US researchers have discovered that phenylbutazone, a non-steroidal anti-inflammatory drug commonly prescribed in horses, can affect the ability of a mare’s egg cells—called ‘oocytes’—to become viable embryos, which is a crucial step in assisted reproduction in horses.
This discovery by the team at the Texas A&M School of Veterinary Medicine & Biomedical Sciences—and published in Theriogenology—is significant because of the time and money that horse owners often invest in assisted reproduction.
Just like humans, horses sometimes need help from science in order to reproduce. When they do, special steps are needed for a successful pregnancy because of the unique properties of equine sex cells.
“In horses, the process of in-vitro fertilisation (IVF) is more complex than it is in humans,” Dr Luisa Ramirez-Agamez said.
“First, a mare’s oocytes need approximately 30 hours to mature in the laboratory once they have been collected before they can be fertilised. Then, we have to inject the eggs with sperm to induce fertilisation, a process known as intracytoplasmic sperm injection (ICSI).
“We discovered that phenylbutazone, commonly known as bute, can affect both the ability of a mare’s eggs to mature correctly when cultured and whether the fertilised eggs will develop into a viable embryo.
“In either of those cases, the eggs affected by bute cannot be used in assisted reproduction.”
Assisted reproduction is an important resource for many horse owners, especially those who make a living from their herds. Many horse owners also care deeply about producing offspring from their favourite horses in order to carry on their legacies.
In some cases, mares who are chronically lame and unable to support a pregnancy themselves may become egg donors, with their eggs fertilised in a laboratory and carried to term by a surrogate.
“Mares who are chronically lame are likely going to be on bute because it helps with pain management—especially in the musculoskeletal system—which, according to our results, will hinder their ability to participate in assisted reproduction programs,” Dr Ramirez-Agamez said.
The good news is that bute’s effect on equine oocytes appears to wear off within a few weeks.
“We collected the eggs at three days post-treatment, then 33 days, and then 77 days,” Dr Ramirez-Agamez said.
“We found that eggs collected three days after administration of bute were not able to produce embryos, but those collected at 33 days were successful.”
