1: Well-written

Check for WP:LEAD:

  1. Check for Correct Structure of Lead Section:  Done
  2. Check for Citations (WP:LEADCITE):  Done
  3. Check for Introductory text:  Done
    • Check for Provide an accessible overview (MOS:INTRO):  Done
      • Major Point 1: Characteristics "Kiger Mustangs are most often dun in color, although they are found in other solid colors. Compact and well-muscled in appearance," (summarised well in the lead)
      • Major Point 2: History "Originally feral horses with specific conformation traits discovered in 1977, the name also applies to their bred-in-captivity progeny. " & "DNA testing has shown that Kiger Mustangs are descended largely from Spanish horses brought to North America in the 17th century, a bloodline thought to have largely disappeared from mustang herds before the Kiger horses were found." (summarised well in the lead)
      • Major Point 3: BLM management and private ownership "The Bureau of Land Management (BLM) administers two herd management areas for Kiger Mustangs in the Burns District—Kiger and Riddle Mountain, in the Steens Mountain area." (summarised well in the lead)
    • Check for Relative emphasis:  Done
      • Major Point 1: "Kiger Mustangs are most often dun in color, although they are found in other solid colors. Compact and well-muscled in appearance," (the lead gives due weight as is given in the body)
      • Major Point 2: History "Originally feral horses with specific conformation traits discovered in 1977, the name also applies to their bred-in-captivity progeny." & "DNA testing has shown that Kiger Mustangs are descended largely from Spanish horses brought to North America in the 17th century, a bloodline thought to have largely disappeared from mustang herds before the Kiger horses were found." (the lead gives due weight as is given in the body)
      • Major Point 3: BLM management and private ownership "The Bureau of Land Management (BLM) administers two herd management areas for Kiger Mustangs in the Burns District—Kiger and Riddle Mountain, in the Steens Mountain area." (the lead gives due weight as is given in the body)
    • Check for Opening paragraph (MOS:BEGIN):  Done
      • Check for First sentence (WP:LEADSENTENCE):  Done
        • The Kiger Mustang is a substrain of Mustang horse located in the southeastern part of U.S. state of Oregon.
      • Check for Format of the first sentence (MOS:BOLDTITLE):  Done
      • Check for Proper names and titles:  Done
      • Check for Abbreviations and synonyms (MOS:BOLDSYN): None
      • Check for Foreign language (MOS:FORLANG): None
      • Check for Pronunciation: None
      • Check for Contextual links (MOS:CONTEXTLINK):  Done
      • Check for Biographies: NA
      • Check for Organisms: NA
  4. Check for Biographies of living persons: NA
  5. Check for Alternative names (MOS:LEADALT):  Done
    • Check for Non-English titles:
    • Check for Usage in first sentence:
    • Check for Separate section usage:
  6. Check for Length (WP:LEADLENGTH):  Done
  7. Check for Clutter (WP:LEADCLUTTER): None
 Done

Check for WP:LAYOUT:  Done

  1. Check for Body sections: WP:BODY, MOS:BODY.  Done
    • Check for Headings and sections:  Done
      • Heading 2 History is not accurate because from Heading 3 BLM management and private ownership onwards, the timeline is from 2007 to 2013. Refer this FA - Marwari horse, Heading 2 is History and Heading 3 is 1900s to today which renders clarity to the timeline. Also refer this FA - Andalusian horse, Heading 2 is History and "Heading 3"s are Early development, Dissemination, etc..
      • In this case, I'd recommend using BLM as Heading 2 instead of History. In the History section, after the statement "In 1971, the Wild and Free-Roaming Horse and Burro Act was passed ...", BLM becomes the focal point.
    • Check for Section templates and summary style:  Done
    • Check for Paragraphs (MOS:PARAGRAPHS):  Done
  2. Check for Standard appendices and footers (MOS:APPENDIX):  Done
    • Check for Order of sections (WP:ORDER):  Done
    • Check for Works or publications:  Done
    • Check for See also section (MOS:SEEALSO): None
    • Check for Notes and references (WP:FNNR):  Done
    • Check for Further reading (WP:FURTHER): None
    • Check for External links (WP:LAYOUTEL):  Done
    • Check for Links to sister projects: None
    • Check for Navigation templates:  Done
  3. Check for Formatting:  Done
    • Check for Images (WP:LAYIM):  Done
    • Check for Links:  Done
    • Check for Horizontal rule (WP:LINE):  Done

Check for WP:WTW: None

None

2: Verifiable with no original research

 Done

Check for WP:RS:  Done

Cross-checked with other FAs: Icelandic horse, Marwari horse, Andalusian horse, Haflinger (horse), Boulonnais horse, Poitevin horse

  1. Check for the material (WP:RSVETTING): (not contentious)  Done
    • Is it contentious?: No
    • Does the ref indeed support the material?:
  2. Check for the author (WP:RSVETTING):  Done
    • Who is the author?:
      • (Kiger Mesteño Association)
      • (The International Museum of the Horse)
      • Dutson, Judith (Storey Publishing)
      • (U.S. Geological Survey)
      • (Bureau of Land Management)
      • (Steens Mountain Kiger Registry)
      • (Kiger Horse Association and Registry)
      • (Portland State University)
      • Steves, David (Eugene, Oregon: Guard Publishing)
      • (Return to Freedom American Wild Horse Sanctuary)
    • Does the author have a Wikipedia article?:
    • What are the author's academic credentials and professional experience?:
    • What else has the author published?:
    • Is the author, or this work, cited in other reliable sources? In academic works?:
  3. Check for the publication (WP:RSVETTING):  Done
    • Kiger Mesteño Association
    • The International Museum of the Horse
    • Storey Publishing
    • U.S. Geological Survey
    • Bureau of Land Management
    • Steens Mountain Kiger Registry
    • Kiger Horse Association and Registry
    • Portland State University
    • Eugene, Oregon: Guard Publishing
    • Return to Freedom American Wild Horse Sanctuary
  4. Check for Self-published sources (WP:SPS):  Done
 Done

Check for inline citations WP:MINREF:  Done

  1. Check for Direct quotations:  Done
  2. Check for Likely to be challenged:  Done
  3. Check for Contentious material about living persons (WP:BLP): NA
 Done
  1. Check for primary sources (WP:PRIMARY):  Done
  2. Check for synthesis (WP:SYN):  Done
  3. Check for original images (WP:OI):  Done


3: Broad in its coverage

 Done

Cross-checked with other FAs: Icelandic horse, Marwari horse, Andalusian horse, Haflinger (horse), Boulonnais horse, Poitevin horse

  1. Check for Article scope as defined by reliable sources:
    1. Check for The extent of the subject matter in these RS:
    2. Check for Out of scope:
  2. Check for The range of material that belongs in the article:
    1. Check for All material that is notable is covered:
    2. Check for All material that is referenced is covered:
    3. Check for All material that a reader would be likely to agree matches the specified scope is covered:
    4. Check for The most general scope that summarises essentially all knowledge:
    5. Check for Stay on topic and no wandering off-topic (WP:OFFTOPIC):
b. Focused:
 Done
  1. Check for Readability issues (WP:LENGTH):
  2. Check for Article size (WP:TOO LONG!):


4: Neutral

 Done

4. Fair representation without bias:  Done

  1. Check for POV (WP:YESPOV):  Done
  2. Check for naming (WP:POVNAMING):  Done
  3. Check for structure (WP:STRUCTURE):  Done
  4. Check for Due and undue weight (WP:DUE):  Done
  5. Check for Balancing aspects (WP:BALASPS):  Done
  6. Check for Giving "equal validity" (WP:VALID):  Done
  7. Check for Balance (WP:YESPOV):  Done
  8. Check for Impartial tone (WP:IMPARTIAL):  Done
  9. Check for Describing aesthetic opinions (WP:SUBJECTIVE):  Done
  10. Check for Words to watch (WP:YESPOV):  Done
  11. Check for Attributing and specifying biased statements (WP:ATTRIBUTEPOV):  Done
  12. Check for Fringe theories and pseudoscience (WP:PSCI): None
  13. Check for Religion (WP:RNPOV): None

5: Stable: No edit wars, etc: Yes

6: Images  Done (PD)

Images:
 Done

6: Images are tagged with their copyright status, and valid fair use rationales are provided for non-free content:  Done

  1. Check for copyright tags (WP:TAGS):  Done
    • Image (Mesteno.jpg): This work is in the public domain. The creator permanently relinquished all rights to the work.
  2. Check for copyright status:  Done Free
  3. Check for non-free content (WP:NFC): None
  4. Check for valid fair use rationales (WP:FUR): NA

6: Images are provided if possible and are relevant to the topic, and have suitable captions:  Done

  1. Check for image relevance (WP:IMAGE RELEVANCE):  Done
    • Image (Mesteno.jpg): Relevant.
  2. Check for Images for the lead (WP:LEADIMAGE):  Done
    • Appropriate & Representative
  3. Check for suitable captions (WP:CAPTION):  Done
    • Caption: "Mesteño, a Kiger Mustang stallion" succinct and informative

As per the above checklist, the issues identified are:

  • To improve the flow of the prose, I recommend changing Heading 2 History to something more appropriate.

This article is a very promising GA nominee. I'm glad to see your work here. I'm putting the article on hold. All the best!