The distribution of ovulations from the ovaries of merino and Border Leicester x merino ewes and its effect on the survival of their embryos

Correlates of reproductive tract anatomy and uterine histomorphometrics with fertility in swine

Economic potential of the swine industry hinges upon the reproductive performance of sows, which may be enhanced by improving uterine capacity, a component trait of litter size and piglet productivity. Previous attempts at characterizing morphological traits indicative of high uterine volume have not been completely successful, resulting in the continued need for a reliable method of predicting reproductive value to improve production efficiency of the sow. Hence, the main objective of this study was to scrutinize macro- and micro-morphology of the sow's reproductive tract for quantitative correlations with fertility indices. Reproductive records from Polish Landrace × Polish Large White sows were used to examine the associations between fertility and ovarian/uterine morphology (n = 34) or uterine histomorphometry (n = 10). Several measures related to the ovary, including right and left ovarian weight (r = 0.50, p = 0.005 and r = 0.49, p = 0.006, respectively), were positively correlated with the litter size, while left ovarian number of corpora lutea (r = -0.38, p = 0.04) was negatively correlated with the mean litter size. Analysis of histomorphological characteristics of the uterine wall collected during the luteal phase of the estrous cycle revealed correlations between mean litter size and myometrial vascular content (r = 0.75, p = 0.03), the proportion of myometrial stroma (r = -0.68, p = 0.03), and the variability of endometrial thickness (r = -0.72, p = 0.02) in sows. Eight ovarian, vaginal and uterine characteristics were significantly correlated with mean lifetime numbers of live born and stillborn piglets/litter or the last litter size before slaughter. In conclusion, several anatomical and histomorphological metrics that relate to reproductive performance of swine may be used to inform production protocols and as a tool for selection of elite breeding sows, warranting future research into non-invasive or minimally invasive techniques for obtaining such measures.

Early embryo loss, morphology, and effect of previous immunization against androstenedione in the ewe

In a naturally mated cycle, ova and viable embryo number as well as embryo size were assessed on Day 4, 10, 14, 18, and 30 of gestation in Romney ewes (n = 38-44 per gestational group). For Days 4-18 of gestation, embryos were recovered by flushing the reproductive tract after slaughtering of the ewe. Ovulation rate was determined by counting the number of corpora lutea present on both ovaries. For the Day 30 group, number of ovulations was measured by laparoscopic examination of the ovaries at Day 9-12 of the cycle, and number of embryos present was determined by ultrasound examination at approximately Day 30 of pregnancy. Most of embryo loss occurred before Day 14 of gestation with 6% loss before Day 4, and 12% loss between Day 4 and 14 of gestation. A similar proportion of viable embryos per number of ova ovulated were recovered on Day 14 and 18 (82%) and Day 30 (81%) of gestation. Fertilization failure was estimated at 1%. Conceptus and embryo size was most variable on Day 14, representing a period of rapid growth (conceptus length ± standard deviation); Day 4 (169 ± 8 μm), Day 10 (379 ± 93 μm), Day 14 (23 ± 32 mm), Day 18 (embryo length ± standard deviation; 5.0 ± 0.7 mm). Vaccination with commercially available fertility vaccines targeting androstenedione (Androvax and Ovastim) in previous seasons resulted in reduced conceptus size compared with controls. However, no difference in the proportion of viable embryos was observed between treatments, signifying maternal tolerance for considerable variation at this stage of development. Furthermore, the finding that most of loss occurs within the first 14 days of gestation highlights the importance of both oocyte quality and the uterine environment for the embryo to successfully overcome the challenges leading up to and including pregnancy recognition in the ewe.

Ovarian activity, transuterine embryo migration and prenatal losses in Ethiopian highland ewes

A study was conducted on 1442 Ethiopian highland ewes to determine the seasonality of ovarian activity, intrauterine embryo migration and prenatal reproductive wastage. Assessment of ovarian follicular activity revealed that a higher (p < 0.01) proportion of ewes ovulated in the dry season than in the heavy and light rainy seasons. However, there was a tendency (p = 0.057) of decline in the mean number of ovulations per ewes during the light rains. The mean diameter of the largest follicle on the ipsilateral ovary was higher (p < 0.01) in both ewes with single and those with twin corpora lutea (CL) than on the contralateral ovary; and, compared to ewes with single CL, it was higher (p < 0.05) in those with twin CL. The right ovary was more active (p < 0.001) only in single-ovulating ewes. Similarly, a higher (p < 0.001) proportion of ewes were pregnant in the right horn. Embryos migrated to the opposite horn in single-, twin- and triple-ovulating ewes. There was a higher (p < 0.001) tendency for the left-to-right migration than the opposite. There was significant (p < 0.01) association between embryo loss and site and number of ovulations. Embryo loss was higher (p < 0.01) in ewes with twin ovulations on the right ovary. It is very likely that these results indicate a better chance of embryo survival in the right uterine horn.

Effect of age of donor on embryo production in Morada Nova (white variety) ewes participating in a conservation programme in Brazil

In order to evaluate embryo production in Morada Nova (white variety) ewes superovulated with porcine follicle-stimulating hormone, 20 cycling ewes were used as embryo donors and allocated into two groups according to age: group 1 (ewes aged 1-2 years; n = 9) or group 2 (ewes aged 3-4 years; n = 11). Embryo recovery was performed by laparotomy 5-6 days after oestrus. The evaluation of embryos was made under stereomicroscope according to International Embryo Transfer Society rules. The overall recovery rate was 64.6% (5.0 +/- 0.7 structures per ewe) and 86.3% of the recovered structures were fertilized. Group 1 was superior (p < 0.05) to group 2 according to recovered (6.6 +/- 0.9 vs 3.6 +/- 0.8) and fertilized structures (5.6 +/- 1.1 vs. 3.5 +/- 0.7) per ewe. In conclusion, the ovarian response and the embryo production in Morada Nova (white variety) sheep subjected to a standard superovulation treatment were considered satisfactory. In addition, the use of multiple ovulation and embryo transfer in younger ewes ( < or = 2 years old) of this sheep breed appears to be an efficient tool to accelerate the preservation of the Morada Nova (white variety) breed, since younger ewes are as responsive as older ones.

A review of the effects of supplementary nutrition in the ewe on the concentrations of reproductive and metabolic hormones and the mechanisms that regulate folliculogenesis and ovulation rate

This paper discusses the phenomenon of nutritional flushing in ewes whereby increased nutrition stimulates folliculogenesis and ovulation rate. In addition the paper reviews recent findings on the effects of increased levels of nutrition on the blood concentrations of reproductive and metabolic hormones in the ewe and some of the intraovarian changes that take place in response to nutritional stimulation. Finally, in the paper, we propose a model of the physiological mechanism for the nutritional stimulation of folliculogenesis and we review how closely the model fits recent published and unpublished evidence examining the mechanism of flushing. Nutritional stimulation alters the blood concentrations of some metabolic hormones. By using short-term models of nutritional flushing, we have shown that as the blood concentrations of insulin and leptin increase that of growth hormone decreases while that of IGF-I appears unaffected by the nutritional flushing. Nutritional flushing also alters the blood concentrations of some reproductive hormones. Again, using the same model, we have shown that there is a transient increase in FSH and a decrease in oestradiol concentrations in the blood. The changes in oestradiol are particularly evident in the follicular phase of the oestrous cycle. In the ovary, the effect of nutrition is to stimulate folliculogenesis. These changes are associated with intra-follicular alterations in the insulin-glucose, IGF and leptin metabolic systems. The stimulation of these intra-follicular systems leads to a suppression in follicular oestradiol production. The consequence of these direct actions on the follicle is a reduced negative feedback to the hypothalamic-pituitary system and increased FSH secretion that leads to a stimulation of folliculogenesis.

Fertility in South Australian commercial Merino flocks: sources of reproductive wastage

To identify reasons for low fertility in the Merino in South Australia, we defined the extent and sources of reproductive wastage in flocks of maiden (n=14) and mature age (n=54) Merino ewes managed on 43 properties over 4 year. In a second study, reproductive wastage was examined in a very high ovulating flock of mature age South Australian Merino ewes heterozygous for the FecB gene, mated to lamb in either the autumn or spring. Losses in the latter flock were examined in less detail than the large-scale study, but allowed wastage to be partitioned between pre- and peri/post-natal sources. In the first experiment, reproductive wastage between mating and weaning was estimated at 59.7 potential lambs or ova lost per 100 ewes exposed to rams, representing 42.4% of ova shed. The main source of wastage occurred at lambing (55.6% of total loss), with death of twins a major contributor (35.3% of total loss). Other important sources of wastage were from partial failure of multiple ovulation (PFMO; 20.4% of total loss) and from ewes mating but not lambing (13.2% of total loss). Reproductive wastage did not vary with either age of ewe (maiden versus mature) or season of mating (October-December versus January-March). Mean ovulation rate, estimated as 141 per 100 ewes ovulating (range 100-200), varied with age of ewe (129 versus 144; maiden versus mature) but not with season of mating or year (1990-1991). Values for fertility, fecundity and lamb survival were 90, 127 and 73%, respectively. Fecundity of maiden ewes was lower than that of mature ewes (116 versus 130). Survival of single and twin lambs between birth and tail docking was 83 and 56%, respectively. Net reproductive efficiency, or lambs weaned per 100 ewes exposed to rams, averaged 81 (range 31-122). In the second experiment, mean ovulation rate of FecB Merino ewes was 316 per 100 ewes ovulating, with 242 ova (potential lambs) lost between ovulation and tail docking. This loss was equally shared between pre- and peri/post-natal sources (123 versus 119), and demonstrates severe limitation of the Merino to successfully bear and rear multiple litters. We concluded that future research in commercial Merino flocks be focused on lamb mortality, particularly of twins, and on PFMO, the major source of embryo loss.

Fertility in South Australian commercial Merino flocks: relationships between reproductive traits and environmental cues

High levels of reproductive loss have been reported in commercial Merino flocks (n=68) from the cereal/livestock and high rainfall zones in South Australia (Kleemann DO, Walker SK. Fertility in South Australian commercial Merino flocks: sources of reproductive wastage. Theriogenology 2005;63:2075-88). Relationships between reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival) and environmental end points (liveweight, condition score, temperature at mating, chill index at lambing) are reported in this paper. They were analysed within season of mating (October to December; January to March) and age of ewe (maiden as 1.5-year-old, mature as older). Incidence of estrus was positively related (P<0.05) to condition score in the October to November interval. Return rate to service was positively (P<0.05) influenced and fertility was negatively (P<0.05) influenced by the number of days ambient temperatures were > or =32.0 degrees C during mating, indicating that high ambient temperatures may reduce embryo survival. Liveweight and, to a lesser extent, condition score, accounted for significant proportions of variation associated with ovulation rate (39.3 and 12.7%, respectively). Ovulations per 100 ewes increased by 1.8 per kg increase in liveweight over all flocks. Ovulatory response to liveweight increased (P<0.01) from the October to December to the January to March period of mating (1.5 versus 3.4 ovulations per kg, respectively). Overall, a flock's fertility and fecundity increased by 0.27 and 1.42% per kg increase in liveweight, respectively. Reproductive wastage from partial failure of multiple ovulations (PFMO) was positively related to liveweight (P<0.01) and ovulation rate (P<0.001). Survival of single lambs was positively and curvilinearly related to maternal liveweight and condition score measured in late pregnancy (P<0.05). Linear relationship of these variables for twin lamb survival was significant for condition score only. Single and twin lamb survival were also positively related to liveweight and condition score at mating (P<0.05). We concluded that nutritional cues have a major impact on reproductive traits in commercial Merino flocks in South Australia; it sets the potential number of lambs (ovulation rate) and influences survival of lambs as early as at mating. Indications are that high ambient temperatures may influence embryo survival. It is recommended that future research efforts focus on: (a) prenatal nutritional influences on the physiology of mother-offspring behaviours at birth; and (b) possible peri-conceptional dietary factors controlling embryo loss resulting from partial failure of twin ovulations, to improve reproductive efficiency in the Merino.

Ovulation rate and distribution in the thoroughbred mare, as determined by ultrasonic scanning: the effect of age

Ovarian activity was monitored in 2181 oestrous cycles from 1136 thoroughbred brood mares to accurately determine overall ovulation rate, the relative distribution of ovulations between left and right ovary, whether mare age had an effect on these parameters and whether ovulation pattern in one cycle affected the pattern within the next. Ultrasonic scanning was used in preference to rectal palpation and slaughterhouse material due to its greater accuracy. Mare's ages ranged from 3 to 22 years. The results obtained indicated a similar incidence of ovulation occurring on the right (49.5% of all ovulations) or left ovary (50.5%). Multiple ovulations (MO) occurred in 22.4% of oestrous cycles. Significantly (P<0.01), more double ovulations (DO) were bilateral (57.2%) than unilateral (42.8%); 20.7% were unilateral right and 22.1% were unilateral left. There were 828 mares grouped into six age groups: A (3-5 years), B (6-8 years), C (9-11 years), D (12-14 years), E (15-18 years), F (18-22 years). The distribution of ovulation between the left and right ovary was not affected by age group, but significant association (P<0.01) was evident between age and MO. Group A had 15% of cycles resulting in MO compared to 19.4, 24.6, 25.8, 28.6 and 35.1% in groups B-F, respectively. A significant (P<0.01) association between MO in successive cycles was also demonstrated, with a greater chance (P<0.05) of successive single ovulations (SO) being on alternate ovaries. There was no significant repeatability of the classification of DO in one cycle compared to the next. We conclude that: (i) the mare is a symmetrical ovulator; (ii) 22.4% of cycles yield MO (ovulation rate 1.23); (iii) this MO incidence increased (P<0.01) with age; (iv) the exhibition of MO in one cycle was linked to an increased probability (P<0.01) of a MO occurring at the next one and (v) SO in one ovary was more likely (P<0.05) to be followed by a SO on the alternate ovary during the next cycle.

Ovulation and luteal characteristics following removal of the ovine corpus luteum (lutectomy) at four times during the oestrous cycle

The life span of the corpus luteum (CL) may depend on follicular development. To provide evidence relating to this hypothesis, each of 32 ewes was randomly assigned to have its CL removed on day 2, 3, 4 or 10 after oestrus. Twenty ewes were treated with 1000 IU of human chorionic gonadotrophin (hCG) 36 h after CL removal to induce ovulation; the other 12 ewes were not treated with hCG. Blood samples were collected daily to monitor the ovulatory response and the characteristics of the next cycle at the first sign of oestrus and up to day 21 after surgery or hCG administration. Every animal ovulated within 7 days of hCG administration, regardless of when its CL had been removed. It was concluded that the follicles found in the ovary as early as the second day after oestrus respond to endogenous or exogenous ovulatory stimuli affecting the life span of resulting CL.

An abattoir survey of ovine reproductive tracts in Ireland

Reproductive tracts were collected from 870 ewes slaughtered at an abattoir in County Dublin over a 9-m.o. period from September 1993 to June 1994. Ovarian activity was evident in 59.3% of the tracts examined. The mean ovulation rate was 1.26 +/- 0.045 (mean +/- SEM). The spatial relationship between corpora lutea (CL) and dominant follicles was established. Ten percent of the ewes examined were pregnant. Embryonic transuterine migration was observed in 12% of the single ovulating ewes and in all ewes pregnant with twins which had double ovulations on one ovary. Based on the observation of tracts with contemporaneous double ovulations and a single fetus, the prevalence of embryonic loss was 17.2%. Overall, 9.4% of the tracts showed evidence of pathological change, and 5.5% of the tracts had abnormalities likely to impair fertility.