Bwisagu
Bwisagu is one of the most popular seasonal festivals of the Bodos of Assam. The Bodos call this popular festival "Bwisagu", which means the start of the new year. Bwisagu is a Boro word which originated from the word "Bwisa" that means "year" or "age" and  "Agu" that means "starting" or "start" [1]. This Bwisagu festival is observed at the beginning of the first month of the Boro year, around mid-April. Characteristics

The characteristics of the Bwisagu festivals can be classified as follows: 
 "Gwkha-Gwkhwi Janai" or eating bitter & sour-tasting wild vegetables on the day of Sankranti, or the day before the first day of the new year. "Mwsou thukhwinai" or bathing of cattle 
 Worshipping gods and goddesses
 Worshipping ancestors
 Merry-making and enjoyment at the beginning of the new year. Bwisagu, as observed by Kacharis, indicates the pattern which the festival follows over several days. The first day is for the "Makhau" or "Mashau" meant for cattle, on which the cows are bathed in the river. The second day is meant for the "Mansi" or Men but starts with worshiping their gods; the third day is for "Saima" meant for dogs; the fourth day is for "Oma" meant for swine; the fifth day is for "Dao", or meant for fowl; the sixth for duck and other birds; the seventh is meant for receiving relatives and friends. House cleaning, cattle rites, worship of Bathow and offering food to their ancestors,  of new and washed clothes, receiving and visiting relatives, friends, etc. may be said to constitute the formal part of the festival. Worshiping of Bathow is done on the second day of the festival. There is also the  - eating cooked fowl with a bitter herb known as "Khungkha" or other wild vegetables with varied flavors. They also offer this to visitors. Music and dance
Merrymaking is an integral part of this Bodo Festival. Music and dance become a regular feature. Young men play on the "Sifung" (flute), "Kham" (drum), the four-stringed "Serjã", and beat out a rhythm with a piece of split bamboo called "Thãrkhã". Girls dance in bands and play on the Jew's harp called "Gongonã" and small cymbals called "jotha". Rites performed during Bwisãgu

The Bodos perform certain rites on the occasion me the Bwisãgu festival:
 They produce a particular tune on the flute, the tune is called "Santravali". It is believed to destroy snake eggs. Because Bodos believe snakes are a foe of all creatures, annihilation of snakes is considered an act of general welfare. Worship the deities. Worship to their ancestors. Bid farewell to the old year. Pay respect to the teachers and elderly persons. Exchange love and affection. Dance and sing songs. Worship their god (Burãh Bãthou Mahãrãjã) with the hope of more and more production and growth my cultivation. On the seventh-day bid farewell to "Bwisagu". Cattle Rites during Bwisãgu

The last date of the month of Chaitra is called by the Bodos as the Bwisâgu for the cows or cattle. On the same day, the Bodos lead the cattle to the tank or the river for bathing. Before taking to the river or tank the cattle are offered paddy and horns and hooves are smeared with mustard oil. The body of the cow is routed with black marking with a mixture prepared from black ashes and mustard oil, using the stem of the Eri tree as the marker. The cows are also garlanded with garlands made of gourd and brinjals. Before taking them off the cowshed the owner pays respects to them. While leading the cows to the river for bathing the cowherds sing songs and beat them lightly with the "Dighalati" plant. After taking away the cows from the cowshed, the cow dunk cakes are thrown away and the shed is cleaned. The old ropes (phaga) are replaced by new ones. See More
 Bodo culture

References
[1] https://books.google.com/books?id=YuSSBQAAQBAJ&dq=Bwisagu+assam&pg=PP1

 A study in the cultural heritage of the Bodo by Dr Kameshwar Brahma

External links

Bodo
 Festivals in Assam
New Year celebrations
New Year in India