Dipti Nain1*, Surajit Das1, Arsha Shaji1, Raju kumar Dewry21PhD scholar, ARGO, ICAR- National Dairy Research Institute, Karnal, Haryana-13200, India
2SRF, Division of Animal & Fisheries Sciences, ICAR Research Complesx for NEH Region, Umiam, Meghalaya-793103
Goats are spontaneously ovulating and seasonally polyestrous animals. The reproductive cycle of a goat is affected by photoperiod. This article aimed at the different breeding protocols of goats during the non-breeding season. Today, for the induction of ovulation mainly used method is intravaginal progesterone releasing devices inserted in the vagina of females. PGF2 alpha and eCG are administered after 9 days, 24-48 hours before the removal of p4 releasing device/sponge. Shortening of progesterone priming method is also developed and proves to be a rational method. IMA.PRO2 and the male effect both are combined to be a great advance to improve goat breeding. Research should be done on these subjects in future using different goat breeds in different regions of the world.
Goats are seasonally polyestrous animals. Sheep and goats are both short-day breeders and the photoperiod has a significant impact on their reproductive cycles. The production and reproduction of goats are impacted by this peculiarity of reproduction. Breed, climate, physiological stage, male influence, breeding system, and photoperiod are just a couple of variables that affect when the breeding season begins. The main elements influencing goat fertility are follicle recruitment, development, selection, and ovulation. Nowadays, goat farming has emerged as a desirable livestock venture for small-scale farmers in rural areas of our country and goat milk, meat and cheese are good industry products. Therefore, there is a significant impact on the industries during the non-breeding seasons. However, estrus synchronisation and artificial insemination are currently utilised to boost the production rate during the non-breeding season. Initially, selection programmes were used as a good strategy. Fixed-timed AI eliminates the requirement for estrus detection in advance. During the non-breeding season, oestrous synchronisation is mostly accomplished through progesterone-based approaches. For use with goats during the non-breeding season, certain innovative techniques have been developed.
For synchronising estrus in goats, the use of progestogen sponges and pregnant mare serum gonadotropin (PMSG) has traditionally produced positive results. Controlled internal drug release (CIDR) or intravaginal polyurethane sponges impregnated with progesterone or their synthetic counterparts, such as melengestrol, flourogestone acetate, and medroxyprogesterone, are the most often used and primary protocols for goats. Along with progesterone, prostaglandins (PGF2 alpha) and equine chorionic gonadotrophin (eCG) are also employed. In goat reproduction, this is the simplest and often utilized protocol.
In this method, 20-40 mg of flourogestone acetate, 50-60 mg of medroxyprogestreone or 0.3 grams of p4 are being used. These devices are inserted intravaginally in the goat for 11 days or more. 24 or 48 hours before the withdrawal of progesterone device/sponges, PGF2 alpha and eCG both are administered intramuscularly. After this 11 days progesterone priming, eCG and PGF2 alpha protocol, if the animal is inseminated with good quality semen 43-46 hours after the withdrawal of the sponge, the kidding rate will get increased up to 65-70%.
Progesterone has a negative feedback effect on the pituitary gland for the secretion of luteinising hormone. So it modifies the GnRH secretion of the hypothalamus. As long as the sponge remains in the body cavity of the animal progesterone is slowly secreted in blood circulation. Progesterone concentration remains high for 11 days. It helps in the maintenance of the corpus luteum and no growth of the follicles takes place during this period. Withdrawal of the progesterone device is followed by a pre-ovulatory surge. PGF2 alpha and eCG are also given 24 hours before the removal of the progesterone device. This PGF2 alpha causes the lysis of the corpus luteum and eCG helps in the development of the antral follicles. eCG has primarily an FSH-like effect and secondarily an LH-like effect. It primarily affects at the level of the ovaries. It is a glycoprotein hormone that produces antibodies when given two times in a row. When administered throughout the subsequent anestrous season as well, it has detrimental effects on goat fertility. It is therefore not advisable to use it repeatedly. In synchronised animals, the presence of these antibodies has been associated to a delay in the onset of estrus, the LH peak, and ovulation, which may account for the reduced fertility if the fixed insemination time is not adjusted properly. Progesterone priming, according to Levya et al. (1998), enhanced the number of follicles triggered by eCG and, as a result, the ovulation rate in anestrous ewes. Progesterone priming can also synchronize the ovulatory wave. PGF2α or its analogues have a luteolytic function and two injections administered 11 days apart in cycling females give satisfactory results.
Side effects of this protocol
The use of the progesterone devices may cause the excretion of the hormone in the milk which can cause serious public health issues. Corteel et al. (1988) observed that the use of progestagen sponges in “long protocol” treatments (18–21 days) has been shown to result in lower fertility rates, possibly due to poor semen transport. Another study observed a high residue concentration in milk in the first few days after the sponge insertion impregnated with 20 mg of fluorogestone acetate (Lopez-Sebastian et al., 2014). Long-used devices remain in contact with the mucosa of the vagina for a long time so it can cause oxidative stress on the animal. There may be contamination in the vagina and bacterial growth takes place leading to inflammation in the reproductive tract of the animal. A decrease in fertility rate in the ewes/doe after a 13-day intravaginal permanence of polyurethane sponge impregnated or with 60 mg of medroxyprogesterone acetate was also observed. These devices probably cause vaginal contamination because of a long time of contact of the device with the vagina and this bacterial contamination is not found in natural estrous. These all factors can cause a decrease in the fertility of the goats.
Alternative recent protocols for inducing synchronization in goats
1. Short priming protocol
In this protocol, progestagen is used only for 5 days and 200-300 IU, eCG is administered at the time of sponge removal. In anoestrous goats, plasmatic P4 levels were higher (>5 ng/mL) for 3 or 4 days following device insertion than those seen in cyclic females during the mid-late luteal, but they then dropped to subluteal levels (2 ng/mL) until the end of the treatment (Rubianes et al., 1998). It has been hypothesised that the conventional 11-day progesterone priming induces low plasmatic P4 concentrations after treatments, which affects LH secretion pattern and, in turn, follicular development (oocyte health and ovulation), as well as fertility. Menchaca and Rubianes (2007) observed that the device P4 insertion affected the lifespan of the largest follicle of wave 1 and advanced the emergence of wave 2 in the early phase of the oestrus cycle. It was hypothesised that the effect of P4 on follicular dynamics claimed an unjustified long progestogen/P4 priming after several studies in cycling dairy goats subjected to short P4 priming (5-7 days) and suggested that this short priming protocol can be used effectively in both anoestrous and cycling goats. The best fertility following artificial insemination was found to be attained after one intramuscular injection of 50 g two days before sponge removal, as per tests on lowering cloprostenol doses from 200 to 0 g. Short P4 priming combined with 200–300 IU of eCG and PGF2 produced positive outcomes in small dairy goats during the breeding and anoestrous seasons (Menchaca and Rubianes, 2007). Globally, estrus behaviour rate is reaching 90 % and pregnancy rate reaching 60% after timed artificial insemination, without significant differences between seasons. In the non-breeding season (April), the oestrus behaviour rate (50%) and pregnancy rate (62.5%) after a 6-day short-term progestogen (20 mg of fluorgestone acetate) priming followed by male effect treatment (in substitution to eCG) and AI is also acceptable in goats. So, the short-term progestogen/P4 priming (and reduction of device P4 concentration) seems to be a rational protocol and should be widely tested in different breeds in both cyclic and anoestrous goats. Progesterone causes the regression of the dominant follicle in regressing phase. It will also cause the emergence of a new follicular wave. PGF2 alpha administered 24 hours before the removal of P4 releasing device causes luteolysis and helps in the development of follicular wave. eCG also plays a major role in the growth of antral follicles.
Other than this various protocol has been tested in goats. In a study, fluorogestone acetate (20 mg) containing device was inserted for 12 days. eCG (500 IU) and cloprostenol (50 µg) were injected 2 days before sponge withdrawal. Timed AI was performed after 43 hours. 100% estrus rate and 69% pregnancy rate were observed. Other than this, medroxiprogesterone acetate (60 mg) was given for 5-6 days. eCG (250 IU) and delprostenate (160 µg) were inserted at the time of sponge withdrawal with timed AI at 54 hours. 91.7 % estrus rate and 63.7 % pregnancy rate were observed in the alpine goat breed. Other short priming protocol includes fluorogestone acetate (45 mg) for 5 days, eCG (300 IU) and cloprostenol (50 µg) at the time of sponge withdrawal with natural mating. In this protocol, 79% estrus rate and 61% pregnancy rate were observed. These are the various protocols which have been tested in different breeds of goats (breeding and anestrous both) in different countries. However, more precise synchronisation of ovulation in treated goats is necessary for intrauterine insemination using frozen-thawed semen to be effective. This quick priming technique is a very reliable and logical way to breed goats.
2. Male effect
The male effect is the most natural way of stimulating the ovulatory process in anestrous females. Goats in their estrous season don’t show cyclicity. When a male is introduced to the flock after a long time, the pituitary gland of the goat gets activated. Doe experiences endocrine changes on the introduction of the male. LH secretions increase due to an increase in GnRH from the hypothalamus. Pre-ovulatory LH surge occurs after 51-53 hours after the introduction of male. Doe ovulates after 22 hours of the LH peak. The frequency of LH pulses increases from 0.3 pulses per 3 hours to 2.2 pulses per hour stimulating follicular growth. After ovulation, corpus luteum formation takes place. 1st cycle will be short of 5-7 days. A low amount of progesterone secretion occurs from this small CL. After the luteolysis of this CL, a new cycle begins with a new pre-ovulatory LH surge. This will be the normal cycle of 21 days, a good quality CL formed this time and normal progesterone secretion occurs.
Almost all the females show heat after 8 days of the introduction of the male during the 2nd cycle. The effectiveness of the male effect depends upon the sexual activity of males and the receptivity of females. The male should be capable of generating a stimulus in females. Many factors play a good role in the male effect-pheromones, male-female interactions and stress factors. All the pathways like olfactory, tactile, visual and hearing are involved in this effect. A proportion of one buck per 12 females is used.
The effectiveness of the male effect also depends upon the anestrous intensity of the doe. There are two methods to decrease the intensity of anestrous in females and sexually stimulate males. These are photoperiodic stimulation of females/ males and melatonin implants. Some animals are strictly seasonal means they don’t come in heat out of breeding season. Prior photoperiod treatment should be given to the does which are unable to respond to the male effect. Females can be given progestagens for 11 days before the breeding season after 90 days of 16 h of light, followed by 60 short days, to work the male effect properly. AI performed 52 h after sponge removal and male-female contact, and the fertility results obtained were similar to those achieved with classical hormonal treatment. In small ruminants, progestagen treatments can synchronize oestrus and ovulation if administered for long enough and the luteal phase of the cycle is mimicked.
The aim of using progesterone plus the male effect is to synchronize the first ovulation and then generate a normal cycle. Progestagen (Norgestomet) for both long and short periods during the transition towards the breeding season does not increase the capacity of females to respond to the stimulus provided by the males. Neither treatment improved the response of the females to the males over that induced by control animals. It is believed that the administration of CIDR for just 5 days prior to male-female contact is sufficient to produce fertile, synchronised oestrus in does that are in anoestrus during the transition to the breeding season. A 5-day short (0.3g) P4 priming plus male effect was also tested by some researchers with success in 126 dairy goats (French Alpine, Saanen and Toggenburg breeds) during anoestrous season (April and May) at latitude 20º N (Mexico).
The progestagen-free guidelines for non-breeding season use by Flock-Reprod recommend synchronising ovulation via the male effect and giving PGF 17 days after male-female contact. The degree of the seasonality of the does, as determined by breed and latitude, determines whether photoperiod treatment is required before male-female contact. In this protocol, AI is carried out 70 hours following PGF administration.
Community based breeding programs has also been implemented in some countries like Liberia. Farmers were actively involved in all the activities of breeding program including identifying and designing the appropriate programs, goat management with cooperation to the technical stakeholders (Karnuah et al., 2018). This type of programs helps in improving the genetic resources of the livestock and increases the income of poor farmers.
3. IMA.PRO2 method
IMA.PRO2 method is proposed by Lopez-Sebastian et al. (2014). This method induces ovulation through the male effect and a single dose of progesterone (25mg) is given at the time of buck exposure. 75 µg of cloprostenol is administered 9 days later for early lysis of the induced corpus luteum. They did the experiment in which IMA.PRO2 method was compared with intravaginal progesterone impregnated sponge followed by 75 micrograms of cloprostenol and 350 IU eCG after 9 days. All goats were inseminated by the same semen sample and by the same operator. Results were checked for 2 years. In 1st year the pregnancy rate in animals synchronized with IMA.PRO2 was 62.9% and in the intravaginal progesterone method was 45.3%. In 2nd year pregnancy rate for IMA.PRO2 and intravaginal progesterone were 65.2% and 49.4% respectively. So, in both the years, they got higher pregnancy rates with IMA.PRO2. It is seen that IMA.PRO2 is an adequate alternative for estrous synchronization during the non-breeding season.
Advantages of IMA.PRO2
As eCG is a hormone of animal origin hence there are health-related issues. The use of eCG is a major drawback in goats as it decreases the ovulation rate, delays the estrous and further affect fertility of animal. Use of eCG can be avoided by using this protocol.
Progestagen use is highly regulated by legislation that forbids the presence of residues in meat and milk in the European Union and many other nations. Additionally, it impairs sperm viability and transport, both of which affect fertility; moreover high concentration of progesterone can be avoided with this technique.
The delivery of cloprostenol in the early luteal phase is the method’s unique component. Treatment given in the early luteal phase result in tighter synchronization, which permits ovulation during the initial postovulatory follicular development wave. The synchronization achieved was greater even than that related to the classic progestagen methods.
The use of P4 or progestagens remains crucial for the synchronization of fertile ovulation if we want to maximize fertility during the anoestrous season. However, several recent studies suggest that it is possible to reduce the exogenous P4/progestagens exposition on females using short progesterone priming protocols. Photoperiod treatment along with male effect or even the lower P4 concentration in some devices played a great role in enhancing the fertility in anestrous period of goats. IMA.PRO2 is an adequate alternative to the conventional methods based on the use of progestagens, given the high degree of estrus and ovulation synchronization and the high fertility rates obtained to a single timed AI. This method is having the advantage of avoiding the use of progestagens and eCG and also because, the technique provides the added advantages of lower expenses (treatment and animal handling costs) and less harmful effects on animal welfare (reduced vaginal handling, vaginitis and related diseases) can be prove useful. Some community based breeding programs can also be implemented to improve the genetics of livestock to provide benefits to the farmers.