Troubleshooting Oxidized Flavour Problems in Bulk Milk
Published: October 2, 2008
By: Information published by the Government of Manitoba, Agriculture, Food and Rural Initiatives
An "off" (or objectionable) flavour that is described as tasting "cardboardy," "metallic" or "oily" in nature.
The Oxidation Process
Oxidation is a chemical reaction between oxygen and the polyunsaturated fatty acids of the membrane that surrounds each milk fat globule. Reaction end products include aldehydes and ketones, which impart a distinctive oxidized flavour at levels as low as one part per billion (ppb) in the milk. The oxidation reaction can occur either spontaneously or it can be induced by external (environmental) factors.
Basic Facts Concerning Oxidized Milk Flavours
•Resolving an oxidized milk flavour problem can be very difficult and time-consuming since different factors or combinations of factors may cause the problem.
•Although laboratory techniques exist for detecting aldehydes and ketones, smell and taste are the primary methods used for quick, on-farm detection of oxidized milk flavours.
•Milk is usually not oxidized when first taken from the cow; however, an oxidized flavour can develop within 24 hours during refrigerated storage under conditions which promote the oxidation reaction. In some instances, it may take from 48 to 72 hours to develop following milking.
•Once milk fat begins to oxidize there is a tendency for the chemical reaction to continue but at an accelerated rate, thus causing the milk to become oxidized much more rapidly. Milk agitation in the bulk tank and the pumping of milk from the bulk tank further accelerates the oxidation reaction.
•Sometimes milk fat that is susceptible to oxidation will not impart a detectable flavour at farm pick-up; however, a pronounced flavour may develop by the time it arrives at the processing plant or, worse yet, after it has been comingled and stored in a silo with good milk from other farms.
•Mixing of oxidized milk from one farm with non-oxidized milk from other farms in the same bulk truck can result in the oxidation of the whole load of milk.
•Oxidized milk flavour may be caused or influenced by any one or more of the following factors: dietary changes; diet composition; age and quality of stored forages; fibre intake and quality; excessive changes in body conditioning; milking procedures; equipment design and sanitation; water quality; animal stress; age of cow; high individual cow milk yield; and stage of lactation.
Marketing and Processing Oxidized Milk
•Oxidized milk poses no health risks; however, it presents significant risk to retail sales. Consumer rejection of off-flavoured dairy products can result in temporary to permanent loss of sales to dairy competitors.
•Oxidized milk that is rejected at farm pick-up and must be disposed of by the producer represents an immediate loss in potential income for the producer.
•If milk from one farm begins to develop an oxidized flavour while it is in transit from the farm to the processing plant or while it is stored at the plant in a silo containing multiple bulk truck loads of milk, the off flavour can become so severe as to cause the loss of the whole silo.
•Although pasteurization can slow down the oxidation process, it cannot stop it entirely.
•While waiting for corrective measures to take effect, possible short term solutions could include daily pickups and immediate processing.
Oxidized Flavour Formation
Light Induced
Light can increase the reactivity of oxygen on milk fatty acids, thus accelerating oxidized milk flavour development. Exposure of milk to light is usually not a problem on-farm; however, it can be a problem once it leaves the farm (ie, milk exposed to direct light in retail stores for a prolonged period of time can be susceptible to oxidation).
Prevention of oxidized flavours at the retail level:
1. Packaging material that is dark and less transparent to light (ie, paper board versus clear glass bottles)
2. Any retail display technique that minimizes milk container exposure to direct light yet maintains visual
appeal to consumers
3. Milk containers stored and displayed in crates in retail stores reduces exposure to light
Non-Light Induced
This type is primarily caused by environmental factors such as excessive aeration or agitation of the milk, milk contact surfaces that are either unclean or coated with high residual levels of cleaning agents, or using a water source that has high copper, iron or sulphur levels.
Prevention of Oxidized Flavours
Eliminate Excessive Air Leaks, Milk Agitation and Foaming
Seldom are they the sole cause; however, all can contribute indirectly to oxidized flavour development. First, they promote an intimate mixing of reactants thus stimulating oxidization activity. Secondly, they tend to intensify an oxidized flavour problem that already exists by disrupting the outer protective membrane surrounding each milk fat globule, thus making the fat more susceptible to oxidation. Potential problem areas to examine include: air leaks at milkline valves; milkline slope and flooding problems; excessive air admission through the claws when units are attached or taken off; excessive on-off running of the milk pump connected to the receiver jar; a short milk discharge pipe that allows milk to "free-fall" into the bulk tank cooler; and a bulk tank agitator paddle that runs too long or that is not submerged in the milk.
Milk Contact Surfaces
Ensure that all milk contact surfaces are made of approved materials for the safe handling and storage of milk. These materials could include glass, stainless steel, rubber and plastic.
Clean Milk Contact Surfaces
Ensure that all milk contact surfaces are clean. Fat or protein build-ups on any milk contact surface can oxidize and contaminate normal milk touching these surfaces. This in turn "seeds" or stimulates the oxidation of what was previously normal milk. Fat build-ups are identifiable by a greasy-like feel to the surface and hanging water droplets following system sanitation. Protein build-ups on a dry surface impart a blue, rainbow-like hue.
Chlorine Sanitizers
Proper use of chlorine sanitizers is very important. High residual levels of chlorine on any milk contact surface can act as a strong oxidizing agent upon contact with milk. To minimize this risk, never exceed 200 parts per million (ppm) chlorine in the sanitizing solution. Ensure that the milking system has adequate slope to permit rapid and complete drainage of all sanitizing solution. If an oxidized flavour persists, consider switching to an iodine sanitizer and use at 25ppm in solution.
Copper, Iron, Sulphur and pH Levels in the Water
Collect representative water samples from both the cold and hot water supplies used for milking equipment sanitation and have the samples tested by an accredited testing lab for pH, copper, iron and sulphur levels. Prior to sample collection, check with the testing lab for recommended sample containers, collection, handling, storage and delivery procedures. Since copper, iron or sulphur can act as potent catalysts of the oxidation reaction, as little as 0.1ppm (also reported and expressed as milligrams/litre or mg/L) of copper, iron or sulphur in the water supply can contribute to flavour development. If present in the water supply, system sanitation can introduce and deposit these minerals on all milk contact surfaces. This in turn can contaminate the milk supply and increase the susceptibility of milk fat to oxidation. Flushing the milking system with an acid rinse prior to milking is strongly recommended when water mineral levels are a concern. Consideration should be given to installing a water treatment system when the water contains 0.1ppm or greater of copper, iron or sulphur. Copper and iron water lines can act as potential sources of water contamination. In the case of copper lines, they can represent a significant source of water contamination when the pH of the water is lower than 7.0 (ie, acidic water). When such conditions exist, it is highly recommended that copper lines be replaced with plastic tubing.
Spontaneous Oxidized Flavour
This type of oxidized flavour usually relates to milk that is prone to oxidation within 24 to 72 hours after leaving the udder. Depending upon the severity of oxidized flavour development in milk from individual cows, this flavour may not be detectable in bulk milk until at least 20% of the cows in a herd are affected. In severe cases, as many as 65% to 70% of the cows can be affected. Although other factors are known to cause spontaneous oxidized milk flavour, the primary cause appears to be nutrition-related. More specifically, when an imbalance exists in the milk in favour of pro-oxidants (ie, compounds that encourage oxidation) over antioxidants (ie, compounds that prevent or combat oxidation), the milk becomes quite prone to oxidized flavour development.
Non-Nutritional Factors
Lactation Number
Field observations from farms having chronic problems with oxidized milk have revealed that milk from first calf heifers has a tendency to be more prone to oxidized flavours than the milk from second lactation and older cows. This may be related to the plane of nutrition received by first calf heifers prior to calving. It may also be related to higher levels of copper in their milk because they are lower in production than second lactation and older cows. The heifer nutrition program for the four-month period prior to first calving should be reviewed for proper mineral balance and consumption. Imbalances should be corrected immediately.
Stage of Lactation
Milk from early lactation cows tends to be higher in copper content and lower in fat than milk from mid to late lactation cows. This higher concentration of copper relative to fat in the milk increases the risk of oxidation and accelerates the reaction once it starts. Other practices to control or reduce the risk of oxidized milk must be emphasized in herds where there is a high proportion of fresh and early lactation cows.
High Milk Production
Milk from higher producing cows tends to be lower in fat content which, for the same reasons stated above for stage of lactation, can result in fat that is at higher risk of oxidation. In addition, the membrane surrounding each milk fat globule is more fragile and susceptible to oxidation in higher producing cows. Paying close attention to recommended practices that control or reduce the risk of oxidized milk must be a management priority with high producing cows and herds.
Body Conditioning
Milk from cows that are thin or mobilizing body fat at an excessive rate in early lactation is quite susceptible to oxidized flavour development. The rationale lies behind the fact that milk fat derived from body fat is lower in vitamin E content (a powerful antioxidant) and higher in unsaturated fatty acids. Examine body condition scores from a cross-section of cows in the herd including dry cows, just fresh cows, and cows at 60, 120 and 200 plus days in milk. If cows appear to be losing excessive body weight in early lactation (ie, greater than one unit of condition score), then the ration should be re-evaluated and corrective measures implemented immediately.
Cows Under Stress
Any factor that stresses cows appears to increase the risk of oxidized flavour development. Examples include: calving; cows in heat; metabolic and infectious diseases; high temperature and humidity; heavy parasite load (ie, lice); sudden change in temperature; feet and leg problems; poor housing and overcrowding. The bodies of cows under stress produce elevated levels of free radicals. These free radicals attack and oxidize the fat cell membranes, which in turn results in oxidized milk. Identify and immediately eliminate any stressors that could be part of the problem.
Late Lactation Cows
Low yielding, late lactation cows can contribute to the problem. In herds where an oxidized milk flavour problem exists, consider drying off late lactation cows or divert their milk away from the bulk tank.
Breed Differences
Limited data suggests that the milk from typically high fat testing breeds is more susceptible to oxidized milk flavours than the milk from other breeds. Attention to management practices that reduce the risk of oxidized milk flavour development may need to be emphasized more with high fat testing breeds.
Cow Families
Some experts believe that there is a genetic component to the equation and that certain cow families and sires within each breed are more prone to oxidized milk flavour development. Solid evidence to prove or disprove this belief still does not exist.
Nutritional Factors
Age of Stored Forages
Active vitamin E levels are highest in pasture and greenchop forages and forages harvested and stored no longer than three months as hay or silage. Vitamin E levels in forages stored longer than three months are significantly reduced, which in turn results in much lower total daily intakes of biologically active vitamin E (see Table 1 for a comparison between stored forage versus fresh forage). As vitamin E consumption drops, milk fat gradually becomes more susceptible to spontaneous oxidation. This scenario represents a bigger risk to herds that feed stored feeds year-round.
Table 1. Comparison of daily vitamin E intake from stored versus fresh forage
|
Measurement |
Stored Forage* |
Fresh Forage |
|
I.U.** Vitamin E/cow/day | ||
|
Vitamin E |
250 |
9,000 |
|
* Stored forage: has been in storage for greater than three months; same type as fresh forage |
Forage Quality and Preservation
Heat, oxygen and moisture all act to destroy vitamin E. Forages that are moldy, heat damaged, weather damaged or of poor quality tend to have little to no active vitamin E compared to well preserved, quality forages. If a herd is being fed a poor quality, damaged forage and is also experiencing oxidized milk flavours, substitute all or at least a high proportion of the forage with medium to high quality forage.
Effective Fibre Intake and Length of Cut
A ration will have a tendency to depress milk butterfat test and increase the concentration of unsaturated fatty acids if it lacks effective fibre, if the forage is chopped too fine, or in the case of a total mixed ration (TMR) it has been overmixed thus reducing the effective fibre level. This in turn increases the susceptibility of milk fat to spontaneous oxidation. Total ration dry matter (DM) should contain a minimum of 19% acid detergent fibre (ADF) and 26% to 30% neutral detergent fibre (NDF). Forages should provide at least 75% of the total ration NDF. Use a portable particle separator to evaluate forage particle length. For hay crop silage and haylage, most of the material should have an actual length of cut 2.0cm to 2.5cm. For corn silage, most of the material should have an actual length of cut of 1.5cm to 2.0 cm. Consult with your nutritionist or feed advisor to ensure that ration fibre level and fibre intakes are adequate. If it is a problem, then substituting a small amount of long hay or long chopped hay should be considered.
Forage to Concentrate Ratio
Overfeeding concentrates, particularly very starchy grains, and underfeeding forages or utilizing a feed delivery system that allows cows to sort feed and thus consume excessive concentrates relative to forages will depress milk butterfat test. It also results in more fragile fat membranes and increases the concentration of unsaturated fatty acids, both of which increase the susceptibility of milk fat to oxidation. If hay, hay crop silage or haylage are the predominant forages in the ration, at least 40% of the total ration DM should come from forage and no more than 60% from concentrates. If well-eared corn silage forms the predominant forage in the ration, at least 50% of the total ration DM should come from forage and no more than 50% from concentrates.
Dietary Changes
Avoid abrupt changes in feeds. Always rebalance the ration each time a new feed is introduced, or when there are changes in feed moisture levels or feed quality. Failing to manage dietary changes properly can predispose cows to oxidized milk flavours.
Dietary Fat Supplementation
Diets which are supplemented with either natural or rumen-protected sources of unsaturated fats and oils (ie, sunflowers, canola, cottonseed, soybeans and Megalac which is a rumen-protected fat source) tend to increase the concentration of unsaturated fatty acids in the milk and increase the susceptibility of milk fat to oxidation. If an oxidized milk flavour exists, then consider reducing the level of unsaturated fats and oils in the ration and substituting with fats of animal origin (ie, tallow), which are more saturated in nature and less susceptible to oxidation. Also, for every 1.0% increase in ration fat concentration above the normal level of 2.0% to 3.0% fat on a DM basis, add 5 I.U. vitamin E/kg of DM intake.
Ration Nutrient Balance
Representative samples of all ration ingredients including forages, concentrates and supplements should be collected and submitted to an accredited feed testing lab for a complete nutrient analysis. Collect and record actual consumption levels of all feeds including minerals and vitamins. Have a nutritionist or feed consultant evaluate the ration to ensure it is nutritionally balanced for fibre, energy, protein, minerals and vitamins and that feed DM intakes are within the desired range.
Copper (Cu), Iron (Fe) and Manganese (Mn) Intakes
Excessive dietary intakes of any of these three minerals can increase the susceptibility of milk fat to oxidation. Pay particular attention to Cu, Fe and Mn levels in the total ration DM. Look for possible surpluses of each that might be conducive to oxidized flavours. Current National Research Council (NRC) requirements for Cu, Fe and Mn are 10, 50 and 40 ppm respectively in the total ration DM. All should be supplemented and fed at levels equal to or slightly greater than NRC requirements. Copper levels in the total ration DM that exceed 40ppm to 50ppm can cause oxidized milk flavours to develop.
Antioxidant Antagonists
Various conditions can lead to the presence of antioxidant antagonists, which in effect makes the milk fat more susceptible to oxidation. Naturally occurring compounds exist in soybeans and legumes that are antagonistic to the vitamin E antioxidant effect. High nitrates and nitrites in feed or water are also antagonistic to vitamin E. High sulphur levels in feed or water inhibits selenium absorption, which in turn reduces the efficiency of vitamin E absorption and function. Also, feeds harvested under unfavorable weather conditions (ie, drought, frost) can contain antagonistic factors that reduce antioxidant activity.
Selenium (Se) Intake
Selenium is part of an enzyme system that protects unsaturated fatty acids in the fat cell membranes from oxidizing. Selenium serves a complimentary role to vitamin E absorption and function. A low-ration Se level will result in low blood and milk Se concentrations, which in turn reduces the antioxidant effect of vitamin E even when vitamin E is fed at recommended levels. Dietary supplementation with vitamin E to correct an oxidized flavour problem is more effective when Se is included in the total ration DM at the recommended NRC level of 0.3ppm or 0.3mg of Se/kg ration DM.
Vitamin E Intake
Vitamin E is essential to the integrity and optimal function of body systems related to reproduction, muscle contraction, blood circulation and immunity. Vitamin E is the most important fat-soluble antioxidant in the body and milk. It scavenges for peroxide and converts it to harmless water. It also prevents the formation of free radicals and by doing so, it protects cell membranes from undesirable damage. Inadequate daily intakes of vitamin E coupled with advancing age of stored forages appears to be a major factor in increasing the susceptibility of milk fat to spontaneous oxidation. Adequate consumption of vitamin E goes a long way in preventing or correcting a milk fat oxidation problem.
NRC vitamin E requirements for dry cows and heifers prior to calving are 15 I.U./kg ration DM or 150 I.U./cow/day. However, current industry recommendations to maintain a viable antioxidant defence system is to include 100 I.U. vitamin E/kg ration DM or to feed 1,000 I.U. vitamin E/dry cow/day. Dry cows and heifers pre-calving normally require more vitamin E due to a range of factors that may include the following:
•low quality feed
•low daily DM intakes
•dietary fat levels that are too low to carry adequate vitamin E
•high deposition of vitamin E into the colostrum
•a depressed immune system at calving
•blood vitamin E levels that typically drop at calving due to stress
NRC vitamin E requirements for lactating cows are 15 I.U./kg ration DM or 300 I.U./cow/day. However, based on the results of University studies the recommended level of vitamin E should be increased to 25 I.U. vitamin E/kg ration DM or to feed 500 I.U. vitamin E/cow/day. For those herds feeding supplemental fats that result in an increase in dietary fat above the normal 2.0% to 3.0% fat level in the total ration DM, ration vitamin E levels should be increased to 50-75 I.U./kg ration DM or to feed at levels of 1,000 to 1,500 I.U./cow/day and maintained at these levels at all times. Herds diagnosed with an oxidized milk flavour problem can benefit from vitamin E supplementation by either topdressing extra vitamin E or through individual cow injections of vitamin E.
In the case of feeding extra vitamin E, it is important to realize that the efficiency of transfer from the topdress through the digestive system and into the milk is very low at 2.0% to 5.0%. Up to 80% of what is fed is excreted in the manure. Topdress or include in the ration extra vitamin E to achieve a total intake of 5,000 to 6,000 I.U. vitamin E/cow/day. This may take from ten to 20 days before any noticeable change in milk oxidation level can be expected. Once the oxidized flavour disappears, gradually reduce the amount topdressed or included in the ration to a level no lower than 1,500 to 2,000 I.U. vitamin E/cow/day. Maintain at this level until cows are turned out to pasture or receive new crop forage. At that point, vitamin E concentration in the ration can be returned to normal recommended levels (ie, 500 I.U. vitamin E/cow/day).
Table 2. Cost to feed supplemental vitamin E*
|
Total Daily Intake** |
Supplemental Vitamin E |
Supplemental Amount Fed |
Supplemental Amount Fed |
Extra Cost/Cow/Day |
|
2,000 |
1,500 |
37.5 |
1.3 |
7.3 |
|
2,500 |
2,000 |
50.0 |
1.8 |
9.8 |
|
3,000 |
2,500 |
62.5 |
2.2 |
12.2 |
|
4,000 |
3,500 |
87.5 |
3.1 |
17.1 |
|
5,000 |
4,500 |
112.5 |
4.0 |
21.9 |
|
6,000 |
5,500 |
137.5 |
4.9 |
26.8 |
|
* Using a product containing 40,000 I.U. vitamin E/kg at $39.00/20 kg |
To achieve an immediate increase in milk vitamin E content and to help protect milk fat from oxidizing, administer an injectable, concentrated source of vitamin E. An injection of vitamin E will increase milk vitamin E concentration within hours and reach peak levels about two to three days later. Following that, the level gradually falls to about 50% of peak levels after six to eight days. By that time, the effect of feeding topdressed vitamin E will have started to take effect. The standard recommendation is to inject all cows immediately with 3,000 I.U. of vitamin E. The injection should be given intramuscularly or, to prevent any possible shock response, subcutaneously. Prior to administration, read product label instructions regarding proper use. It is also advisable to inject 3,000 I.U of vitamin E in all dry cows and first calf heifers immediately after calving if they did not receive an injection when the rest of the herd did.
Injectables containing both vitamin E and Se are not approved for lactating cows. A new Canadian approved injectable vitamin E product called Vit-E-AD is now available. It is manufactured by Servi-Vet Inc. (Montreal, Quebec) and can be administered intramuscularly. It contains 300 I.U. vitamin E/ml, 100,000 I.U. vitamin A/ml and 10,000 I.U. vitamin D/ml. Injecting vitamin E, feeding a vitamin E topdress or adding extra vitamin E to the ration may correct an oxidized milk flavour problem. However, this does not mean that low vitamin E levels were the primary cause of the oxidized flavour. Although injecting vitamin E provides an immediate increase in blood and milk vitamin E levels and helps to stabilize milk fat from oxidation, the feeding of extra vitamin E is quite effective in reducing the severity and duration of an oxidized flavour problem once it has been fed at higher levels for 10-20 days. Injectable Se is not approved for milking cows unless administered via extra label use under veterinary direction. Injectable Se products are approved for cows at drying-off or before calving. However, the 30-day Se withdrawal period prior to slaughter must still be adhered to.
Ensuring that desired levels of vitamin E and Se are fed to dry and lactating cows has many other benefits. A few of these include:
•43% decrease in new intramammary infections
•30% decrease in the incidence of clinical mastitis
•45% decrease in the duration of mastitis infections
•62% decrease in the percentage of cows with somatic cell counts >200,000
•55% decrease in the number of quarter days infected
•Significant increase in the percentages of E. coli and Staphylococcus aureus organisms naturally killed
by the animal’s immune system
•Increased vigour of newborn calves and reduced muscular dystrophy
•Reduced incidence of retained placentas
•Stronger heat signs and improved conception rates
Steps to Correct an Oxidized Milk Problem
1. Upon being notified of an oxidized milk flavour problem, immediately arrange for daily bulk milk pickup by phoning Manitoba Milk Producers at 204-488-6455 or the 24-hour emergency phone number, 204-781-5180. This is a temporary measure until the problem is under control. Daily pickup may not be an option if the oxidized flavour is quite pronounced before 24 hours of storage.
2. Immediately contact the dairy farm inspector or milk quality advisor for your area and arrange to have milk samples collected from the first milking in the bulk tank and from individual cows in the herd. These samples will then be flavoured at times 0, 12, 24, 48 and 72 hours to determine the severity of the problem and what proportion of the herd is producing oxidized milk. If herd size is fewer than 50 cows, collect milk samples from all cows. For herd sizes of more than 50 cows, collect milk samples from at least 35 to 50 cows.
A. When collecting samples from the bulk tank:
•Use the same sample vials as carried by your bulk truck transporter.
•Identify or label the sample vial and fill to 1/2 to 2/3 full. Allow enough "head space" for vapours to
accumulate.
•Store and keep sample cool at 2°C to 4°C. (36°F to 39°F.).
•Flavour at times 0, 12, 24, 48 and 72 hours.
•Prior to flavouring, check for odour. Warming the sample to 15°C to 20 °C. (or 60°F to 70 °F.) helps
vapours to accumulate in the "head space" between the cap lid and the milk surface. Swirl the sample
as it is warmed, then only open the lid when it is as close as possible to your nose.
•Then, proceed with flavour testing and spit out afterwards.
B. When collecting samples from individual cows:
•Use same sample vials as used for collecting bulk tank sample.
•Collect a representative composite milk sample (equal amounts of milk from each quarter and mixed
together as one sample) by hand from each cow and NOT through a milk meter or the equipment.
•Fill sample vial to 2/3 full.
•Store and keep samples cool at 2°C to 4 °C. (36°F to 39 °F.).
•Flavour at times 0, 12, 24, 48 and 72 hours.
3. Immediately contact your veterinarian and purchase a "concentrated injectable vitamin E product" in sufficient quantity to inject intramuscularly all milking cows with 3,000 I.U. of vitamin E. The marketplace now carries concentrated injectable vitamin E products that can be used for this purpose. They may contain only injectable vitamin E or a combination of injectable vitamins A, D and E. Prior to administration, read product label instructions regarding proper use. DO NOT USE an injectable vitamin E-selenium product. In addition to being NOT APPROVED for use in lactating cows, injectable vitamin E-selenium products generally do not contain sufficient vitamin E to correct an oxidized milk flavour problem.
4. Once steps 1 to 3 have been completed, proceed with steps 4.A to 4.D as soon as possible.
A. Immediately contact your nutritionist or feed advisor to ensure that dry cow and milking cow rations are providing 1,000 I.U and 500 I.U. vitamin E/cow/day, respectively and that higher levels of 1,000 to 1,500 I.U. vitamin E/milking cow/day if feeding supplemental fats.
B. After completing step 4.A, arrange through your feed company representative to acquire and either topdress or include in the milking cow ration sufficient vitamin E to elevate total vitamin E intake to 5,000-6,000 I.U. vitamin E/cow/day and maintain at this feeding rate.
C. Once the oxidized flavour disappears, reduce daily feeding rate to 1,500-2,000 I.U. vitamin E/cow/day and maintain at this level until cows are turned out onto pasture or receive new crop forage.
D. Once cows are turned out onto pasture or receiving new crop forage, reduce milking cow ration vitamin E concentration to normal recommended levels (ie, 500 I.U. vitamin E/cow/day).
5. Inject 3,000 I.U. of vitamin E in all dry cows and first calf heifers immediately after calving if they didn't receive a vitamin E injection at the same time as the rest of the herd.
6. Consult with your milk quality advisor, dairy extension specialist, dairy equipment dealer and nutritionist or feed advisor to review your herd's status with respect to all factors listed in this factsheet that are known to be potential causes of an oxidized milk flavour problem. Implement corrective measures for all weaknesses identified.
7. Once the oxidized problem appears to be under control, arrange to have your bulk tank samples flavoured periodically to ensure that the problem has been truly corrected and doesn't resurface.
Conclusion
Troubleshooting an oxidized milk flavour problem is a time-consuming, difficult task. It requires immediate attention and the full cooperation of regulatory authorities, the extension specialist, the nutrition advisor of the dairy and the producer in order to prevent significant losses resulting from discarded, off-flavoured milk. Oxidized milk flavours are caused by a wide variety of non-nutritional and nutritional factors. By following certain steps, it is possible to return a farm to normal milk shipments with minimal interruption and milk loss. However, many of these steps are only temporary solutions that provide the producer with extra time until longer term corrective measures have had a chance to take effect. No herd is immune from experiencing an oxidized milk flavour problem. It is to the benefit every producer to be aware of what oxidized milk is, which factors cause it and what can be done to correct it if it ever occurs.
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