- Donald Duck, Bristol
P.S. I made up a name
Though this question is based on a brief Snapple cap fact, it will provide us with a lot of material. We first went to the Snapple facts website to find the one you mentioned. It is written as follows:
Snapple fact #980 "When grazing or resting, cows tend to align their bodies with the magnetic north and south poles."
We'll briefly cover some background first. Like a bar magnet, Earth has two magnetic poles, one in each hemisphere. As they both shift, the poles' locations change gradually. As of now, the Northern Magnetic Pole is 86.3 degrees North and 160.0 degrees West. The Southern Magnetic Pole is 64.28 degrees North and 136.6 degrees East. (Unlike the geographic poles, the magnetic poles are not antipodal: i.e. they are not necessarily separated by 180 degrees.)
These magnetic poles are connected by magnetic field lines as seen on these images.
Some animals possess "magneto-reception," the ability to sense Earth's magnetic field lines and to orient themselves accordingly. Homing pigeons, big brown bats, and sharks are examples of such animals gifted with this capability. In 2008, Dr. Hynek Burda, a zoologist with the University of Duisberg-Essen, Germany, issued a paper in "Proceedings of the National Academy of Sciences" indicating that cows also possessed "magneto-reception." Burda based his findings on surveys of Google Earth maps that seemed to indicate that when grazing or at rest, cows aligned themselves toward magnetic north. This analysis consisted of 308 images of different pastures and 8,510 resting and grazing cattle. Within this sample, researchers determined that 60 - 70% of the cows were aligned toward the north magnetic pole.
Analysis of these images lead Burda to propose that cows were magneto-receptive and therefore capable of aligning themselves magnetically. Of course, in science, one must be able to re-produce the results yielded in the initial experiment or observations. In 2011, a research team from the Czech Technical University of Prague analyzed 232 images and a total of 3,412 cows. Unlike the first team which focused on herds of cows, the Prague researchers examined each cow individually. Through their study, they found no preferred orientation in the cows. Some were standing toward the north, but others are aligned at a variety of angles. The 60 - 70% predominance noted in Burda's study was not confirmed by the follow up. Statistically, the sample sizes involved shouldn't produce as profound as discrepancy as occurred between the two results. The Prague team pointed out that cows and other grazing animals will often tend to align themselves relative to the wind and for warmth. The Prague team also raised the issue of bias, the tendency of scientists, sometimes acting subconsciously, to make the data fit the hypothesis.
Burda, himself, disputed the Prague findings. He noted that some cattle were close to power cables, the electric field of which will interfere with magneto-reception. Burda further added that some of the cows in the Prague study were on slopes that can alter the perceived angle.
As of now, very little research has been conducted since 2011 on the issue of cow magneto-reception. Though the notion of grazing cows aligning themselves with Earth's magnetic field has insinuated itself into popular culture (hence, the Snapple Cap), some researchers have strong doubts.