1 Reproductive Management in Goats Lionel J. Dawson 002 Farm Road Boren Veterinary Medical Teaching Hospital Oklahoma State University Stillwater, OK 74078 Phone: 405-744-8580 Fax: 405-744-6265 Lionel.Dawson@okstate.edu
2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Abstract Goats are generally classified as a seasonally polyestrous or short day breeders in the U.S. The degree of seasonally varies among breeds and their location (latitude).the annual reproductive cycle of goats in a temperate region can be divided into breeding season or period, nonbreeding season or physiologic anestrous period and transitional period. Transitional period is between the nonbreeding and the breeding season. The onset of the breeding season commences after June 21 st (summer solstice). In July and August or during their transitional period, some of the does will show estrus activity, but majority of the does will start cycling regularly in late September, resulting in the kids born late winter or early spring. With the rapid increase in meat goats in the U.S., estrus synchronization has been used as an effective tool in the reproductive management of these herds. Synchronization early in the breeding season, will allow increased proportion of doe s becoming pregnant early, older and uniform size of kids at weaning, take advantage of the niche in the market during religious events and rising price trends in the market. Synchronization of estrus in does includes techniques such as alteration of light patterns, manipulation of social interaction with the buck exposure early in the breeding season, and manipulating the estrous cycle by extending or shortening the luteal phase of their cycle. In does during the breeding season the opportunity to control their cycle is greater during the luteal phase, which is of longer in duration and is more responsive to manipulation. 19
3 20 21 Introduction Reproductive Management in Goats 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 The goat (Capra hircus) and sheep (Ovis aries) are two distinct species in the family Bovidae. The world sheep population is estimated at 1.3 billion and the goat population around 1.0 billion. Both species were among the first to be domesticated by man for meat and fiber. There are different breeds seen throughout the world. The goats tend to be located in the more arid areas of the world while the sheep are raised in very diverse environments. In North America goats are seasonally polyestrous or short day breeders. The length of the breeding season is influenced by photo period, breed, location and nutrition. There is not only great variation between breeds as regards to the length of the breeding season, but there are variations within breeds. Selecting a breed, and also individuals with long breeding season could be utilized as a management tool in managing goats for production. Photoperiod and its influence on the secretion of melatonin from the pineal gland are important signals for cyclicity of does in the fall. The influence of photoperiod, and its effect on cyclicity, is mediated through the release of gonadotropic releasing hormone (GnRH) from the hypothalamus, and the release of luteinizing hormone (LH) from the anterior pituitary gland. Reproductive management: Breeds: Common lactating breeds seen in North America are Alpine, Saanen, Toggenburg, Nubian and LaMancha. Meat breeds seen are Boers, Spanish, Kiko and Tennessee Stiff Legged. Fiber producing breeds seen are Angora and Spanish (Cashmere). Nubian, Nubian crosses and Boers tend to have a longer breeding season (June-March) due to their origin near the equator. In contrast British and European goat breeds (Saanen, Toggenburg and French 1, 3-5 Alpine) have a more restricted breeding season (September February).
4 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Puberty: Puberty in goats is defined as onset of changes when the doe or buck becomes sexually mature and able to reproduce. It is the maturation of the hypothalamo pituitary ovary/testicular axis. 1,3-5 Onset of puberty in goats primarily depends on age, breed, nutrition, body weight or size, management, season and disease status of the herd. Goats reach puberty around 6 to 8 months of age, some breeds or individuals within a breed may reach puberty as early as 3 months. The range is around 3 to 15 months. Bucklings usually reach puberty earlier than doelings. Cross breeds usually reach puberty earlier than the purebreds. Size or body weight plays an important role when the doe will reach puberty, and it depends on genetics, nutrition and management. Doelings which grow faster in size and weight and will reach puberty earlier. Time of year when kids are born plays an important role when the kids will reach puberty. Kids born early (Jan-Feb) more likely to reach puberty and cycle that fall. Late born kids (March- June) may not reach puberty and breed until the 2 nd fall after birth. Chronic diseases or conditions in the doelings (Parasites internal and external, Caseous Lymphadenitis, and Pneumonia etc.) will delay puberty. Bucks: Scrotal circumference in rams plays an important role, when their sons and daughters will reach puberty, and also has influence on the twinning rates in their daughters. Bucks with scrotal circumference will potentially produce good quality semen; and have a positive influence on fertility and litter size. 6, 7, 11-13 Seasonality: The underlying influence of photo period effect on estrus activity is mediated through the secretion of luteinizing hormone (LH) from the anterior pituitary gland. Final maturation and ovulation of ovarian follicles is dependent on sufficient LH secretion. During the anovulatory (anestrus) season, estrogen secretion from the follicles strongly inhibits LH release. As photoperiod begins to decrease (late summer-fall), this inhibitory effect is lost
5 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 and there is increased LH release leading to ovulation and cyclicity. 7 Alternating inhibitory influence of estrogen from cycling to non-cycling seasons may be due to changes in melatonin production from the pineal gland, mediated through changes in light perceived by the eyes. Regardless, the important point to remember is that the does become anestrus due to reduced LH secretion. Thus, without sufficient LH, the ovaries are virtually inactive. To get anestrus does to cycle out of season, one must increase the LH release by increasing follicular growth, by providing Follicular Stimulating Hormone or gonadotropins containing FSH to stimulate ovarian activity. 1,3-6 Under natural circumstances the onset of estrus activity within a group of does is characterized by an increasing percentage of the group exhibiting estrus over a time. The time of the year, 90% of the group will cycle regularly will depend on the breed, location and nutritional status. Majority of the does will exhibit estrous activity in fall, between September to November in North America. Buck exposure: Exposure to bucks during the non-breeding or off season can trigger low percentages of does to cycle. The male effect is probably mediated through pheromones produced by the buck and increasing LH production in the does. Exposure of does to vasectomized or intact bucks late in the transition period induces estrus and ovulation in the majority of the does. 30-60% of the does will later short cycle in 8-10 days due to premature luteal regression after buck exposure. Normally there are three peaks of estrous activity when first introduced to bucks in late transition (3-4 days, 7-12 days, and 28-35 days). 1-6 Flushing: To increase the ovulation rate in does, a period of nutritional flushing (increased energy intake) for 4 weeks is effective prior to breeding. Flushing seems to help does which are poor in body condition during the transition period.
6 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 Estrous cycle: The normal length of their estrous cycle during the peak of their breeding season is around 19-23 days (average 21 days). The peak of the breeding season in the mid-west is between October to December. The estrous cycle length in Angora s are shorter, and is around 16 to 18 days, whereas for a pygmy is greater than 21 days. The period of receptivity or estrus is around 24 (12-36 ). Doelings are in estrus for about 24, and does 24 to 48. Ovulation is towards the end of the estrus period. Usually 12 after the onset in a doeling, and 24-36 after the onset in a doe. 1-5 Bucks: Bucks are seasonal breeders too. Decreasing the daylight stimulates the pulsatile release of GnRH. Thereby stimulating the release of LH and FSH, resulting in increasing spermatogenesis and testosterone production in the testes. Increased androgens in turn stimulates accessory sex glands and sexual behavior (libido), increase in testicular size ( 3-5 cms of scrotal circumference), testicular weight and gonadal sperm reserve.sperm quality like motility, morphology and concentration are lower during the longer daylight or anestrus period. 11-13 Estrus: Estrus behavior seen in a doe are, restlessness, increase vocalization, occasional mounting, rapid tail wagging, swollen vulva, mucus discharge, frequent urination and decrease in milk production. Bucks will nose the perineum and udder, flick their tongue, strike with their forelimb and make low bleating sounds. He may butt or push doe s hindquarters with his shoulder, and line up directly behind the doe and mount. 1-6 Breeding: Common breeding techniques used in goats are, hand mating, pen mating and artificial insemination. Hand mating is a common practice done in dairy goats, by taking the doe to the buck to be bred. Pen mating is leaving the buck with the does for a certain period in a pen or pasture. Artificial insemination is a technique to deliver the semen other than a buck to the
7 110 111 112 113 114 115 116 117 118 119 120 121 doe. And are usually performed 12 and 24 after onset of estrus, when the cervical mucus changes from clear to cloudy. 1-5 Estrus detection is very important if artificial insemination is going to be practiced. 1) Does actively seek the buck. 2) Does prefer bucks with intact scent glands. 3) Buck jar rub cloth or rag over the scent glands of intact bucks and place it in jar. Opening the jar and exposing the rag to the does may be helpful in detecting estrus in does when there is no buck present. 4) Buck beard trimmed during the breeding season, put in a zip lock bag and the bag opened and exposed to does once or twice a day. 5) Fence line exposure by exposing the buck across the fence to the does. 6) Use of intact bucks with breeding aprons or teaser bucks in the pens with the does. 1-4 122 123 124 125 126 127 128 129 130 131 132 Inducing cyclicity in a doe is mainly done by a) male effect during the late transitional period and early breeding season, b) light effect and 3) using exogenous hormones. During the transitional period (late July to early September), buck effect is a powerful tool to induce estrus (Table1). Sudden introduction of previously isolated bucks will stimulate a surge of LH followed by ovulation, and majority of the doe s exhibit estrous within 48-72. 1,7-13, 21-23 30 to 60 % of the does will cycle back or short cycle and show estrus behavior and ovulate again within 3-5 days or 7-12 days after introduction of the buck. Three peaks of activity have been observed, after the introduction of the buck, 3-5 days, 7-12 days and 28 to 35 days after introduction to the buck. 1, 21 This phenomenon of cycling back in 7 to 12 days is described as early luteal regression (ELR). 15, 16, 21-24 The current thinking is that early luteal regression maybe due to lack of
8 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 progesterone priming of the uterus during anestrus period, and thereby having positive effects of estradiol from the follicles on the uterus. Estrogen increases the availability of oxytocin receptors, leading to the release of endogenous prostaglandin from these receptors, and thus lysing or regressing the corpus luteum. Doe s that were supplemented with progesterone in late- transition, and removed on the day the bucks were introduced, had higher percentage of does showing estrus, and reducing the number of short cycles. 1,16-18 Buck effect and exogenous progesterone are methods commonly employed to induce estrus in the transition period and to prevent ELR (Table 1). 24-26 Photoperiod manipulation is done by altering the day length. Decreasing day length will increase the levels of melatonin produced by the pineal gland. Melatonin production may influence the secretion of LH from the anterior pituitary gland, and hasten the cyclicity. 37-50 Melatonin will increase the pulsatile release of GnRH, thereby increasing the frequencies of FSH and LH release. Increase levels of LH release will cause ovulation, and thus enabling doe to cycle regularly. Changes in light exposure or decreasing day length require at least 45-60 days to induce a doe to cycle. Gradual change is not necessary, the amount of change that is perceived by the eye is important. A reduction of light is effective to trigger cyclicity in 30 to 60 days in a 31, 36, 51, 52 doe. In does during the breeding season the opportunity to control their cycle is greater during the luteal phase, which is of longer in duration and is more responsive to manipulation. Strategies can be employed for synchronization, is to extend the luteal phase by supplying exogenous progesterone (Table 4) or to shorten this phase by prematurely regressing the existing corpus luteum (CL) by using prostaglandins (Table 3). 1,14-19 Hormones have been used in goats to manipulate the estrous cycle, but none have been approved for use in goats in the U.S.
9 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 Extending the luteal by supplying exogenous progesterone is best done by using Controlled Internal Drug Release devices (CIDR), intravaginal sponges and feed supplements. 14 Regressing the corpus luteum is best done by utilizing prostaglandins. Progesterone or progestagens products commonly used are CIDR s and sponges (Veramix, Repromap, Sincrocel, Cronolone and Chronogest). Shortening the luteal phase is best done by using Lutylase (Dinoprost tromethamine) and Estrumate (Cloprostenol). 1,14-19 To better control or synchrony of estrus and ovulation, extending the luteal phase with progesterone, along with a gonadotropin (FSH) and prostaglandin have been used. The gonadotropin like equine gonadotropin (ecg) is commonly used because of its longer half-life. The drawback of using higher doses ecg may result in larger number of anovulatory follicles, and repeated doses can cause declining fertility due to the buildup of antibodies against ecg. 1,14,20 ecg is not commercially available in the U.S. But a product containing ecg and a Human Chronic Gonadotropin (HCG), which has been labeled to be used in swine (PG 600) has been tried and has been in goats. Dosage of PG 600 utilized in does is 200 units of ecg + 100 units of HCG (1/2 dose) during the breeding season or 400 units of ecg + 200 units of HCG (full dose) during the non-breeding or off season. If ecg is used, 200 units of ecg during the breeding season and 400 units of ecg during the non-breeding or off season. Out of season breeding in doe s could be done manly by using hormones or manipulating the photo period to fasten the onset of estrus. Out of season breeding will enable the farmer or producer to take their kid crop to market when prices are higher, have year round milk production in dairy animals and also increase the number of kids born to the doe during her life time. Hormones are commonly used effectively to synchronize estrus in this period. Incorporating a follicle stimulating hormone into the protocol is very essential to stimulate
10 179 180 181 follicular waves during the non-breeding season or off season. Equine Chorionic Gonadotropin (ecg) is commonly used. In the U.S., PG 600 which contains ecg is available in the US and has been used successfully used in goats (Table2). 182 183 Table 1 Different methods employed to hasten cyclicity during the transition period Method Duration Estrous 1.Buck effect Late transition 24-96 4,9-11,20 184 185 2. Progesterone(12-14 days) + equine chorionic Early transition 24-72 21 gonadotropin(ecg) on the day or 24-48 prior to removal 3. Progesterone(12-14days) + ecg on the day or 24 to 48 Late transition 24-48 22 prior to removal 4. Progesterone(10days) +ecg(removal) +prostaglandin 48 prior to removal Late transition 10.9+- 3.2 23 This table is adapted from Current Therapy in Large Animal Theriogenology
11 186 Table 2 187 Methods employed during the non-breeding season Method Duration Estrus Progesterone 12-14 days 24-96 1,14,15 + Equine Chorionic Gonadotropin On the day of removal or 24-48 before +Prostaglandin On the day of removal or 24-48 before 44.6 + 8.2 27 25 + 5 22-30 <72-90% in estrus Artificial lights Mimic long days for 60 days followed by short days for 60 days or natural light 40-70 days during short days 31 Melatonin (Implant, oral, or injection) 60-100 days 30-60 days Artificial lights + melatonin Mimic long days for 60 days followed by melatonin for 60-100 days Buck exposure 60 days into melatonin treatment; estrus 2-3 days 36 188 189 190
12 191 192 193 Table 3: Lutalyse (Dinoprost tromethamine) Shortening the luteal phase Product Dosage Treatment Route Estrus 5-10 milligrams Estrumate (Cloroprostenol) 50-150 micrograms 2 injections, 11 to 12 days apart in does 2 injections, 11 to 12 days apart l/m 24-72 (48-60 ) TAI + 50-52 l/m 24-72 (48-60 ) TAI=50-52 194 195
13 196 197 Table 4: Progesterone in Combination with Prostaglandin & Gonadotropin 198 Product Dosage Location Duration ecg Prostaglandin Season Estrus Breeding PG Rate CIDR-G 330mg Progesterone Vagina 16 days + Removal Breeding Season 47% 53 CIDR-G CIDR-G CIDR-G CIDR-G CIDR-G 330mg Progesterone 330mg Progesterone 330mg Progesterone 330mg Progesterone 330mg Progesterone Vagina 9 days + Removal + Removal Vagina 9 days + Removal Vagina 13 days + Removal Vagina 5 days + Removal Vagina 11-14 days + PG600 + [1] with CIDR-G insertion Breeding Season Breeding Season Breeding Season Breeding Season or Non- Breeding Season + Non- Breeding Season 27.2 + - 0.4 24-36 24-72 40.2 + - 10.5 24-36 AI 48-60 after sponge removal Natural Service Natural Service AI after the onset TAI AI 54 TAI AI 48 Natural Service 95% 54 65% 54 63% 55 63% 56 49% 56 60-70% (Dawson)
14 Extending the luteal phase CIDR/ Lutylase 0 5 10 12 13 Insert CIDR NS or A.I.= 24 after standing estrus TAI= 52 to 56 after CIDR removal Removed 5-10mg Dinoprost tromethamine (1-2cc Lutylase)
15 199 200 201 CIDR + PG 600 +Lutylase CIDR/ Lutylase 0 Insert CIDR 0 5 Insert CIDR NS or A.I =24 after standing estrus TAI = 42 to 48 after CIDR removal NS or A.I.= 24 after standing estrus TAI= 52 to 56 after CIDR removal 5 10 5-10mg Dinoprost tromethamine (1-2cc Lutylase) 10 12 12 13 Remove CIDR Give 5cc PG600 during the off season 13 ½ dose during the breeding season (400 units ecg and 200 units HCG) Removed 5-10mg Dinoprost tromethamine (1-2cc Lutylase) 202 203
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