4 True Anestrum, Types, Etiology and Pathogenesis

Transcript

Hi! Friends greetings,

In the last session, we discussed False Anestrum, Diagnostic methods, and Therapeutic interventions. In continuing the lecture on Anestrum, we will be focusing today on True Anestrum, as we discussed in lecture 1, the True Anestrum means, the ovary is smooth, there will not be any corpus luteum on the ovary, so it means in True Anestrum you could able to find small inactive ovaries, often it will be spindle-shaped also, without a functional corpus luteum. It may be due to insufficient release of gonadotropins or the failure of ovaries to respond, often you could be able to find the ovaries there will not be any corpus luteum rather you could be able to find small multiple follicles. In all structures of the True Anestrum, you will be finding, the ovary will be smooth either with the presence of a small follicle medium or large molecule also but there will not be any functional corpus luteum. So, what are all the factors which are being contributed for True Anestrum:

Etiological factors-

The first one is a low plane of nutrition if the animal is not in a proper nutritive status, which is the main primary problem for True Anestrum, so it is the most common cause of the lack of energy and protein deficiency of minerals especially phosphorus(P), cobalt(Co), iron(Fe), copper(Cu), iodine(I), and manganese(Mn) along with vitamin A. If the mineral deficiency is there, definitely the animal will enter into the period of True Anestrum, there will not be sufficient quantities of GnRH release, in turn, estrous signs will not be exhibited, so nutrition plays a very important role in regulating the reproductive cyclicity. In addition to that, the second most important factor is heavy lactation, so negative energy balance. So often we are encountering cases like the transition, during the transition period, before calving, during calving, and after calving. So during the last few weeks of parturition, most of the farmers are not interested in giving enough for surplus feeding to the animal, the reason behind this is that if they give more feed, they are having an impression that the fetus will be growing larger which will end up in Dystocia, but that was a condition that has been noticed many decades back when we are using an imported summons, but right now all the bulls which have been reared under local conditions and accordingly it has been inseminated, so that concept is absolutely wrong. So, during the transition period, the farmer has to give additional importance to maintaining the regulation of the dam as well as the fetus, so during the transition period if the nutritive status is not good then definitely during lactation or even during the calving itself the animal will go for downer, and it will enter into the period of negative energy balance.

The other one is Chronic debilitating diseases like joining disease, tuberculosis, etc. If the animal is very poor, then probably animal will not show clinical signs of estrum, that is why I prefer to say that the reproduction of breeding is a sophisticated one, which means that if normal physiological functions of the animal are quite okay, then only the animal will enter into the period of breeding. So other causes which include seasonal and environmental influences, huge variation in season also can affect the release of the gonadotropins, for example, extreme summer affect the release of the gonadotropins, which is commonly noticed in the case of buffaloes. The other one is closely confined dark stables, lack of exercise combined with nutritive factors, if the farm is poorly managed then that is also one of the factors for contributing to the True Anestrum.

So Suckling-During suckling, the prolactin reduces the ovarian sensitivity, so unless suckling is where the animal will be in the period of Anestrum, that is why here weaning plays an important role in entering the dam into the next cyclicity.

So Pathogenesis: in what way is the pathogenic mechanism being involved in regulating the estrum in Anestrum, so usually the concentration of gonadotropin is almost negligible in late gestation, so high progesterone, which is being secreted by the corpus luteum during pregnancy or end of gestation along with the placenta, also secret progesterone and estrogen from the placenta during the last trimester of pregnancy and put together these hormones causing negative feedback, which results in inhibition of hypothalamic pituitary-axis and because of that sufficient quantities of GnRH are not being released in addition to that FSH and LH is also being affected, in turn, the animal is entering into the period of True Anestrum with reduced ovarian activity.

So now Types of True Anestrum:

In the type, one is Physiological, another one is Pathological: – In physiological Anestrum: you would be able to find Pre-pubertal Anestrum, which means that before animals attaining puberty there will be Anestrum, which you will be finding, small follicles or medium size follicles which are quite a normal one. Another one is Gestational Anestrum, so which means that the animal will be pregnant, the ovary will be having a corpus luteum, this secretes progesterone and this suppresses the GnRH and because of that animal is entering into the period of Anestrum and this is also very common in pregnancy.

The next one is Postpartum Anestrum, all the animals after parturition, will undergo a period of Anestrum, which is quite normal. In the case of cattle, it is comparatively shorter than the buffaloes during this period. This period is referred to as Puerperium, this is a period from the period of calving till the resumption of the next ovarian cyclicity and during this period all the uterine involution and uterus will come back to their original position, and after that, the ovarian rebound will happen and subsequently, the follicular development activity will be initiated. Lactational Anestrum, during lactation Anestrum, as we said earlier prolactin is a dominant hormone which is suppressing the GnRH activity, so during lactation, the animal will be in the period of an Anestrum, that is why weaning plays a very important role in the resumption of next ovarian cyclicity. Almost all Prepubertal, Gestational, Postpartum, and Lactational are Physiological.

If this Postpartum Anestrum is going beyond two to three months, then it is considered to be Pathological.

The next etiological cause is the Congenital and Hereditary cause of True Anestrum. These three conditions are Ovarian agenesis or dysgenesis, Ovarian hypoplasia, and Freemartin.

Ovarian agenesis means the complete absence of an ovary, this condition is very very rare, it is due to autosomal dominant genes and in this condition, the animal will not be expressing any signs of estrum.

The other one is Ovarian Hypoplasia, this is due to the simple autosomal recessive gene with incomplete penetration and in this condition probably the ovary is not developed properly, it may be unilateral or even bilateral. In this condition also the animal will not show any signs of estrum.

Another one is Freemartin, this is a sterile female born co-twin with the male, because of the placental anastomosis and hormonal exchange, there may not be proper development of the ovary which results in absence of expression of heat signs. So, another type of True Anestrum is Pathological True Anestrum: Here I have categorized it into one, two, and three. Type one is Emergence, type two is Deviation, and type three is Growth. So, this chart will be able to explain in a better way about the Pathological Anestrum based on the recent concepts, based on ovarian dynamics. From the Follicular Pool, there are four types of follicle growths are happening, For example: In the case of type 1, there will be a small follicle, which is being recruited from the follicular pool and after that, there is no progress, so no deviation is happening. So, in this condition, you could be able to correlate in diagnosis you will be able to find only small follicles in the ovary. In type 2, there will be a recruitment of the follicle, the follicular will be developing into the next stage, that is Growth is happening followed by Atresia. Here you could find the size of the follicle is comparatively larger, but it is ending up with Atresia. Another one is type 3, in this, you could be able to find, the follicle will be recruited from the wave pool, and after that development is happening and after that, it is attaining the dominant size also but there is no ovulation is happening. So, either the large follicle will persist, and it gets regressed or sometimes the presence of the follicle persistent results in follicle assist or sometimes after follicle assist, partial luteinization happens and it becomes a luteal cyst, all possibilities are there.

The other type is, there will be a development of the follicle, growth happens to attain dominance after that ovulation happens but after that, there will not be any regression of corpus luteum. So it is being acted as prolonged corpus luteum, in this, we will exclude type 4 because CL is there, we will take only till type 3, so in this condition what is happening often we could able to find, one follicle is getting developed in a smaller size that is Emergence so Emergence of the follicle is happening after that no activity, so this is Deviation, so after Emergence, the follicle is developing further but after that, it is getting deviated and the 3rd one is, it is attaining to the dominant stage, it has attained the growth but ovulation is not happening. So at any True Anestrum, you could able to find all these three types of varieties of follicles based on the size and this condition is mainly due to low pulse of LH release and increased sensitivity to negative feedback of estrogen on gonadotropin and some of the growth factors like insulin growth factor, epidermal growth factors, also contributing factor for this. Often, we are examining the animals of True Anestrum with the follicle size of more than 6mm diameter, so this is the recent concept in Anestrum classification based on the variant dynamics. So, the summary of today’s lecture, we have seen what is mean by True Anestrum and what are all the causative factors which are being contributed for True Anestrum, in addition to that we have seen the Types of True Anestrum in which Physiological Anestrum, Congenital Anestrum, and Pathological Anestrum and our intervention will be mainly focusing on how to approach a case of Pathological Anestrum.

With this, we will conclude today’s session and we will continue the Diagnostic and Therapeutic portion in the next session.

Thank you.