Introduction:

Successful reproduction is defined as the ability of animals to mate, capacity to conceive, to nourish the embryos and deliver the viable young one at the end of normal gestation period¹. As the world’s population grows, global demand of milk for human consumption is predicted to rise by more than 50 per cent by 2050². World milk production has increased by 27 per cent between 1997 and 2007³. Land area will be the new key factor limiting production indicating more producers may adopt confinement systems⁴. The major herd infertility problems are those arising from manage mental factors and which involve more than one causal factor in this more than 85 per cent problems are manage mental and other factors and less than 15 per cent problems mainly or in part of mineral imbalance.

Factors Affecting Reproduction:

Factors affecting reproductive process are environment, endocrine, heredity and infectious which lead to conditions like anoestrus, infertility, fetal death, abortion, mummification, still birth and neonatal death⁵. Any endocrinological imbalance or reproductive abnormalities which results in to poor reproductive efficiency may lead to the higher embryonic mortality. Repeated embryonic mortality which become prolong the inter-calving interval. That’s why it’s a major limitation to exploit production potential⁶.

Record keeping:

The first step in establishing any form of effective management is setting up and maintaining detailed records for individual animals. Record keeping is one of the most important parts of reproductive management of the dairy herd. Accurate, simple and complete records about the entire reproductive life of the individual animal are required. It is important to develop a system for collecting permanent records of each adult cow in the herd. This facilitates extracting data to calculate the above measures. Permanent records should include the following information like Cow identification number, which should also be on an ear tag (preferably two tags, in case one falls off), Birth date, Ancestry, such as dam and sire number and breed type, may be grand dam and grand sires number and breed type and cow’s breed type, Vaccination dates, Important disease problems during rearing, Lactation number, Dry off date of previous lactation, Calving date, Each insemination date (this is generally the important data that is not routinely recorded), the date when confirmed pregnant by rectal palpation, the estimated age of the fetus, Peak milk yield or estimated full lactation yield and any diagnosed health problem.

Delayed puberty and sexual maturity:

Age at puberty and first conception will influence lifetime productivity of cattle, reflected in the number of calves⁷. Though puberty may be genetically controlled yet nutrition, season and proper health management are the critical factors governing puberty in heifers⁸. The major reasons for delayed puberty and sexual maturity are the Low plane of nutrition or malnutrition, heavy parasitic infestations and poor care and management at neonatal stage and onwards.

Nutrition:

Nutrition directly affects production and reproduction in dairy animals ‘Milk is from the mouth of the cow’. Severe negative energy balance at early post partum and its associated metabolic alterations have shown major cause of reduced fertility⁹. Nutrient either in deficient amount or in higher amount has been shown to be capable of altering reproduction¹⁰.

Table.1 Effect of Negative Energy Balance (Martinez et al.¹¹)

Functions	Negative energy balance
Metabolic/ Endrocrine	1. Reduced GnRH, LH, glucose, insulin 2. Mobilization of tissue reserves 3. Reduction of Body Condition Score (BCS) 4. Metabolic disorders
Ovarian changes	1. Low or absent estrogens 2. Delayed or absence LH peak
Clinical changes	1. Poor estrous signs 2. Poor oocyte quality 3. Early Embryonic Death (EED) 4. Short estrous cycle 5. Impaired endometrial function
Breeding consequences	1. Low pregnancy /calving rates 2. Extended Calving Interval 3. Repeat Breeder

Body Condition Scores (BCS):

Body Condition Score (BCS) is an internationally accepted subjective visual and tactile measure of body condition and temporal changes in the BCS are used to monitor nutritional and health status of high producing cows during their productive cycle¹². Loss of more than 2.0 units of BCS results in 21.0 percent conception rates¹³. BCS at parturition or 1-2 month post partum is significantly correlated to reproductive performance in cows. BCS and the loss of BCS are important predictors of potential reproductive efficiency scores are done on a 1 to 5 scale. Whereas, 1 is being emaciated and 5 is being obese cow. BCS 3.5 at calving, 2.25 to 2.75 at peak yield, 2.5 at breeding, 3.25 at late lactation and 3.5 at Dry off. Cows which are over conditioned at dry off with a BCS >4 more likely to experience reproductive diseases in their next lactation than cows having BCS 3 to 3.5.

Age at First Calving (AFC):

Decreasing AFC has a positive effect on genetic progress because the generation interval decreases¹⁴. AFC can reduce rearing costs due to decreased feed, labour and building costs. Reducing AFC from 25 to 24 or 21 months decreased replacement costs by 4.3 per cent or 18 per cent respectively¹⁵.

Heat detection:

One of the most important and most time consuming tasks in the dairy animals is the heat detection. Visual heat detection requires more labor hours per cow and is therefore more sensitive to increasing labor costs than a synchronization program¹⁶. Increasing herd size reduces estrus detection performance and satisfactory levels cannot be achieved without technological aids¹⁷. About 10 per cent of the reasons for failure to detect heats can be attributed to cow problems and 90% to management problems¹⁸. Any successful breeding program in a herd where heat detection is well done, 75 per cent of the cows must be seen in heat at least once in 60 days following calving. The non-observation of heat during the 2 months following calving reveals two types of problems, one is the cow was not in heat (true anoestrus) and another is the detection was poor.

Approaches to estrus detection:

Tail-painting and use of chalk:

Tail chalking involves placing a mark on the cow’s tail head, so that when she stands to be mounted, this mark will be erased, or at least changed. Therefore estrus can be diagnosed based on the absence or change to the mark, in combination with secondary signs of heat and farm records.

Heat-mount detectors:

A heat mount detector such as the KaMaR can be used. This consists of a soft, translucent plastic dome attached to a rectangle of canvas in which there is placed a soft plastic vial of red dye, which is fixed with adhesive just cranial to the base of the tail. When a cow is mounted and the vial subjected to sufficient pressure, i.e. at standing estrus, the vial is compressed, the dye escapes and the dome becomes red. False-positives can occur when a cow rubbing the underside of a rail or in crowded collecting yards when a cow that is not in estrus cannot escape the attentions of mounting cows activates the detector. It is important that these should be applied using a brush against the line of the hair to ensure good adhesion before smoothing in the direction of the hairline. There should be regular inspection of the paint so that repainting can be done if necessary.

Chin-ball devices:

The chin ball marker is one such aid. It is a device worn beneath a detector animal's chin that works like a large ball point pen, leaving a mark on the back of the cow that has been mounted.

Use of teaser animals:

This has not been very popular largely because teaser bulls with good libido present a major safety hazard when allowed to run loose with the herd. Furthermore, where venereal diseases are present they represent a major health hazard because of their ability to transmit such diseases.

Vaginal probes:

The electrical resistance (ER) of vaginal fluids decreases during proestrus and through the estrus period as a result of chemical changes in the vagina as the cow approaches the time of breeding. Several probes that measure the ER of vaginal fluids are now commercially available. Monitoring the relative changes within cows during the estrous cycle can provide the herder with additional information and can serve as a heat detection aid if cattle are probed frequently.

Pedometers:

During estrus the cow shows greater movement and activity. One method that has been used to identify this is the attachment of pedometers to the individual animals. Since then a number of devices have been made to record the frequency of movement; as yet their reliability is not good and they are expensive. With the rapid developments that are occurring in electronics, it is likely that some simple, inexpensive and reliable instrument will be developed.

Spinnbarkeit:

The ability of cervical mucus to be drawn in to thread or to stretch to form threads when drawn apart. Cows that had spinnbarkeit value of 11 cm or below did not conceive.

Use of milk progesterone assays:

The return to estrus in non-pregnant cows can be anticipated by the measurement of progesterone concentrations in sequential milk samples.

Cow activity changes:

When the cow is in estrus during that time activity of cow is change like Bellowing, reduced feed intake, restlessness and nervous, frequent micturation, etc.

Use of closed circuit television:

Television cameras, recorders and monitors are now much cheaper and more reliable than before. During the night, provided that there is adequate lighting and good animal identification, a continuous video recording can be made of the loafing areas of the yard where cows are housed. The herd’s man can then rapidly scan the recording in the morning and identify cows that are in estrus.

Use of dogs:

Dogs can be trained to detect odors associated with estrus in cows. The sources of the odors are widespread throughout the genital tract and also appear in milk and urine.

Timing of AI:

The best time to breed the cow is in the middle or end of standing heat. With good heat detection, follow these guidelines when breeding your animals. A cow first observed in standing heat in the morning should be bred the afternoon of the same day. A cow first observed in standing heat in the afternoon or evening should be bred the following morning. First insemination is an extremely important control point in reproductive management. There are significant effects of insemination site and inseminator on conception rate.

Conception rate:

The conception rate (CR) is the percentage of inseminations that are successful and result in pregnancy. Herds can have high conception rates but poor 100 day-in-calf and high 200 day-not-in-calf rates. 100 day-in-calf rate, this calculates the percentage of the cows in the herd that become pregnant by 100 days after calving. It also describes how many cows will calve within 12 to 13 months of their previous calving. 200 day-not-in-calf rate, this calculates the percentage of cows not pregnant by 200 days after calving. Many cows not calved more than 15 to 16 months after their previous calving.

Early Embryonic Mortality (EED):

Embryonic mortality is classified as Very Early Embryonic Mortality (day 0-7), Early Embryonic Mortality (day 7-24), Late Embryonic Mortality and early Fetal mortality (days 24-285)¹⁹. Mortality is more common during early than the late embryonic period, i.e., from day 8^th to 16^th at the hatching of blastocyst and initiation of elongation and commencement of implantation²⁰. About 80 per cent of this loss occurs before days 16 to 17; nearly 10-15 per cent between days 17 to 42 and 5 per cent after 42 days.

Genetic factors:

Genetic abnormalities account for approximately 10 per cent of the embryonic losses and generally result in pregnancy failure within the first two weeks. Expression of lethal genes can cause death of the embryo within the first 5 days of pregnancy. Another genotypic factor contributing to embryonic death is an abnormal chromosome number in some or all of the embryonic cells that results in abnormal growth of the embryo, and usually death within the first trimester of gestation.

Endocrine factors:

Failure of release of LH results in delayed ovulation. Since there is delay, the sperm cells have become poorly viable as they do in the cow within 24 to 48 hours and because of the aged conditions of the sperm cells, early embryonic death may result. Injections of estrogen at the time of estrum or within several days after ovulation will affect the transport of the fertilized ova in the oviduct resulting in too rapid transport or tubal locking of the ova and death of the zygote. A decreased level of progesterone also results in EEM. There are two major reasons for a lack of progesterone. Corpora Lutea (CL) has a short lifespan (6-12 days). Thus, luteolysis occurs before the embryo has time to signal its presence through secreting bTP-1. The second category includes those CLs that have a normal lifespan (more than 14 days) but secrete low levels of progesterone, which does not suppress the luteolytic affects of the prostaglandin.

Nutritional factors:

Effects of Energy and Protein: Dietary energy and protein levels play a role in pregnancy success. Cows will have less embryonic mortality if they are gaining condition, while those losing condition will tend to have higher embryonic loss. Excesses of protein: Crude protein in the total diet greater than 17 to 20 per cent has been implicated in lowering conception rates with increases seen in the number of services per conception and days open.

Immunological factor:

If the mechanism of immunosuppression is not going well, then the antibodies will interfere with the development of the embryo in the uterus. The feto-placental unit can be considered as a foreign body in the uterus, paternal antigens are normally not rejected by the maternal immune system. Therefore, the immune system is involved in the successful outcome of the pregnancy by creating conditions that prevent rejection of the conceptus.

Temperature or heat stress:

Cows exposed to heat stress from day 8 to 16 after breeding had decreased progesterone concentration and increased uterine prostaglandin secretion.

Genital infections:

Infection of the embryonic environment can be caused by specific and non-specific uterine pathogens. Specific uterine infections are caused by a number of viruses, bacteria and protozoa that enter the uterus by the haematogenous route or via the vagina. Non-specific pathogens are mainly bacteria that enter the uterus by ascending infection. Uterine pathogens may cause EM by changing the uterine environment (endometritis) or by a direct cytolytic effect on the embryo.

Uterine environment:

After fertilization, embryos cleave at different rates, sometimes causing the maturity of the embryo to differ from that of the uterus. The uterine environment may be toxic to these embryos that are out of phase, resulting in the death of the embryo. Maternal recognition occurs around days 15 to 17 of pregnancy.

Effect of palpation:

Generally, rectal palpation does not affect the survivability of embryos if palpated gently. Palpation between days 34 and 41 of pregnancy using the fetal membrane slip technique did not affect embryo or fetal viability.

Other possible factors:

Age: Heifers are generally considered to have higher pregnancy rates, and this increase seems to be associated with less embryonic mortality than cows. Older cows nearing the end of their reproductive life will also have an increase in embryonic mortality. Among dairy cattle, both early and late embryonic losses increased among cows with increasing age. Breed: Little difference in embryonic mortality across breeds has been shown. Cattle are line-bred or inbred have been noted to have an increased rate of embryo mortality.

Early pregnancy diagnosis:

Identification of early pregnancy factor (3 days after insemination):

Identification of early pregnancy factor/early conception factor early pregnancy factor (EPF) is an immunosuppressive glycoprotein associated with pregnancy. Commercially available test kits are available which use the ‘dip-stick’ principle and can detect early conception factor (ECF) in serum and milk from as early as 3 days after artificial insemination, although more accurate results are obtained if samples are taken later at 7 to 8 days. USG (12-20 Days): There are different types of machines available. The most commonly used machines today are B-mode real-time, meaning that they produce an acoustic image in real time. They usually range from 3.5 to 7.5 MHz with greater MHz you see more detail but have less depth penetration that they produce an acoustic image in real time.

Milk ejaculation test (18-22 days after insemination):

This test is performed generally 3 hrs prior to the evening milking in dairy cows (18 to 22 days after insemination). Place the teat cannula in the left fore-teat and leave it for milk flow from teat cistern. When the milk flow ceases, a small dose (2.5 mg or 0.5 ml) of Dinoprost (LutaIyse) is administered intravenously through ear vein. If the corpus luteum of pregnancy is present, alveolar milk starts to flow about one minute later. Principle behind use of PGF₂α in non-luteolytic dose induces the release of oxytocin from the corpus luteum which causes let-down of milk in the lactating and pregnant cows.

Assay of pregnancy specific protein B (24 days of gestation):

This protein has been identified in the maternal serum of cows from 24 days of gestation the concentration is measured by radio-immunoassay It is secreted by the binucleate cells of the trophoblastic ectoderm and thus its presence can be used to confirm pregnancy. At present, it can only be measured by radioimmunoassay (RIA) but, with the development of suitable enzyme-linked immunosorbent assay (ELISA) methods also detected.

Progesterone concentration in plasma and milk (21 days):

Since the CL persists as a result of the pregnancy, if a blood sample is taken at about 21 days after the previous estrus, progesterone levels remain elevated. If the cow is not pregnant and is close to or at estrus then the progesterone levels will be low although this is a perfectly valid and reliable laboratory method, it has the one disadvantage that it requires the collection of a blood sample. Progesterone crossed the mammary gland and appeared in milk and progesterone is very soluble in milk fat there were higher concentrations per unit volume in milk than in the blood or plasma.

Calving Interval:

Calving Interval can be divided in to voluntary waiting period, interval from end of to voluntary waiting period, interval to 1^st AI (service period) and interval from 1^st AI to conception and gestation period .

A calf per cow per year:

The constraint of a 365 day inter-calving interval requires that cows must resume cyclicity, display estrous behavior, and be mated to conceive successfully during a mating period beginning 83 days after a designated planned start of calving irrespective of time postpartum. Reproductive efficiency can be improved by Shortening Post-partum interval increasing Submission Rates and increasing conception Rates.

Voluntary waiting period:

The voluntary waiting period is the standard postpartum interval in which cows are not inseminated with the ultimate goal of avoiding breeding at a time in which fertility is poor because of uterine regression and clearance, recovery to a favorable nutrient balance, and resumption of estrous cyclicity. Cows inseminated very early postpartum typically have depressed fertility²¹. 75 per cent of all dairy herds have a voluntary waiting period that ranges between 41 and 60 days postpartum²².

Repeat breeding:

Repeat breeder animal is usually defined as sub-fertile animal which is mated three or more times during the proper period and does not become pregnant and continually return to service in the absence of any obvious pathological disorder in the genital tract and normal estrus cycles²³. Incidence of typical RB ranges from as low as 1.51 per cent to as high as 35 per cent amongst Indian cattle and in buffaloes ranges from 0.61 to 29.80 per cent²⁴.

Subestrus and Silent estrus:

A condition in which the genital organs are undergoing normal cyclical changes and ovulation do occur as confirmed by progesterone profile and per rectal examination but overt or behavioural signs of estrus are either not manifested or too weak to be observed²⁵. Silent estrus is common during post pubertal period in heifers and early postpartum in cows. Incidence of silent estrus in cattle is 21.38 per cent and 27.32 per cent in buffaloes.

Lameness:

Lameness is associated with increased number of services per conception and consequently lower conception rates to first service²⁶. Cows that were lame within 30 days post calving were also 2.63 times more likely to develop ovarian cysts. The histamine and endotoxins released during the decline of ruminal pH in animals suffering rumen acidosis act indirectly to destroy the microvasculature of the corium causing laminitis. These substances can also potentiate their affects at the neuroen docrine and ovarian level and compromise the LH surge system Secondly, stress induced hormones may alter the GnRH and/or LH surge system. Finally, the degree of NEB may be greater in lame cows and hence affect the somatotropic axis. Lameness could reduce estrus intensity by reducing progesterone concentrations before estrus without affecting estradiol or cortisol milk profiles²⁷.

Heat stress:

Among all environmental stressors, the temperature and relative humidity are the major factors, which affect the reproductive performance of dairy cows. Incidence of Lowest Conception rate, longer calving to conception and calving intervals are more during summer months. Percentage of abortion and retained placenta were highest for cows calving during summer. Fertility of dairy animals is markedly declined during summer season²⁸. Heat stress can act in more than one way to reduce fertility in lactating dairy cows. Heat Stress can reduce dry matter intake to indirectly inhibit GnRH and LH secretion from the hypothalamo-pituitary system. However, it is not clear if heat stress can also directly inﬂuence the hypothalamo-pituitary system to reduce GnRH and LH secretion. Heat stress can directly compromise the uterine environment to cause embryo loss and infertility.

Culling rate:

Cow replacement is a major cost of dairy production²⁹. Parity and stage of lactation affect the economic losses of a culled cow³⁰. Failure to conceive is a major reason for cows are culled³¹. The risk of culling is increased with parity. Hazard ratios of cows leaving the herd were 1, 1.51, 2.14, 2.68, 3.11, and 3.46 for parities 1 to 6, respectively cows having single male calves had a 5 to 7 per cent greater hazard of culling than cows having single female calves cows having twins had a 23 to 46 per cent greater hazard of culling.

Table.2 Herd Average for Cattle and Buffalo (Walsh et al.¹⁹)

Parameters	Cattle	Buffalo
Age at first estrus	12-18 months	18 -24 months
Age at first breeding	14-15 months	24-30 months
Age at first calving	24-25 months	35-40 months
Interval to first postpartum observed estrus	Less than 50 days	Less than 50 days
Days to first service	Average 75 days	Average 75 days
Days open	95-100 days	95-100 days
Calving interval	12-13 months	13-14 months
First service conception rate	50 % or greater	50% or greater
Services per conception	Less than 1.7	Less than 1.7
Percent heats observed (Efficiency)	Greater than 70 %	Greater than 70%
Retained placenta	Less than 10 %	Less than 10 %
Cystic ovaries	Less than 10 %	Less than 10 %
Metritis (Uterine infection)	Less than 10 %	Less than 10 %
Reproductive cull rate	Less than 8 % of the herd or less than 25 % of the animals those were culled.	Less than 8 % of the herd or less than 25 % of the animals those were culled.

Future Prospect and conclusions:

Mainly focus on early postpartum period, minimizing duration and degree of NEB and resolving uterine infection. Detection of estrus is proper and following AI must be at correct time. Future efforts to improve fertility in dairy cow’s needs to focus on genetic and management solutions to improve the physiological events associated with the establishment of pregnancy. From a practical point of view, however, maintaining an optimum level of reproductive efficiency is largely a matter of matching the genotypes to the available resources and appropriate management strategies to allow the animals to express their full reproductive potential.

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Received on 23.03.2016 Modified on 05.04.2016

Research J. Science and Tech. 2016; 8(2):99-106

DOI: 10.5958/2349-2988.2016.00013.9