Officers were called to a property in the Ashton area, near Helson, Cornwall, after midnight on Friday.
A 36-year-old man from Penzance has been arrested on suspicion of murder, and remains in custody, according to Devon and Cornwall Police.
Her next of kin have been informed, police added.
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Detective Inspector Pete Gee said: "A police cordon has been established at the scene, and inquiries are ongoing.
"At this time, I would like to reassure the community that incidents of this nature are very rare, but if anyone has any concerns, I encourage them to approach and speak to our officers.
"A heightened police presence is expected to remain in the area over the next few days as inquiries are ongoing."
The animals, which are 2ft 8in tall, are believed to have been taken between 8pm on 27 May and 1am on 28 May.
A gate was also damaged during the incident on Marsh Green Road, near Edenbridge.
Investigators have released images of the stallion and are appealing to members of the public for help in finding the pair.
Officers have carried out house-to-house inquiries and looked at CCTV, as they urged local residents who might have footage to contact them.
The stolen animals are a breeding pair of Argentine Falabella horses.
The stallion is described as white with brown spots, while the mare is described as black.
The Falabella breed originated in Argentina during the mid-19th century through careful and selective breeding, according to the Northcote Heavy Horse Centre sanctuary.
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Over time, these miniature horses became prized for their consistent size, refined appearance, and friendly temperament, the sanctuary has said.
Although often mistaken for ponies, Falabellas are horses in miniature form, it added.
Chiedza Nyanjowa, from Cheshire, was taken to Alder Hey Children's Hospital after getting into difficulty while swimming on Formby beach on Bank Holiday Monday, 25 May.
Emergency services were called to reports of a concern for safety around 3.30pm.
Chiedza died in hospital on Saturday.
In a tribute, her family described her as a "bubbly person" who "loved Christ and going to church".
"She loved cooking, she was a giver and wanted to be [a] nurse when she grew up so she could give back," they said.
"She will be greatly missed and remembered for her kind spirit."
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Listen: Why are so many young people drowning in open water?
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High temperatures have attracted many to open water swimming, and there have been fatalities in South Yorkshire, West Yorkshire, Cornwall, Hampshire, Warwickshire, Cheshire, Pembrokeshire, Lincolnshire and Lancashire.
The Royal National Lifeboat Institution (RNLI) has issued a water safety warning following the spate of deaths, urging people to follow key safety advice if they find themselves in trouble in open water.
It warned that: "While the sea or open water may look inviting during hot weather, it remains dangerously cold, putting even the strongest of swimmers at risk of cold water shock."
Cold water shock is a physiological reaction that happens when a sudden change in skin temperature occurs - for example, from hot air to cold water.
It can cause uncontrollable gasping and an increase in blood pressure and heart rate, which can lead to panic and drowning very quickly.
Sky News meteorologist Christopher England said Saturday was the last of the really hot days of the current dry spell.
Near-average temperatures are expected for the next week, with some rain as well.
The US rapper had been due to perform in the city of Reggio Emilia this summer.
But local official Salvatore Angieri ordered its cancellation because of concerns over the potential for protests, with West, known as Ye, having faced a wave of cancellations following years of antisemitic remarks.
The northern city has also banned a concert from Travis Scott, another American rapper.
Scott has faced scrutiny over safety at his concerts since a 2021 crowd crush at the Astroworld festival in Houston, Texas, that killed 10 people and injured hundreds.
He had been due to perform at the Pulse of Gaia Festival on 17 July at the 103,000-capacity RCF Arena, with West scheduled to appear the following day.
Angieri said the decision was taken following requests from a consumer group and the Jewish community in Modena and Reggio Emilia, which had raised concerns about West.
Italian authorities cited the close timing of the two shows and the high influx of spectators expected within 24 hours as factors behind the ban.
They also pointed to the cancellation of other West concerts in Europe, and the "concrete risk" of protests.
This year's Wireless Festival was cancelled in April after West was blocked from coming to the UK.
The ban was announced as his presence would "not be conducive to public good" after a backlash over West being booked to headline all three nights of the London event.
In response, West offered to meet members of the British Jewish community.
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Later that month, a concert in Poland was cancelled, and he also postponed a Marseille show after reports that the French government had sought to block it.
West has apologised for his past remarks, saying they were linked to untreated bipolar disorder.
He said in January: "I am not a Nazi or an antisemite. I love Jewish people".
West is set to hold concerts in the Netherlands next month after its migration minister said there were no legal grounds to deny him entry.
Dutch politicians had urged the government to bar West, citing his past remarks and expressions of admiration for Nazism and Adolf Hitler.
Lucas, who was married to director George Lucas between 1969 and 1983, died on Wednesday surrounded by loved ones in Rancho Mirage, California, from metastatic cancer, a lawyer for her family said.
She was the editor of the original 1977 Star Wars film, 1983's Return of the Jedi, as well as George Lucas's earlier films THX 1138 and American Graffiti.
In the decades since the film franchise's release, Lucas has come to be recognised as a pivotal creative force behind the development of the first Star Wars film, which is now known by its subtitle A New Hope.
She was pivotal in developing Obi-Wan Kenobi's plotline by convincing her then-husband that the character, played by Alec Guinness, should have a lightsaber battle with Darth Vader and become a spirit guide to Luke Skywalker, played by Mark Hamill.
When she was editing the space opera, she was acknowledged for being able to make sense of the raw footage, including the climactic rebel attack on the Death Star, which could have descended into narrative chaos.
"It was extremely complex and we had 40,000 feet of dialogue footage of pilots saying this and that. And she had to cull through all that, and put in all the fighting as well," Lucas told Rolling Stone a few months after the film was released.
"Nobody really has ever tried to interweave an actual plot story into a dogfight, and we were trying to do that."
Lucas was also part of the team that edited director Martin Scorsese's 1970s films Taxi Driver, Alice Doesn't Live Here Anymore and New York, New York.
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Lucas was born Marcia Griffin in Modesto, California shortly after the end of World War II. She moved to Los Angeles with her mother after her parents divorced as a small child.
She began working as a film librarian and moved into working as an editor.
Lucas was an assistant editor on the documentary Journey to the Pacific, where she met George Lucas, who was then a film student.
They became engaged soon after.
After they divorced, she was married to Tom Rodrigues, a production manager at the Skywalker Ranch production centre, from 1983 to 1993.
"Her influence on film is indelible, but those who knew her best will remember the way she made life feel more vivid, more beautiful, more fun, and more full of love," her family said in a statement released on Friday.
"Her work was known for its emotional intelligence, rhythm, and humanity - a rare ability to find the truth of a scene and bring heart, momentum, and clarity to the screen."