When a pigeon is flying, in a long race that is, is he digesting food as he flies or is he living on food stored in his liver and muscles? Have you ever felt the crop of a bird just home from a 500-mile race? Then you know that he does digest food while flying. Since this is so, what should our birds be fed which will furnish the most food in the smallest amount of bulk? Foods rich in protein, carbohydrates, or fat? Since every gramme of fat burns into 21 times as much energy as I gramme of either protein or carbohydrate, it would seem sensible to provide high fat foods.
But we must remember that the pigeon has a great deal of fat stored in his body, and sugar too, in liver and muscles. For short races these are sufficient. Perhaps an investigation of the foods which have been fed to human athletes or to dogs which are called upon for long, gruelling periods of exertion, will help in determining the answer.
Lumberjacks use so much energy in their work that some eat six meals a day. Their food is greasy to such an extent, that persons on a sedentary diet would become nauseated from the high percentage of fat. They consume large amounts of sugar for quick available energy. Marathon runners use fat and sugar.
The experienced hunter, whose foxhounds often run for 24 or more hours at a stretch, learned long ago that a high-fat diet keeps hounds running and builds them up more quickly after the chase than any other kind of food. The sled-dog driver feeds his dogs pemmican, which usually contains about 70 per cent fat, and these dogs pull heavy loads for hours at a time.
Protein, of course, is necessary because it repairs muscles, but fat releases the most energy per ounce, and for that reason should be the kind of food chosen for the long races. Here, for example, are two grains: peanuts and maize. Suppose a pigeon eats 25 grammes (a little less than I oz.) of either one. Which would supply the most energy?
Peanuts with 30 per cent protein, U .6
per cent carbohydrates, 47.5 per cent fat.
Maize with 9.3 per cent protein, 70.3 per cent carbohydrates, 4.3 per cent fat.
One hundred grammes of peanuts would have 41-6 grammes of protein and carbohydrate combined:
41-6 x 4 = 166-4 calories
Fat 47-5 x 9 = 427-5 calories
Total 539.9 calories
One hundred grammes of maize would have
79-6 grammes of protein and carbohydrate combined:
79-6 x 4 = 318-4 calories
Fat 4-3 X 9 = 38-7 calories
Total 357 1 calories
Thus, a cropful of peanuts would supply our 500-mile flier with 563-9 units of energy vs. 357-1 in a cropful of maize.
This is not to say that peanuts make the ideal racing food. There may be reasons why they are not, but the comparison indicates that we can, by thought and action, help our birds sustain themselves by what we feed them. Perhaps mixtures of high fat foods are the answer. For one day's racing we need not be concerned with vitamins, amino acids and other essentials. Racing takes energy and the essentials beyond that can be supplied before and after the race.
In long-distance races the food in the bird's crop is that fed them in the baskets. What is fed in the last meal in the loft before the pigeons are basketed will last no more than over night. Therefore, the food fed the pigeons in the basket must be food which all the birds have been trained to eat, and thus no one has an advantage from his study of nutrition, unless he can find a way of feeding which will load his birds with stored nutrients.
What is the quickest way to fill the storage capacity in the liver and muscles? Obviously, the way is to feed enough protein, which need not be more than 14 per cent, and see that the ration is high in fat and that it contains a reasonable amount of carbohydrates. Some maize and a fairly high percentage of oily seeds should suffice.
You may see a list of digestible calories in various foods and wonder at the discrepancy in your own calculations. But you need not wonder if you will remember that some of the food eaten is not digestible. At the present state of our knowledge, it is not possible to present a table showing the digestible calories for all species. Most of the tables available show the percentages which cattle can digest. Some tables have been worked out for dogs and human beings, but neither of these species can begin to extract the amount of nourishment from foods which cattle can, because cattle can digest much of the fibre.
To compute digestible calories for pigeons, the fibre must be subtracted from the total carbohydrates and, even then, not all of the remaining carbohydrate is digestible. It is a safe rule to figure the digestible protein and carbohydrate about 10 per cent less than the total.
In some tables one reads 'nitrogen-free extract'. This need not confuse one either if one remembers that protein contains nitrogen. The fat is removed and measured and the elements left are protein and carbohydrate. The element left after the protein is removed and measured is the extract, free of nitrogen: nitrogen-free extract or carbohydrate. Subtract the fibre from this and one has the total of starches and sugars, most of which is digestible.
One study on pigeon digestion in which a variety of ingredients were investigated, showed that pigeons could digest almost all of the starch in the foods, but the ability to digest non-starch carbohydrates ranged in percentage from 7 to 49. Protein digestion measured from 78 to 95 per cent, and fat from 62 to 100 per cent, depending on the food.
We must not draw conclusions about pigeon digestion from the results obtained from studying the same processes in chickens. Pigeons digest fat and protein better than chickens do, but chickens can utilise fibre and nitrogen-free extract better than pigeons.