Even in the era of world-wide communication ad media, triplet calves are very rare and worth a news story. Cows are biologically capable of producing twins but generally have only one calf at a time. Triplets are extremely rare. Triplets are slightly more common with older cows and in family lines with a previous record of producing triplets.
Some farmers are selecting for triplet calving to increase the incidence. However, calves from twin or triple pregnancies are less likely to survive, and females with male sibling in utero may be infertile. So it is not a win/win situation. Most farmers are happy to have singletons and occasionally twins.
Because bovine twins are rare and, let's face it, rather by cute, they are a subject found in antique and vintage photographs by proud farmers. Some examples are shown below, with the year marked when it is known.
Even More Unusual
A cow in the United Kingdom even gave birth to triplet calves of different breeds after being inseminated with sperm from more than one bull.