With Shavuot just around the corner, many of us will be preparing dairy meals. Did you know that the milk products we are using (including chalav yisrael) are likely to contain at least 10% treif milk!?
Kosher until proven treif
In the past few years, some interesting questions have been raised regarding the kashrut status of the milk we drink. These issues are not related to the rabbinic injunction of chalav yisrael nor to any of the additives that are added to the milk products, but rather to the fact that the milk itself may be actually treif!
By Torah law, milk from a non-kosher animal is forbidden. It makes no difference whether the animal is a non-kosher species or a kosher species that became treif due to an injury or abnormal condition. Consequently, milk from a treif cow is forbidden. However, we usually know that a cow is kosher only after it is slaughtered and its lungs are checked, so how can we know if the milk we drink is from a kosher cow? Obviously, we don’t wait until the cow is slaughtered. Instead, we invoke the majority rule which states that since the majority of cows are kosher  (רוב בהמות כשירות), all cows are assumed kosher until proven otherwise.
For example, given a glass of milk that was taken from a single, random cow, it can be either 100% treif (if it came from a treif cow) or 100% kosher (if it came from a kosher cow). Statistically we know that between 10% to 35% of all slaughtered cows are found to be treif , so most cows are kosher. Applying the majority rule, we can assume that the milk in our glass came from a kosher cow and is therefore 100% kosher.
The whole is the sum of its parts
In reality, however, the milk we drink does not come from a single cow. Modern dairies process the milk from large numbers of cows together, so our glass of milk contains a mixture derived from hundreds or thousands of cows. We can no longer claim that the milk in our glass is 100% kosher. In fact, we can be quite certain that it is contains at least 10% treif! The majority rule no longer applies when we have a mixture that certainly contains some treif. Instead, we should apply the rule of batel b’shishim meaning that the treif part of a mixture becomes negligible only if it is no more than 1 part in 60, or 1.6%. So how can our milk still be considered kosher when we know that there is much more than 1.6% treif milk in the mixture?!
Most authorities will answer that the kosher status of the milk is determined at the time of milking. When an individual cow is milked, the majority rule asserts that its milk is kosher unless we actually know that the cow is treif. Once we determine that the milk is kosher, its status doesn’t change just because the statistics say that some of it is probably treif. The mixture of milk is made up of many such portions of kosher milk and therefore it is considered entirely kosher.
Other authorities disagree with this opinion arguing that the majority rule only applies when we drink the milk from each cow separately. It is not logical, they claim, to permit the consumption of a mixture, when we know statistically that a significant percentage of that mixture is not kosher.
Dairy cows – not so kosher
But even if we accept the lenient view, there is a more serious issue to contend with. It seems that among dairy cows, grown primarily for milking, the percentage of treif is significantly higher than in the general cattle population. As far back as 1978, Rabbi Dr. Israel Meir Levinger, a zoologist and noted kashrut expert, reported that the rate of treifot in dairy calves in Israel is almost double that of calves raised for beef. More recently, a kashrut supervisor in Johannesburg, S. Africa, observed that up to 95% of the dairy cows were found to be treif due to sirchot (lung adhesions). Similarly, on a dairy farm in the US, 80% of the slaughtered cows were found to be treif. These high rates of treifot in dairy cows are attributed to a number of factors such as a heavy grain diet , the weaning process for calves and excessive milking (3X a day) .
Although these figures are not a representative sample, no one has presented statistics to the contrary. It is difficult to accurately determine the percentage of kosher dairy cows because dairy cows are not usually slaughtered for kosher meat. If, however, we were to find that the majority of dairy cows are indeed treif, we would have a very serious problem on our hands. We would no longer be able to invoke the majority rule and assume that every cow is kosher unless proven otherwise. In fact, it would seem that every cow should be assumed treif unless proven to be kosher. This concern is relevant to both chalav yisrael and chalav stam.
Don’t throw out the milk yet.
Most poskim (halachic authorities) agree that in spite of the reported incidents of treif cows, currently there is no reason to stop drinking milk. They bring several arguments to support this view.
1) Exaggerated statistics. The reported rates are exaggerated because they are based on examinations of slaughtered dairy cows that are no longer fit for milking. It is known that older cows have a higher rate of sirchot. The treif rate for the entire dairy cow population should be much lower.
2) Safek sfeika. Often we can rule leniently on a Torah prohibition if two doubts can be raised concerning the circumstances of the prohibition. In our case, even if a cow is found to be treif because of a sircha, we can still rule that the milk that came from that cow is kosher because: a) we cannot be sure that the sircha was already developed at the time of milking, and b) although we may have judged the sircha to be treif, our understanding of sirchot is limited and in reality the cow may still be inherently kosher. Based on these 2 doubts, milk would still be permitted even if most of the cows are later found to be treif.
3) Treifah Einah Chayah. If we accept the position recorded in the Talmud that a treifah (e.g. an animal with a sircha) cannot live more than 12 months, then we can use the following reasoning: If slaughtered cows are found to be treif, then the sirchot must have existed for no more than 12 months (otherwise the cow would have died sooner). It follows that most live cows do not have such sirchot. On the other hand, if these sirchot did exist longer than 12 months, then they are apparently not the type of sirchot that render the animal treif.
While most halachic authorities, including all the major kashrut organizations, rely on these and similar arguments, others reject them and question the kosher status of milk today. With rates of 95% or 80% treif, it is difficult to conclude that the majority of dairy cows are still likely to be kosher. The situation warrants further research to better understand the extent of trefot among dairy cows.
It is rumored that Rav Herschel Schachter, a highly regarded Talmudic scholar and posek, personally abstains from milk and dairy products due to the dubious status of the milk. “Most of the rabbanim assume that the milk is kosher”, states Rabbi Schachter, “I just don’t understand why!”
 Rabbi Avraham Gordiner, Kashrus – Milk From Possibly Treif Cows, (See references below)
 “… it turns out that from calves, approximately 10% percent of slaughtered meat ends up being ‘treif’, about 40% kosher, and around 50% ‘chalak’. In older cows, 35% are ‘treif’, about 55% are kosher, and 10% ‘chalak’.” – Harav Melamed: The Difference Between Galtt and Kosher Meat
  “R. Levinger also compared the terefah rates of cows raised for beef and cows raised for dairy in Israel. He discovered no statistically signiﬁcant difference among older cows. However, the rate of terefot in calves raised for dairy was almost double that of calves raised for beef. R. Levinger attributed the discrepancy to the prevalent practice of dairy farms to wean their calves in a drastic fashion. The change of diet leads to colds and coughing, which cause adhesions to develop.”
– The Kashrut of Commercially Sold Milk” by Rabbi Michoel Zylberman (see related links below)
 “The Kashrut of Commercially Sold Milk” by Rabbi Michoel Zylberman
 Rabbi Avraham Gordiner,Kashrus – Milk From Possibly Treif Cows
 “The Kashrut of Milk Today”, Shut B’Mareh Habazak, end of note 3 (Hebrew)
 Ibid (55:23)
References and Related Links
“Kashrus – Milk From Possibly Treif Cows” by Rabbi Avraham Gordiner ,March 16, 2009, YU Torah Online
“The Kashrut of Commercially Sold Milk” by Rabbi Michoel Zylberman, Journal of Halacha and Contemporary Society, 2007. For a summary of the halachic sources (Hebrew) see: “ענין חזקה שלא נתבררה בשעתה, חזקה הבאה מכח רוב, וכשרות החלב בזמנינו” by Rabbi Michoel Zylberman, Tuesday March 20, 2007, YU Torah Online
הבאר כא כב – אדר ניסן תשס”ג p. 106ff A lengthy analysis of the halachic issues with answers from 4 prominent halachic authorities, Rav Menashe Klein, Rav Nechemia Goldberg, Rav Asher Selig-Weiss, Rav Levi Yitzchak Halperin. (Hebrew)
“The Kashrut of Milk Today”, Shut B’Mareh Habazak, Eretz Hemda, Vol.7 (Hebrew)