The Alpha Centauri Chicken Plague

Alpha Centauri has never been home to much livestock, simply because of the difficulty in getting it there. Some of the early colony ships did, however, bring some chickens with them. As the human population slowly grew, so did that of the chickens. Since few of the later immigrants bothered to bring more, even in the 2180s most of the system's chicken population was still descended from the initial few.
This of course left the gene pool dangerously small, and the chickens vulnerable to disease. Centaurian veterinarians did indeed have their work cut out for them, but apart from the occasional localized outbreak, they managed to keep things under control for most of the century.
That changed in 2184, though. An unknown sickness spread like wildfire through the chicken population. Over 90% died to the illness or had to be put down to control the spread of the disease. Eventually, the cause of the epidemic was determined: A strain of the seasonal flu had jumped species from humans to chickens. With this knowledge, a vaccine was quickly developed. Ironically, the role of chicken eggs in vaccine production had been a key motivation in establishing chicken farming in the first place.
Today, the Alpha Centauri chicken plague is considered eradicated. It did, however, leave the chicken population at unsustainably low levels, especially after the dangers of a shallow gene pool had made themselves known so drastically. The 2190s thus saw the beginning of the first systematic effort in establishing a large and sustainable population of a livestock in Alpha Centauri. Many interstellar ships now also carry a small flock of chickens, accompanied by a volunteer farmer or veterinarian.

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