A collection of articles that are relatively short compared to the large blocks of text that I usually write.

The grinding power of the gizzard

The digestive tract of birds is very different from that of humans - it performs the same basic functions but doesn't always do it in the same order or in the same way. Birds don't have teeth, and many species have a holding pouch called the crop at the base of the throat (esophagus).  The stomach of a bird is different from humans too - it's a two-part organ consisting of a proventriculus that secretes digestive chemicals and a ventriculus that grinds up the food. The ventriculus is commonly called the gizzard, and all birds have a gizzard (contrary to what some people may tell you on the internet).  After food leaves the gizzard it progresses to the intestine.  Some bird species have side pouches called ceca extending from the intestine to help with further digestion, but parrots do not.

The gizzard is a muscular organ lined with hard koilin plates, which protect the walls of the gizzard and help with food grinding. Birds can keep stone and other hard materials (grit) in the gizzard to help with the grinding, but they can also process their food effectively without it.  See the Grit article for more information on the subject. 

A bird's gizzard is much more efficient at grinding up food than human teeth are. Perry reports that "the gizzard has a remarkable ability to grind all organic constituents of feed to a very consistent particle size range regardless of the original size of the feed, with some ground as finely as 0.05 mm".

This is smaller than the particles in many flours made for human consumption. 0.05 mm is 50 microns. I've seen sources saying that the most pleasing particle size for flatbread flour is 100 microns or less. The best particle size for noodle flour is 250 microns, and some flours are considerably coarser than that. Human hair ranges from 30-100 microns in diameter (Shopify).

Hetland et al did find some differences in feeding chickens ground grains versus whole grains, but the particle sizes they found in the gut were all within the range of particle sizes for milled flour made for human use.

The available studies were all on poultry of course. Do parrots and other pet birds grind their food as small as chickens do?  We don't know for sure, but the available evidence suggests that they do. The proof is in the poop. Parrots eat a lot of foods that are hard for humans to chew well, like sunflower seed and nuts. Humans will pass noticeable undigested chunks of these foods out of the body.  But parrot poop isn't usually chunky - it's smooth and uniform like it was pureed in a blender. The birds don't chew their food well before they swallow, just break it into bite size pieces. The gizzard mashes it up and turns it into the smooth blend that comes out the other end.

It's possible that the average parrot diet is not as hard as the average chicken diet (assuming that natural foods are being fed in both cases rather than some kind of pellet). But it's not unusual for parrot mixes to contain some of the same foods that are fed to chickens, like dried corn kernels and whole grains of wheat. Many chickens are given the opportunity to eat grit to help with grinding, while many pet parrots are not. Parrots have the ability to remove the hulls from seeds before eating them (although they don't always bother with small seeds). Chickens don't have this ability, potentially increasing the work load for their digestive tract. 

But in any case, the gizzard is like any other muscle.  It adjusts its size and strength to meet the demands that are made on it. Based on the texture of their output, it looks like parrot gizzards are very effective at reducing all the food they eat to a fine mush.   

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The glycemic index

The glycemic index is a measure of how quickly a specific food makes blood sugar rise. A higher number means a faster rise, with pure glucose (a type of sugar) given a value of 100.  The glycemic index is directly related to the amount of carbohydrates in a food, especially simple carbohydrates (sugar). It's also related to how quickly your body can process the food and convert the complex carbohydrates into simple carbohydrates.

It's an imperfect measurement however, because blood sugar changes in the real world will be affected by any other foods that you eat at the same time.  Drinking a sugary beverage on an empty stomach will give you a quick spike in blood sugar.  Using that same beverage to wash down a high-protein high-fat meal (like a burger and fries) will not give the same results.

The glycemic load measures the total amount of carbohydrates in a food. A food with a high glycemic load contains more carbohydrates than a food with a low glycemic load.  But there's a tradeoff here. In any food, the carbs+fat+protein = 100% of the calories. The food with the lower glycemic load has more fat and/or protein than the one with the higher glycemic load.  Trading carbs for protein is generally not a bad thing, but trading carbs for fat can be bad because a gram of fat has twice as many calories as a gram of carbs. 

For years we have been told that we humans must pay careful attention to the GI, and avoid high-GI foods to protect our health. But now questions are being raised about whether the GI actually matters for anyone but people with certain health conditions like diabetes (Reuters). And it's not considered to be all that important even for people with diabetes (Diabetes Forecast).

The GI concept is sometimes extended to birds, with owners being told to avoid giving their birds foods made with flour (like bread) because of flour's high GI. But the importance of the GI is even more dubious for birds than it is for humans. As explained in the Gizzard article above, it looks like birds in general grind all their food as fine as flour before the main digestion process begins. As far as their intestines are concerned, everything they eat is made of flour. But it takes some time for birds to grind up hard food. So when the bird eats intact whole grains and grinds them into flour, the food is expected to reach the intestine more slowly than grains that were turned into flour before the bird ate them.

Birds have a good reason for grinding their food so finely: small particles can be digested a lot faster than bigger chunks. The energy demands of flying are VERY high, and birds have a faster metabolism rate than humans even at rest.  Food needs to have a fast transit time through the body to provide fast energy, and also not weigh the bird down unnecessarily while it's flying.  Lafeber's avian nutrition glossary defines Mean Retention Time as

According to Clench & Mathias, the transit time for most wild birds is 12 minutes to 12 hours depending on species, with some penguins taking up to 22 hours.  For the Birds DVM says "Transit times vary by the size of the bird with smaller birds having a faster transit time. Most medium sized parrots will take less than 4 hours to pass ingested food." (It's under X for X-ray).

Compare this high rate of speed to the average transit time for healthy humans of 39 to 51 hours, with 2.5 to 5 hours of that time spent in the stomach alone. (VIVO). Carbohydrate digestion occurs in the small intestine not the stomach, and many birds can process food all the way out of their body while humans are still in the first phase of digestion. There's obviously a big difference in the way birds do it versus the way humans do it, and for all we know a high GI might be desirable for birds.

Certain products made with flour are undesirable for reasons that are not related to their GI.  Some birdie bread recipes are undesirable because they are high in fat, and products made with refined white flour are undesirable in general because white flour is less nutritious than whole grain products.

But this doesn't mean that all products made with flour are automatically bad, and some may not have a high GI whether they're good or bad. Pellets are made from ingredients that have been ground into flour, and they're generally considered to be very beneficial (see Pellet article for more info). They're not expected to behave like a high GI food because of their protein and fat content. The better birdie bread recipes are not high in fat and sugar, and contain a substantial amount of protein.  Pasta products in general have a fairly low GI, even though the flour in them may have been refined considerably (University of Sydney).

But relevant or not, here's some information on the glycemic index and glycemic load of commonly used whole grains and the flour made from those grains. Soy is included too, since it's frequently used in pellets. Enriched white flour is thrown in for comparison purposes. Pretty much everything but the soybeans has a high rating for both GI and GL.

Glycemic index: Low=1-55, Med=56-69, High=70+ Glycemic load: Low=1-10, Med=11-19, High=20+	Glycemic Index		Glycemic Load
	Intact grain	Flour	Intact grain	Flour
Yellow corn	??	70 (DC)	45 (ND)	48 (ND)
Wheat	??	69 (DC)	35 (ND)	36 (ND)
Enriched white flour	N/A	85 (DC)	N/A	53 (ND)
Soybeans	??	25 (DC)	10 (ND)	13 (ND)
Millet	??	71 (DC)	44 (ND)	??
Oats	??	44 (DC)	37 (ND)	??
Hulled barley	??	53-66 (DC)	35 (ND)	42 (ND)

A note on "whole grain" labeling:  It's sometimes said that if a product in the US is labeled "whole grain" rather than "100% whole grain", then the bran/germ of the grain might actually be missing.  But this would violate the FDA guidelines (AACC), which say that:

In other words, you can't call something whole grain unless it's actually made with grain that has not had any part removed. If it doesn't say "100% whole grain" then it's possible that some of the grain in the product is not whole. But the FDA takes a dim view of deceptive advertising, and you are risking their wrath if you label something as whole grain without having a significant amount of whole grain in your product. All the grain in the product may have something missing if the word "whole" doesn't appear at all.

The Whole Grains Council advises manufacturers to use the words “whole grain” in the name of a product only if the product contains more whole grain than refined grain (meaning that at least 51% of the grain is whole grain). They also explain that the FDA only allows statements on the label about the health benefits of whole grains if the product contains at least 51% whole grain by total weight of ingredients (including the water/moisture in the total), and the whole grains in the product contain at least 11% fiber.

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Lutein and zeaxanthin

Lutein and zeaxanthin are yellow-colored pigments called xanthophyll carotenoids.  They have important functions in the body, and are even more important to birds than they are to humans. The USDA lumps both of them together for reporting purposes, so it’s hard to get information on them individually. But they are not interchangeable with each other. Their chemical makeup is similar, which may have made it hard to tell them apart at one time, but that problem has apparently been solved now and it is possible to find studies on one or the other individually. The body can not produce carotenoids and must obtain them from the diet, but a recommended daily intake for lutein and zeaxanthin has not been established for either humans or birds. The poultry research on lutein and zeaxanthin is focused on giving egg yolks and meat an appealing color, not on meeting the birds' nutritional requirements.

Cohen et al report that

This makes sense because the xanthophylls (especially lutein) are the primary carotenoid in dry seeds including grains, which are a big part of the diet for many bird species. Birds put these carotenoids in their egg yolks to help protect the embryo, and the L+Z in egg yolks is what makes them look yellow. Studies indicate that the level of these carotenoids in the yolk has an impact on breeding success (Bird Coloration Vol 1 page 203, 205-206, 223). Table 1 of Sommerburg et al indicates that egg yolk has a lutein: zeaxanthin ratio of 60:40.

Birds that use carotenoid coloring in their feathers get their yellow coloring from lutein and zeaxanthin (Bird Coloration Vol 1 page 512). Parrots make their own yellow pigment and don't rely on dietary carotenoids for this purpose, but they have approximately equal amounts of lutein and zeaxanthin circulating in their bloodstream at the time of feather growth (McGraw & Nogare). Birds can store excess lutein and zeaxanthin in their bodies, with a preference for zeaxanthin (Phelan, McGraw et al).

Surai et al report that the concentration of L+Z in the blood, skin, and yolks is correlated to the amount in the diet (pg 12-16). So the papers listed above may be more of an indication of what the birds were eating, rather than how much L+Z they actually need. Carotenoids stored in the body can be liberated for use in yolk (pg 17). Chicken eggs contain almost no beta carotene, and their carotenoid content is almost exclusively xanthophylls (pg 19). Pages 9-11 talk about the absorption rate of carotenoids, which is rather low.

Lutein and zeaxanthin are the only carotenoids that accumulate in the retina of the human eye, where they help to filter damaging blue light.  Zeaxanthin has been called “the most prevalent macular pigment” for humans (Sommerburg et al page 909). Birds have high concentrations of carotenoids in their eyes, including colored oil droplets (something that humans do NOT have). The yellow droplets contain zeaxanthin (Stavenga & Wilts).

Sources of L+Z

Lutein is plentiful in green vegetables, and almost any leafy green vegetable will be an excellent source of it. The chart at left shows that many leafy vegetables contain large amounts of lutein while having no zeaxanthin at all, or a very small amount.  Zeaxanthin is a lot harder to find than lutein, and this is why the combined reporting of L+Z is so frustrating. It takes a special effort to find out which foods are good sources of zeaxanthin, and for many foods we still don't know the breakdown between L and Z. The main sources reporting the zeaxanthin levels in a variety of foods are Sommerburg et al, Perry et al (see Table 3 for corn, Table 4 for egg, and Table 5 for fruits and vegetables), Sajilata et al (Table 2), Abdel-Aal et al (Table 1), and Arimboor et al (Table 1).

Sources of Zeaxanthin

The chart on the right shows foods in order of their zeaxanthin content.   Orange peppers appear to be an outstanding source of zeaxanthin, while red peppers may or may not be; the levels reported for them are extremely variable, with some very high scores and some very low scores. Arimboor et al says that “The wide variation in the carotenoid composition in same species [of peppers] in different reports may be attributed to the variations in agro climatic and post-harvest conditions and/or limitations in analytical methods”, and it also says that there are some problems with the measurement techniques. It looks like goji berries may be the world's best source of zeaxanthin, although the information is sparse (Lam, Niro, Weller), and the numbers that are being reported are so high that it makes me wonder if the berries have some characteristic that throws the measurements off.

Although there are vegetables that have much higher levels of either lutein or zeaxanthin, corn is the best overall source for getting a good balance of both at the same time. Table 1 of Sommerburg et al shows that the both the quantity and the proportion of lutein to zeaxanthin in corn is strikingly similar to that of egg yolk, and this proportion is also roughly similar to that in the bloodstream of parrots (McGraw & Nogare).

NutritionData says that 100g of feed corn has 1355 mcg of L+Z and 100g of egg yolk has 1094, confirming that the combined totals are fairly similar. What this apparently means for an egg-laying hen is that she'd need to eat an amount of corn that’s approximately the same size as the egg yolk to get enough L+Z to put in the egg yolk. For small birds like cockatiels, the egg yolk is about the same size as a kernel of corn. That’s nice and tidy, isn’t it? This doesn’t tell us anything about how much L+Z is needed to meet the need in the rest of the body, but at least we know how much it takes to supply an egg.

Corn and zeaxanthin

Corn is a major ingredient in many "complete" pellets, so they are an easy way to provide a steady supply of lutein and zeaxanthin. Only one pellet company (Lafeber) reports the amount of L+Z in their product. It ranges from 6.79 to 9.04 mg per kg depending on which pellet you get. They don't tell us how much is lutein and how much is zeaxanthin, but based on what we know about the ingredients, it seems likely that it's about half and half. 

Zeaxanthin in grains and legumes

Vegetables have more L+Z than other foods so they get most of the attention.  But there are several grains and beans/legumes whose L+Z content has been studied (Abdel-Aal, El-Qudah,  Hussain, Kaliyaperumal 1, Kaliyaperumal 2, Kanemaru, Lamberts, Lee, McGraw, Monma, Paznocht, Seguin, Tang, Taylor, Yano, Zhang 1, Zhang 2). These are "mainstay of the diet" type foods that will make a slow but steady contribution.  Combining grains with beans/legumes is the best way to provide an adequate amount of protein (see Protein article), and getting some additional L+Z from the combination is a nice bonus.

What happens to L+Z when food is cooked?  It looks like cooking causes some loss of xanthophyll content but increases its bioavailability, which often results in a net gain (Chung, Eisenhauer, Granado-Lorencio, Nimalaratne, Wang). The USDA database frequently shows a higher level of L+Z for cooked vegetables than for the same vegetable in the raw state (NutritionData table). But they don't take water loss during cooking into account, which may be an important factor.

Chopping up raw food is another way to increase the bioavailability of the L+Z for humans (Oregon State, Nolan et al). But the grinding power of a bird's gizzard may be all the "chopping" that is needed for birds.

What about using egg yolk as a source of L+Z?  It's not a good idea to feed a lot of egg yolk to birds because it's high in fat and cholesterol, and that can cause problems (see the Protein article for more information). High-xanthophyll plant foods are a healthier choice.

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Salt

The pet bird community's basic advice about salt is to never, ever let your bird eat anything that contains the slightest amount of added salt.  But let's take a realistic look at the issue.

Sodium and chlorine are both essential nutrients.  The Expert Panel on Companion Bird Nutrition recommends that each should be 0.12% of the diet, for a combined total of 0.24%.  Ordinary table salt (aka sodium chloride) contains an equal amount of each, for a perfect balance.  Plant foods in general don't provide enough salt to meet the recommendation, so pellet companies add salt to their product to bring the amount up to an acceptable level.  If you read the ingredient list you will see it there. Page 256 of Klasing agrees that this is appropriate, saying, "Supplementation of sodium and chloride is usually accomplished by providing common table salt (NaCl)". 

So how much is 0.24% of the diet? The Expert Panel recommends that food have an average of 3700 calories per kg.  0.24% of this is 2.4 grams per kg, or 2.4 milligrams per gram of food (it's not clear whether this is dry matter or nutrient-dense food). It can also be expressed as 0.65 milligrams per calorie.  You can estimate your bird's calorie requirements using the chart in the Calories article.

Too much salt is dangerous of course - salt toxicity is a very real problem.  But how much is too much?  Surprisingly, the Expert Panel didn't set a safe upper limit for salt, and neither did any other source that I looked at.  Instead, all sources indicate that the availability of fresh, salt-free water is a critical factor in determining how much salt is toxic, because the birds can use increased water consumption to compensate for increased salt consumption.  Klasing page 255 says that Ringneck Pheasants and Bobwhite Quail can tolerate a diet of 5% salt - a HUGE amount - by increasing their water consumption and urine production.  Juveniles are more sensitive according to Klasing, and the Merck Veterinary Manual says "Wet mash containing 2% salt has caused salt poisoning in ducklings. High salt content in wet mash is more likely to cause poisoning than in dry feed, probably because birds eat more wet mash.  Remember that fresh, nonsalty drinking water is essential to regulating the salt level in the body when a lot of salt is eaten. " They also say that chickens can tolerate up to 0.25% salt in their drinking water but are susceptible to salt poisoning when water intake is restricted.

Clinical Avian Medicine says "Salt glands are present in almost all birds." Salt glands help birds eliminate large amounts of salt safely without involving the kidneys, but these glands aren't functional in all species. The birds with functional salt glands are mostly seabirds who drink seawater for hydration, ducks and geese that can alternate between freshwater and saltwater habitats, and desert birds who need to eliminate excess salt, retain water in the body, and cope with high temperatures all at the same time. There's no information on whether any parrots have a functional salt gland, but some do come from arid habitats where a salt gland might be useful.

The only information I could find on parrots is from Beaufrere et al, who indicate that parrots have slightly higher levels of salt and other electrolytes in their bodies than mammals, and different studies show conflicting results on whether there are differences between parrot species. They also said,

Feeding Your Pet Bird (written by a veterinarian) says, "water deprivation can promote salt toxicity; if water is freely available it will take high levels of salt to cause salt toxicity, however, if water is restricted, lower levels of salt can have toxic effects". It also says, "The occasional grain of salt is not harmful, provided your bird always has access to plenty of fresh water" but warns against letting your bird eat a lot of salt.

What about non-lethal amounts of salt?  For humans, the main health concern with salt is its effect on blood pressure.  But it looks like the risks may have been seriously overstated (Scientific American, New York Times, CEI).  Does increased salt intake affect the blood pressure of birds?  I don't know.  There are studies showing that bad things happen when you put lots of salt in the drinking water of birds, so that they can't use fresh water to self-regulate (Stamler & Katz, Mirsalimi et al, Dawson et al).

But I couldn't find a study or medical book reporting what happens to a bird's blood pressure when you give it lots of salt AND all the fresh, salt-free water that it wants. Bird kidneys and their way of dealing with salt are fundamentally different from mammals (Schulte et al), so they may not respond the same way. Brummermann & Simon found that Pekin ducks actually lowered their blood pressure in response to increased salt intake.  But these are salt-adapted birds, and parrots may have a different reaction.

If you're wondering how you check a bird's blood pressure, Lichtenberger has information and pictures.

Note: There's a delicate balance between sodium, chlorine, and potassium, and more of one means that we also need more of the other two. So increased consumption of sodium chloride increases the need for potassium.

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Turmeric

Turmeric is frequently promoted as a wonder drug for people and their pets including birds. A compound in turmeric called curcumin may or may not have real anti-inflammatory properties - the research is still ongoing for that. There are some potential side effects too, but turmeric also comes with hidden risks that have nothing to do with the spice itself.

Contamination issues. There are significant problems with contamination and adulteration with turmeric and imported spices in general. People who use turmeric for medical reasons and believe they're getting good results from it might want to see if they can buy the root and chop/grind it themselves instead of buying turmeric powder. The root is likely to have fewer contamination issues than the powder. It's possible to find it in U.S. stores sometimes, particularly natural grocery stores.

It's estimated that 80-90% of the world's turmeric is produced in India, which also accounts for 60% of the turmeric exports. Most of the rest comes from Pakistan, China, Haiti, Jamaica, Peru, Taiwan, Bangladesh, and Thailand. There's no indication that the US, Europe, and Australia produce any turmeric at all, so it should be assumed that all turmeric in these places was imported from countries with major quality control problems. (Aaditya, Turmeric)

There have been several recalls of turmeric in the US and other countries due to lead contamination. Many sellers illegally add lead chromate to turmeric to artificially enhance the color. This is prohibited in India but a study by the Indian Council of medical Research said that 99% of their samples were contaminated with lead, and about half were also contaminated with arsenic and/or cadmium (The Tribune).

Lead is toxic and it does build up in the body over time, so if you and your bird are regularly consuming lead-contaminated turmeric, you could end up with lead poisoning. Cadmium also accumulates in the body. Arsenic can accumulate in hair and nails but doesn't accumulate appreciably in other body parts.

Metanil yellow - another substance banned in India - is also frequently used as a coloring agent. Studies that fed it to rats showed a significant effect on brain chemistry, and the changes were not reversible in growing rats (Nagaraja & Desiraju).

It's also common for turmeric to be adulterated with more benign substances like chalk, sawdust, or rice powder. If you're into home chemistry, there are websites like the Epicurean Digest and Turmeric for Health telling you how you can test your turmeric for purity.

An FDA study found that 12% of imported spices in general were contaminated with insect parts and rat hair (FDA). The report says that the rat hair is a sign of fecal contamination - the rats groom themselves and excrete the hair in their feces. 7% of the samples were contaminated with salmonella. Imports from India tied with Mexico for the highest rate of overall contamination (New York Times, Scientific American).

The Indian press reports that the curcumin in turmeric may encourage the growth of salmonella (Zeenews).

Effectiveness issues. There have been a number of very promising early results from studies showing that curcumin (the active ingredient in turmeric) may have anti-inflammatory effects.  But this early promise has been largely derailed by a study finding that curcumin is the type of substance that gives a lot of false positive results - researchers call these substances IMPS and PAINS (Nelson et al). The abstract says "This manuscript reviews the essential medicinal chemistry of curcumin and provides evidence that curcumin is an unstable, reactive, nonbioavailable compound." Science Translational Medicine goes into more detail about the low bioavailability and high instability of curcumin. NeurologicaBlog says that with substances like this, "the preclinical and preliminary studies are a horrible guide to actual clinical effects."

From the National Center for Complementary and Integrative Health (which exists to find out which 'alternative' remedies actually work and integrate them into mainstream medicine): "Claims that curcuminoids found in turmeric help to reduce inflammation aren’t supported by strong studies." This is an old statement, and the site apparently hasn't been updated to reflect the more recent finding that curcumin's bioavailability is so low and its chemical volatility is so high that it's unlikely to have any effect.

It's likely that most if not all of the preliminary studies with positive results were using a refined medical-grade curcumin extract, not ordinary turmeric that you can buy at the grocery store.  This is expected to have a considerable effect on the outcome, even if curcumin was not an "IMPS and PAINS" kind of chemical.

The bioavailability issues with curcumin were known for a long time before the Nelson study was issued. A mixture of turmeric, black pepper, oil, and water called Golden Paste is frequently hyped as a way to avoid this problem. The pepper is supposed to boost the bioavailability of the curcumin by 2000% (Shoba et al), but this is based on a single paper published in 1997 so we can't be sure that it's actually correct. The study used purified extracts not the actual spices.

The alleged anti-inflammatory effects of turmeric hasn't prevented rheumatoid arthritis and osteoarthritis from being major public health problems in India (the world's largest consumer of turmeric), with the same disability rate as the US (Times of India, Tucson.com).

Turmeric is generally considered safe when it's not contaminated with nasty stuff, but it's not risk free. Science-Based Medicine says

High doses are what's recommended for treating arthritis and other problems, so it could be an issue.

There are large numbers of people who swear that turmeric has helped them and/or their pets, but this could be an example of the placebo effect. An animal has no expectations about what turmeric will do for them of course, but giving unproven medical treatments to an animal can affect the perceptions and behavior of the owner, which in turn can affect the behavior of the animal.

In most cases there's no reason to give turmeric to a bird. It's considered to be a spice not a food in the sense of having a lot of nutrients. If you've got a bird with arthritis and you think that turmeric makes a visible difference in the bird's comfort level, then you need to consider whether it's worth the risk. But it doesn't seem like a good idea for a healthy bird.

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Wikipedia: Water memory - a description of the Benveniste water memory studies, which established that water remembers when proper scientific procedures are not followed, and forgets when proper procedure IS followed.

The SkeptVet - information on the dangers of veterinary use of homeopathy.