A number of poisonous plants have a considerable influence on the milk yield of animals which eat them, reducing it in volume or in fat content, or imparting to it an unpleasant flavour which renders it unfit for human consumption, and even affecting the butter made from it. Other plants not actually poisonous also affect milk by “tainting” it, and must therefore be considered harmful otherwise than as mere weeds. Still others affect milk by causing it to be stained with blood, and in some cases the toxic principle of the plant concerned is even stated to have rendered the milk poisonous. It will be useful to give here a brief account of milk-affecting plants, though it is probable that there may be others which are not mentioned.

The plants best known in this connection are the Garlics (Allium oleraceum L., A. ursinum L., A. vineale L., and others), which impart to milk a strong “oniony” flavour. These plants also seriously affect the flesh of animals which eat them, even rendering it unfit for consumption. A case came before the author several years ago in which a considerable number of sheep had eaten a quantity of Allium ursinum, which was growing in a field in which they had been grazing for some days. The meat was so strongly tainted that, as the owner (a butcher) stated, it was quite unfit for sale. The only thing to be done was to pasture the sheep elsewhere for a time.

Pott notes that species of Ranunculus give rise to reddish or bitter milk (Mölkereizeitung, 1897), while Caltha palustris causes loss of milk production in cows.

Ranunculus repens imparts a strong unpleasant flavour to the milk of cows that have eaten it, and the butter made from such milk is distinctly bitter in taste (Güssow).

Ranunculus sceleratus causes a falling-off in milk-yield. (Cornevin.)

Alliaria officinalis Andrz, imparts an oniony flavour to milk.

Achillea Millefolium L. is stated to impart its bitter taste and strong odour to dairy products when eaten by cows. It contains an alkaloid, Achilleine (C₂₀H₃₈O₁₅N₂) having a peculiar odour and bitter taste.

Chrysanthemum Leucanthemum has also been suspected of imparting a bad flavour to butter.

According to Pott the milk of cows eating Oxalis Acetosella is with difficulty converted into butter.

The poisonous principle of Colchicum autumnale is stated to find its way into the milk of animals consuming it, and Müller states that the milk of goats which have eaten it has caused the poisoning of infants.

Müller states that a cat died after drinking the milk of a cow suffering from poisoning by Narthecium ossifragum.

Mercurialis annua is said to cause milk to be thin, “blue,” and poor in fat; while in a case already mentioned (p. 68) M. perennis entirely stopped the secretion of milk.

According to Chesnut, goats may eat quantities of Euphorbia Lathyris, and it is said that their milk then possesses the poisonous properties of the plants. Ingestion of other Euphorbias appears to have the same effect.

Cornevin remarks that Melampyrum arvense is considered to influence cows to produce more milk.

According to some authorities species of Equisetum check milk production or cause it to cease, and E. palustre is stated by Weber to cause the milk of affected cows to become watery, poor in fat, and give rise to a greasy and unappetising butter, while the yield may soon quite fail.

The ingestion of the foliage of the oak (Quercus sp.) is stated by Cornevin to induce Maladie des Bois, with reduction or entire loss of milk production (see p. 69). Acorns have also affected milk production, and a case is recorded (The Dairy, 1913) in which it is stated that cheese made from the milk of cows which had fed on acorns developed a sharp acid flavour when about four weeks old, though the texture was good. It is not clear, however, how it was proved to be due to the acorns.

In one case recorded a reddish tinge was observed in the milk of a cow suffering from Rhododendron poisoning (p. 46), and in general reduced milk production appears to occur.

In addition to the foregoing, there is good authority for saying that the following plants may impart a disagreeable flavour to milk, and in many cases the butter made from it:—

PLANTS WHICH CAUSE MECHANICAL INJURY.

There are a number of plants which, while not necessarily physiological poisons, may induce injuries of a severe character when taken by animals, and by causing festering may bring about septic poisoning. For example the sharp pointed fruits of Stipa pinnata and Nardus stricta may cause injury to the skin and mouth, piercing the palate and causing inflammation, and when eaten may even perforate the wall of the intestine and cause death; and the awned glumes of species of Bromus or the spikelets of Hordeum may injure the gums, causing inflammation, ulceration, sores, the formation of pus, and loss of teeth. The Bromus and Hordeum, also, together with over-matured “heads” of Trifolium incarnatum, may give rise to Phytobezoars or balls in the stomach of horses and cattle (60, 119). The sharp pointed fruits of Erodium cicutarium may cause local irritation by working into the wool of sheep. Aira caespitosa may also cause injury to the mouth of stock.

A case is recorded in New South Wales in which cattle and horses ate Shepherd’s Purse (Capsella Bursa-pastoris). The cattle were unaffected, but the horses scoured, though most of them soon recovered when removed from the cultivated paddock containing the weed. Two young horses, however, showed signs of colic, became bloated, and died. It was then found that they contained balls of fibrous material (one weighed 1 lb. 9½ oz.) which consisted to the extent of nearly 50 per cent. of fibres from Shepherd’s Purse, and death was due to simple mechanical obstruction of the bowel (155).

Chickweed (Stellaria media) has been found to cause digestive disorder in lambs and sheep when eaten in large quantities (48), and has caused the death of many a lamb. It would appear to be due entirely to the formation of large lumps of the weed in the stomach, and subsequent fermentation (Farmer and Stockbreeder, Mar. 16, 1908).

According to Cornevin, Black Bindweed (P. Convolvulus L.) may prove injurious, owing to the occurrence of the hard, trigonous, and pointed “seeds” in cereal grains. Galtier published facts which show that oats which contain too many of the “seeds” may, by prolonged use, occasion a more or less serious enteritis, which is sometimes fatal, particularly when the grain is fed to greedy horses which scarcely grind their food (73). The fruits or “seeds” of Knot-weed (Polygonum Aviculare L.) may similarly prove injurious, and probably the seeds of other plants.