1 Introduction, Estrous Cycle, Endocrine Regulation and Hormonal Concentration

Transcript

Greetings friends!

Today we are going to see about Estrous Synchronisation in bovines. It is one of the Important topics to tackle the various Infertility problems in the field condition also. You know Animal husbandry is the backbone of the rural economy, many farmers of rural India are depending on the animals’ productivity for their daily income. Their daily bread and need are satisfied by the income of the Animal husbandry activity. Although we are the highest milk producers in the World, the milk yield of the cow in India is very less, so the number of cattle herds available in India is very high. And our Desi cows with because of the low genetic makeup for milk production, are low producers. But if you take Exotic and Crossbred cows, although they have early maturity and high milk yield, there is less disease resistance and more Infertility problems.

After the introduction of the Cross Breeding program in India, the Infertility problem has become very high. So, to tackle the Infertility problem many recent reproductive techniques are available, with the reproductive Biologist. So, one such technique is the Estrous Synchronisation program. In this Topic, we are going to discuss various Principles, Advantages, Disadvantages, and the methods of the Estrous Synchronisation program in cows and buffaloes. If you adopt these techniques in the field condition, you can treat Infertility problems, at the same time even without Infertility problems in your Herd or at the Farm level, you can synchronize many animals at a time to bring into Estrous.

Now, we are going to see -What is the fixed expectation from an ideal cow? Ideal dairy cows should have aged at puberty -18 months, age at first calving about 30 months, conception date which would have 80%, AI per consumption is 1.3 to 1.7. The calving interval must be 12 to 18 months, it should not exceed beyond this level. Calving to conception must be 60 to 90 days. So, Ideal dairy cows should have all these parameters so that the farmer can get benefit out of rearing the cow.

The Delay in consumption rate, after 90 days of parturition, led to the loss of milk production up to 32% loss. Then medicine costs 13%. Calf loss 13%. The added Breeding cost comes around 11%. Then dairy animal maintenance comes to 31%. So, this is how the reproductive parameter, that is infertility causes, heavy economic laws to the farming community. To avoid this, there are very many techniques available in our hands, to manipulate the reproductive system to help the farmer to get more benefit from Animal husbandry.

Before entering into the Estrous Synchronisation program, as per this topic, we must know about the Bovine Estrous Cycle. It is the basic thing, then only you will understand what the Estrous Synchronisation program is. As you all know, what is the Estrous cycle? The estrous cycle is a Physiological functional rhythm of the reproductive system. It comprises Proestrous, Estrous, Metestrus, and Diestrus. That is, Proestrus and the Estrous together is called the Follicular phase. Metestrus and Diestrus are together called the Luteal phase. The cows and buffaloes are throughout the year cyclical, which is why they are called PolyEstrous.So, we can manipulate the Estrous cycle at any point in time in the year, that is why we call this a Polyestrous Animal and the total length of the Estrous cycle varies from 18 to 21 days. We all know how the expressive stage of the Estrous Cycle is only Estrous. So, always Estrous is 18 to 24 hours duration in cows and buffaloes. Of course, in buffaloes, it is a little bit high. Estrus Duration is 8 hours high; it may go up to 30 hours. Although it is a silent Estrous animal, the duration of Estrous is a little bit higher in buffaloes than in cows. So, Estrous, if you take 18 to 24 hours i.e., one day, the manifestation of Estrous can be seen from outside. So, when we calculate the Estrous cycle we will take it as a day 0, but the duration of Estrous is one day. Then following Estrous is Metestrus, it is 3 days. So up to day 1, day 2, day 3, it will be in Metestrus and then Diestrous comes, it is about 12 to 14 days. Then Proestrus comes, it is 3 days. If you want to remember the duration of the Estrous stages (3-1-3-13, you can remember in this way, 3 days Proestrous – 1-day Estrous – 3 days Metestrus – 13 days Diestrous).

What are we studying these things for? There are two structures present in the Ovary, one is Follicle, and another is Corpus Luteum. When we are doing an Estrous Synchronisation program or Synchronisation of Ovulation program, we cannot manipulate the Follicle, but we can manipulate the Corpus Luteum, so what we are doing is, we are implementing the program during Diestrus. So, the best period we have is Diestrus that too I told you to start this is on day 0, Metestrus on day 3, then again in 3 days, you take in Diestrus. So, after six days you will have matured Corpus Luteum in the Ovary, either one of the Ovary will have matured Corpus Luteum. So, from day 6 to day 16, another 10 days are there. If you deduct 3 days from this,9 to 10 days are available for us, so from day 6 to day 16, there will be definitely the presence of matured Corpus Luteum in the Ovary. This Corpus Luteum you can manipulate.

You can cause regression of this Corpus Luteum. Once at the end of the Diestrous, what happens in normal animals, if there is no conception, no embryo in the uterus then the uterus will secrete PGF2 Alpha, the PGF2 Alpha will cause a rise up the Corpus Luteum during the Proestrus period, during this period Corpus Luteum regresses. So complete regression takes place during these 3 days, then when it comes to Estrous, no Corpus Luteum and Progesterone level will be very less. Very less means, less than 0.5 nanograms per ml (< 0.5 ng/ml) in the Serum. So, at the end of Diestrus, if there is no conception in the uterus, the Corpus Luteum is regressed by the secretion of PGF2 Alpha from the uterus. So, the animal again comes to heat, this is what happens during the cyclicity. So you remember, the ovulation takes place in the case of cows and buffaloes 12 to 14 hours after the end of Estrum,i.e., during the Metestrus period it takes place. So, during Proestrous there is a Follicle development and during Estrous the Follicle reaches the maximum diameter and the animal shows Estrous signs, Ovulation takes place during a Metestrus and Corpus Luteum development occurs. The corpus luteum fully matures in the Diestrous. At the end of the Diestrous, if there is no pregnancy, the animal enters into the Proestrum. During Proestrum, Corpus Luteum regression takes place. This is the whole cyclicity, if you know this one, it will be very easy to understand the Synchronisation program.

So, this is a Chart form–Estrous Cycle=>Proestrous–>Estrous–>Metestrus–>Diestrous I already told these two i.e (Proestrous–>Estrous) is called a Follicular phase or Estrogenic phase, because as the follicle grows, it secretes Estrogen at its prime central nervous system and it primes the genitalia. So, the animal comes to Estrous.

Once Metestrum comes, Corpus Luteum is formed, Progesterone comes and these two i.e (Metestrus–>Diestrous) is completely dominated by Progesterone. That is why it is called a Progestational phase or Luteal phase. So, I told you Ovulation takes place during Metestrus. The cervix relaxes only during Estrum and Estrous is about 12 to 24 hours in the case of cows and buffaloes.

This is a Hormonal background, just for information. And before going to the Estrous Synchronisation program, this is very important for any field to know this. So, this is the Hypothalamus, Hypothalamus Secretes GnRH, it goes to the Anterior pituitary and the Anterior pituitary secretes FSH, this happens during Proestrus, from FSH reaches the Ovary, all this hormone will be secreted in one place, and it will be acting on the target organ. so pituitary secrets, but the target organ is Ovary, within the ovary the target structure is the follicle. So, under the influence of FSH, the follicle starts growing. When the follicle matures, it produces Estrogen. Estrogen acts on the central nervous system and also it improves the blood supply to the genitalia. It causes increased secrete activity in the genitalia. When the Estrogen reaches the peak, it stimulates the Hypothalamus to increase LH secretion. Estrogen after reaching the peak level suppresses the FSH. But it favors the release of LH and also Inhibit secreted from the follicle, suppresses the release of FSH but favors the release of LH.So the Luteinizing hormone is secreted, this Luteinizing hormone again comes and acts on the follicle. The final maturation of the follicle is brought up by LH, LH not only causes Ovulation, but the final maturation of the follicle is also caused by LH. So, after the final maturation Ovulation takes place. Up to the final maturation of the follicle, it is in the Estrous stage. Once it enters into the Metestrus phase, Ovulation takes place. After the Ovulation again, LH is necessary for the maintenance of the Corpus Luteum, then in Luteinization, full Corpus Luteum is formed. I told you from Metestrum it enters into the Diestroum, fully. matured Corpus Luteum is formed, then the end of the Estrous cycle day 16 or 17, if there is no conceptus in the Uterus, PGF2 Alpha will be secreted from the uterus Luteinization occurs again, when the Corpus Luteum secretes progesterone, it will suppress the release of FSH and LH, so during the Diestrous stage animal should not come to heat except only a few animals that may come to heat during the mid-cycle also, that we will discuss later.

But strictly speaking, the progesterone suppresses the release of FSH and LH, so animals will not ovulate, and the animal will not come to heat during Diestrus. So, at the end of Diestrous, if there is no conception, Corpus Luteum gets sliced because of thePGF2 Alpha. Again, animals enter into the Proestrus. So, what I wanted to stress is, the Corpus luteum can be manipulated from Day 6 to 16 of the Estrous cycle. This is what I wanted to stress.

Going to see the Graphical Representation of the Hormonal secretion during the Estrous Cycle. As I told you, when there is no pregnancy, the progesterone level goes down because of the secretion of PGF2 Alpha from the Uterus. When the progesterone level goes down during the Proestrus, the progesterone block on the GnRH release is removed, so the FSH starts to secrete. When FSH starts to secrete, it acts on the follicle, so Estrogen starts to come to play a vital role. Estrogen acts on the central nervous system and the genital tract. Once Estrogen reaches the peak, it selectively suppresses the release of FSH but stimulates the release of LH from the anterior pituitary. When the LH reaches the peak during the Estrous Period, it causes the final maturation of the follicle. Again, it prefers the follicle for Ovulation. Ovulation takes place during the Metestrus period. Once Corpus Luteum is formed, again Progesterone level increases.

Dear friends!

So far, we have seen the Bovine Estrous cycle and the Endocrinology of Bovine Estrous Cycle and Hormone secretion during the Estrous Cycle that too particularly with Follicular Phase. We will stop here today. We will continue with the Basic principles and Approaches of Estrous Synchronisation in the next class.

Thank you.