50 C.F.R. § 14.161 – Primary enclosures.

(a) Except as provided in § 14.106(j), ventilation openings must be located on at least two walls of a primary enclosure. When the required ventilation openings are located on two opposite walls of the primary enclosure, these ventilation openings shall comprise at least 16 percent of the total surface area of each ventilated wall. When openings are located on all four walls of the enclosure, the openings shall comprise at least 8 percent of the total surface area of each wall. At least one-third of the minimum area required for ventilation shall be located on the lower one-half of the enclosure, and at least one-third of the total minimum area required for ventilation shall be located on the upper one-half of the enclosure.
(b) No more than one terrestrial mammal (other than rodents) shall be transported in a primary enclosure. However, a mother and her nursing young may be shipped in the same primary enclosure if the shipment complies with the provisions of § 14.105(b).
(c) More than one rodent may be transported in the same primary enclosure if they are members of the same species and are maintained in compatible groups. Rodents that are incompatible shall be transported in individual primary enclosures that are stored and transported so they are visually separated. A female with young being transported for medical reasons shall not be placed in a primary enclosure with other animals. The following chart specifies maximum densities minimum space for transporting rodents that fall within the specified weight limitations. Max. No. refers to maximum number per primary enclosure; Space/animal refers to minimum area of floor space per animals. Rodents weighing more than 5,000 grams shall be transported in individual enclosures.
Density Guidelines for Rodents
Max. No. Space/Animal Ht. of Box
cm 2 in 2 cm in
wt. in grams of rodent:
220 or less 20 194 30 15 6
220-450 12 388 60 20 8
450-1000 6 770 120 25 10
1,000-5,000 2 2,310 360 30 12
(d) A primary enclosure used to transport terrestrial mammals shall be large enough to ensure that each animal has sufficient space to turn around freely in a normal manner. The height of the primary enclosure shall provide adequate space for the animal to stand upright in a normal posture with space above its head. The length of the primary enclosure shall be great enough to enable the animal to lie in a full prone position.

	Max. No.	Space/Animal	Ht. of Box
cm 2	in 2	cm	in
wt. in grams of rodent:
220 or less	20	194	30	15	6
220-450	12	388	60	20	8
450-1000	6	770	120	25	10
1,000-5,000	2	2,310	360	30	12