Agro industrial-post-partum anoestrus, Biology

Post-partum anoestrus

Reproductive efficiency among animals greatly depends upon detection of estrus. This is even more important in reference to small herds managed under tropical or subtropical environments because, high air temperatures shorten the duration of estrus and lower its intensity as demonstrated under controlled environments. Though estrus in cattle and buffaloes is manifested on an average of 21 days cycles, in the tropics bovine and bubaline heat expression is not good especially during the summer . The intensity of estrus behavior in tropical buffaloes was found to be much less than in cows. The determination of when a buffalo is in estrus is difficult because, often the animal shows few external signs of “heat”. The usual weak symptoms of estrus in the normal breeding season (September to February) become still weaker during the summer. Studies conducted on Murrah buffaloes at NDRI have demonstrated a diurnal pattern of estrus behavior with 59 % of estruses recorded between 10 pm and 6 am. The maximum occurrences of heat symptoms were observed during winter (November to February) while the lowest occurrences were during summer (March to August). The main heat symptoms recorded were frequent urination,vulval engorgement, bellowing, bull mounting and restlessness, which contributed to 85 % of the total observations. Mucus discharge, licking of the female by the bull and chin resting by the bull were minor symptoms. During the summer frequent urination is the most prominent heat symptom in buffaloes. The average incidence of silent heat in buffaloes throughout the year is very high ranging between 30and 40%; incidence of silent heat is lowest in the winter (~ 10 % in December to January) when environmental temperatures are lowest, compared to extremely high incidence of silent heat in summer ( ~ 50-70% in April to August) when the buffaloes are exposed to extremely high environmental temperatures in North India. Due to the high incidence of silent heat large numbers of buffaloes are left unbred and substantially contribute to a high service period in this animal. Hence, month of calving also has a profound influence on the service period (days taken postpartum for the animal to become pregnant); buffaloes calving from December till June will have a much higher service period than in those calving in the months of July to November. It is imperative therefore  that the herdsman observes the animals 3-4 times during the 24 hr each time for not less than 20 min. for larger herds. Early morning or late evening and night observations are recommended.

Major causes for postpartum anoestrus are: true anestrum (discussed separately in detail) infrequent observation of animals for heat symptoms, inadequate knowledge of heat symptoms, improper maintenance of heat records or heat expectancy chart for each animal, animals tied in a barn and not allowed to move about freely in groups (which rules out mounting behaviour which is an important heat symptom), negative energy balance especially in high-milk yielding animals resulting in a loss of body mass due to reduced feed intake not commensurate with the high-milk production, lameness, slippery footing, and, high ambient temperature leading to heat stress. Uterine infections also delay onset of cyclicity post-partum. Detailed description of uterine infections postpartum and their influence on fertility are given separately. True anestrous cattle and buffaloes lack ovulatory cycles; their ovarian activity varying from some growth, without maturation of follicles, to complete absence even of follicles in non- pregnant sexually mature female livestock.

Congenital ovarian inactivity: It is a genetic disorder caused by the inheritance of a recessive gene resulting in hypoplastic ovaries which are devoid of primordial follicles and hence never ovulate. Hypoplasticity is mostly confined to the left ovary. Although unilateral cases can ovulate since the other ovary remains unaffected, these animals should be immediately culled from the herd since they transmit the hereditary defect. The diagnosis of ovarian hypoplasia can be confirmed and completed by repeated rectal palpations; these investigations will reveal the presence of one or occasionally two very small ovaries without follicles or corpora lutea (CL) and also in some cases a degree of hypoplasia of the entire genital tract. Incidence of chromosomal hypoplasia is also known to occur although these are even less in number. It is caused by the accidental absence of one of the female sex chromosomes. These animals are definitely sterile and exclude themselves from breeding.

Developed ovarian inactivity : It is a situation which however, is very common especially in tropical and sub-tropical countries. In these animals the ovaries are normal but they neither ovulate nor show heat. Poor nutrition perhaps combined with parasitic or diseased state leading to marked loss in weight and milk yield are some of the causes leading to pituitary unresponsiveness to GnRH secretion or reduced pulsatile release of GnRH itself from the hypothalamus. Developed anoestrus is a reversible disorder that much depends on the general recovery of body condition with better feeding, protection against high temperatures and solar radiation by providing shades or showers. Wallowing in buffaloes is especially useful. Good results can also be expected by administration of synthetic hormone analogs of pregnant mare serum gonadotrophin, human chorionic gonadotrophin or GnRH. However, these treartments are more effective when combined with other ameliorative measures.

Corpus luteum persistens: It is another condition wherein the corpus luteum developed during an estrous cycle survives beyond the normal life-span of the cyclic corpus luteum. This corpus luteum continues to secrete progesterone at a high enough  level to prevent development of next crop of follicles, oestrus and ovulation. This condition is common, very often combined with uterine infection ( pyometra, endometritis). Although uncommon, about 1to 2% incidence of corpus luteum persistens are also known to occur even in animals with a normal uterus. Administration of prostaglandin F2á  analogs is perhaps the most recommended choice of treating such cases with animals coming to heat in 2-3 days post injection. Over 80% of treated cows and buffaloes do ovulate and fertility is normal unless the uterus is diseased.

Cystic ovarian disorder :
It refers to a condition where the Graafian follicles show a continuous and disordered growth without ovulation; neither do they regress nor become atretic. There is an increased volume of fluid accumulation within the follicle. Seen more often in cows than buffaloes (about 5-10% animals) infertility is complete unless the animals are treated or normal cyclicity is restored. Cysts in ovaries are common during first weeks after calving, but these are usually not accompanied by the ususal complex of symptoms viz. taking an excessive interest in her herd -mates which come in heat. On the contrary, the genuine syndrome develops after two months post-partum and shows very little tendency to spontaneous recovery. In these animals the balanced secretion of GnRH is possibly affected which leads to a reduced production of LH from the pituitary. The walls of the enlarging follicle degenerate, the oocyte dies and in about 25 to 30% of affected animals some luteinization also takes place in the cyst wall. Such animals will show high blood progesterone concentrations. Hence, two situations are possible with respect to development of cysts; cows affected with thin walled follicular cysts with low blood progesterone, and high blood oestrogen concentrations, and, cows affected with a luteinized cyst in which blood progesterone concentrations (and sometimes androgens) are high and blood oestrogen concentrations are low. However, there can also be instances where the concentrations of both the hormones are low. The animal may exhibit either no sexual behavior, or may be nymphomaniac or masculine though generally it is a mixture of both. Manual rupture of the cyst per rectum is one of the oldest known therapy for treating such cases. Administration of hCG or GnRH have also yielded satisfactory results with over 70% positive response. ProstaglandinF2á treatment in cases of luteal cysts has been found to be most effective.

Posted Date: 9/17/2012 4:00:10 AM | Location : United States

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