27 May 2014

2 minute read

The return to normal cyclic ovarian activity after calving usually occurs, on average, by 30 to 35 days postpartum. The first heat is usually silent, and the first cycle after this heat is usually short (8-12 days). This means that most cows should have commenced displaying behavioural oestrus by days 38-47 post-calving or earlier.

Failure to show signs of heat by 60 days after calving is called Postpartum Anoestrus. This can be due to either True Anoestrus or Suboestrus.

• Suboestrus is when cows have normal cyclic ovarian activity, but are not detected in oestrus due to weak or silent heats, or due to inadequate observation.
• True anoestrus is when cows have inactive ovaries.

Approaches to resolving suboestrus should include improving heat detection technique, and ensuring that observations are long enough (30 minutes) and frequent enough (3 – 4 times per day). On-farm milk progesterone kits may also be helpful (if progesterone is high, then the cow is cycling).

Resumption of cyclicity after calving is influenced by nutritional status, body condition score, milk yield, calving difficulty, uterine infection, breed, age, and concurrent disease.

Treatment of true anoestrus should first examine the nutritional status and body condition score. These can be improved by increasing pasture allowance, increasing concentrate feeding, and/or reducing the energy output in milk by restricting anoestrus cows to once a day milking.

If calving records indicate that some of the anoestrus cows had calving difficulty, or had retained foetal membranes or metritis after calving, these cows should be examined for the presence of pyometra or endometritis. If present, these will first need to be eliminated before treating for anoestrus.

Hormonal treatments can be used to stimulate a resumption of cyclicity, and are most effective if combined with increased energy intake.

Treatments involve use of progesterone-releasing devices (e.g., CIDR, PRID) which result in ovulation, and resumption of normal cyclicity. At this stage of the year (late May), it is desirable to breed cows to the ovulation induced by the progesterone treatment (i.e. breed them as soon as possible).

The treatment outlined at the bottom of the page stimulates resumption of cyclicity, and also facilitates fixed-time AI (FTAI) at the end of the hormone protocol. Fixed-time AI means there is no requirement for behavioural oestrus behaviour, and hence heat detection is not required.