An attempt to define the sodium requirement of lactating dairy cows in a tropical environment

Abstract

Consumption of a daily ration formulated to contain the current Na requirement set by the NRC appears to provide too much Na for lactating cows under tropical conditions. A tentative value of 1.2 g kg(-1) DM is proposed as the Na requirement for dairy cows under tropical conditions.

Response of saliva Na/K ratio to changing Na supply of lactating cows under tropical conditions

“…The clinical observations of Na deficiency were associated with decreased salivary Na and increased salivary K concentrations, leading to a salivary Na/K ratio of <4.3, which is indicative of Na deficiency. 18 The current observations on salivary Na and K concentrations are in line with data reported by Thiangtum et al, 5 who reported that the salivary Na/K ratio decreased to 4.8 when a ration was fed containing 0.4 g Na kg −1 DM for 32 days. In the latter study, however, no clinical signs such as pica were observed.…”

“…The data clearly show that supplemental Na did not restore the salivary Na/K to values of >6 . This was unexpected as the highest level of supplementation was calculated to exceed (1.7 g kg −1 DM) the dietary requirement (1.2 g kg −1 DM) of lactating dairy cows in a tropical environment. The actual Na consumed was found to be 1.6 g kg −1 DM for the HNa group.…”

“…The issue on Na losses with sweat in cattle remains and requires further research to obtain accurate values. The lack of unequivocal estimates on the Na losses with sweat, in combination with the fact that the Na‐supplemented cows did not restore their salivary Na and K concentrations, hinders potential refinement of the previous recommendation regarding the Na requirement of lactating cows under tropical conditions …”

“…Furthermore, Schneider et al reported an increased DM intake when the Na content of rations of lactating cows during heat stress was raised from 1.8 to 5.5 g kg −1 DM. The issue of Na requirement of dairy cows in tropical countries was addressed by Thiangtum et al , who arbitrarily suggested that dairy cows require a dietary Na content of 1.2 g kg −1 DM under tropical conditions. However, generalization of this tentative value of 1.2 g Na kg −1 DM is currently not warranted owing to a dearth of studies addressing the issue of Na requirements of dairy cattle in the Tropics.…”

“…As such, the use of salivary Na/K is a sensitive diagnostic tool to detect Na deficiency in ruminants. 4 Previously, Thiangtum et al 5 showed the value of salivary Na/K in detecting Na deficiency in dairy cows housed under tropical conditions. The current recommendations regarding an adequate Na supply for dairy cows ranges from 0.7 to 2.2 g kg −1 dry matter (DM).…”