Selenium requirements in grazing dairy cows: a review

Area of Science:

• Animal Nutrition
• Trace Mineral Requirements
• Dairy Cattle Health

Background:

• Conflicting selenium (Se) intake recommendations for dairy cattle exist between New Zealand and other countries like the USA.
• Advisors in New Zealand often suggest higher Se intakes than current recommendations, causing farmer confusion.
• The study reviews evidence to assess the adequacy of New Zealand's Se recommendations for dairy cows on pasture-based diets.

Purpose of the Study:

• To evaluate the scientific basis of New Zealand's dietary selenium (Se) requirements and status thresholds for dairy cattle.
• To determine if changes in fodder crop usage affect Se requirements in New Zealand dairy cows.
• To clarify the appropriate Se intake levels for dairy cattle based on available evidence.

Main Methods:

• Review of published scientific literature on selenium requirements and status in cattle.
• Analysis of factorial models and on-farm experimental studies relevant to New Zealand conditions.
• Consideration of nutritional data concerning pasture and fodder crops in New Zealand dairy cow diets.

Main Results:

• The scientific basis for current New Zealand selenium (Se) requirements is robust, supported by validated models and studies.
• Increased use of fodder crops is unlikely to significantly alter Se requirements in New Zealand dairy cows.
• Existing New Zealand Se-status thresholds are generally supported, with no evidence of benefit from higher supplementation in marginal herds.

Conclusions:

• Current New Zealand selenium (Se) recommendations for dairy cattle are scientifically supported and unlikely to be too low.
• Claims for significantly higher Se intakes (e.g., 10x current) are not supported by the available evidence base.
• Further research on vitamin E and fatty acid content of fodder crops is needed for complete confirmation.