Date of this Version
The influence of three levels (1.31, 1.03 T and 0.29% K) of dietary potassium on 40K count, blood serum and muscle tissue potassium was determined using 36 crossbred Angus-Hereford steers. A balanced 3 x 3 latin square experimental design was utilized which allowed estimates of carry-over effects of diets to be evaluated. Diets were fed for 2-week periods and appropriate samples and measurements were collected at 14-day intervals over a 60-day period. Measurements were made on steers unshrunk and after 24 hr. off feed and water. Carry-over effect means were nonsignificant for each trait. The steers on the high potassium diet had 447.5 higher unshrunk 40K counts per minute and 218 higher shrunk counts per minute than steers on the low potassium diet (P<.01). The steers on the high potassium diets had higher blood serum and muscle potassium concentrations than those on low potassium diets although these differences were not significant. Animal to animal variation in potassium concentration was an important source of variation in this study. It appears tissue potassium concentrations are not constant between animals and that this variation could be a limiting factor to the precision of estimating lean in live animals by 40K counting. These data indicate that the primary influence of dietary potassium to 40K counting is the effect on potassium content of the gastrointestinal tract contents.