“THE BOAR'S HEAD IN HAND BEAR I"
In a group of petroglyphs from Litsleby in West Sweden, one image depicts a man driving a plow pulled by two horned draught animals. In one hand he holds a budding branch or a small tree and in the other an undefined object which may be a hammer or a seedbag. Two furrows are indicated by horizontal lines at the bottom of the picture and the man is clearly shown at the beginning of a third. Hilda Ellis Davidson compares this Bronze Age scene with a nineteenth century custom recorded in Uppland of plowing three special furrows on the first day of spring. She writes:
“[Oscar] Almgren (1927, p. 301) …describes how the sod had to be turned up in the direction of the sun, and some of the earth rubbed on the forelocks of the horses, while the plowman was given bread which had been baked at Yule and stored in the corn-bin. A branch from a fruit-bearing tree was carried by the plowman or fixed on the horses reins; this custom was known in Småland and Scania up to 1921.”[Davidson, Roles of the Northern Goddess, p. 59].
The scene Almgren describes is remarkably similar to the one depicted on the petroglyph above and consistent with later tilling customs recorded in England and Germany. In the folk-customs of northern Europe, particularly the practice in Hesse and Meiningen of roasting a pig on Ash Wednesday or Candlemas (Feburary 2nd) and keeping the bones till sowing-time, when they are put into the field or mixed with the seed. The corn from the last sheaf is often kept until Christmas and made into a boar-shaped cake. In the spring it is broken and mixed with the seed. In Scania, a salted pig’s head from the Yule feast was kept and given to the plowman and his horses to eat on the first day of plowing in the spring.
In Thesmophoria, it was customary to throw pigs, cakes of dough, and pine branches into caverns sacred to Demeter and Persephone. During the next annual festival, women who had been ritually purified for three days descended into the caverns to retrieve the decayed remains of the pigs, the cakes, and the pine-branches and brought them to an altar. The decayed matter was then sown with the grain to ensure a good crop. This ancient ritual was explained by a legend that held that when Pluto carried off Demeter’s daughter Persephone, a swineherd named Eubuleus happened to be herding swine on the spot and his herd thus vanished along with Persephone
Besides their capacity for breeding, wild pigs have long snouts and tusks and their ability to turn over soil when foraging may account for their association with agriculture. In northern European iconography, the use of the boar emblem is pervasive. In one of the earliest accounts of Germanic pagan customs, Tacitus speaks of a Germanic tribe known as the Aestii whose language resembles that of the British (Germania, ch. 45). They worship the Mother of the Gods and wear the figure of a wild boar as the emblem of her cult. Here the boar is connected not only with a Mother goddess but with agricultural activity.
A close connection between the boar and agriculture survived for many centuries. Grimm cites an early Latin commentary by Verelius (seventeenth century) on Hervararsaga which says that Swedish peasants, after baking a cake known as the jula-galt,  dry some of it and keep it until spring. They then grate a portion of it and feed it to the plow-horses and another part to the plow-men. In the popular belief of Thuringia, whoever abstained from eating until dinnertime on Christmas, would catch sight of a golden pig. In practical terms, this may have been the last and finest course of the meal, since a Laueterbach weisthum of 1589 decrees that a goldferch, a hog gelded before it is weaned, be led around the benches on Three Kings’ Day (therefore Yule), probably before it was slaughtered.
 jula-galt , literally “Yule-boar,” a loaf or cake baked in the shape of a boar; Grimm, ibid., p. 51, probably related to the sonargaltr, sacrificial boar dedicated to Freyr annually.
In the same region, when the wind sets the corn stalks in motion, they sometimes say, “The Boar is rushing through the corn.” In the Netherlands, “Derk with the boar” makes his rounds and looks after the plows. In the same vein, when Freyr rides to Baldur’s funeral in Snorri’s Edda, he is said to drive in a cart drawn by his shining boar, Gullinbursti (“Golden-bristles). Freyr’s connection with grain is made clear in Lokasenna 45-46, where his servant is named Byggvir, derived from bygg, “barley.” He is expressly associated with ale, made from barley, and his job is to “distribute food among men,” deila með mönnom mat. In Skáldskaparmál 14, Freyr is called árguð, harvest god. Gylfaginning 24 confirms this, saying hann ræðr fyrir regni ok skini sólar ok þar með ávexti jarðar, ok á hann er gott at heita til árs ok friðar, “he is ruler of rain and sunshine, and thus of the produce of the earth, and it is good to pray to him for prosperity and peace.” From all this, it is evident that a long history of agricultural customs associated with ritual and ceremony with close affinities to those of other Indo-European peoples have existed in northern Europe since the prehistoric era.
-Excerpts from Odin's Wife (2018) by William P. Reaves