Troubleshooting Dairy Nutrition
A nutritionist may design a ration, a producer may choose to modify it, but it is the cow which decides what she will eat if she is allowed to do so. |
This section is NOT about "how to formulate a ration to improve production."
Here, we will consider those aspects of nutrition that can be associated with lameness and that can go wrong, sometimes without you even knowing it.
The Problem
You have come to the conclusion (or your veterinarian has told you) that the major problem is "sub-clinical laminitis."
You strongly suspect that something may be wrong with the nutrition of your cows.
Acidosis
Acidosis (increase in acidity - pH) in the rumen occurs when large amounts of easily digestible carbohydrates are available to lactic acid-producing bacteria which eventually displace other organisms beneficial to the cow.
Acidosis is controlled by sodium bicarbonate in the saliva. Fibre plays an important role in stimulating salivation.
Acidosis should be considered a tug-of-war between carbohydrate and fibre. |
Acidosis of the rumen has been associated with the production of poisons that cause changes in the blood vessels of the feet (Shaver 1996).
Sub-clinical acidosis is not eliminated in high-producing, well-managed herds; it is managed (Nocek 1995).
Danish workers have shown that similar deleterious changes take place in other body organs (Mortenson et al 1982).
A ruminal pH (acidity) that is too high can be thought of as a lost opportunity; energy intake and microbial protein will be sub-maximal and milk production will be sub-maximal (Allen & Beede 1996). Detection of Subclinical Acidosis (Allen & Beede 1996)
The following, taken together, are the best indicators that sub-clinical acidosis is present in a herd.
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Relative Decrease
in Milk Fat %
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Decrease in Rumination
Time
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| This may indicate a reduced ruminal pH. High-producing cows in early lactation are less sensitive to changes in ruminal pH; changes in fat percentage may be due to other factors. Milk-fat tests from bulk samples are unrealizable so the use of this indicator alone is unreliable. | If you observe a decrease in rumination time, it may be an indication of sub-clinical acidosis. This also is not an infallible indicator, however, a noticeable reduction in the fraction of cows ruminating, particularly one or two hours after eating, should be considered as separating evidence. |
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Changes in Feed
Intake
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Consistency of
Manure
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| Rapid reduction in dry-matter intake is a useful on-farm monitoring tool. This monitoring system must be based on objective data in order to be reliable. | This should be monitored at least weekly. A significant change in appearance within 12 to 48 hours following the introduction of a new feed is a useful indicator. The moisture content of the forage might be evaluated in conjunction with this observation. |
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Ruminocentesis
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This is a procedure that may be conducted in two groups, each of six animals.
Samples are taken (with a long needle through
the animal's flank) 2 to 4 hours after concentrate feeding. |
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Carbohydrates
High levels of carbohydrate consumption are necessary for high levels of milk production BUT the amount of fermentation acids produced over time MUST be limited to the rate of acid removal from the rumen.
Each of the following factors must be reviewed in any herd in which laminitis is suspected. In each case you will be searching for recommended guidelines that are being exceeded.
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Overconditioning
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Carbohydrate-to-Forage
Ratio
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Cows must not be overconditioned when they calve. |
The incidence of laminitis increases when the level exceeds 50:50 (Livesey & Flemming 1983). NEVER exceed 60:40. |
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Digestibility
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Frequency of Feeding
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Some carbohydrates, such as barley, naturally have high digestibility. Finely ground grain or that with a high percentage of moisture has an increased rate of digestibility. Highly fermentable grain sources should be limited to 35% (Shaver 1996). |
Encourage cows to consume many small meals per day. "Slug Feeding" Feeding high levels of concentrate only once or twice each day will result in the pH dropping below acceptable levels following each meal. |
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Moisture Levels
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Lead Feeding
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Moisture levels exceeding 32% must be limited in the diets of dairy cows. |
Cows should be consuming about 5kg of concentrate dry matter at calving in order to stimulate the development of rumen villi. Villi are the small finger-like folds in the lining of the rumen wall which increase the surface area of the rumen and improve the absorption of volatile fatty acids (Dirsen et al 1985). |
Changes in the Ration
If a herd lameness problem has been building up over a period of years, it is likely that production levels are being pushed too far. If a problem appears over a short time span, a sudden change in the diet is likely to have occurred.
Sometimes these changes occur without the producer being aware. |
Carbohydrate Intake after Calving
Cows should consume no more than 5 kg per day at calving and for the next 3-4 days. The concentrate intake can be increased at the rate of 0.25 kg/day until peak lactation. Heifers should be limited to an increase of 0.20 kg/day.
Dry Matter Intake (DMI)
The National Research Council (1988) estimates dry matter intake of dry cows to be 1.8% to 2.0% of body weight (BW). There is a decline of 15% between the far-off dry period (6-4 weeks) and close-up dry period (3 to 2 weeks) before calving. The decline may rise to 30% during the last week before calving (Van Saun 1992).
The above two factors must be monitored in herds that are component fed. Sudden jumps in the carbohydrate-to-forage ratio is a common cause of problems in such herds. Check moisture content of wet forages, grains and by products to recalculate DMI's.
Fibre
The effective fibre in a diet provides bulk in the rumen which stimulates the contracting churning action of the organ and slows down the passage of nutrients. Rough "sticks" in the forage are believed to stimulate rumination and the flow of saliva. Saliva neutralizes acidity. The quality of the effective fibre can be estimated by the % of acid detergent fibre (ADF) in the diet. Although analysis of the ADF is not completely reliable, a sudden change by as much as 10% can be disastrous.
Forage
For large herds there is an increasing tendency to purchase forage in bulk. The major problem with this practice is that the analysis of one load may be different from that arriving a month later.
A substantial variation in the effective fibre of one batch of forage from another can be responsible for a serious ruminal disturbance. Therefore, test the neutral detergent fibre (NDF) and ADF of each newly arriving batch. Keep sufficient amount of the old batch to mix with the newly arrived batch to last over a ten-day period.
Silage
Some workers, myself included, believe that feeding silage can be associated with disturbances in the environment of the rumen. Softer-than-normal manure can be one sign that a problem exists. Over-mixing a total mixed ration (TMR) can reduce the effectiveness of fibre. Feeding 10% of the forage as long hay tends to have a positive effect.
Making silage in tower silos and bags is prone to more problems than is the case if pits are used. The reason for this is that cutting from the face of pit silage enables silage harvested at different times to be properly mixed which may not be the case with the layers from a tower. It is essential to have an overlap period of at least 28 days during which old silage can be mixed with new.
Protein
In one study it was found that during the period 3-26 weeks after calving the prevalence of lameness increased as dietary crude protein concentration was increased from 16% to 20% (Manson and Leaver 1988).
Conclusions
An obsessive drive to improve production can come at a cost. On the other hand, it is not possible to identify the nutritional cause of lameness in every case. By all means, be obsessive about the effects of changing the ration, changing the management or, in fact, any change that can affect your cows. Make yourself very well informed about the implications of dietary changes.
