How to monitor the performance of a dairy diet

As well as being essential for feed-to-yield concentrate allocation systems, good regular monitoring of performance is important to ensure diets are delivering the required results.

Cow performance and dietary sufficiency can be monitored through:

• Milk output
• Feed intake
• Body condition score
• Gut fill and dung consistency
• Metabolic profiles
• Health and fertility

Since it is always one of the first things to be affected by the diet – positively or negatively – milk yield is the most essential element of performance to monitor.

Daily bulk milk sales have the benefit of being the simplest and most immediately available measure of yield.

They can be very useful as an immediate indicator of improvement or difficulty.

However, changes in herd milk production need to be interpreted with care because they can be disproportionately affected by the performance of a few animals or one particular group.

Bulk milk sales will, of course, also be affected by a number of non-feeding factors, including the weather, other management changes and large numbers of bulling cows.

Individual records of milk production – either through daily measurements or official milk recording – are more valuable tools for performance monitoring.

They are essential for the most accurate feeding to yield but may be considered unnecessarily costly or time-consuming for flat-rate concentrate feeding or TMR systems.

By identifying performance adequacies, inadequacies or changes in individual animals or particular groups of cows, individual milk records allow dietary effects to be separated from non-feeding factors far more accurately than bulk milk records.

Lactation curves plotted for individuals or groups of animals provide a very graphic illustration of performance.

These can be plotted manually using milk recording data or may be exported from data collected by your parlour software.

If milk yields are not as expected, it is advisable to check whether:

• Feed intakes are as expected
• The diet is effectively balanced
• Feed ingredient analyses remain accurate
• Cows are grouped correctly
• The calving pattern has changed
• More or fewer than planned cows have calved in the past three months
• The milk from a number of cows is being withheld from the bulk tank
• Extreme weather patterns may be having an effect (such as heat stress)

Butterfat and protein levels are valuable indicators of diet adequacy.

While butterfats can change within days of any change in diet, milk protein changes may reflect the dietary position several weeks earlier.

Among other things, low butterfats may result from:

• Poor forage intakes
• Poor forage quality
• Low dietary fibre levels
• Low fibre levels in spring grass
• Clinical or subclinical rumen acidosis
• High yields in early lactation
• High dietary oil levels

Among other things, low milk proteins may result from:

• Low dietary energy levels
• Inadequate dietary protein
• Poor nutrition during autumn grazing
• Poor body condition or excessive weight loss
• High yields in early lactation

Milk urea nitrogen (MUN) monitoring, available on a weekly basis from most milk companies can provide a useful indication of the efficiency of rumen protein utilisation.

It is important to appreciate that MUN levels can vary widely throughout the day and between cows at different stages of lactation.

Careful interpretation is also essential as levels reflect an inter-relationship between energy and protein metabolism so can mean different things under different conditions.

• Lower limit: 0.015% or 150 mg/litre. Insufficient rumen protein or very efficient use of protein
• Target: 0.025–0.035% or 250–350 mg/litre. Sufficient rumen protein in good balance with energy
• Upper limit: 0.035% or 350 mg/litre. Excess nitrogen from rumen degradable protein

Feed intake is so critical to providing the right degree of nutrition that intake monitoring can provide a good early warning of difficulties, as well as a way of pinpointing particular problems identified through milk monitoring.

Intakes can vary due to several cow, food and management factors. A continual visual check on feed consumption is always advisable.

Large amounts of food remaining uneaten or cows running out of food too long before the next feed are reliable indicators of problems.

If forage intakes are less than expected, this may be because:

• Dry matter levels are lower than analysed or assumed
• Cows are suffering from acidosis
• Feed access is insufficient
• Silage is deteriorating in the trough
• Feed trough hygiene is insufficient
• Access to clean water is inadequate
• Concentrate feeds are depressing forage appetite

Body condition scoring (BCS) provides a good measure of a cow’s energy balance to inform feeding and management.

Cows can be scored in any situation, preferably restrained in a race or crush, with the assessment made over the tail-head and the loins by sight and feel.

With practice, experience shows most managers can gauge body condition score very well by eye, supported by feel.

To make the most of BCS, herds should:

• Make condition scoring a routine element in herd management, alongside rumen fill scoring and assessments of dung consistency as indicators of cow health, feed intake, lameness and overall ration adequacy
• Record condition scores for all relevant animals – using record sheets that allow active utilisation and interpretation of the information
• Focus on animals deviating from the norm – excessive BCS loss in a group of stock or the whole herd rather than just a few individuals indicates action is necessary
• Assess group trends, in particular, from one scoring session to the next – to highlight critical BCS changes
• Use condition scoring records actively in fertility management
• Consider condition scoring retraining and calibration sessions

Although very subjective, the degree of rumen fill and consistency of dung are useful ways of keeping an eye on digestive efficiency and health.

For the greatest efficiency, cows’ rumens should be well filled throughout the day.

Insufficient rumen fill among groups of cows or individuals should raise immediate questions over feed availability or animal health.

It is important to appreciate it will often take 7–10 days after calving for rumen fill to reach acceptable levels.

Gut fill should be assessed on a scale of 1 (very empty) to 5 (very full) by looking at or feeling the triangle behind the last rib below the transfer spinal processes and in front of the hips on the left side of the animal (see picture on the right).

If the rumen is completely full, the triangle will bulge out slightly, whereas if it is very empty, it will be concave in appearance and easy to push the fingers under the transverse spinal processes.

Gut fill should ideally be assessed just prior to new feed being offered and again three hours later to identify any obvious differences.

Comparing cows with heifers is also a good way of identifying any problems with shy feeders.

Continual assessment of dung provides a very good indication of the balance of the diet, as well as overall efficiency of digestion.

The dung should:

• Be soft but maintain its shape in a pat
• Sound like a slow hand clap rather than a round of applause
• Be consistent across the herd
• Contain little or no undigested fibre or grains

Any problems with the dung suggest diets need reformulating or their presentation needs improving.

While loose dung generally indicates faster than ideal passage through the gut, it is acceptable with cows on grass only or forage crops.

Dung that is too firm and forms mounds suggests the diet may be too low in protein or high in fibre.

Dung that is too loose and thin, spreading easily, suggests an excess of protein, too little fibre, acidosis or the presence of mycotoxins.

Analysis of blood samples from a representative group of cows for a range of energy, protein and mineral parameters can be very valuable in assessing exactly what the cows think of the diet.

Cows in negative energy balance, for instance, have high concentrations of non-esterified fatty acids (NEFAs) and beta-hydroxybutyrate (BHB) or ketone bodies in their blood.

Survey work involving 15,000 cows in one UK metabolic profiling scheme has shown that a high proportion of modern dairy cows are in energy deficit in early lactation.

It has also underlined the value of monitoring the adequacy of feeding through metabolic measures that enable dietary imbalances to be identified and corrected before they seriously impact production, fertility or health.

Metabolic profiling, with blood sampling undertaken at key times of the lactation cycle, has been found to be a valuable management tool when organised as part of a routine herd health scheme.

Blood sampling needs to be conducted with veterinary supervision, and the involvement of both a vet and nutritionist is recommended in interpreting and acting upon the results.

This is especially important since recent work has suggested that slightly raised BHB and NEFA levels may not be the problem once thought.

Furthermore, some experts consider that NEFA levels should be allowed to rise in late pregnancy in order to condition cows for early lactation.

Given the wide impact dietary problems and imbalances can have on productivity, monitoring specific aspects of dairy health and fertility can be very valuable in feeding management.

Even though production monitoring may suggest dairy rations are adequate in their energy supply, they can compromise fertility performance.

The time delay between lack of energy in the ration and any resulting oestrus expression or pregnancy rate problems means nutritional inadequacies often go unrecognised until it is too late to do much about them.

This is compounded by the fact that fertility has not traditionally been given sufficient prominence within rationing programmes.

Whenever a ration is being prepared, it is always worth questioning:

• If the ration is necessarily adequate for good fertility just because it is appropriate for the level of milk production
• If ration formulation has actually taken into account fertility performance and potential problems
• If there are ways of monitoring the performance of the ration in terms of fertility as well as milk production
• If sufficient focus has been placed on cow condition as a measure of ration adequacy

Calving interval – CI (the number of days between one calving and the next) is the easiest measure of fertility, although it fails to account for cows already culled from the herd and is generally too historic to be of immediate management value.

Calving to conception interval – CCI (the average number of days from calving to the service at which cows get pregnant) is less readily available to all herds, although provided by most milk and fertility recording services.

CCI is of far greater use as a practical measure of fertility, especially when calculated for individuals or groups of cows (by month of calving perhaps) to avoid hiding extremes within a whole herd average.

CCIs typically range between 80 and 120 days. The target CCI for reasonable fertility is 70–90 days.

Poor fertility tends to be caused by a number of different factors, including inadequate heat detection and healthcare, as much as nutrition.

Disorders like acidosis, ketosis, displaced abomasum and fatty liver are clear signs of dietary problems, especially if they affect a number of animals rather than just the odd individual and occur regularly rather than occasionally.

More than occasional problems with milk fever and grass staggers are also invariably linked to diet, although generally brought on by non-dietary stresses like calving or cold weather at turnout.

A high incidence of such metabolic disorders in early lactation cows often results from inadequate nutrition and management in the dry period or around calving.

Like fertility, lameness is recognised as being caused by a number of factors, including inadequate nutrition.

Apart from incurring significant veterinary and medicine costs, it can have a seriously depressing effect on both milk production and fertility.

A significant incidence of lameness observed in the herd or identified in cattle heath records suggests diets should be checked for excess levels of starchy energy or protein.

Mobility scoring provides a good snapshot of the current incidence and severity of lameness.

Compared to target levels for lameness, a 7,000 litre herd with 10% of cows at Score 3 and 15% at Score 2 could be losing an average of 400 litres/cow – worth £140 at 35p/litre.

Mobility scoring can be time-consuming and is, like gut fill scoring, subjective.

However, regular scoring is an extremely valuable way of ensuring sufficient attention is paid to foot condition in herd management and lame cows are identified and treated early.