Vitamin A and Carotene Requirements of Fattening Beef Cattle

During the last 25 years, several experiments have been conducted to study the amount of vitamin A and carotene needed by cattle. More emphasis has been devoted to carotene since cattle rations contain varying amounts of this precursor of vitamin A. Increasing market demands for lightweight cattle have brought about changes in methods of feeding. Cattle are being fattened rapidly at young ages using rations which contain a large amount of concentrates. Such rations are often low in carotene and need vitamin A or carotene supplementation. Recently, several research workers have questioned the adequacy of present recommended vitamin A and carotene requirements for cattle, based largely on research conducted several years ago, under current feeding systems using young cattle fed for rapid rates of gain. The need for re-evaluation of the requirements has been given increased attention recently, since some investigators have reported vitamin A deficiency symptoms in animals that were receiving vitamin A and/or carotene considered adequate by recommended standards. It is apparent that there is a need for additional information, particularly on the vitamin A requirement for cattle and the vitamin A value of carotene for them. There is also a periodic need to re-evaluate nutritive requirements of livestock as changes occur in methods of feeding and management. The research project reported in this thesis was conducted to study the value of various levels of vitamin A and carotene in meeting the vitamin A need for fattening steers. The rations fed were all-concentrate rations consisting of rolled barley and protein supplement. The rations were formulated to provide different levels of either vitamin A palmitate or carotene from dehydrated alfalfa meal, with the vitamin A and carotene intakes being adjusted to body weight at periodic intervals. It was the purpose of this experiment to provide information concerning the amounts of vitamin A as well as carotene needed to satisfy the animal’s need for vitamin A. In addition, since several levels of both vitamin A and carotene were provided, the results were expected to provide information concerning the vitamin A value of carotene for cattle. The criteria of evaluation in this experiment were weight gain, feed consumption, feed efficiency and vitamin A and carotene values of the plasma and liver. Blood samples were obtained at regular intervals throughout the study, and liver samples were obtained at the time of slaughter