In the United States of America, cattle feed consists primarily as hay or silage mixed with a grain, such as corn, barely and wheat. A high-protein supplement usually made from soybeans or rendered animal parts - typically chickens or pigs - is then added.
Some farms collect the blood of slaughtered cattle and feed it to cattle in dehydrated form. Spray-dried cow and pig blood is used in feed to provide protein, as a soluble product to mix in animals' drinking water and most commonly, as a milk replacement for calves. Cattle are feed ground-up remains of other animals (including pigs, dead and sick animals), gelatin, derived from cattle hoofs and other exempted materials.
The cattle which are fed blood, pig's ground up meat, bones and gelatin, are their foods are Halalan Taaiibaan (2:168) and would these cattle be Halaal to slaughter?
Sources of information:
Go to Google.com
Search for "Cattle feed" and click on the following:
1) The Seatle Times: Local News: New questions about high proteins.
2) USAToday.com - Consumer may have a beef with cattle feed.
3) Consumer groups point to holes in cattle feed rules, published on Saturday, January 3, 2004 by Reuters.
4) Seattle Post - Intelligencer: Weekly Farm: Cattle feed ban allows.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Animal feed that contain impure ingredients like pig, blood and dead animals are not permissible to use as food for animals if such impurities remain in those products. The animal that is fed on such manufactured products that are made of impure ingredients, takes the ruling of the animal that is fed on impurities; if its feed is mostly of those manufactured products or shows the effect of impurity in its breath, or taste. It is not permissible to eat an animal that is fed on impurities as the Prophet prohibited the meat of donkeys and prohibited to ride the animal that eats impurities or to eat it. [Abu Daawood and An-Nasaa'ee] The Hanbali and some scholars of the Shaafi'ee school are of the view that it is forbidden to eat the animal that eats impurities because of the prohibition mentioned in the narration, among whom is Ibn Daqeeq Al-'Eed and other outstanding scholars.

Therefore, it is not permissible to eat the meat of cattle that are fed mainly on such manufactured products or products mixed with impurities the effect of which lasts. However, if the animal is kept away from eating those products for three days before slaughtering, then it becomes permissible to eat. The evidence is that Ibn Abu Shaybah reported that Ibn 'Umar used to prevent the animal from eating such feed for three days.

However, if the impurities do not cause any effect and is transformed when manufactured into other materials, then according to many scholars it takes the ruling of the material to which it was transformed to, and therefore there is no harm in using such products as a feed for animals and there is no harm in eating the animals that are fed on them.

Allaah knows best.