Heat is the time of the highest reproductive activity of animals. It is characterized by a set of behaviors which are a sign of readiness to copulate. A cow or heifer must be inseminated about 30 hours after the first signs of heat. She will then ovulate. Not noticing this moment can cause huge economic losses.
The length and stages of the heat cycle
The oestrus cycle in cattle, as in other livestock animals, is the period from the first day of external oestrus symptoms to the last day (without oestrus) before the next oestrus. The length of the oestrus cycle is approximately 21 days on average for cows (average deviation 3,68 days). In heifers it is slightly shorter, lasting about 20 days (average deviation 2,33 days). The duration of the estrous cycle is an inherited feature, depending on the persistence of the corpus luteum.
The course of the estrous cycle is determined by the changes that take place in the ovaries, i.e. ripening of the follicle, ovulation and development of the corpus luteum. During the oestrus cycle two periods are distinguished: short (heat) and long (without heat). Changes in the reproductive organs and changes in the behavior of a cow or heifer during the heat result from fluctuations in the level of gonadotropic hormones and estrogens. Gonadotropic hormones are secreted by the anterior pituitary lobe and their production is conditioned by the activity of the hypothalamus. The cow’s pituitary gland in heat releases luteinizing hormone (LH) under the influence of a high level of luteinizing hormone releasing factor in the hypothalamus, the so-called LRF or LH-RF (releasing factor, RF). When LH concentration in blood increases, the level of FSH and PRL hormones in blood increases. Such large amounts of hormones cause the follicle to rupture and the ovum to spill, i.e. ovulation.
Cow’s reproductive readiness
A cow’s reproductive readiness is visible in her behavior, so the main way to detect heat is to observe the animals. They are then strongly excited, nervous, anxious, show increased mobility and sensitivity to bull pheromones. In the so-called ” typical heat” phase, cows have a „tolerance reaction”. – accepting the bull, standing to be mounted, mounting other cows, swelling and reddening of the vulva, without folds. A large long viscous, clear elastic strands of mucus hanging from the vulva. In addition, cows in heat often vocalise, have increased motor activity and are restless. Very often in heat there is a decrease in milk production due to poor feed intake. After an average of 18 hours the symptoms disappear.
What is the „silent heat” and how to avoid them?
The heat symptoms described above can sometimes be less noticeable. One of the causes of „silent heat” in dairy cows is the slippery, wet floors, which can reduce the number of estrus behaviors by up to 50%. Other disorders in the expression of heat behaviors may result from dysfunction of the cow’s locomotor system, heat stress, excessive stocking of cows in the barn or the position of a particular cow in the herd hierarchy. It should be remembered that important factor may be nutrition which could negatively affect of heat detection.
7 most important tips to help you detect heat
How to increase the efficiency of heat detection in the herd?
- Use the time spent observing heat effectively. Spending 20-30 minutes observing your herd early in the morning and late in the evening, in addition to other activities such as milking and feeding, increases the probability of detecting a cow heat.
- Take a notes of calving and record the exact dates when the cow is in heat.
- Provide proper maintenance – the right (not slippery) floor and the right temperature and humidity.
Reduce the incidence of leg and hoof disorders.
- Use heat synchronization programs as necessary.
- If there is a lack of workers, consider installing a heat detection support system for your herd.
- Enter the correct feeding program for your cows.
Heat is one of the most important problems that cattle breeders are increasingly mentioning. Observing the first symptoms is very important in practice. Proper breeding of animals affects the profitability of breeding and milk production.