Heat in cattle (Estrus) is the period when a cow or heifer is receptive to a bull. Heat occurs as a result of the release of estrogen from a maturing follicle in the cow's ovaries before ovulation and the secretions from the reproductive tract act as lubricant for breeding and help sperm swim to the uterus. Cows and heifers normally go into heat every 17 to 24 days average to 21 days. Poor heat detection may mean servicing a cow too early or too late leading to low conception rates hence lengthening the calving intervals. Successful heat detection on the other hand will result in more calves and milk from your cows, attracting more profits to the farm. It is therefore advisable to spend some time observing your cows to be familiar with their behavior so as to easily compare how they behave when in heat or not in heat. Some animals do not show signs of heat (anoestrus) or show very little signs calling for much closer observations. The best time to observe any behaviours is in the morning and the evening.
Anoestrus and Silent heat
Anoestrus describes cows that do not show heat signs for a long time after calving. It means no ovulation is taking place. This condition results when there is an infection or inflammation of the uterus and underfeeding of the cow especially with minerals.
Silent heat occurs when a cow ovulates but shows little or no signs of heat. The heat signs might be weak and therefore not observed.
To reduce chances of anoestrus and silent heat occurring, ensure proper feeding and mineral supplementation of dairy cows by giving adequate quantity and quality roughage with mineral supplementation free of choice. Allowing interaction of animals is also encouraged for facilitation of mounting activity of the cows that are in estrus. Closer observation of suspected cows should be during early morning and late evening as the behavioral signs of estrus are more pronounced during this period.
Understanding the signs of heat will also help achieve accurate and efficient heat detection for timely service. The signs are categorized into physical and behavioural:
1. Physical signs
Mucus Discharge - You can see long viscous, clear mucus hang from the vulva in a long string. This may also be smeared on the tail, thighs, flanks, or perineal region.
Swollen and Red Vulva - The vulva look enlarged through swelling and its interior becomes moist and red. In mid-cycle the lips of the vulva become pale and get more difficult to separate.
Rubbed Tailhead Hair and Dirty Flanks - As a consequence of being mounted, the hair on the tailhead and rump get fluffed-up, rubbed, or matted, and the skin may be exposed. This happens when there is more than one bull in the herd creating competition. The legs and flanks may also be smeared with mud or manure.
Chin Resting and back rubbing – Before mounting, cows often rest or rub their chin on the rump or back of the cow to be mounted. This may be considered a test of being receptive for mounting.
Raised tail - The cow’s tail may be slightly raised and off to one side.
2. Behavioral signs
Mounting - Cows or heifers that stand to be mounted shows the most accurate sign of standing heat. The average duration of standing heat is normally 15 to 18 hours, but may vary for hours among cows. A cow either stands still to be mounted or move forward slightly with the weight of the mounting bull but cows that move away quickly when mounted are not in true estrus.
Bellowing, Trailing and Restlessness - Cows in heat are more restless and alert to their surroundings, they also moo a lot and when allowed to interact with others, they persistently trail behind to try to mount other cows. They also wander around in search of a mate.
Sniffing Genitalia - Sniffing or nudging the genitalia and licking the vulva of other cows also occur much more frequently.
Head Raising and Lip Curling - This follow sniffing of the genitalia and occur more frequently if the cow is in heat and frequently urinates. If a bull is present, he will sniff and nudge her vulva region and do the ‘Flehmen’ response (where he curls back his nose, raises his head in the air to smell the pheromones she's emitting in her urine and vaginal secretions).
Reduced appetite and Milk Yield - Cows on heat have reduced feed intake as they spend less time feeding. There is generally a drop in milk yield too.
Metestrous Bleeding - Some cows and most heifers show bloody mucus discharge one to three days after heat. High estrogen levels during heat causes blood to leak from vessels near the uterus. This discharge indicates that such a cow was in heat and does not mean that she did not conceive instead should be watched closely for a return to heat.
Best time to inseminate
Proper timing of insemination means a large number of sperms being available to fertilize the eggs released. Ovulation occurs after standing heat therefore cows should be inseminated about 10-14hours after showing standing heat. This means cows first seen in standing heat in the morning (a.m.) should be inseminated in the afternoon (p.m.) and those observed standing in the evening should be served the following morning (AM-PM rule).
This process targets cows to come on heat through using hormones like Gonadotropin Releasing Hormone (GnRH) and Prostaglandin F2. It enables the farmer to reduce the cost of inseminations as it brings uniform calving and weaning which is cheaper than having individual cows on heat spread throughout the year.000