionist to ensure that the ration for the milking herd is correctly formulated to optimise herd health and performance. However, this factsheet provides some practical guidance on nutritional requirements, useful rules of thumb for different feeding systems and ways to assess feeding efficiency.
Dry matter intake (DMI)
The key to feed efficiency and optimising productivity is to maximise DMI. This will also help to drive more milk from forage. Cows should have access to feed 24 hours a day, with refusals around 2 to 5% to help maximise feed intake.
Dry matter intake varies according to body weight, level of milk production, stage of lactation and feed characteristics, but can also be influenced by a number of management and housing factors. Predicted intake is generally based on cow weight and so knowing the average mature cow weight in the herd is important for accurate ration formulation. Guidance is that cows will eat in the region of 3 to 3.5% of their body weight in dry matter (and up to 4% in early to mid-lactation), as shown in table 1. In the first two weeks of lactation, DMI may be as low as 2% of body weight.
Table 1. Average DMI depending on body weight.
| Body weight (kg) | Expected total dry matter intake (kg) |
|---|---|
| 450kg | 13.5 – 15.75 |
| 500kg | 15 – 17.5 |
| 550kg | 16.5 – 19.25 |
| 600kg | 18 – 21 |
| 650kg | 19.5 – 22.75 |
| 700kg | 21 – 24.5 |
| 750kg | 22.5 – 26.25 |
If DMI is lower than expected it could be due to:
- Poor trough management i.e. old feed not cleaned out, empty trough (or feed is present but cows cannot reach it i.e. not pushed up often enough), inconsistent feeding times.
- Inadequate feed space.
- Feeding very high or low dry matter forages (target the base ration to be around 40% dry matter).
- Low salt intake (if cows are deficient in salt, they may be seen licking urine off the floor).
- Restricted water intake or water quality issue.
- Heat stress.
- Metabolic disorders e.g. acidosis.
- Cows are smaller than predicted.
Energy requirements
Energy requirements are based on the energy needed for maintenance, milk production and pregnancy. The requirements for milk production will vary depending on the fat and protein content of the milk. It is important that supply is sufficient to meet the needs for the majority of cows in the herd, while also aiming to minimise body condition loss in early lactation.
Requirements for maintenance are calculated as follows:
Maintenance = (Bodyweight in kgs x 10%) + 10MJ
so a 650kg cow needs 65 + 10 = 75MJ for maintenance.
As a rule of thumb, it takes 5.3MJ of energy to produce 1 litre of milk at 4% fat and 3.3% protein. However a Jersey cow with higher milk solids (e.g. 5.5% fat and 4% protein) will require 6.5MJ of energy for each litre of milk produced.
so a 650kg cow producing 35 litres at 4% fat and 3.3% protein requires 75MJ + (35 x 5.3) = 260.5MJ.
Energy requirements throughout pregnancy are minimal (+1MJ/day) for the first five months of pregnancy. Long walking distances to and from the parlour will increase energy requirements for a given yield and when feeding a separate heifer group, an additional 10MJ/day should be factored in to allow 0.3kg growth/day.
Protein requirements
It is important to avoid overfeeding protein to minimise feed costs and nitrogen excretion to the environment. Cows do not have a requirement for a percentage of crude protein in the diet, but a requirement for grams of metabolisable protein (MP) for a given level of milk output. However, a rough guide is for the milking ration to sit around 16 to 17% crude protein on a dry matter (DM) basis. Below 16% runs the risk of methionine (amino acid) deficiency and milk production being compromised.
The diet should contain a good balance of both rumen degradable protein (from which the rumen bugs manufacture microbial protein) and digestible undegradable protein (rumen bypass protein). Good sources of bypass protein include soyabean meal, protected rapemeal products, prairie meal and to a lesser extent maize distillers dark grains and most distillery by-products. The higher the milk yield, the higher the requirement for MP from bypass protein (see Figure 1) as the amount of microbial protein that can be produced from rumen microbes is limited.
Figure 1. MP requirements with increasing milk yield.
Source: Dr Cara Campbell, SAC Consulting.
Diets higher in crude protein (close to 18% and above) may result in higher milk urea levels, which increases nitrogen excretion (environmental concern) and can impact fertility, as well as being more expensive to feed. With careful formulation, it can be possible to lower the protein content of the ration and reduce feed costs without affecting milk output.
When overfeeding protein, there is an energy cost to breakdown and excrete excess protein as urea. By reducing excess protein in the diet and increasing the supply of high energy feed sources, the result is more milk with less protein.
A general rule of thumb when feeding concentrate (parlour cake) to yield is that with a base ration of around 16% to 16.5% crude protein on a DM basis, an 18% (as fed) crude protein cake is more than sufficient. If feeding a 20% crude protein cake, the base ration can be around 15 to 15.5% crude protein on a DM basis.
It is best to take nutritional advice if you are thinking about reducing the amount of protein sources in the diet to ensure that MP requirements are still met.
Feeding to yield (PMR or partial mixed ration) principles
When feeding to yield in the parlour, out of parlour feeders or robots, a rule of thumb is that cows should be fed cake at a rate of 0.45kg/litre over the base ration.
For example, if a cow is producing 45 litres of milk and is fed cake twice a day in the parlour at a rate of 7kg/day, this provides energy for around 15 litres:
7kg ÷ 0.45 = 15.5 litres
Another way to look at the energy requirement is:
7kg cake x 88% = 6.2kg of DM. If the cake has an energy content of 13MJ/kg DM, then 6.2kg x 13MJ = 80.6MJ of energy. Assuming it takes 5.3MJ to produce 1 litre of milk, then 80.6/5.3 = 15.2 litres. Therefore the base ration needs to support M+30 litres in order to meet a 45 litre cow’s energy requirements. This can hard to achieve without exceptional forage quality.
However, we can assume that in early lactation cows will lose mobilise body reserves to support milk production and ideally the goal is that cows lose no more than 0.5 body condition score unit in the first 60 days. This equates to around 0.5kg weight loss/day, which should provide additional energy for around an extra 2 litres of milk, so a base ration of M+28 litres will suffice.
TMR (total mixed ration) principles
A complete TMR assumes no additional cake is fed out with the ration either in the parlour or through out of parlour feeders. It is a balance between meeting the requirements of the highest yielding cows but avoiding cows gaining too much condition in late lactation. The system works as higher yielding cows eat more to support their higher yield and later lactation cows tend to eat less, which limits their energy intake. A rule of thumb for providing sufficient energy is to pitch the diet at 20% above the herd (or group) average production level, as shown in table 2 below.
Table 2. TMR feeding guidelines.
| Group average yield (litres) | TMR ration target (M+litres) |
|---|---|
| 22 | 26 |
| 25 | 30 |
| 28 | 34 |
| 31 | 37 |
| 34 | 41 |
If the herd is split into groups such as a high and low yielders group, then each diet can be pitched at 10 to 15% above the group average. For a separate heifer group, aim for 30% over the group average to allow additional energy for growth.
Nutrition for robotic herds
The aim when feeding robotically milked herds is to pitch the ration at a level which encourages visits to the robot. This can be achieved by formulating the base ration for 7 litres under the herd average milk yield e.g. a herd averaging 35 litres of milk should have a base ration formulated for M+28 litres. This means that the majority of cows will not have their nutritional requirements met by the base ration, and so are driven to visit the robot to receive additional feed. Pitching the ration at 7 litres under the herd average will also help limit the number of cows overfed from the base ration i.e. have their requirements met, so are less likely to visit the robot, increasing the number of “collect cows” that haven not been milked within a desired period of time.
When it comes to cake allocation, the rule of 0.45kg/litre still applies. It is common for the quantity of cake to be built up to the maximum level in the first two to three weeks of lactation, and then fed at this level for 60 to 70 days before transitioning onto a feed to yield curve. The same is typical in parlour fed herds.
Mineral and vitamin nutrition
This is a complex area of nutrition and generally the background levels of minerals in forages and other feeds will be insufficient to meet animal requirements. For further information on major minerals, trace elements and vitamins and their role in cattle please see: https://www.fas.scot/article/cattle-mineral-supplementation/
If you suspect a mineral deficiency, this can be determined through blood sampling, but a good starting point is to analyse all forages for minerals and have your nutritionist assess the diet, taking into account all sources of minerals (including background levels in feeds).
It is important to ensure that multiple sources of minerals do not put your herd at risk of toxicity. A common example is copper toxicity, which can occur in dairy herds fed minerals from multiple sources. The recommended level of copper in the total diet for milking cows is 11mg/kg DM and the legal limit is 40mg/kg DM. Note that legal limits exist for all trace elements and vitamins. It is important to know that blood testing is not accurate to determine copper status; it is better to take liver biopsies on cull cows for an accurate assessment of copper status.
The importance of water
Milking cows have a high requirement for water and the rule of thumb is that a cow needs between four to five litres of water for every litre of milk she produces. It is estimated that around 50% of the total daily water requirement is consumed immediately after milking. Water intake will vary with DMI, the dry matter of the ration, water temperature and ambient temperature (heat stress greatly increases requirements). Therefore, availability and water quality must be adequate.
Recommendations are as follows:
- Provide a minimum of 10cm/cow of water trough space.
- Have more than one water access point for each group of cows.
- Typical drinking rate is around 14 litres/minute and so flow rate must be able to accommodate this for the number of cows in the group and number of troughs available.
- Regularly empty and clean water troughs to maintain water quality and encourage intake.
- If in doubt, have your water tested for cleanliness (i.e. pH, nitrates, sulphates, total dissolved solids and minerals) and hygiene quality.
Cow portions
You should be taking note of how well cows are clearing up their ration and adjusting the number of portions fed up or down depending on the level of refusal. The ration should be reformulated if the number of portions fed per number of cows in the group is out by more than 5% either way. It is worth getting forages reanalysed to see if the DM content has changed, as this can be the main reason for feeding significantly more or less portions than the number of cows.
If intakes are lower than expected (feeding less portions than the number of cows), this could be due to:
- Forage DM is higher than the analysis suggests (i.e. drier and cows cannot eat as much on a fresh weight basis).
- Cow body weight is smaller than predicted.
As a result, cows will be eating less concentrate than recommended, so are underfed, potentially affecting milk production, body condition and fertility over time.
If intakes are higher than expected (feeding more portions than the number of cows), this could be due to:
- Forage DM is lower than the analysis suggests (i.e. wetter and cows can eat more kgs on a fresh weight basis).
- Cow body weight is higher than predicted and so they can physically eat more.
As a result, cows will be overfed concentrate and while they should be milking well, they are being overfed for their level of milk production, leading to increased feed costs.
Monitoring feed efficiency
Feed efficiency (FE) can be defined simply as the kgs of milk produced from the kgs of dry matter eaten and calculated as follows:
FE = kgs of milk produced / kgs of dry matter intake
While FE will vary depending on the stage of lactation, milk yield, forage quality etc, regular monitoring enables you to look at trends and where performance has dropped or improved. It tends to be highest in early lactation and a low FE can indicate a low feed intake, poor forage quality and a diet short on energy.
Feed efficiency can be more difficult to evaluate where cows are fed concentrate to yield compared to a TMR system, as you need to know the total DMI of both the base ration and cake. The average cake usage per day (in DM) can be calculated from kgs of cake fed x 0.88, and this should be added to the DMI of the partial mixed ration to get the total DMI. Note that refusals should also be weighed to accurately calculate DMI for the herd or group.
For example, a herd producing on average 32 litres of milk = 32 x 1.03 = 32.96kg of milk. With a DMI of 22.9kg, FE = 32.96/22.9 = 1.44.
The following figure gives guidance on target FE figures depending on milk yield and dry matter intake. If in doubt, your nutritionist can help you with the calculation.
Figure 2. Feed efficiency targets.
Source: https://www.josephmorton.co.uk/how-to-measure-feed-conversion-efficiency-fce
There are various other measures that can be used to benchmark feed efficiency, such as concentrate use per litre and milk from forage. Margin over purchased feeds per litre and per cow are also common benchmarks, although these figures will vary over time with changes to milk price and feed costs. As a guide, concentrate use should be below 0.4kg/litre. According to the recent Kingshay Dairy Costings Focus Report for 2023, annual rolling results for the year ending March 2023 showed an average herd yield of 8,458 litres, with a concentrate use of 0.32kg/litre. Milk from forage was 2,776 litres or 33% of total yield from forage. The best farms manage around 50% of their total yield from forage. For more information please see: https://www.kingshay.com/wp-content/uploads/Kingshay-Dairy-Costings-Focus-Report-2023.pdf
Summary
Nutrition can be a complex subject and optimising nutrition in the milking herd relies on having a combination of accurate and up to date forage analysis, good feed management practices and a close working relationship with your nutritionist. While some rules of thumb have been provided in this factsheet for concentrate provision and feed management in different systems, accurate and regular ration formulation with rationing software is essential to ensure that the herd’s energy, protein and mineral requirements are met and to keep purchased feed costs to a minimum.
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