Proceedings of the New Zealand Society of Animal Production, 1996,
56: 138-142
Proceedings of the New Zealand Society of Animal Production, 1996,
56: 138-142
Twelve rumen cannulated ewes, weighing 45±2.5 kg, were used and randomly allotted according to a thrice-replicated 4x4 Latin square change- over design. Animals were offered 750 gDM/d (80% concentrate and 20% chaffed lucerne hay). Four levels of KCl were infused intraruminally to raise total K intake to 15, 25, 35 and 45 g/d, spanning the range of dietary concentration and intake normally experienced on spring herbage in New Zealand. A 14-d balance study followed by a 48-h continuous p.d. measurement was used.
Diurnal variation in p.d. was relatively small, less than 5 mV, but p.d. increased from 45.8±1.21 to 52.6±0.82 mV as K intake increased from 15 to 25 g/d and showed little change with higher levels. The relationship between p.d. and rumen K concentration was curvilinear and was described as y = 18.89 + 0.66(±0.175) [K] - 0.003(±0.001) [K2].
Apparent Mg absorption, as judged by urinary Mg excretion, decreased from 0.43±0.02 to 0.34±0.02 g/d, most of the depression occurring as K intake increased from 15 to 25 g/d. On the other hand, plasma Mg concentration decreased (p<0.05) linearly throughout the whole range of K intake from 1.08±0.03 to 0.90±0.01 mmol/l.
The results suggest at least two mechanisms of effect of K on Mg homeostasis and these are discussed.
Keywords: NZSAPAB; Magnesium, potassium, potential difference, absorption, sheep
