Over a 10-year period 104 farms in the North Island were attended on a consultancy basis, and of these, 29 farms were identified as having clinical signs associated with iodine deficiency (high peri-natal calf mortality, poor conception rate and/or low pregnancy rate). Mean pasture iodine concentrations (n=24) were 0.28 mg/kg (SD=0.16) (‘adequate’ range: 0.40-0.80 mg/kg). Mean animal plasma inorganic iodine (PII) concentrations (n=17) were 40.6 μg/L (SD=16.28) (‘inadequate’ range <45 μg/L). Marginally low iodine status (20-45 μg/L) was present in 13.5% of farms (14 of 104). The overall average deficit for the farms with low pasture iodine (n=19) was calculated to be 3.0 mg iodine per cow per day. Corrective treatment was computed for each farm and made pri-marily through weekly addition of iodine to the drinking water. Following iodine supplementation, mean animal PII was 60.8 μg/L (SD=19.50), a 50% increase over initial values. For individual cattle, there was a significant reduction in the proportion (73.5% to 23.5%) whose PII was marginally low (P=0.001). Clinical responses in livestock were monitored, and on the iodine supplemented farms there was some evidence for a reduction in peri-natal calf mortality and an increase in conception rates, but the amount of data was limited. Iodine supplementation was seen to contribute to an overall increase in pregnancy rates on ten farms (from 79.4% to 91.1%). It is concluded that iodine deficiency is common in North Island pasture-based livestock farms, that it is responsive to dietary supplementation, and that supplementation may be associated with improved reproductive performance.

PD, Anderson, DON McGhie, and TJ Parkinson

Proceedings of the New Zealand Society of Animal Production, Volume 77, Rotorua, 77-81, 2017
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