ARTIFICIAL INSEMINATION IN FARM ANIMALS - Phenix-Vet

More documents

Recommendations

Info

168Artificial Insemination in Farm Animals2.1 SeasonSeasonal variations are described as a limiting factor in sheep reproduction. In naturalconditions, seasonality, which is mediated by photoperiod, modifies hormonal balance andcauses seasonal reproductive variations in sheep (Karsch, et al. 1984; Yeates, 1949), givingrise to a decrease in reproductive activity during long days (anoestrous season).Photoperiodic information is translated into neuroendocrine changes through variations inmelatonin secretion from the pineal gland (Bittman, et al., 1983). Melatonin, secreted inpineal gland, triggers variations in the secretion of luteinising hormone-releasing hormone(GnRH), luteinising hormone (LH) and follicle stimulating hormone (FSH) (Arendt, et al.,1983, Karsch, et al., 1984). In any case, seasonal changes in reproductive activity are clearlydefined in sheep breeds from high latitudes (>40º)(Pelletier, et al., 1987), where thedifferences in daylight duration between short days and long days are more notable.As in natural mating, season affects fertility after AI, although hormonal treatment is usedto synchronise and induce oestrus. Windsor (1995) reported low cervical AI fertility rates innon-breeding season in Merino ewes, a shallow seasonal breed. According to this, Anel et al.(2005) found a season effect on the AI fertility in Churra ewes, which was more important incervical than laparoscopic artificial insemination. In cervical AI, semen is deposited in theexternal portion of the cervix and the sperm transport is affected by cervical mucus quality.Theses authors suggest that photoperiod could alter progestagens and so cervical mucuscharacteristics, making it scarcer and more viscous. In consequence, sperm transport in thecervix can be interfered with. It is important to note that seasonality affects the ramreproductive parameters in the same way and changes in seminal quality during anoestrousseason may decrease the fertility results after AI.Moreover, subcutaneous melatonin implants are widely used to bring the breeding seasonforward and improve reproductive performance in non-breeding season (Chemineau, et al.,1991; Haresign, et al., 1990). Melatonin treatments act by mimicking a short-day-likeresponse (O'Callaghan, et al., 1991) and induce oestrus during the non-breeding season. Notonly an increase in the percentage of pregnant ewes (fertility) has been described aftermelatonin implant treatment in anoestrous season, but also the number of lambs born perewe (litter size) (Abecia, et al., 2007; Arrebola, et al., 2009; Chemineau, et al., 1992). Thisimprovement could be due to a higher rate of embryonic survival, an improvement in lutealfunction or a reduction in the antiluteolytic mechanisms (Abecia, et al., 2008). In AI, afertility rate increase has been reported with melatonin implant treatments (Laliotis, et al.,1998; Legaz, et al., 2000) after cervical AI.2.2 AgeAnother important factor affecting fertility after cervical AI is ewe age. In comparison withadult ewes, young and maiden ewes have lower fertility, probably due to impaired spermtransport combined with low mucus production in the cervical canals during oestrus(Selaive-Villarroel & Kennedy, 1983a, b). After that, most studies have described a decreasein AI success with increasing female age. Shackell et al. (1990), predicted 2-3% fertilityreduction per year of age for different breeds. Esmailizadeh et al., (2009) reported that as theage of the ewes increased from 2 to 7 years, the proportion of barren ewes significantlydecreased from 29 to 5%. In a more recent study in the Spanish Churra dairy breed, Anel etal. (2005), described how, after 1.5 years of age, the lambing rate decreased by 1.74% peryear for cervical AI. The highest rates of fertility declining with age were described in theLacaune breed by Colas et al. (1973), who reported a drop in fertility of 15% per year.
Management Factors Affecting Fertility in Sheep 169Paulenz et al. (2007), observed that the age of the ewes had a significant effect on the nonreturnrate, but not on lambing rate, whereas in Fukui et al. (2010), both the pregnancy andlambing rates in the ewes significantly declined as age increased. The detrimental effect ofincreased fertility age could be explained by the fact that aged ewes have increased risks ofreproductive disorders and decreased ovulation rates with quality ovulated oocytescompared with younger ewes.The question is: what is the optimal age for cervical AI? Alabart et al. (2002) , studied theinfluence of age on fertility in a total of 3819 Rasa Aragonesa ewes aged 1 to 12 years. In thisstudy, maximum fertility (56.7%) was observed at 3 years, and ewes aged from 2 to 5 years(79.5% of the inseminated ewes) had mean fertility values above 50%. These results partiallyconfirm the observations by Colas et al. (1973), who reported a significant decrease in thefertility of ewes inseminated when over 3.5 years old, and Gabiña and Folch (1987), whoobserved a strong fall in the fertility of ewes inseminated at 4 or more years of age. Anel etal. (2005) recorded the best fertility rates in ewes aged between 1.5 and 4.5 years; beyondthis age, fertility declined remarkably. Fertility also decreased depending on the number ofprevious parturitions. In other studies, the maximum fertility was obtained at around 2years of age, with a progressive fall afterwards (Fantova, et al., 1998). It may be concludedthat insemination groups should be made up of 2 to 5 year old ewes while younger andolder ewes should be used for natural mating.2.3 Lambing-AI intervalThe need for a resting period for the ewe after lambing to allow uterine involution is wellknown. However, sometimes the increasing reproductive rate imposed by the demandingproduction system involves short resting periods from lambing to AI, which affects fertility ina negative way. According to Bodin et al. (1999), reducing the lambing-AI interval to below 40-50 days induces a significant decrease in fertility, even after natural mating. Most authorsrecommend not inseminating ewes any sooner than 50 days post-partum (Anel, et al., 2005).2.4 BreedEwe breed is also a significant source of variation in fertility after AI (Donovan, et al., 2004;Fukui, et al., 2007; Papadopoulos, et al., 2005; Salamon & Maxwell, 1995). Differences in themean time of ovulation and ovulation rates in different breeds of ewes at differenceslocations may explain the variation in fertility (Salamon & Maxwell, 1995).Alternatively, variation may be due to differences in the morphometric characteristics of thecervix (Eppleston, et al., 1994). In this sense, Kaabi et al. (2006), carried out a morphometricstudy in four ovine breeds (Assaf, Churra, Castellana and Merino) showing importantdifferences in length, width, number of folds and distance between folds, which originatesbreed variations in the depth of catheter penetration into the cervix during AI. In this study,the breeds yielding lower fertility after AI resulted in higher cervical complexity, andachieved a lesser degree of cervical penetration of the catheter during cervical AI. Asexplained below, different studies have found a positive correlation between cervical AIdepth and fertility (Kaabi, et al., 2006).2.5 Body weight and body condition scoreFor an adequate response in a breeding programme, ewes must be suitably nourished andmaintained in good body condition. Clearly, ewes with a good nutrient intake respond most
Page 3 and 4:
VIContentsChapter 9Evaluation of a
Page 5:
XPrefaceless stress to the female,
Page 8 and 9:
2Artificial Insemination in Farm An
Page 10 and 11:
Page 12 and 13:
Page 14 and 15:
Page 16 and 17:
10Artificial Insemination in Farm A
Page 18 and 19:
Page 20 and 21:
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
100Artificial Insemination in Farm
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125: 118Artificial Insemination in Farm
Page 224 and 225:
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Page 254 and 255:
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
Page 264 and 265:
Page 266 and 267:
Page 268 and 269:
Page 270 and 271:
Page 272 and 273:
Page 274 and 275:
Page 276 and 277:
Page 278 and 279:
Page 280 and 281:
Page 282 and 283:
Page 284 and 285:
Page 286 and 287:
Page 288 and 289:
Page 290 and 291:
Page 292 and 293:
Page 294 and 295:
Page 296 and 297:
Page 298 and 299:
Page 300 and 301:
Page 302 and 303:
Page 304 and 305:
Page 306:
show all

ARTIFICIAL INSEMINATION IN FARM ANIMALS - Phenix-Vet

Create successful ePaper yourself

Delete template?

Save as template?