Hydrated Lime

What are the allowances for hydrated lime in organic livestock production?

By Nick Stansbury

Hydrated lime is a synthetic material that consists primarily of calcium hydroxide. It can also contain magnesium hydroxide, along with other trace minerals. To produce it, manufacturers heat limestone to form solid quicklime (calcium oxide, CaO) and gaseous carbon dioxide. They then hydrate the quicklime with a slow addition of water. 

Lime, hydrated appears at §205.603(b)(6) on the list of “synthetic substances allowed for use in organic livestock production” as an external pest control. However, it carries an annotation that prohibits its use in cauterizing physical alterations or deodorizing animal wastes. This prohibition includes use as a material for spreading on livestock facility floors to prevent slipping. 

Hydrated lime has other uses that are allowed in organic livestock production as well. As a form of calcium hydroxide, hydrated lime can be used as a trace mineral (§205.603(d)(2)). Likewise, calcium hydroxide is also allowed in pesticide formulations as an inert ingredient per §205.603(e). It may also be allowed as an excipient in some circumstances, described at §205.603(f).

The annotation for the Hydrated lime (calcium hydroxide) category in the OMRI Generic Materials List^© explains that it is restricted for use as an external pest control (categorized by OMRI under Livestock External Parasiticides and Pesticides, or LP). However, calcium hydroxide is also included as an allowed or restricted substance (either explicitly or implicitly) in other categories: 

• Calcium (Livestock Feed Ingredients, LF)
• Inerts, List 4 (LP)
• Excipients (Livestock Health Care, LH)

While the uses as a trace mineral, inert or excipient are relatively straightforward, what qualifies as an “external pest control” use is more complex. Materials listed at §205.603(b) are generally allowed for use as topical treatments, external parasiticides or local anesthetics—provided they are listed without annotation or are specifically allowed for those uses based on the individual annotations. The annotation for Lime, hydrated states that the material is allowed for use as an external pest control. OMRI considers the terms “topical treatment” and “external parasiticide” to qualify as “external pest controls.” External pest control is the control of pests on animal bodies (e.g., to control fleas or ticks). The materials allowed as external parasiticides at §205.603(b) may not be administered internally; the parasiticides allowed for internal use appear at §205.603(a)(17).  

This article was originally published in the spring 2019 edition of the OMRI Materials Review newsletter, and was revised in August 2024 by Research and Education Manager Peter Bungum.