Split Heat in Dogs: What It Is and How It Affects Breeding Timing

A split heat catches breeders off guard because the female appears to come into heat, then seemingly stops before ovulation. Here is what is actually happening and how to handle it.

A split heat — also called an interrupted heat or a false start — is a heat cycle in which a female shows early oestrus signs (swelling, bloody discharge, attractiveness to males) but then the cycle pauses before ovulation and LH surge. After a pause of days to weeks, the cycle resumes and ovulation occurs normally.

If you breed based on visual signs during the first phase and do not progesterone test, you will miss the actual ovulation and the breeding will fail.

What Causes a Split Heat?

A split heat is caused by an insufficient initial surge of follicle-stimulating hormone (FSH) and luteinising hormone (LH) — the cycle starts, follicles begin developing, but the process stalls before the LH surge that triggers ovulation.

Split heats are:

• More common in young females during their first or second heat
• More common in certain breeds (Basenjis, which typically only cycle once annually, are particularly prone)
• Occasionally seen in females under stress or with nutritional deficiencies
• Occasionally a sign of underlying hormonal irregularity

Most females have one or two split heats in their lifetime, then cycle normally. Repeated split heats in an adult female may warrant a reproductive vet workup.

How to Recognise a Split Heat

Signs that may indicate a split heat:

• Swelling of the vulva and bloody discharge appear, then swelling recedes without the female reaching full standing heat
• The female is attractive to males initially but loses interest and males stop pursuing her
• Discharge changes and then stops before you would expect ovulation
• Progesterone remains in the baseline range (< 1 ng/mL) when you would expect it to be rising

Progesterone testing is the definitive tool. If you are running serial progesterone tests and values stay flat or rise only slightly before declining, the cycle has stalled. In a normal cycle, progesterone rises steadily from around 1 ng/mL at the LH surge to 5+ ng/mL at ovulation.

What to Do

Do not breed during the false start. Breeding a female during the initial phase of a split heat before ovulation will not result in pregnancy.

Wait. Most split heats resume within 1–6 weeks. Keep monitoring with periodic progesterone testing. When progesterone begins rising again and you see renewed oestrus signs, resume your full testing protocol.

Continue progesterone testing when the cycle resumes. Treat the resumed cycle as a new heat for timing purposes — start from the beginning of the protocol.

Communication with the Stud Owner

Contact the stud owner as soon as you suspect a split heat. If you had a breeding planned, explain the situation and ask whether the contract covers this circumstance. Most stud owners are familiar with split heats and will accommodate the delay. Some contracts specify a rescheduling window; check yours.

Summary

A split heat stalls before ovulation — the female shows early heat signs but does not ovulate on that cycle's timeline. Recognise it with progesterone testing: values that stay flat or drop before rising indicate a stall. Do not breed during the false start. Wait for the cycle to resume — typically 1–6 weeks — then run a full progesterone protocol from the beginning.