Raw Milk and Other Safety Issues

Few topics elicit such heated discussion among goat own­ers as the raw versus pasteurized milk controversy. People who have drunk raw milk all their lives or whose babies returned to good health after being switched from cow to goat milk find it hard to believe that such a “natural” food should be anything but healthful.

Zoonotic Diseases

Many industrialized countries have regulations requiring pasteurization of milk to be sold unless very stringent sanitary requirements are adhered to. These laws were generally formulated in an attempt to prevent human infection with brucellosis or tuberculosis. In regions where those two diseases have been eradicated, the laws seem, to the layperson, quite antiquated. In the mean­time, however, an ever-growing number of additional infectious agents have been isolated from goat milk (Pritchard 1987; Klinger and Rosenthal 1997). These are listed in Table 14.2.

Supporting references for acquiring these conditions from goat milk products include the following: brucel­losis (Stiles 1950; Renoux 1957; Young and Suvannoparrat 1975; Wallach et al. 1994; Vogt and Hasler 1999; Wyatt 2005; Gupta et al. 2006), caseous lymphadenitis (Goldberger et al. 1981; Schreuder et al. 1990), listeriosis (Loken et al. 1982; Tham 1988; Azadian et al. 1989; Eilertz et al. 1993; Abou Eleinin et al. 2000), louping-ill (Reid et al. 1984) and other tick- borne encephalitis diseases (Heinz and Kunz 2004; Balogh et al. 2012), melioidosis (Olds and Lewis 1954), Q fever (Caminopetros 1948a, 1948b; Ruppanner et al. 1978; Fishbein and Raoult 1992; Hatchette et al.

E. coli (McIntyre et al. 2002), salmonellosis (Jensen and Hughes 1980; Galbraith et al. 1982; Desenclos et al. 1996), and yersiniosis (Hughes and Jensen 1981; Walker and Gilmour 1986). Many more recent reports have been published.

Many of these diseases are not serious in immuno - competent, healthy people. Chronically ill babies, old people, pregnant women, people receiving cancer ther - apy, and those infected with the acquired immune defi­ciency syndrome (AIDS) virus are less able to withstand infection with these agents. Goat owners wishing to avoid legal or moral responsibility for illness in their milk-drinking customers should continue to pasteurize, or at the very least explain the need for and method of pasteurization of the milk they sell. The American Veterinary Medical Association has taken a stand against the use of raw milk (Summers aιnd New 1^cJ8^5^), as have the US Centers for Disease Control and Prevention (CDC).

In the United Kingdom, 47% of 100 samples of raw goat milk offered for sale did not meet the regulatory dairy prod­uct standards (Little and de Louvois 1999). When raw milk is to be used for cheese production, standard coliform screening detects lapses in proper milk hygiene and thus an increased likelihood of potentially dangerous fecal con­taminants. Raw milk cheeses aged for at least 60 days are generally considered to be safer than fresh raw milk cheeses (Brooks et al. 2012).

Home Pasteurization

Several types of commercial home pasteurizers are avail­able to simplify making goat milk safe for human con­sumption. They are also very convenient for implementing programs to control milk-borne diseases of goats such as CAE and mycoplasmosis.

When a pasteurizer is not available, the milk can be treated in a similar way in a double boiler or in glass jars placed in a heated water bath. A cooking thermometer and frequent stirring and heat adjustment are necessary, and the utensils may be a source of recontamination. An instant pot with low temperature settings heats the milk and holds the temperature in a more controlled fashion. Alternatively, once the milk has been heated to the desired temperature, it can be poured into a thermos that was preheated with boiling water. The milk must be checked at the end of the holding period to verify that it remained at or above the target temperature. Finally, although testing with Listeria and Coxiella has not been performed, the home microwave oven has been shown capable of greatly reducing bacterial counts and increasing shelf life of goat milk. Heating to 65 °C (149 °F) for 30 minutes is recommended, using a tem­perature probe with “temperature hold” feature (Thompson and Thompson 1990).

Alkaline phosphatase activity is reported to be low in goat milk relative to cow milk, and the activity in sheep milk is 10-20 times higher than in goal, milk (Raynal-Ljutovac et al. 2007; Lorenzen et al. 2010). Bovine standards for phosphatase activity as evidence of proper pasteurization may not be applicable to goat milk (Klinger and Rosenthal 1997; Vamvakaki et al.

Toxins Excreted in Milk

The possible presence of toxins of feed or iatrogenic ori­gin is not limited to raw milk or necessarily affected by pasteurization. However, home-produced goat milk is more likely than commercially marketed milk to cause human illness, because the protective effects of toxin dilution by admixture with normal milk are often lost. It should be noted that pasteurization does not destroy preformed staphylococcal enterotoxins, which may be present in the milk of goats with either S. aureus or non- aureus (coagulase-negative) staphylococcal infections (Valle et al. 1990). The potential for contamination of milk by natural plant toxins has been reviewed (Panter and James 1990; Lopes et al. 2019). Numerous other chemicals, including pesticides, have the potential to be excreted in milk and are unlikely to be affected by pasteurization. Research performed with cattle should be largely applica­ble to goat milk. Neonates, because of incompletely developed detoxification pathways, may be especially susceptible.

Pyrrolizidine Alkaloids

Plants of the genera Senecio, Crotalaria, Heliotropium, Echium, Amsinckia, Symphytum, Cynoglossum, and Festuca contain pyrrolizidine alkaloids that cause hepato- toxic and veno-occlusive disease and may be carcinogenic. These toxins may be excreted in goat milk (Dickinson and King 1978; Deinzer et al. 1982; Goeger et al. 1982). Of spe­cial concern is Symphytum (comfrey), because some goat owners intentionally feed this plant to their livestock.

Tremetol

Ageratina altissima (white snakeroot, synonym Eupatorium rugosum) and Haplopappus (Aplopappus) sp. (rayless gold­enrod, synonym Isocoma wrightii; McGinty 1987) both contain a mixture of benzofuran ketones referred to as tremetol, a higher alcohol that is excreted in milk and not destroyed by pasteurization.

Other PlantToxins and Mycotoxins

There is a single report of skeletal abnormalities and red cell aplasia in a child in California whose mother drank goat milk from goats grazing lupine (Lupinus latifolius) (Ortega and Lazerson 1987). Puppies from a dog fed the same goat milk were also malformed, as were several aborted goat kids. Quinolizidine alkaloids such as anagyr- ine were thought to be responsible for this outbreak, which resembled crooked calf disease. Anagyrine appeared in the milk of a goat experimentally fed lupine seeds (Kilgore et al. 1981).

Milk collected from cows and ewes consuming Astragalus lentiginosus contains a toxin (probably swainsonine) that causes foamy cytoplasmic vacuolation when the milk is fed to the animals (James and Hartley 1977). Swainsonine inhibits α-mannosidase, causing a lysosomal storage disease.

At least of theoretic concern is the occurrence of carcino­genic, toxic, and mutagenic compounds (ptaquiloside) in the milk of cows, sheep, and goats grazing bracken fern (Pteridium aquilinum) (Hopkins 1990; Virgilio et al. 2015). Also of note is the goitrogenic effect of milk from goats fed goitrogenic plants (White and Cheeke 1983). Thiocyanate has been shown to transfer from dams administered potas­sium cyanide (KCN) daily to suckling kids via the milk (Soto-Blanco and Gorniak 2004).

A variety of plants in Australia, South Africa, and South America contain extremely toxic levels of sodium mono­fluoracetate. Kids born to dams consuming these plants have been reported to die very rapidly after colostrum con­sumption (Lopes et al. 2019).

Aflatoxins (from the consumption of moldy grain), and especially aflatoxin M1, are excreted in the milk of dairy cows consuming moldy feeds (Osweiler et al. 1985).

Antibiotics and Anthelmintics

Antibiotic contamination from intramammary or systemic medication of the goat or from consumption of “medi­cated” feeds may lead to allergic reactions in sensitive peo­ple, interference with cultured products, or regulatory action against the producer. As noted before, the com­monly used B. stearothermophilus assay may be inappropri­ate for goat milk. Because withdrawal periods have rarely been established for goat milk, especially for sick animals, veterinarians should advise exaggerated withdrawals (longer than for dairy cattle) to allow for different rates of metabolism or excretion. If goats kid less than two months after receiving a dry-period intramammary treatment, a withdrawal of 14 days has been recommended (Bergonier et al. 2003). Toxic parasiticides that have not been approved for dairy cows should not be used for dairy goats either.

Thiabendazole has antifungal properties that inhibit Penicillium while enhancing several undesirable mold species. Thus, thiabendazole at 200 mg/kg clearly inter­fered with proper curing of goat cheese, while 50 or 100 mg/kg sometimes did so, especially in milk from ani­mals with low production (Toussaint et al. 1976). By con­trast, pyrantel (25 mg/kg), morantel (10 mg/kg), or double these doses did not perturb the fabrication, appearance, or taste of the cheese. In another study, a taste panel detected a decrease in quality of a soft cheese made from milk of goats treated with netobimin (20 mg/kg 12 hours before) or albendazole (8 mg/kg 24 hours before). Morantel tar­trate (10 mg/kg), pyrantel tartrate (20 mg/kg), oxfendazole (5 mg/kg), and diamfenetide (240 mg/kg) had no effect, while the deleterious effect of tetramisole (12 mg/kg 24 hours before) was judged to be not significant (Cabaret et al. 1987). Even if the chemical cannot be tasted in the finished product and the consumer is not allergic, the sale of milk or cheese containing these compounds is illegal. With regard to the avermectins, moxidectin is more lipo­philic than ivermectin and persists longer in goat milk, up to 21 days after oral administration in one study (Porto Filho et al. 2019).