A Survey of the Postpartum Reproductive Performance of Dairy Cows with Fertility Problems in Southern Iceland

The purpose of this survey was to evaluate the reproductive performance of dairy cows on problem farms in southern Iceland. In all 229 cows on 6 farms were studied. The animals were examined clinically by rectal palpation, once a month. Blood samples were taken 2–5 and 7–10 weeks after calving. The blood samples were analysed for the contents of glucose, urea, inorganic phosphate, calcium and magnesium. Milk samples for progesterone profiles were taken, by the farmer, every 4th day from day 10 postpartum until first oestrus. Because of this sampling method, 128 cows had no rise in progesterone levels, when milk sampling was stopped. These 128 animals were excluded from the study. The results are based on 101 animals. There was a large variation between cows in postpartum reproductive performance. In the total material 1st ovulation occurred later than reported in many other countries. Fifty percent of the cows had ovulated 35 days after calving and 90 percent 70 days after calving. The first luteal phase was short in about 60 % of the cows. The progesterone values assayed from those short cycles were lower than the values assayed from the following cycle. First artificial insemination (ai) was on the average 77 days postpartum (pp). The conception rate to first service was 49 %. Of 100 milk samples taken at the time of ai, 20 had high progesterone value. This indicates a high frequency of luteal phase inseminations. Clinical ketosis was diagnosed in 35 cows. Of these, 31 had a low glucose value. Cows with clinical ketosis ovulated, on the average, later than other animals and 24 ovulated later than 40 days pp. The results indicated that the fertility problems of these cows studied were late ovulations, low conception rate, probably in part, due to luteal phase inseminations, and a high frequency of ketosis which could be caused by low quality feedstuff.     

Efficacy of intermittent or continuous administration of GnRH in inducing ovulation in early and late seasonal anoestrus in the Père David's deer hind (Elaphurus davidianus)

Père David's deer hinds were treated with GnRH, administered as intermittent i.v. injections (2.0 micrograms/injection at 2-h intervals) for 4 days, or as a continuous s.c. infusion (1.0 micrograms/h) for 14 days. These treatments were given early (February-March) and late (May-June) in the period of seasonal anoestrus. The administration of repeated injections of GnRH increased mean LH concentrations from pretreatment values of 0.54 +/- 0.09 to 2.10 +/- 0.25 ng/ml over the first 8 h of treatment in early anoestrus, and from 0.62 +/- 0.11 to 2.73 +/- 0.49 ng/ml in late anoestrus. The mean amplitude of GnRH-induced LH episodes was greater (P less than 0.01) in late (4.03 +/- 0.28 ng/ml) than in early (3.12 +/- 0.26 ng/ml) anoestrus, but within each replicate (early or late anoestrus), neither mean LH episode amplitude nor mean plasma LH concentrations differed significantly between the four periods of intensive blood sampling. On the basis of their progesterone profiles, 6/12 hinds had ovulated in response to treatment with injections of GnRH (1/6 in early anoestrus and 5/6 in late anoestrus), and oestrus and a preovulatory LH surge were recorded in all of these animals. Oestrus and a preovulatory LH surge were also recorded in one other animal treated in early anoestrus in which progesterone concentrations remained low. The mean times of onset of oestrus (91.0 +/- 1.00 and 62.4 +/- 0.98 h) and of the preovulatory LH surge (85.8 +/- 3.76 and 59.4 +/- 0.25 h) both occurred significantly earlier (P less than 0.001) in animals treated in late anoestrus. Continuous infusion of GnRH to seasonally anoestrous hinds resulted in an increase in mean plasma LH concentrations, but this response did not differ significantly between early (2.15 +/- 0.28 ng/ml) and late (2.48 +/- 0.26 ng/ml) anoestrus. Ovulation, based on progesterone profiles, occurred in 2/7 hinds in early anoestrus and in 4/6 hinds in late anoestrus. Oestrus was detected in all except one of these hinds. The mean time of onset of oestrus occurred earlier in animals treated in late anoestrus (66.2 +/- 0.32 h and 46.7 +/- 0.67 h, P less than 0.01). The administration of GnRH, given either intermittently or continuously, will induce ovulation in a proportion of seasonally anoestrous Père David's deer. However, more animals ovulate in response to this treatment in late than in early anoestrus (75% compared with 23%).     

Hierarchy of factors affecting behavioural signs used for oestrus detection of Holstein and Normande dairy cows in a seasonal calving system

As oestrous expression of dairy cows has decreased over the last decades oestrus detection has become more difficult. The objective of this study is to identify the main factors that affect oestrus detection in seasonal calving dairy cows, and to establish their relative importance. In each of 5 years 36 Normande and 36 Holstein cows were assigned to a Low or High winter-feeding level group. Half of each group was then assigned to a Low or High pasture-feeding group. The Low-Low strategy resulted in the lowest milk yield and the greatest body condition (BC) loss from calving to nadir BC score (6302 kg; -0.98 unit). The High-High strategy had the converse effect (7549 kg; -0.75 units). Low-High and High-Low strategies had intermediate values. The Normande cows had lower milk yield and BC loss than Holstein cows (6153 kg versus 7620 kg; -0.82 unit versus -1.20 unit). A database of 415 observed spontaneous oestruses was created. Oestruses were classified according to detection signs: (1) standing to be mounted, (2) mounting without standing, (3) other signs without standing or mounting (slight signs). Presence of another cow in oestrus, access to pasture, Normande breed and Low-Low strategy increased standing detection. In the Normande breed, 97% of oestruses were detected by standing while combining the presence of a herdmate in oestrus and access to pasture with a milk production of less than 6550 kg. Holstein cows had a higher frequency of slight signs oestruses than Normande ones, which was associated with a decreased subsequent calving rate (P<0.05). In multiparous Holstein cows, the odds of slight signs detection was multiplied by 7.8 for the High-High group in comparison with the Low-Low group (P<0.05). In our study milk yield had an effect on oestrus detection which was not explained by BC loss. As High-High cows produced more milk than others, we logically found that an increase in milk yield increased slight signs detection. Conversely, as they lost less BC than others, BC loss improved the chance of standing or mounting detection. These two results show that an increase in milk yield may reduce oestrous behaviour even if BC loss is moderate. Oestrus detection is crucial in seasonal compact calving systems. High phenotypic milk yields appear unsuitable with such systems in regard to depressed oestrous behaviour.     

Luteinizing hormone, oestrogen and progesterone levels in peripheral serum of anoestrous and cyclic ewes as determined by radioimmunoassay.

Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean plus or minus S.E. value of 2-3 plus or minus 0-9 ng/ml. High LH values of 20-0, 41-2 and 137-5 ng/ml were observed in three ewes on Day - 24 of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0.11 plus or minus 0-01 ng/ml) before Day - 25 of anoestrus. A major rise occurred on Day - 12 of anoestrous and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4-40 plus or minus 0-1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5-2 plus or minus 0-3 pg/ml. A well-defined peak of 13-3 plus or minus 0-7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day - 25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.     

Induction of oestrus in the camel (Camelus dromedarius) during seasonal anoestrus

Injection of 7000 i.u. PMSG induced oestrus in 7 camels during the last part of seasonal anoestrus. Mature follicles developed and a CL was formed after fertile mating. However, pregnancy was not maintained by Day 60 in the 3 females detected as pregnant by rectal palpation and increased progesterone concentrations at Day 50. A single male camel mated with 4 of the females 2-16 days after the PMSG injection, and 2 or 3 matings occurred. The failure of pregnancy after induction of oestrus and mating during seasonal anoestrus was probably due to inadequate luteal function.     

Seasonal sexual activity and post-partum anoestrus in two Moroccan breeds of sheep: Beni-Guil and Sardi

Twenty-four Beni-Guil and twenty-six Sardi ewes were regularly checked for oestrus during 19 consecutive months following lambing using penis-deviated rams and for ovulation by endoscopy or plasma progesterone level. Fifty percent of the Beni-Guil and Sardi ewes had a first ovulation at 41 and 71 days and first oestrus at 85 and 132 days, respectively. The seasonal anoestrus in both breeds occurs from February to May and is characterized essentially by a lack of expression of oestrous behaviour.Compared to other breeds located at higher latitudes, the two breeds studied showed a more rapid resumption of sexual activity following lambing and a seasonal anoestrus of reduced length and intensity.     

Total unconjugated oestrogen and progesterone concentrations in peripheral blood during the oestrous cycle of the dog.

From the beginning of pro-oestrus to the end of metoestrus, daily peripheral blood samples were withdrawn from six bitches. Further samples were obtained during anoestrus. Oestrogen values rose from the onset of pro-oestrus to attain a peak value of 25-3 +/- 4-8 pg/ml on Day 1 of oestrus. Progesterone concentrations began to rise 2 days before the oestrogen peak, and reached their highest levels of 18-9 +/- 1-0 ng/ml 16 days after the end of oestrus. After oestrus, an oestrogen rise was detected which reached a peak at Day 18 of metoestrus. The duration of oestrus was unrelated to the length of time that oestrogen levels were raised, or the maximum values were attained. No significant oestrogen levels were detected during anoestrus.     

Reproductive responses of early postpartum dairy cattle to continuous treatment with a GnRH agonist (deslorelin) for 28 days to delay the resumption of ovulation

An experiment was conducted to investigate the potential of chronic delivery of a potent GnRH agonist (deslorelin) via subcutaneous implants to delay the resumption of ovulatory cycles in postpartum dairy cattle. Cows received either a single deslorelin implant (n=40; DES) within 7 days of calving or were untreated (n=24; CON). Blood samples were collected thrice weekly during the period the implants were in place. Plasma concentrations of progesterone (P4) and 17beta-oestradiol (E2) were measured along with selected serum metabolites. Implants were removed after 28 days and cattle monitored daily for behavioral oestrus. Serial weekly blood samples were collected to detect the occurrence of ovulation. Cows were artificially inseminated as they were detected in oestrus from 30 days after implant removal. Pregnancy status was subsequently determined by manual palpation of uterine contents at strategic intervals.Insertion of implants induced ovulation in 3/40 cows as determined by a rise in progesterone 7 days later. Deslorelin implants delayed the onset of ovulatory cycles compared with untreated herdmates (mean 43.4+/-4.2 versus 57.3+/-1.6 days postpartum; P<0.001). A noticeable delay of at least 12 days was observed between implant removal and the first animals ovulating. Mean plasma E2 concentrations during the period the implants were in place were similar for DES and CON cows that experienced a prolonged spontaneous postpartum anoestrus (low P4 >60 days), although both groups had concentrations only 20% of CON cows that had ovulated prior to 30 days postpartum.The patterns of recovery following implant removal were highly variable. A number of DES cows showed a low and transient rise in plasma progesterone around 21 days after implant removal. Some cows displayed oestrus but did not appear to form a fully functional corpus luteum with this phenomenon being more prevalent among DES cows (7 of 37 versus 1 of 21; P<0.05). Overall, significantly more DES cows were detected in oestrus without ovulating compared to CON cows. Final pregnancy rates did not differ between DES and CON groups. The mean time to conception for DES cows was longer (21.2+/-5.6 versus 41.1+/-7.4 days, CON versus DES; P<0.01). This difference was not present if the time from first ovulation to conception was compared (50.5+/-5.3 versus 43.5+/-9.3 days, CON versus DES; P>0.05). Deslorelin implants provided a reliable method of inducing anoestrus when treatment was initiated prior to 3 days postpartum. A variable pattern of recovery was observed which delayed conception but did not ultimately reduce the final proportion pregnant at the completion of mating. The study demonstrates the potential of GnRH agonists to control postpartum reproductive function to manipulate the fertility of dairy cows.     

Peripheral plasma levels of oestradiol-17 beta and progesterone in the bitch during the oestrous cycle, in normal pregnancy and after dexamethasone treatment.

Plasma oestradiol-17 beta concentrations in Labradors increased during pro-oestrus to an average maximal concentration of of 79-7 +/- 10-9 (S.D.) pg/ml, and then fell rapidly. In 6/7 bitches the peak occurred within 1 day of oestrus. No consistent changes in plasma oestradiol levels were observed during pregnancy and at parturition and the values were similar to those in late anoestrus. Plasma progesterone levels did not increase markedly during pro-oestrus. At oestrus, progesterone values rose and maximal concentrations, which varied from about 20 to about 55 ng/ml, were reached within a few days of the oestradiol peak. Plasma progesterone decreased in late pregnancy and in one of the three bitches studied in detail low or undetectable levels were reached 10 days before parturition. In the other two bitches an abrupt decrease in progesterone occurred just before parturition. Dexamethasone treatment (2 X 5 mg daily for 10 days) from Day 30 of pregnancy resulted in intrauterine death and resorption of the fetuses in the two bitches studied. Treatment from about Day 45 resulted in the birth of dead fetuses at Days 55 and 59 of pregnancy. The changes in plasma oestradiol levels were very small. No changes in plasma progesterone levels were seen when dexamethasone was given in late pregnancy, but an accelerated decline occurred after treatment in mid-pregnancy.     

Plasma concentrations of progesterone in female red deer (Cervus elaphus) during the breeding season, pregnancy and anoestrus

Concentrations of progesterone in peripheral plasma of red deer hinds were basal (less than 1 ng/ml) during lactation/seasonal anoestrus, but increased abruptly at the onset of the breeding season. Lactating hinds (N = 19) started ovarian cycles 10 days later (P less than 0.01) and conceived 16 days later (P less than 0.001) than did 13 weaned hinds. There was no evidence, from plasma progesterone values, of silent oestrus at the start of the season. Progestagen/PMSG treatment induced early ovulations in 8 anoestrous hinds but fertility was low, only 2 conceiving and giving birth. Pregnant hinds (N = 42) had high plasma concentrations of progesterone (mean 3-5 ng/ml) which declined just before parturition.     

Induction of oestrus and fertility in the anoestrous ewe with hormones and controlled lighting and temperature

A programme consisting of 14 daily injections of progesterone (10 mg) followed by single injection of PMSG (500 i.u.) and oestradiol- 17 beta (30 micrograms), along with controlled temperature (18-20 degrees C) and lighting (10 h light/24 h), was applied to 60 anoestrous ewes between late May and early August to induce reproductive activity. Breeding started within 24 h of the oestradiol injection and 80.0% of the ewes conceived at the induced oestrus. Dorset ewes had higher conception (95.2 versus 71.8%) and prolificacy (1.74 versus 1.52 fetuses/ewe) rates than did crossbred Suffolk ewes. Plasma progesterone concentrations during progesterone administration were significantly higher than those found during anoestrus and were generally lower in ewes which did not conceive than in those which did. The plasma progesterone data indicated that ovulation had occurred in most of the ewes which were not pregnant at 90-100 days and that many may have been pregnant initially but then lost the conceptus.     

Artificial long days in addition to exogenous melatonin and daily contact with bucks stimulate the ovarian and oestrous activity in Mediterranean goat females

One experiment was conducted to determine whether the treatment with artificial long days and exogenous melatonin can induce reproductive activity during spring (seasonal anoestrus) in Mediterranean goats that are in daily contact with bucks and whether this treatment causes a variation in the reactivation of the reproductive activity in the normal breeding season. The experiment started on 4 November 2005 and finished on 27 October 2006. Thirty-four adult and barren does were used, distributed into two groups balanced according to their live weight (LW) and body condition score (BCS). Seventeen females were exposed to long days (16 h of light/day) from 14 November 2005 to 20 February 2006. On 20 February, they received one s.c. melatonin implant (LD-M group) and were exposed to natural photoperiodic changes in an open shed. The other females during the experiment were placed in an open shed under natural photoperiod and remained as the control group (C group). The C and LD-M groups were keeping in contact with males during the whole experiment. During the experiment, the LW, BCS and plasma progesterone concentrations were measured weekly, oestrous activity was tested daily using entire aproned bucks, and ovulation rate was evaluated by laparoscopy 7 days after positive identification of the oestrus. A clear treatment-time interaction was observed for plasma progesterone concentrations (P < 0.001), with a period of high progesterone concentrations during the natural seasonal anoestrus in the LD-M group. Although 94.1% of females in the LD-M group presented ovarian activity during this period, no female in group C did. Resumption of ovarian activity in the subsequent natural breeding season was 2 weeks later in the LD-M group in comparison with group C (P < 0.05). We can conclude that in Mediterranean goat breeding systems, when females are in daily contact with bucks, the treatment with 3 months of long days and melatonin implant at the end of the light photoperiodic treatment can induce ovarian and oestrous activity during the seasonal anoestrus. Finally, this treatment causes a short delay in the subsequent reactivation of ovarian activity in the natural breeding season.     

Post partum ovarian activity and uterine involution in the suckled swamp buffalo (Bubalus bubalis)

Ovarian activity and uterine involution were monitored by rectal palpation, oestrus detection and plasma progesterone analysis from 3 to 4 days to approximately 150 days post partum in 38 suckled swamp buffaloes (Bubalus bubalis). The intervals from parturition to regression of the corpus luteum (CL) of pregnancy and involution of the uterus were 10 and 28 ± 6 (S.D.) days respectively. First detected oestrus and first elevation of plasma progesterone (> 0.7 ng/ml) occurred at 88 ± 26 and 96 ± 22 days in 8 and 12 buffaloes respectively. During the first 150 days post partum, 26 of 38 suckling buffaloes (68%) were acyclic (anoestrus) and of 12 animals (32%) exhibiting ovarian cycles, 4 were not detected in oestrus. The tentative diagnosis, based on rectal palpation, that CL were present between days 30 and 90 after parturition (without concurrent luteal levels of progesterone in plasma) suggests that confirmation should be by laparoscopy. It is concluded that a delay in the resumption of ovarian cyclicity post partum represents an important factor contributing to the prolonged calving to conception interval in the suckled swamp buffalo.     

Superovulation in cows: A relationship between progesterone secretion before ovulation and the quality of embryos

Superovulation was induced in 28 cyclic cows by treatment with FSH and milk progesterone concentrations were studied from the initiation of treatment to oestrus. A negative correlation (r= ?0.66; P < 0.001) was observed between the increase in progesterone concentration observed 2 days after the beginning of treatment and the percentage of transferable embryos collected. During this sampling period progesterone secretion was not related to ovulation rate and number of embryos.     

Direct enzymeimmunoassay of progesterone in bovine milk

A sensitive enzymeimmunoassay has been developed for measuring progesterone in unextracted bovine milk. An N-hydroxysuccinimide ester of 11 alpha -hydroxyprogesterone 11-hemisuccinate has been synthesised and used to form conjugates with beta-galactosidase in buffer at pH 7.0. The degree of incorporation of progesterone into the enzyme was demonstrated using (14C)-labelled steroid and by radioimmunoassay binding inhibition. Standard curves of comparable range and sensitivity to radioimmunoassay were obtained in the presence of whole milk taken from a cow at oestrus. These advances have allowed the development of a simple micro-titre plate enzymeimmunoassay of progesterone in whole milk and will be of particular value in determination of pregnancy, prediction of the day of oestrus and diagnosis of reproductive disorders.     

Progesterone and oestradiol-17 beta concentration profiles throughout the reproductive cycle in harbour seals (Phoca vitulina)

Serum samples of harbour seals kept in captivity were analysed for progesterone and oestradiol-17 beta. The hormone profiles obtained were used to describe a complete reproductive cycle. A clear peak in oestradiol values, indicative of ovulation, was followed by elevated concentrations of progesterone. Implantation probably occurred 3-3.5 months thereafter. Progesterone concentrations rose significantly in the last 3-4 months of gestation, whereas oestradiol concentrations gradually increased after implantation. Lactational oestrus was marked by a peak of oestradiol on average 25 days after parturition and lactation lasted 4-5 weeks. Previous pregnancy had a marked influence on the timing of oestrus; females with offspring started a new reproductive cycle about 14 days later than previously non-pregnant seals. No differences in timing of parturition between the 2 groups were observed. This was probably the result of a flexible period of delayed implantation.     

The effect of nutritional management of the dairy cow on reproductive efficiency

The cause of low fertility in dairy cows is multifactorial. Poor nutrition during the dry and early postpartum periods results in reduced glucose, insulin, insulin-like growth factor (IGF-I) and low LH pulse frequency with concomitant increases in beta-hydroxy butyrate, non-esterified fatty acids (NEFA) and triacylglycerol. Cows must mobilize large lipid, but also some protein reserves, with a consequent increased incidence of such metabolic disorders as hypocalcaemia, acidosis, ketosis, fatty liver and displaced abomasums. The occurrence of milk fever and ketosis affects uterine contractions, delays calving and increases the risk of retained foetal membranes (RFM) and endometritis. The nutritional risk factors that cause RFM are hypocalcaemia, high body condition score (BCS) at calving and deficiencies in Vitamin E and selenium. The risk factors for endometritis are hypocalcaemia, RFM, high triacylglycerol and NEFA. Thus, metabolic disorders predispose cows to gynaecological disorders, thereby reducing reproductive efficiency. Cows that are overconditioned at calving or those that lose excess body weight are more likely to have a prolonged interval to first oestrus, thereby prolonging days open. Nutritionally induced postpartum anoestrus is characterized by turnover of dominant follicles incapable of producing sufficient oestradiol to induce ovulation due to reduced LH pulse frequency. High nutrition can also increase metabolic clearance rate of steroid hormones such as progesterone or oestradiol. Lower concentrations of oestradiol on the day of oestrus are highly correlated with the occurrence of suboestrus, thereby making the detection of oestrus in high yielding cows even more difficult. Nutrition also affects conception rate (CR) to AI. Cows that develop hypocalcaemia, ketosis, acidosis or displaced abomasums have lower CRs and take longer to become pregnant. Excessive loss of BCS and excess protein content of the ration can reduce CR while supplemental fats that attenuate the production of F2alpha can improve CR. The increased metabolic clearance rate of progesterone (P4), which decreases blood concentrations during early embryo cleavage up to the blastocyst stage is associated with decreased CRs. In conclusion, poor nutritional management of the dairy cow, particularly before and after calving, is a key driver of infertility.     

Effects of breed, ovarian steroids and season on the pulsatile secretion of LH in ovariectomized ewes

The effects of season and of oestradiol and progesterone on the tonic secretion of LH were studied in ovariectomized Merino and Suffolk ewes, two breeds which differ markedly in the seasonal pattern of their reproductive activity. In the absence of exogenous steroids, the frequency of LH pulses was lower and the amplitude of the pulses was higher in anoestrus than in the breeding season for Merino and Suffolk ewes 30 days after ovariectomy. In long-term (190 days) ovariectomized ewes, this seasonal change in LH secretion was observed in Suffolk ewes only. During seasonal anoestrus, treatment of ewes with subcutaneous oestradiol-17 beta implants (3, 6 or 12 mm in length) decreased the frequency of LH pulses in a dose-dependent manner, with Suffolk ewes being far more sensitive to the inhibitory effects of oestradiol than Merino ewes. The lowest dose of oestradiol (3 mm) had no effect on the secretion of LH in Merino ewes, but reduced secretion in Suffolk ewes. Treatment of ewes with the highest dose of oestradiol (12 mm) completely abolished LH pulses in Suffolk ewes, whereas infrequent pulses remained evident in Merino ewes. During the breeding season, oestradiol alone had no effect on the pulsatile release of LH in either breed, but in combination with progesterone there was a significant reduction in LH pulse frequency. Progesterone effectively decreased LH secretion in both breeds in both seasons. It was concluded that differences between breeds in the 'depth' of anoestrus could be related to differences in the sensitivity of the hypothalamus to both negative feedback by oestradiol and the direct effects of photoperiod.     

Assisted reproductive technologies in the reproductive management of small ruminants

In modern agriculture, assisted reproductive technologies are being used for out of season oestrus induction, enhancement of reproductive performance and genetic improvement. In addition, they can have substantial contribution in preservation of endangered species or breeds, as well as in eradication programs of various diseases. While their applications are widespread in cattle, in small ruminants it is almost restricted to artificial insemination. The main limitations of a wider application in small ruminants are the naturally occurring anoestrus period, the variability of response to superovulatory treatments, the fertilisation failure and the need of surgery for collection and transfer of gametes and embryos. Nonetheless, during the last 30 years, considerable progress has been made in sheep and goat embryo technologies, especially in the fields of oestrus synchronisation, superovulation and in vitro embryo production. This paper reviews the status of assisted reproductive technologies in sheep, analysing the prospects offered by recent advances in in vivo and in vitro embryo production from mature and juvenile lambs.