Krdytkyu

In David Blight’s biography of Frederick Douglas, he explains the young Frederick witnesses several violent beatings and or rapes by the age of 7 or 8.

It’s also unclear weather or not the head of the plantation or his sons has been Frederick’s father via rape.

How common was this practice? What % of enslaved women were raped at least once? What % of overseers or owners raped enslaved persons?

Question:

What % of slave owners in the anti bellum south raped their slaves?

Short Answer:

The best modern scholarship marks white rape on female slaves wide spread and systemic. Beyond that rape perpetrated upon female slaves in the antebellum south was so prevalent it could be termed endemic.

Detailed Answer:

My answer is indirect to your precise questions and thus probable unsatisfying but let me try to put a scope on both white rape upon female slaves and rape in general perpetrated on female slaves.

Without giving you the percentage you asked for I have found suggestive data on the topic. Two modern genetic studies measuring European DNA found in a statistically significant sample of African Americans as well as African DNA found in a sample of Americans of European descent.

The first study's conclusion is given be low. It finds that the genetic markers from African Americans are unlike those of native Africans and that the mostly likely reason for this is the proportion of European genes in the population.

Characterizing the admixed African ancestry of African Americans
Conclusions:

These results are consistent with historic mating patterns among African Americans that are largely uncorrelated to African ancestral origins, and they cast doubt on the general utility of mtDNA or Y-chromosome markers alone to delineate the full African ancestry of African Americans. Our results also indicate that the genetic architecture of African Americans is distinct from that of Africans, and that the greatest source of potential genetic stratification bias in case-control studies of African Americans derives from the proportion of European ancestry.

A second study which came out in 2009 included 5,269 self-reported African Americans, 8,663 Latinos, and 148,789 European Americans. This study made note that the 2000 US Census shows that 95 percent of African Americans and 97 percent of whites acknowledge only a single ethnic identity. Using modern Genome analysis this study showed that the percentage of non African DNA varied widely by state with the average African American possessing 24.0% European DNA.

Given men have X-Y chromosomes and women have X-X chromosomes, comparing the statistical traits on different chromosomes in the same population set, as well as specific characteristics of the different segments of DNA further interesting details were brought out. That African and European Races were mixing six generations ago with significant mixing prior to 1860. That approximately 5% of ancestors of African Americans were European females and 19% were European males. That more than six million Americans who self identify as European descendants carry African ancestry.

The Genetic Ancestry of African Americans, Latinos, and European Americans across the United States

Our estimated rates of non-European ancestry in European Americans suggest that more than six million Americans, who self-identify as European, might carry African ancestry.

....

We used the lengths of segments of European, African, and Native American ancestry to estimate a best-fit model of admixture history among these populations for African Americans (Figure S3). We estimate that initial admixture between Europeans and Native Americans occurred 12 generations ago, followed by subsequent African admixture 6 generations ago, consistent with other admixture inference methods dating African American admixture. A sex bias in African American ancestry, with greater male European and female African contributions, has been suggested through mtDNA, Y chromosome, and autosomal studies.6 On average, across African Americans, we estimate that the X chromosome has a 5% increase in African ancestry and 18% reduction in European ancestry relative to genome-wide estimates (see Table 1). Through comparison of estimates of X chromosome and genome-wide African and European ancestry proportions, we estimate that approximately 5% of ancestors of African Americans were European females and 19% were European males

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That the higher the state proportion of African Americans, the more African ancestry is found in European Americans from that state, reflecting the complex interaction of genetic ancestry, historical admixture, culture, and self-identified ancestry.

Broadly Female Slaves and Rape.

To quote Fredrick Douglas:

Much like believing an underage person could consent to sexual relations with an adult, the notion that an enslaved person could consent to any sexual relation with a master is perilously fraught. The plantation system dismantled any notion of consent by the enslaved. Indeed, if there is a central tenet of slavery it is depriving agency from one human and placing it in the craven hands of another.

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The rape of female slaves was systemic, prevalent and is one reason slavery was self sustaining and profitable. Given the importation of slavery was ended in the United States Jan 1 1808, slavery was thus by Fredrick Douglas's definition an institution based upon rape for nearly six decades prior to emancipation. Female slaves were systemically bred to produce more slaves.

Thomas Jefferson to John Wayles Eppes
I know no error more consuming to an estate than that of stocking farms with men almost exclusively. I consider a woman who brings a child every two years as more profitable than the best man of the farm. what she produces is an addition to the capital, while his labors disappear in mere consumption.

....

Women and the Domestic Slave Trade in the Antebellum South

In this same manner, the domestic slave trade confined slave women’s roles to this traditional sphere of motherhood. Fueled by the demand for more slaves, slave traders realized the potential of a female slave’s reproductive abilities to bring a profit.
...
By the end of the eighteenth century, “a woman’s reproductive ability had clearly become part of her appraised value” (28). Meanwhile, single men and women who could not have children were sold before couples who produced children (270). At auctions, a woman’s reproductive abilities could be “assessed” by looking at her genitals and examining her breastfeeding abilities (264). This clearly shows that the domestic slave trade placed value on slave women in accordance with their ability to reproduce.

As for empirical evidence

• We know Elizabeth Keckly, a slave for 3 decades who won her freedom for herself and her son and then later became a famous seamstress famous for providing dresses for Lincoln's wife, Mary Todd Lincoln. Ms. Keckly wrote in her autobiography, "Thirty years a slave", that she was repeatedly raped in her youth.
  ...
  Keckly’s mother, Agnes, was an enslaved woman assaulted by Armistead Burwell, her master. The sexual exploitation was generational and resulted time after time in white men owning their children in bondage just as Chesnut described.

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The Loathsome Den Sexual Assault On the Plantation

In 1868, Elizabeth Keckly published Behind the Scenes: Or, Thirty Years a Slave and Four Years in the White House. The memoir detailed the 50-year old Keckly’s three decades as a slave, how she secured freedom for herself and her son, and her friendship with the Lincolns during the Civil War. Also within the pages of her book was Keckly’s public revelation that she had been routinely raped by a white man when she was a young woman. Although revealing the abuse, Keckly chose to “spare the world his name.”

THE LOATHSOME DEN– SEXUAL ASSAULT ON THE PLANTATION
white Southerner Mary Chesnut in 1861 as “the thing we cannot name.” Chesnut continued by noting the delusion needed to ignore sexual misconduct: “[E]very lady tells you who is the father of all the Mulatto children in everybody’s household, but those in her own, she seems to think drop from the clouds or pretends so to think.”

Fredrick Douglas

“My father was a white man. He was admitted to be such by all I ever heard speak of my parentage. The opinion was also whispered that my master was my father; but of the correctness of this opinion, I know nothing; the means of knowing was withheld from me.”

Solomon Northup in "twelve years as a slave".

The plight of Patsey is a central part of his memoir. Edwin Epps, master of Northup and Patsey in Louisiana, routinely assaulted Patsey sexually, physically, and emotionally. Master Epps’s abuse of Patsey brewed an intense jealousy on the part of Mistress Epps, who was effectively powerless to stop her husband’s behavior. She futilely begged him to end the rapes. Reaching that dead end, Mistress Epps herself began to physically abuse Patsey as the only retaliatory recourse against her husband. As Northup summarized, “The enslaved victim of lust and hate, Patsey had no comfort” as she endured the status of abused pawn in the Epps’s marriage.

Harriet Jacobs in her memoir, Incidents in the Life of a Slave Girl Jacobs would lament that it was “criminal” for “a favorite slave…. to wish to be virtuous.”

Systemic Evidence

Slave auctions had an entire class of slaves suitable for exploitation by their purchaser. These "fancy" slaves were purchased at a premium.

historians like Walter Johnson, who have researched slave auctions. Johnson identified that “favorite” or “fancy” female slaves sought for sexual exploitation could make handsome profits for slave dealers. A trafficker named Phillip Thomas in Richmond, Virginia, described one such purchase: “13 years old Girl, Bright Color, nearly a fancy for $1135.”

Why did LBJ, a staunch segregationist, champion and sign the 1964 Civil Rights Bill?

Sources:

• American Journal of Human Genetics: AJHG


• AJHG: The Genetic Ancestry of African Americans, Latinos, and European Americans across the United States


• Wiki: Female Slavery in the United States


• The Loathsome Den Sexual Assault On the Plantation


• Fredrick Douglas


• Women and the Domestic Slave Trade in the Antebellum South