This post illustrates the so-called branched chain design. This is an improved type of chain that seems most suited as a starting point towards providing proper enrichment (as required by e.g. EU legislation) for conventional, intensively-farmed pigs. However, also pigs on straw may benefit from such chains. Below the description of the branched chain design you can find some pictures and video clips of branched, anchor-type chains for pigs (conventionally-housed weaners and growing fattening pigs, and gilts kept on straw).

Specification of the branched chain design

1: Object-design: A branched chain consists of a vertically-positioned long chain with its end resting on the solid floor over a distance of 20 cm. Two or three additional chain ends (branches) end at or slightly below the nose height of the smallest and middle-sized pigs reared in the pen.
2: Material: The chains are stainless-steel anchor chains (for at least the last 5-10 links of each chain end). Recommended dimensions are 7mm for growing-fattening pigs, 5-6 mm for weaners, 4-5 mm for piglets and 8 mm for sows.
Anchor chains have links which are more round and heavier than the cheaper, more oval-shaped c-chains. Note that the indicated sizes refer to the diameter of the metal, not the diameter of the links. For example, a 7 mm anchor chain for finishers has links measuring 36×23 mm.  Preferably various chain sizes should be provided in the pen, esp. when the pen may contain pigs of variable sizes (e.g. from 25 to >100 kg). Stainless-steel anchor chains are more expensive, but only the last 5 or so links need to be replaced when worn e.g. every 5 – 10 years.
3: Availability and placement: One branched chain is provided for every 5 pigs.The chains are spaced apart as much as possible, preferably with at least one pig length between 2 branched chains in a pig pen. The branched chains are attached at the top end of the pen wall, over the solid floor, and not in the dunging area.

The description of the branched chain design was derived from: Bracke MBM, 2017. Chains as proper enrichment for pigs (incl. supplement). In: Spinka M, editor. Advances in Pig Welfare: Elsevier.

Table. Anchor-chain link dimensions

Pictures of branched anchor-type chains

Short chain and ball. Note the bite marks on the ball. The ball is hanging on a c-chain (oval shaped). The short chain resembles an anchor chain but isn’t (links not massive enough).	Short chain, ball and branched chain made of suboptimal c-chain links. This type of branched chain uses only 1 fixation point (reducing costs).	Branched anchor-type chain with 3 branches. Only top left branch is made of c-chain in order to ‘test’ pig preferences for the anchor-type chains (top right branch).
Four stainless-steel anchor chains. Two middle chains are worn by long-term use (5-10 years). Outer chains show original shape.	Branched chain provided to weaned piglets	Occasionally a pig will be reaching up. But normally they show downward-directed behaviour.
Branched chain for fatteners	Most manipulation of the branched chains is floor directed. Both rooting and biting/chewing/playing.
Floor directed ‘rooting’.		The pig’s nose really ‘fits’ a floor-directed orientation.
	Also some more horizontal chewing	Sometimes more pigs are interested in the same thing.
Side-way chewing (fits into cheek fold for canine teeth).	Taking a whole branch (10 links) into the mouth.	Three pigs all at once.
Some occasional pulling.	Empty straw-bricket container. The floor plate may be used to keep a chain from getting stuck in the slats and/or repair when the floor below the branched chain gets worn.	Gilt in a straw pen next to a branched chain between the lying area (front) and dunging area in the back of the pen.
Floor-directed chain manipulation may be labelled ‘rooting’ …	…not just because there is also some straw…	…it resembles stone chewing seen in outdoor sows.
A second branched chain in the same pen containing four gilts.	Grabbing the chain horizontally, showing the cheek fold.	A branched chain in another pen containing two gilts on straw.
Floor directed behaviour	Biting the chain occasionally.	Fixation of the floor chain using the right front leg. True ‘manipulation’ (as manus in Latin means ‘hand’).
Branched chain worn temporarily as an ‘ear ornament’.	Two gilts playing with the branched chain at the same time.	Anchor-chain links worn (right) by pig manipulation.

These pictures may be used for non-commercial purposes & publications provided copy-rights (MB) are acknowledged.

The video clips below show the pigs in action.

This video shows that a hockey-type ball may be frustrating for pigs, and that the branched chain design is much more appreciated, even by organic pigs.

Related posts:

Chains as enrichment for pigs (Book chapter with supplement)
Ketting als hokverrijking voor varkens (incl. link naar het supplement)
Pig animation – Improved, branched chain design as proper enrichment for pigs
Branched chains as enrichment for pigs (technical description, pictures and video)
Proper enrichment for intensively-farmed pigs – From review to preview
A collection of pictures of other enrichment materials for pigs can be found here: Prize contest (Prijsvraag) 2011.
Do pigs play with chains? Science versus society