Comes under EU regulation 1/2005 "on the protection of animals during transport and related operations "
If you are putting a crate inside the vehicle then :
Chapter II
1.
Provisions for all means of transport
1.1. Means of transport, containers and their fittings shall be designed, constructed, maintained and operated so as to:
(a) avoid injury and suffering and to ensure the safety of the animals;
(b) protect the animals from inclement weather, extreme temperatures and adverse changes in climatic conditions;
(c) be cleaned and disinfected;
(d) prevent the animals escaping or falling out and be able to withstand the stresses of movements;
(e) ensure that air quality and quantity appropriate to the species transported can be maintained;
(f) provide access to the animals to allow them to be inspected and cared for;
(g) present a flooring surface that is anti-slip;
(h) present a flooring surface that minimises the leakage of urine or faeces;
(i) provide a means of lighting sufficient for inspection and care of the animals during transport.
1.2. Sufficient space shall be provided inside the animals' compartment and at each of its levels to ensure that there is adequate ventilation above the animals when they are in a naturally standing position, without on any
account hindering their natural movement.
1.4. Partitions shall be strong enough to withstand the weight of animals. Fittings shall be designed for quick and easy operation.
1.5. Piglets of less than 10 kgs shall be provided with appropriate bedding material or equivalent material which guarantees their comfort appropriate to the species, the number of animals being transported, the journey time, and the weather. This material has to ensure adequate absorption of urine and faeces.
2.
Additional provisions for transport by road or rail
2.1. Vehicles in which animals are transported shall be clearly and visibly marked indicating the presence of live animals, except when the animals are transported in containers marked in accordance with paragraph 5.1.
2.2. Road vehicles shall carry suitable equipment for loading and unloading.
5.
Additional provisions for transport in containers
5.1. Containers in which animals are transported shall be clearly and visibly marked, indicating the presence of live animals and with a sign indicating the top of the container.
5.2. During transport and handling, containers shall always be kept upright and severe jolts or shaking shall be minimised. Containers shall be secured so as to prevent displacement due to the movement of the means of transport.
5.3. Containers of more that 50 kg shall be equipped with a sufficient number of adequately designed, positioned and maintained securing points enabling them to be securely fastened to the means of transport where they are to be loaded. Containers shall be secured to the means of transport before the start of the journey to prevent displacement due to the motion of the means of transport.
Key points would be
ventilation - so make sure crate has plenty of ventilation slats at the top, and if transporting with windows open and not in middle of day in summer. Early morning for Abattoir is best anyway.
Construction to prevent leakage - so lip at the front.
be cleaned and disinfected - highly critical. A wooden crate with wood inside might not be deemed to pass the test, so you would need it lined in some form to give a cleansible surface.
Ramp and sidegates essential
Chapter III
1.4. (a) Ramps shall not be steeper than an angle of 20 degrees, that is 36,4 % to the horizontal for pigs. Where the slope is steeper than 10 degrees, that is 17,6 % to the horizontal, ramps shall be fitted with a system, such as provided by foot battens, which ensure that the animals climb or go down without risks or difficulties;
So you'll need to pay attention to how big your ramp is, you may need to create a folding one to fit it in !
Chapter III
2. During transport
2.6. Sufficient ventilation shall be provided to ensure that the needs of the animals are fully met taking into account in particular the number and type of the animals to be transported and the expected weather conditions during the journey. Containers shall be stored in a way which does not impede their ventilation.
So make sure crate has plenty of ventilation slates at the top, and transporting with windows open and not in middle of day in summer. Early morning for Abattoir is best anyway.
WARNINGS !!
The above are just the key points I think you would need to consider of this regulation which is 44 pages of small text ! If in doubt suggest you make some strong coffee and go to
http://eur-lex.europa.eu/homepage.html?locale=en and put in year 2005 document 1
Your abattoir can put any other rules in place that it wishes - quite simply if you want to do business with them you have to comply with whatever terms of business they want, so Bloomers point about talking to the abattoir is key
Finally it is up to to the State Veterinary Service (SVS) who are supposed to be in charge of animal welfare at the Abattoir who may deem your transport unsuitable. They have powers to condemn your animal if not transported legally, in which case it is killed and carcass disposed of - you get a bill for killing and disposal from the abattoir, no pig and possible prosecution. However many SVS never come out of their offices as the paperwork for the job makes it impossible to actually do the job - ticking the boxes takes precedence over any actual real welfare, and the risk if you have make a good effort to comply is very small.
Don't be put off by all the above, just go in with your eyes open, and knowing that most officialdom likes the easy answer which is a proper livestock trailer so they don't have to think too hard !
Have fun