Livestock carrier
A livestock carrier is a large ship used in the live export of sheep, cattle and goats. They are specially built new or converted from container ships. Livestock carriers. Seagoing vessels modified or purpose-built for the transportation of live animals. Subject to appropriate regulation, live animals may be transported as part of the cargo on various classes of ship. That particular method of transportation is more common on short sea crossings (e.g. ferries) and usually involves relatively small numbers of animals. Livestock carriers are those ships, which specialise exclusively in the transportation of large numbers of live  animals together with their requirements for the voyage. (food, water, sawdust bedding, medication, etc.). Voyages on livestock carriers generally last from three days to three or four weeks. Some have lasted for months when disease outbreaks are suspected. Types of animals transported. Various species have been transported in this way, but by far the most numerous are the domesticated breeds of sheep and cattle. During the latter half of the twentieth century, millions of sheep and many thousands of cattle were transported on livestock carriers. Other domesticated species which have been transported, though in smaller numbers, include horses, camels, deer , goats and, on at least one occasion, ostriches. The transportation of live fish, on small specialised vessels, is a similar trade which has developed in association with fish farming. National authorities, which permit the export or import of live animals, regulate and monitor the ships and the associated aspects of the trade very closely, in particular to minimise the likelihood of introducing infectious disease. Sizes and capacities. The size of this type of ship varies, according to market demands in different parts of the world at different times. In the latter half of the twentieth century, the principal livestock exporting  nations were Australia and New Zealand and the main importers were nations in the Middle East. Vessels engaged in that trade have ranged in size from to . The limiting factors on ship size are complex. Bigger vessels can achieve economies of scale in their operations but also require more extensive port facilities to handle the larger numbers of livestock likely to be loaded or discharged. Livestock carriers carry more crew members than conventional cargo ships of a similar size. Experienced stockmen are an essential part of the crew. The total number of stockmen required varies according to the number of  animals and also depends on factors such as the arrangement of the livestock pens and the extent of automated systems installed for feeding and watering. During the last three decades of the twentieth century, there was a progressive trend towards large vessels carrying greater numbers of animals. Prior to that, a significant limitation had been fresh water storage capacity on ships. To maintain condition, average-sized cattle require at least forty litres of water per head, per day. Sheep require at least four litres per head, per day. Developments in water production technology (salt water evaporators or reverse-osmosis systems ) eventually led to livestock carriers with equipment capable of producing up to 600 tonnes of fresh water per day. Sheep and cattle also require fodder amounting to at least 2% of their body weight per day. Livestock carriers are required to carry sufficient feedstuffs for the maximum length of the voyage, as well as adequate reserves for emergencies. Medium-sized vessels with capacity for about 30,000 to 40,000 sheep (or 3000 to 4000 head of cattle) are a common size for this type of ship. However, during the last two decades of the twentieth century, there were a small number  of sheep carriers which had capacity for 130,000 sheep. There were at least two other large livestock carriers which specialised in combined cargoes of cattle and sheep. One had capacity for about 7,000 cattle and 70,000 sheep and the other could carry 14,000 cattle and 20,000 sheep. In 2007 the livestock carrier "Deneb Prima" was loading cargoes amounting to 20,000 cattle and 2000 sheep. The numbers detailed above are only general indications. The space allocated to animals on livestock carriers is officially regulated according to their size and weight ranges. Larger and heavier animals are allocated proportionately more space per  head. Safety record. Livestock carriers are twice as likely to be declared an accidental economic loss as other types of cargo vessel.