Usually categorized as rural drama, the film narrates the lives of two Basque families covering the years 1875-1936, which historically were the unstable and bloody years from the Carlist War to the Spanish Civil War.
The aesthetics of the movie established strongly Medem's so-called "dreamy style" (which ironically can be very nightmarish). His expressionist values would contrast rapidly with a time period in the Spanish cinema when the influences from the American movies would multiply (i.e. Alejandro Amenábar). The structure of Vacas is made out concentric circles: European Style--Spanish History--Basque culture--A village--Two houses of that village and, overseeing them all, the cows. The narrative is also very concentric; the film uses a continuous recycling recourse (i.e. the same actors play the three generations, which can be slightly confusing). Medem would also use a loop-like approach in his film Los amantes del círculo polar.
Small segments of Vacas were used by Medem in his documentary film La pelota vasca to illustrate the Carlist Wars.
This is largely because of the essentially stationary and unreactive nature of the domestic cow, which makes them appear wry, as well as their propensity for flatulence, and defecation leaving a "cowpie" anywhere it might stand.
The cow is a photograph that the animators manipulate in such a way as to suggest that the cow is performing all kinds of unusual feats when obviously, it is just a photograph being moved around.
The cow in general is often thought to be slow and lazy, as demonstrated in the advert.
The particular soldiers in the machine gun nest were far removed from the actions on the beaches and would not have had much difficulty in maintaining a supply route, at least not that soon after the landings.
The unlucky cows were caught in a crossfire or artillery barrage and killed.
In the movie, you see the dead cows getting hit by machine gun fire, but they were long dead by then.