Practical Assessment of Nutrition in the Milking Herd
27 May 2024Thanks for subscribing! Please check your email for further instructions.
Nutrition of the milking herd is usually seen as the responsibility of the farm’s nutritionist. However, there are many ways a herd manager or stockperson can assess whether nutrition is adequate or if something is not quite right with feeding. This factsheet covers some visual indicators to help with early detection of nutritional issues and the use of milk composition data in assessing protein nutrition and cow health.
Assessing Manure
Inspecting manure can tell us a lot about yesterday’s feeding. While it cannot give an exact assessment of whether a ration meets the nutritional needs of the herd, it can give a crude indicator as to the protein supply, how well cows are digesting their feed and rumen health.
Manure Consistency
Ideally manure should form a pile that is one to two inches high and have a porridge-like consistency. Consistency will vary depending on the moisture content of the feed, so when particularly wet silages are fed, the manure tends to be looser.
Loose manure can also be due to feeding high levels of protein, particularly rumen degradable protein (RDP), and cows respond by drinking more water in order to increase urinary nitrogen excretion. This can occur in cows grazing lush spring grass, with the higher moisture level and low level of fibre also contributing to looser manure. Cows under heat stress may also show looser faeces.
If manure is very stiff, it could be due to a lack of RDP and likely a low protein content in the diet (below 15% crude protein on a dry matter basis). Stiff manure can also be due to a problem with water availability or feeding very high dry matter and high fibre diets. The manure of dry cows is usually much stiffer than that of milking cows due to them being fed a higher forage (higher fibre) diet.
Click to enlarge images
If cows are scouring, it may be due to infection or parasites. However, if the cause is nutritional, it can be from excessive hindgut fermentation of carbohydrates due to too fast a passage rate through the rumen and insufficient time for digestion and absorption of nutrients in the rumen or small intestine. Manure that contains bubbles (appears foamy) is due to either ruminal acidosis or gas produced from excessive fermentation in the hindgut.
In a herd which is 100% TMR fed (i.e. no concentrate fed outside of the feed pass), manure consistency should, in theory, be fairly uniform across all the cows. However, in herds fed a partial mixed ration and concentrates to yield in the parlour, robot or through out of parlour feeders, there will be a big difference in how much concentrate is fed to cows at peak lactation compared to those in late lactation and producing less milk. Therefore, the cows receiving a higher level of concentrate (and a lower forage to concentrate ratio in their diet) are likely to have thinner manure. Ration sorting can also lead to variable muck consistency.
Manure Content
Undigested feed material in manure can indicate a problem with rumen efficiency. If grains are coming through in the manure, the reason may be:
- Insufficient processing of the grain.
- Fast passage rate of feed through the rumen with insufficient time for digestion. This can be caused by low fibre intakes, high levels of starch and sugars and a low rumen pH (acidosis).
If fibre particles over 0.5 inch long are visible, either by eye or by sieving the manure, this can indicate:
- Poor digestion (poor rumination and rumen fermentation).
- A quick passage rate.
- Possible acidosis.
- Forages are of poorer quality.
Mucus or mucin casts in manure are a sign of inflammation or injury to the large intestine in response to hindgut fermentation and a low pH from acid production.
Manure Colour
Colour will vary depending on the ingredients in the diet, with rations high in maize silage or large amounts of grain having a lighter yellow-olive colour compared to a grass silage-based ration. For cows grazing lush pastures, the manure will be a dark green colour. Any infection in the digestive tract will influence the colour. For example, salmonella can cause a light-green or yellow, watery manure.
Rumination
Rumination Time
Cows spend on average between seven to eight hours ruminating each day, although this will vary with production level, feed intake and diet composition. It can be influenced by lying times, with poor lying times associated with less time spent ruminating.
Monitoring the time spent ruminating can give a guide as to rumen health and whether there is sufficient forage in the diet. It can also indicate if acidosis is present as rumination time will drop, both with subclinical and clinical acidosis.
Cud Chews
In the absence of technology (e.g. collars, eartags or boluses) to monitor rumination time, you can look at the percentage of cows chewing their cud. Ideally at least 60% of cows lying down should be ruminating.
Counting cud chews can give an indicator as to whether there is adequate fibre in the diet. Ideally there should be 60 (±10) chews before swallowing the cud. If there are less than 50 there is likely to be insufficient fibre in the diet and if much over 70, the diet fed is high in fibre and potentially of poor quality, restricting milking performance. A low number of cud chews may also be indicative of stress or a health issue. A drop in rumination time is often seen before any clinical signs of disease, such as mastitis or metritis. Therefore, keeping a close eye on rumination is also useful for early detection and treatment of diseases.
Cud Balls
The presence of cud balls indicates an acidic rumen environment and cows reject their cud due to its acidity and reduced palatability. Unpalatable forage may also result in cud balls e.g. silage that has gone off, such as waste at the top or shoulders of the silage clamp.
If cud balls are present (or if rumination rates are low), the diet should be assessed for forage intake, fibre (NDF) content, forage particle length (is the diet being overprocessed in the mixer wagon?) and risk of acidosis.
Corrective measures include:
- Increasing the forage to concentrate ratio.
- Including a drier forage (if very wet silages are being fed).
- Including chopped straw (0.5-1.0kg).
- A rumen buffer will be of benefit particularly where it is difficult to make changes to the forage portion of the diet.
Rumen Fill
Rumen fill gives an indication of whether a cow has eaten much over the past two to six hours. It can be assessed by looking at the area under the short ribs, in front of the pelvic bone and behind the last rib on the left-hand side of the cow. This area is often called the warning triangle, with a concave triangular area (or hollow appearance) seen in cows that have not eaten much in the last few hours.
Rumen fill is scored from 1 to 5, where 1 is an empty rumen where the cow has eaten very little and a score 5 indicates maximal feed intake with a full, distended rumen.
Milking cows should have a score 3, although in the first week of lactation a score 2 is acceptable. Dry cows should be either a score 4 or 5 (due to the uterus taking up considerable space in the abdominal cavity and dry cows being fed a high forage, high fibre bulky diet).
Rumen fill tends to be lower in the morning than in the evening. Therefore, scoring should be carried out at various times of the day to get a representative assessment of rumen fill. Heifers and low-ranking cows, particularly in systems where stock density is high and feed space is limiting, are most at risk of low scores.
Animals with low rumen fill scores should be closely monitored and if there is a large variation of scores within a group or a high proportion of consistently low scores, further investigation is required and action taken to correct problems associated with ration formulation and feed intake. AHDB Dairy recommend that at least 85% of cows at any one time within a group should be at the target rumen fill score.
Body Condition Score (BCS)
Assessing body condition in early lactation can help gauge whether the diet is providing sufficient energy. Ideally cows should be losing no more than half a BCS unit in the first two months of lactation (which equates to no more than 0.5kg/day). One BCS unit accounts for about 65kg liveweight for a 650kg cow (10%). Given the target BCS at drying off and calving is between 2.5 to 3, the minimum condition score seen should be a 2. A useful guide to condition scoring dairy cows on a quarter point scale is found here: https://ahdb.org.uk/knowledge-library/body-condition-scoring
Coat Condition
Coat condition is a good indicator of general health and it should be smooth and shiny in appearance. Adequate protein, minerals and vitamins support hair follicles for healthy hair growth and so a dull, rough coat can be sign of undernutrition. Heifers that are outwintered will develop a hairy coat which looks rough in appearance and this should not be confused with a dull stary coat from undernutrition.
Heifer Appearance
If 1st lactation heifers are housed with older cows and are holding their condition well, this implies that there is sufficient feed and lying space. However, if stocking rates are high and feed space is limited, it is often the heifers that appear to be struggling and tend to be in poorer condition than the cows, due to competition for resources.
Recommendations are to have at least 5% extra cubicles than animals and provide a minimum of 75cm feed space per head (and ideally more if there is a fresh group of newly calved animals).
Milk Urea
Milk urea is a crude indicator of the balance of protein and energy supply to the rumen. The target range for milk urea is between 0.02 to 0.03% (or 200 to 300mg/litre). Generally, if milk urea is low then it is likely that RDP is deficient and if high, RDP is being fed in excess. However, if milk urea is high and milk protein percentage is lower than normal, this could also be due to a deficiency of rumen available energy.
Figure 1. Milk urea guide to protein and energy supply.
Milk Composition for Ketosis and Acidosis Monitoring
Ketosis is a common metabolic disorder that can occur in early lactation in high yielding cows, due to a lack of energy. Cows that are over conditioned at calving tend to be more susceptible, through a reduction in dry matter intake and excessive mobilisation of body fat reserves in early lactation. The milk fat to protein ratio serves as an indicator as to the risk of ketosis. When cows are excessively mobilising body fat reserves, some of that fat ends up in the milk and combined with a drop in milk yield in ketotic cows, their milk fat percentage increases. In addition, the lack of dietary energy can reduce the milk protein content. Therefore, a high fat and low protein content increases the ratio. A ratio of over 1.27 indicates a cow at risk. For example, a cow with milk fat of 4.4% and a milk protein of 3.1% has a fat to protein ratio of 4.4 ÷ 3.1 = 1.42.
With acidosis the opposite is true. The fat to protein ratio will be lower than 1.27, with a low fat content due to potentially low fibre intake and poor fibre digestion. The milk protein content may be elevated in high concentrate, low forage diets, which are high in energy and starch, the key drivers of milk protein production.
Feed Management
While good feed management will not make up for any nutritional deficiencies in ration formulation, ensure that cows have access to feed 24 hours a day, with regular push ups (6 to 8 times a day) and feed passes/troughs cleaned out daily. Ideally feed for a minimum of 2% of the offered feed as refusals. This will help ensure that dry matter intake is being maximised to optimise cow performance (assuming that feed space is not a limiting factor).
If there is evidence of cows sorting their ration i.e. refusals look vastly different from the freshly mixed ration, with more long, fibrous pieces of forage left over, then ration sorting is occurring. This is more common when feeding rations based on high dry matter forages or insufficient forage chop length. The impact of sorting behaviour on performance can be minimised by adding water to the mix to achieve a dry matter of around 40%. Forage particle length should be around 25mm and no more than 50mm.
Summary
There are several visual indicators that can be used to assess the adequacy of nutrition and feeding management in the milking herd. If you have any concerns, seek nutritional advice and ensure that any dietary advice is based on recent forage analysis.
While milk composition can help identify some nutritional problems, another way to assess nutrition is to carry out metabolic profile testing via blood analysis. This is a useful tool to assess energy, protein and mineral status at key stages of the production cycle, such as close to calving cows and those in the first three weeks of lactation.
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