EFFECTS OF DIETARY CAROTENE CONTENT ON MEAN-VALUES AND RANKINGS OF HEIFERS FOR PLASMA CAROTENE CONCENTRATIONS

An experiment was conducted with six Angus (AH) and six Jersey (JH) he ifers to determine the effects of dietary carotene on plasma carotene concentrations (PCC) and the consistency of the ranking of heifers on PCC. The heifers were divided into high, medium, and low liveweight gr oups and each group of four heifers was placed in a separate pen on a feedpad. The heifers were fed pellets comprising 25% lupin and 75% bar ley grain and containing either 500, 250, or 0 mg added carotene/kg pe llets. The pellets were fed at 1.1% of the mean liveweight of each gro up. Barley straw was available ad libitum. Pellets were given in a seq uence as follows: pellets with 500 mg added carotene/kg were given for 27 days followed by those with 250 mg added carotene/kg for 21 days, and 0 added carotene/kg for 70 days. Blood samples were taken every 2- 4 days and analysed for PCC. There were no significant effects of bree d on PCC except for a more rapid increase in PCC in JH than AH when re turned to pasture after being on the feedpad, and fed pellets containi ng 0 added carotene/kg. When introduced to the feedpad, nine heifers d eveloped clinical signs of acidosis. These effects may have accounted for a low PCC despite the heifers receiving pellets containing 500 mg added carotene/kg. On changing the carotene content of the pellets fro m 250 mg/kg to 0 added carotene/kg there was an exponential decrease i n PCC. Analysis of the data using iterative curve peeling methods indi cated a 2-component exponential model best fitted the data which sugge sted there were two pools of carotene affecting PCC. Despite large dif ferences in overall mean PCC there were high correlations between PCC measured on different days, in the heifers on the feedpad. In conclusi on, the ranking of heifers for PCC was relatively constant provided th e carotene intakes of the heifers were the same. The results also sugg est that acidosis may interfere with carotene absorption.