Any batch of commercial collagen may consist of collagen obtained from cattle or pork or both. Pork gelatin seems to be the most frequently used.
Sometimes food-grade gelatin may be labelled as to the source, porcine or bovine.
It appears it may be sometimes gelatin may get rabbinical approved for kosher use even though it is not from kosher-slaughtered animals.
The specific animal that is the Earthly Origin of the collagen found any food item, medication, cosmetic, etcetera, is generally hard to determine. The source may differ from batch to batch, produced by the same manufacturer, depending, for example, upon market conditions at the time the collagen is purchased by the product's manufacturer.
According to what I can figure out, collagen is the name given to the certain animal proteins that are found in animal tissues, and gelatin is the name often given to these same proteins once they have been commercially extracted from such animal tissues. Such an extractive may be called "glue" or "hide glue" also, if the product is intended to be used as glue. Some extractives may be called collagen. Cosmetics labels frequently say collagen rather than gelatin. Whether the product is called collagen or gelatin or glue may be more related to what they are used for, rather than to their chemical nature or biological source. Though food grade gelatine may be filtered and clarified.
You might want to take a look at this page. It is an article at Fibrogen, a manufacturer of recombinant collagen. The company apparently has also developed recombinant gelatin. Here is another page on their recombinant gelatin products.
According to Materials Handbook by Brady and Clauser, 11th edition (1977), McGraw-Hill Book Co, ISBN 0-07-007069-5...
gelatin [is] a colorless to yellowish water-soluble tastless colloidal hemi-cellulose obtained from bones or from skins and used as... Gelatin differs from glue only in purity. Photographic gelatin is made from skins... "Vegetable gelatin" is not true gelatin, but is algin from seaweed.
Collagen is the gelatin-bearing protein in bones and skins. The bone is dissolved in hydrocholoric acid to separate out the calcium phosphate and washed to remove the acid. The organic residue is called osseine and is the proudct used to produce gelatin and glue. About 25% of the weight of the bone is osseine, and the gelatin yield is about 65% of the osseine... When skins are used, they are steeped in a weak acid solution to swell the tissues so that the collagen may be washed out. The gelatin is extracted with hot water, filtered, evaporated, dried, and ground or flaked.