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XLVets Fact Sheet
Reprduction & Fertility RF
The Oestrus Cycle MISSED HEATS
Detection of oestrus or heat Heat detection and
involves being able to observe and record behaviour associated with cycling. The most reliable sign is dealing with problems
observing a standing response when ridden. There are various reasons why heats are missed; usually because cows are not showing heat strongly or staff are The average oestrus cycle of the cow is 21 days, ranging between 18 – 24 not observing cows when they are days. Heifers start cycling at the onset of puberty and will continue to cycle until they are in calf. The onset of puberty can be affected by various factors The main causes of this are: such as nutrition, growth rate (poorly grown heifers will take much longer to • Increased herd size leading to
reach puberty and start cycling), breed, and disease. After calving mature more cows per member of staff.
cows usually take a minimum of 35-42 days to start cycling again, whereas • Failure to recognise oestrus due
heifers usually take longer – up to 10 days longer. This may be extended in to inadequate staff training.
high yielding cows or those affected by disease post calving. • Looking at the wrong time of day.
The oestrus cycle is governed by the complex interactions of various hormones that are produced in the brain and ovaries; progesterone and • Poor environment: Slippery
oestrogen being two of these. The follicle (egg) grows throughout the cycle floors and overcrowding will and ovulation (the release of the egg) occurs when the progesterone levels reduce the chance of cows drop and the oestrogen rises. A structure called the corpus luteum then forms exhibiting normal oestrus on the ovary, which then produces progesterone. Any cows that haven't cycled after 35-42 days should be examined by your vet to check for any • Short weak oestrus: The average
abnormalities and to help maximise her chances of early conception.
cow is in oestrus for a shorter period than she was 25 years ago. This has partly been blamed • Altered behaviour – such as
on increasing milk yields.
Oestrus is defined as the period of changing order in which she is maximal sexual activity. The average usually milked, coming back to the duration is thought to be only eight shed after milking.
hours for the modern dairy cow, • Clear vulval mucus (‘bulling string').
however it can range from 2 - 30 hours. • Rub marks/sores over the tail head.
There are various signs and different animals will express these to varying • Mounting other cows, particularly
mounting the cow from head on.
Oestrus signs include: • Standing to be mounted.
• Increased restlessness (including
• Saliva or mud marks on the flanks
bellowing) and activity.
from other cows mounting her.
• Decreased feed intake and milk
The Oestrus Cycle Days of oestrus cycle This graph shows the waves of progesterone and oestrogen, with the cow being in heat during the surge in oestrogen. If the cow does not become pregnant this is repeated. If she is pregnant the progesterone level remains high.
XLVets Committed to NZ farming

XLVets The Oestrus Cycle
Reprduction & Fertility RF
Improving heat detection
Heat detection may be further
For good heat detection there must be: improved by:
• Detecting and recording pre mating heats –
Clear identification of cows by freeze branding or clean easy to read ear tags these give an idea of when cows will be on (ideally in both ears).
heat again, and will help reduce the chances of heats being missed if they are quiet. Pre • A good system outlining the staff
mating heat detection will also give an early members responsible for heat detection idea of the herds cycling status and will and how those cows will be identified therefore allow early planning of veterinary or and removed from the herd for AI, or nutritional intervention if needed.
recorded only if bull matings.
• Heat mount detectors. These are stuck on the
• Regular oestrus observation. Try and
on the tail head of the cow and are triggered set aside three periods of 20 – 30 by the pressure of another cow mounting them, minutes throughout the day that are not associated with feeding or milking, for leading to a colour change. Examples of these heat detection. Most mounting activity are Kamars™, or Estrotect™ scratchies.
will take place between 6pm and 6am • Tail paint. This works by a similar principle to above
so it is important to observe cows during with paint rubbed off by mounting behaviour. This this period. A good time of day is two needs to be reapplied when it becomes dry and hours after the cows have been locked cracked, touch ups twice weekly are recommended.
away in the paddock when the majority of cows are settled and sexually active • Motion detectors/pedometers. These are attached
groups may be more apparent.
to either the neck or leg bands respectively and any increases in walking activity are remotely detected and • A good recording system, either
recorded on a computer. These can be very useful computerised or manual, with all heats but care must be used in interpreting them as there recorded into a central place.
may be other reasons for increased activity – such as • Adequate light to ensure cows can be
calves in nearby paddocks or other stock movements seen in heat and identified.
past the paddock.
COST OF LONGER CALVING TO CONCEPTION
There are many costs associated with an extended calving to conception interval – most notably a lower 6 week in calf rate which means less There are various hormone days in milk. The relative cost per day increases the longer the interval treatments available for both cows and includes extra feed costs, loss of milk yield (days in milk/production that have cycled pre mating, and efficiency) and potentially increased veterinary costs. those that are anoestrus (‘not Ensuring cows are at target Body Condition Score (BCS) at calving (5 for cycling'). In some herds it may cows and 5.5 for heifers), as well as having a condensed calving pattern be appropriate to use hormone will help encourage cows to start cycling with sufficient time prior to the regimes to allow fixed time AI or planned start of mating (PSM).
to allow compacted periods of heat detection. There are several Veterinary intervention can be a tool to help detect problems and get options and the most appropriate cows cycling earlier. Prompt and early examination by a vet will lead to one for your herd can be discussed identification of anoestrus ovaries, ovarian cysts and other abnormalities. with your vet.
This can help shorten the time until she is mated (and conceives) which ultimately increases days in milk and shortens time until she is at peak lactation for the next season.
For more information contact your local XLVets practice: XLVets Committed to NZ Farming. Go to www.xlvets.co.nz

Source: http://www.xlvets.co.nz/sites/xlvets.co.nz/files/The%20Oestrus%20Cycle.pdf