Halacha states that milk from a tereifah animal – meaning an animal which suffers from a mortal wound, as understood by Chazal – is non-kosher. (Shulchan Aruch, Yoreh Deah 81:1) This prompts a good question: How can one know whether or not the milk he consumes is from a tereifah cow?

There is another halachic axiom that “Rov beheimos kesheiros”- “Most animals are presumed to be kosher” (and one need not suspect that they are tereifos – Chulin 12a [v.Rashi d.h. Pesach] and Shach s.k. 2 on YD 39:1). Thus, one can safely assume that the milk from a randomly-selected cow is kosher, unless data to the contrary is provided.

In contemporary times, when dairy farms and milk processing have become industrialized and are subject to the demands of a mass-production society, there may be additional factors to consider. Let’s take a look.

As a result of a diet that is heavy in grain, dairy cows sometimes suffer from displaced abomasum (hereafter referred to as “DA” ). This condition signifies that the fourth stomach section – the abomasum – has moved out of position, due to built-up gas or fluid. DA impedes a dairy cow’s maximum functionality, and it is often addressed by veterinary intervention. (See Metabolic Diseases of Dairy Cattle-Displaced Abomasum, BJ Harris and JK Shearer – University of Florida-IFAS Extension.)

Although there are several treatments available to rectify DA, one common treatment involves piercing the three walls of the abomasum by making three unaligned holes, allowing for the release of excess gas when the holes are momentarily aligned. Some poskim have questioned this procedure, suggesting that it might render a cow a tereifah (as a punctured abomasum, or keivah, makes an animal a tereifah – YD 48:1). Other recognized poskim, including those whose opinions are consulted by the accepted national kashrus agencies, have ruled that as a practical matter, there is no concern. Among the arguments for this latter position is that the incisions in the three layers of the abomasum are not aligned, such that there is not a direct puncture flush through the abomasum. Furthermore, the Shach (YD 57:48) rules that an animal of questionable tereifah status can be proven and established to not be a tereifah if it lives for 12 months subsequent to the condition that may render it a tereifah. This may well apply to DA cows, whose halachic status is at worst a questionable one. Some poskim additionally argue for leniency regarding DA cows’ kosher status because the puncture for treatment of DA is totally sealed upon completion of the treatment. (For a complete discussion of the halachic implications of DA treatments, see Rabbi Y. Belsky and Rabbi M. Heinemann in Mesorah v. 10 pp.62-78, Rabbi M. Genack in Tradition 29:2, and Rabbi J.D. Bleich in Contemporary Halachic Problems vol. 5.)

Producers of cholov Yisroel milk are also exposed to the problem of DA cows. Segregating non-DA cows from a herd is an arduous task that requires a large measure of diligence. Mashgichim, veterinarians, farm managers and workers must all be vigilant and cooperate in order to effectively segregate non-DA cows from a large herd.

It must be noted that the halachic status of DA cows is not a very new issue. Surgery on DA cows has been performed for many decades, and prominent poskim (see above) have addressed the issue over the years.

Irrespective of the status of an animal which underwent surgical correction of DA, there is a broader halachic consideration, for an unknown, widely-varying minority ratio of cows in grain-fed herds develops DA, and one needs to question whether or not this divergent minority of DA cows impacts the larger milk supply.

Statistics indicate that 1-9% of cows in a random herd are affected by DA. (Documented mean DA rates are 1.4%-5.8%. See Causes and Prevention of Displaced Abomasum in Dairy Cows, Dr. Randy Shaver – Department of Dairy Science, University of Wisconsin-Madison.)

The incidence of DA depends on several factors, including environment and diet, and there is no set method to calculate the DA risk ratio. Research by this author of two farms in one region of Upstate New York indicates that one farm had a 4% population of DA cows, whereas another farm had less than 1%. The overall national average population of DA dairy cows is 4%, but the truth is that the statistical ratio of DA cows in milk herds which factor in for halachic purposes is somewhat less than this figure, as not all DA cows undergo surgery, and many farmers permanently remove DA cows from their herds as a result of such cows’ poor productivity and long-term stability for milking.

How do the above statistics affect the halachic considerations?

On a d’Oraysa (Biblical) level, we hold in all cases that Min b’mino batel b’rov – the status of a mixture of identical objects goes according to the majority. However, when dealing with min b’mino mixtures of liquids, there is a din d’Rabbonon (rabbinic law) which states that the mixture is kosher only if the amount of heter (kosher substance) present is sixty times the amount of issur (non-kosher substance). In cases of safek (doubt) as to whether there is bittul b’shishim (nullification by sixty), we are lenient, as the entire requirement of shishim is d’Rabbonon. (See YD 98:2 and Taz. Ibid. s.k. 3.) In light of the fact that the presence of DA cows in a given herd can vary greatly, such that a random tanker or silo of milk may be assumed to contain less than 1% or up to 9% milk from DA cows, there is a safek of bittul b’shishim, which would permit any milk. Furthermore, even if one were to assume that the average bottle of milk contains 4% milk from DA cows that underwent surgery, the milk would nonetheless be permissible, as there is a machlokes (halachic dispute) as to whether such DA cows are kosher, and since the matter is one of safek, and the need for bittul b’shishim is only d’Rabbonon, the result is that the milk is deemed kosher.

There is a rule that “Kol d’parish mi-ruba parish” – “Anything that separates out (of a series of sources among which the minority are not kosher) is governed by the status of the majority”. Thus, if there are nine kosher butcher shops and one non-kosher butcher shop in a common area, and an unidentified piece of meat that must have come from one of these shops is found in the public market nearby, the meat is deemed kosher, representative of the majority. (YD 110:3) The same logic may apply to milk from herds with DA cows, for even if we assume the worst – that DA cows are definitely tereifos and the DA cow population is spread out evenly at a 4% ratio – milk which is purchased at the consumer level may nonetheless be said to emanate from the majority of cows, which are kosher. Even though every container of milk derives from large dairy silos which contain blends of milk from hundreds or thousands of cows, the rule of kol d’parish may establish that the product before us is considered to be a blend from the (kosher) majority. (Kol d’parish applies when there is a known source of issur – non-kosher substance. Because a definitive presence of DA cows is not known in any given herd, it is reasonable that the simple rule of ‘Azlinan basar ruba’ – ‘We go according to the majority’ (Chulin ibid.) – may apply instead of Kol d’parish. This approach would yield the exact same result in our case as does Kol d’parish.)

There is also a maxim that “Kol kavu’a k’mechtzah al mechtzah dami” – “The fixed presence of a non-kosher substance creates a 50/50 chance (that an unidentified item taken from the source area is non-kosher)”, such that if one were to enter and purchase meat from one of the butcher shops in the above case and not recall in which shop he made his purchase, the meat purchased has a 50% chance of being non-kosher and can therefore not be eaten (YD ibid.). This rule does not apply to milk from DA cows, as it requires that a Yisroel have knowledge of the definite presence of the non-kosher source at the time the purchase was made (in the case of butcher shops) or at the time the milk was extracted (YD 110:5). In the case of DA cows, there is no knowledge on the part of a Yisroel as to a specific cow’s DA status and that it underwent surgery, for such cows are not recognizable, except to veterinarians (who can detect a cow’s DA surgical history based on scar tissue). The inability to identify a specific source of issur precludes the rule of kavua. (Shach ibid. s.k. 28). Furthermore, even if a DA cow would be clearly-identified as such to a mashgiach or Jewish consumer at the time of its milking, the rule of kavua would not apply to the milk when it is drunk, for milk from DA cows would never present itself to the dairy or consumer in its pure, original form. Because the milk of each cow is blended with milk from hundreds or thousands of other cows at the dairy itself, milk from this hypothetical known DA cow would be diluted to the point at which the regular rules of bittul would apply. Therefore, the din of kavua is inapplicable.

What about tereifah non-DA cows? Isn’t there surely a certain proportion of cows among the herds that are tereifos, especially cows with sirchos – lung adhesions – which are common? (Shach s.k. 2 on YD 39:1)

The truth is that even if, upon shechitah, an animal is determined to be a tereifah as a result of sirchos in its lungs, its milk is kosher. (YD 81:2) This is so because of a s’fek s’feika l’kula – a double doubt in favor of leniency – for there are two factors which combine to permit this animal’s milk: 1) There is a chance that the sirchos developed after the animal was milked, such that the sirchos were absent during the milking, which means that the animal and its milk were kosher upon milking. 2) Every time an animal is ruled to be a tereifah due to sirchos, its status as a tereifah is not definitive, as we are not truly expert in sirchos and are therefore strict in determining tereifah status based on them; thus, cases which are deemed non-kosher based on sirchos may actually be inherently kosher. (See YD ibid. Tur ibid. from Rosh, Be’er Hetev ibid. S.k. 8 and Aruch Ha-Shulchan YD 81:27.)

Based on the above, even if every milk cow would be slaughtered and found to be a tereifah due to sirchos, its milk would be permissible (with the possible exception of milk produced within three days of shechitah – see YD ibid.; this would not be a factor, however, in practical dairy situations.)

Furthermore – and this applies to tereifos of all types (such as punctured or missing organs) – the general chezkas kashrus (presumption of kosher status) of all animals (kosher species, of course) allows one to consume milk without concern for the possible presence of tereifos. (See YD 39:2 with Shach s.k. 8.) Unless one has information to counter an animal’s chezkas kashrus, its milk and meat are permissible.

One may think it logical to ask why we don’t take a totally different approach and reason that since a certain percentage (possibly 10% or more) of cows in the general cow population is comprised of tereifos, and since all milk processed in modern dairies is a mixture of the milk of large herds which on average have some tereifos (likely 10% or more, reflective of the general statistics), why not assume that all milk contains an admixture of 10% or more from tereifos? In short, shouldn’t all milk made from mixtures of large herds be assumed to be non-kosher? Should we not assume that 10% or higher of all milk in dairy silos is from tereifos and thereby renders all milk with which it is blended non-kosher?

The Shulchan Aruch and Remo (ibid.) rule otherwise, stating that a mixture of milk from one known tereifah animal and a herd of 60 cows that are assumed to be kosher is permissible; we do not treat the mixture as containing additional tereifah milk from the likely additional percentage of tereifos in the herd. The Shach (ibid. s.k. 6, quoting the Issur V’Heter and Toras Chattas) and the Gro (ibid. s.k. 11) explain that we can assume the balance of animals in the herd to be kosher, as Rov beheimos k’sheiros, and the Sifsei Da’as (ibid. s.k. 6) specifically notes that we do not suspect that the 60 animals presumed to be kosher are possibly really tereifos, as Rov beheimos k’sheiros is the governing principle. The rationale for this is that each animal’s kosher status is established at the time it is milked, prior to the milk from the herd being mixed together. We therefore view each animal at the moment it is milked as kosher, based on Rov beheimos k’sheiros, and its milk is considered to be kosher when it is subsequently blended.

To illustrate this principle, let’s travel back in time to the pre-industrial era, when a glass of milk derived from one cow rather than from a milk mixture of hundreds or thousands of cows. In this scenario, a dairy farmer who regularly drinks the milk of his own herd will likely consume over the course of his lifetime milk from hundreds of cows. Even though we may assume that at least 10% of cows are tereifos, and on a statistical level the farmer must have consumed some milk from tereifos, we do not view it this way from an halachic stance, as Rov beheimos k’sheiros dictates that each cow had kosher status when it was milked; every cow’s kosher status is determined individually, not collectively. So too in the case of contemporary milk production is the kosher status of every cow established when it is milked, regardless of the fact that its milk will be mixed with milk from hundreds or thousands of cows. Halacha does not look at the aggregate milk mixture and proclaim that the mixture is statistically 10% or more from tereifos; rather, the kashrus of the milk mixture is fixed beforehand, for the status of the milk of each cow which contributed to it was established as kosher upon milking. Therefore, the milk of each cow is ruled to be kosher as its exits the cow, and the fact that a given ratio of milk in any mixture may be 10% or more from tereifos is inconsequential from an halachic perspective.

The kashrus of milk once again attests to the many and complex halachic considerations that factor into what would appear to be of the most simple foods.

A full treatment of the many issues related to the status of DA cows is beyond the scope of this article, which is intended only as a brief introduction to the issue for the general public.