The indirect determination of energy retention in farm animals: I. The development of method

Abstract

1. Methods of estimating water retention in the body of cattle are discussed, and it is shown that methods based on determinations of the initial and final body-water content are of low accuracy and are not suitable for the indirect estimation of fat balance over a period of 24 days.2. Analyses of tissues from young and adult cattle showed that with the exception of serum, brain, skin and bone, water content of the tissues may be predicted from the following equation:Water_(g./100g.)= 0·292 Na_(mg./100g.)+ 0·147 K_(mg./100g.).This equation shows that 1 m.equiv. of the Na of tissues is associated with more water than is 1 m.equiv. of the K.3. No differences between cattle aged from less than 1 week to more than 5 years were observed in the relationship between water and Na and K content.4. The equation applied also to the contents of the digestive tract, other than those of the abomasum which gave low results, ascribed to the presence of a high concentration of H⁺ions.5. Analyses of whole foetuses for Na, K and H₂O showed that their water content could be predicted accurately. The same was true of amniotic fluid, but the water content of allantoic fluid was underestimated by 50%.6. It was shown that despite the anomalous behaviour of brain, serum, skin and bone, accurate predictions of the water content of the animal could be made from simultaneous determinations of Na and K retentions, providing a correction was made for the storage of bound Na in bone.7. Data are presented which indicate that the equations apply equally well to the tissues of the sheep.