The Relationship Between Grit and Digestive Disorders in Poultry

December 1948
W.P. Blount
Wednesday, 01 December 1948
By W.P. Blount

Poultry husbandry is such today that considerable confusion and misapprehension are present where the grit requirements of domestic poultry are concerned. As a result large numbers of chickens receive the wrong type, causing ill health and suffering, and in not a few cases deaths occur. Two quotations from the literature will show the confusion present today.

  1. "It is interesting to note that this experiment indicates that limestone grit cannot be regarded as an efficient substitute for insoluble grit". E. T. Halnan (1946).
  2. "Limestone seems amply capable of serving in the dual capacity of furnishing the minerals for eggshell making and for whatever additional service grit may render in the digestive system." W. Ray Ewing (1947).

Two Types of Grit

There are two main types of grit, each different in function –

  1. Insoluble Grit – useful for its mechanical effects in the gizzard
  2. Soluble Grit – valuable for the calcium, which it supplies to the hen, after it undergoes solution in the gastric juices.

Neither of these two types of grit plays any functional part, as such, prior to our succeeding the gizzard proper. They are not, therefore, of any value in crop or intestinal digestion.

Insoluble Grits

The supply of insoluble grit to poultry is generally made by the use of such substances as flint, quartz, granite, gravel, sand, etc.

In certain quarters there is some prejudice against flint as a grit for poultry because of it s shattering, splitting nature (due to its molecular structure) giving too many of its particles an elongated and sharply pointed nature – yet there is no doubt that more flint grit is used commercially in Great Britain than any other, but there is much to be said for the production and sale of a hard and permanent grit (cuboid in shape) and granite or gravel would appear quite satisfactory. Flint grit cost about 9/- a cwt. and the fact that it is available everywhere in graduated sizes helps to make it popular.

Function of Insoluble Grit

When present in the gizzard in reasonable quantities, flint-type grits have two main functions:

  1. to divide and separate food particles so that the digestive, enzyme-like secretions from the proventriculus and the mineral acid of the gizzard can permeate freely.
  2. grinding and crushing.

Both functions (a) and (b) are dependent on normal gizzard motility. When the gizzard contains both solid food particles and grit a "masticating" effect follows. Grass, leaves and grain undergo pulverization, and with each muscular contraction more vegetable cells are exposed to the action of the digestive juices. Foods of animal origin, including the "wings and legs of insect, worms, slugs, snails, fish and meat also break down mechanically under the grinding process described. There is little doubt, however, that as a result of gizzardectomy experiments, whereas this reaction is invaluable to most birds of a graminivorous nature, we now know it is not absolutely necessary for digestion in the domestic hen, and it is certainly unnecessary for certain carnivorous avian species. At the same time, although modern domestic poultry, when being fed on wet and dry mashes, meals and pellets or grains, do not necessarily require insoluble grits for grinding purposes, these substances do aid better food utilization, and therefore may play an economical and indeed important part in poultry husbandry. For example, in the case of young chicks on a diet consisting solely of pellets and water, whilst there is no need for insoluble grit, a proper amount may aid digestion, whereas an excess will cause indigestion. Whilst there is little doubt regarding the former, it is far better to let the chicks do without grit than to risk ill health through mismanagement. It is the regulation of dosage that is the most important factor to be considered.

Soluble Grits

Those in normal use comprise calcium-rich mineral compounds such as limestone, oyster shell, cockle shell, Malton fossils, rock phosphate, etc. Although in some countries there is a strong prejudice in favour of oyster shell grit for poultry, there is little scientific evidence t warrant this and any soluble lime-containing grit is suitable provided it does not contain unwanted or harmful minerals.

Function of Soluble Grits

On the general poultry farm, where the farmer mixes his own rations, lime-containing grits are used to supply calcium both for growth and egg shell formation. But in the case of commercial foods it is generally only the latter function for which soluble grit is required. For growth purposes sufficient calcium is usually added to chick and growers rations in order to balance the Ca:P ration, and this obviates the necessity of giving limestone grit. In practice, however, the giving of soluble grits is frequently recommended for poultry of all ages and with all rations, and results are often disastrous.

Harmful Effects of Flint-Type Grits

For your chicks in particular the use of flint grit ad lib may be fraught with danger, particularly if the total ration is not well balanced. Also if there is a shortage of calcium in the diet, or a wide Ca:P ration or if there is pica from a cause, there may well be an excessive intake of grit. This will be followed by an overloading of the gizzard, and some of the grit will overflow into the duodenum. This passes rapidly to the exterior with the faeces and in many instances a mechanical laceration of the small intestine occurs. Deaths are not uncommon, and ailing chicks show ruffled feathers and stunted growth, but such cases do not occur if the grit is given in restricted quantities at say fortnightly intervals; whereas the giving of flint type grit in hoppers ad lib, or in heaps in the brooder house runs is often dangerous. When the gizzard does not contain an excess of such grit the appetite for dry mashes is reduced, intestinal motility is increased and foodstuffs pass more quickly than normal to the outside. Post-mortem examination findings are of course characteristic – from overloading of the gizzard to the resulting enteritis. As treatment no further supplies of grit should be given for at least one month and then only if subsequent post-mortem findings show that the gizzard is nearly grit free. If cretapreparata 5 per cent is added to the diet for 7 days, its ingestion assists recovery, as also does chlorodyne, in medicinal doses. Once the diet has been corrected it is best to eliminate flint grit from the ration, providing the chicks are being reared intensively and are not being given feeds of grass or green food.

An absence of grit from the gizzard of poultry may lead to no harm whilst the diet contains no grass, otherwise impactions of the gizzard by grass leaves and grain (entwining themselves into a knotted mass) may occur. Portions of the entangled material may pass also into the small intestines, whilst at other times a complete occlusion of the pylorus is a feature of the malady. Occasionally a secondary cause, such as an impaired gizzard motility – possibly of Fowl Paralysis origin – is present. It should be noted that once the gizzard is impacting itself, then the crop also becomes full of additional grass, mash and leaves, etc., which soon turns sour.

On some occasions birds crave for grass, as seen in Pullet Disease, but often there is little or no clue as to the real cause for eating too much grass.

A heavy intake of grass, particularly semi-dried long grasses, may overtax a gizzard even when some grit is present.

Harmful Effects of Limestone Grits

In the writer's veterinary experience much harm is caused to poultry at all ages by a too free use of soluble lime-containing grits. At times, no doubt, the intake has been excessive, caused by a concomitant absence of insoluble grit, but generally speaking it follows its more or less unrestricted use for young chicks – birds in fact which are neither educated to its use, nor have any special need of its contained calcium. Its use ad lib may cause a special form of indigestion call by the writer "Lime Poisoning". D. S. Farner (1943) has shown that the gastric hydrogen ion concentration is reduced significantly by adding to basic rations calcium carbonate in the form of limestone grits, whilst an investigation at the Kentucky Agricultural Experiment Station (1935) has also shown that extra calcium carbonate retards digestion. Doubtless these two pieces of research have a direct bearing on the aetiology of so-called "Lime Poisoning."

"Lime Poisoning"

In the writer's experience this malady is fairly common in Great Britain, due solely to the indiscriminate use of limestone as a so-called complete grit from hatching onwards.

Clinically, lime poisoning is characterized by a heavy culling rate, particularly in growing stock which should be on the point of lay; affected birds are "light" when handled and a general inspection of the droppings of the flock shows the passage of undigested food. (The limestone grit is, of course, in full evidence throughout the pens, and is available ad lib.) Post-mortem findings show semi-impaction of the gizzard; a catarrhal enteritis of the duodenum, which becomes more acute in the jejunum and is associated with the passage of grossly undigested food. Particles of wheat or maize add grass fibres may be clearly recognizable at all lengths of the gut. The exterior of the duodenum is often characterized by diffuse haemorrhages, but they are often limited to the muscular and sub-peritoneal layers. A characteristic yellowish pigmentation of the duodenal mucous membrane is often present, while the jejunal contents are frothy and clear. Intestinal parasites are secondary and variable. Manifestations of Fowl Paralysis, in one or more of its common forms, are also to be noted on certain occasions. During the past 15 years the writer has achieved considerable success in a number of instances in checking Fowl Paralysis by ensuring that once the diet is balanced no limestone grit is given until the birds are in full production.

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