Fertility in South Australian commercial Merino flocks: aspects of management

Wide variation in reproductive performance of commercial Merino flocks in south central Australia is the result of genetic and environmental influences that are both amenable to change through decisions of management. Relationships of reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival, and lambs weaned) with variables that graziers can change or modify (strain of Merino, day or month of exposure of ewes to rams, ram effect or teasing, length of the mating period, ram percentage, days between weaning and next mating, stocking density and flock size at lambing, ewe liveweight, and condition) are reported in this paper, the third in a series. Small differences were observed between medium and strong-wool South Australian Merino strains for reproductive traits. Choosing the time of year that ewes are exposed to rams, between late spring to autumn, may result in reduced ovulation rate during early summer (December) giving a potentially smaller net reproductive efficiency (lambs weaned). The ram effect or teasing, used by about 50% of graziers to synchronise lambing, could be effectively employed to the end of January. The technique was not reproductively advantageous when compared with flocks that were not teased. The percentage of rams mated to ewes varied widely (approximately 1-3%) and did not alter flock fertility, suggesting that a substantial proportion of graziers could safely reduce the number of rams purchased. A positive relationship between incidence of estrus during the first 14 d of the cycle and the number of days from weaning to next mating and a negative relationship of returns to service with the same variable indicates that managers should consider increasing the time allowed for recovery of liveweight and body condition by adjusting age at weaning, length of the mating period, or both. Lamb survival was curvilinearly related to flock size and not stocking intensity, with the optimum size at about 400 ewes. The number of lambs weaned per 100 ewes exposed to rams increased by 1.0 kg(-1) increase in liveweight at mating. We concluded that the major factor controlling net reproductive efficiency is nutritional in origin through its effects on ewe liveweight and condition, and is a factor that can be largely manipulated through management.     

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.     

The effect of the F gene on male reproductive traits in Booroola × South Australian Merino rams

The effect of the Booroola (Bo) F gene on the reproductive development of Bo × South Australian Merino ($\text{1}\text{2}\text{Bo}$) rams was examined. Half Bo rams were offspring of FF (homozygous carrier), F+ (heterozygous carrier) or ++ (homozygous non-carrier) Bo sires, so that the expected frequency of $\text{1}\text{2}\text{Bo}$ rams carrying the gene should be approximately 1.0, 0.5 or 0.0, respectively. The genotype of each Bo sire was defined on the basis of the proportion of daughters with ? 3 ovulations. The reproductive development of the $\text{1}\text{2}\text{Bo}$ rams corresponding with each sire genotype was studied between 5 and 15 months of age. Traits recorded were: live weight, testicular volume, preputial adhesion score, semen volume, semen density, proportion of rams with ejaculates containing spermatozoa, proportion of rams that mounted and proportion of rams that served oestrous ewes. There were no significant differences among sire genotypes in the traits studied, except for preputial adhesion score (FF < F+ = ++, P < 0.05) and proportion of rams that mounted (FF = F+ < ++, P < 0.05) at 5 months of age. The relevance of these differences is not known but could result from sampling problems. It is concluded that (1) the F gene had no discernible role in male reproductive development between 5 and 15 months of age and (2) the traits examined did not allow a distinction between carrier and non-carrier rams of the F gene.     

Time of ovulation in the South Australian Merino ewe following synchronization of estrus. 1. Variation within and between flocks

Observations were made by repeated laparoscopy to determine the time of ovulation in seven flocks of South Australian Merino ewes treated with pregnant mare serum gonadotropin (PMSG, 400 IU per ewe) and an intravaginal pessary containing 60 mg medroxy-progesterone acetate (MAP). Ovulation most often commenced within 57 h of pessary removal and was completed in all flocks within 81 h. There was, however, significant variation in the time of onset of ovulation; it did not commence until 69 h in one of three observations of Flock 1 and in two of three observations of Flock 2. On the other hand, in a flock of two-year-old nulliparous ewes (Flock 7), ovulation commenced significantly (P < 0.001) earlier than in most observations of other flocks, with 18 39 ewes ovulating within 57 h of pessary removal. The effect of the progestagen (MAP vs flugestone acetate) and the gonadotropin preparation (Pregnecol vs Folligon) on the time of ovulation were observed in separate studies. The characteristic time of ovulation was not influenced in either comparison. However, ovulation occurred significantly (P < 0.001) earlier in ewes treated with progesterone released from a controlled internal drug release dispenser (CIDR). The implications of these findings to artificial insemination and embryo transfer are discussed.     

Fertilization and embryo loss in Booroola Merino x South Australian Merino ewes: Effect of the F gene

The effects of Booroola genotype (F+, ++); the number of ovulations per ewe (one, two or three); and the age of a ewe (2.5 yr vs 3.5 to 6.5 yr) on the percentage of ova fertilized, embryo loss and fetal loss were examined in Booroola x South Australian Merino ewes slaughtered on Days 4, 21 and 90 after insemination. Ewes slaughtered on Day 90 were examined by real-time ultrasound imaging (RUI) on Day 45. Fertilization failure was independent of ewe genotype, ovulation rate and age of ewe, and it was not an important source of wastage (F+, 9.4%; ++, 6.7%). Most embryo loss occurred during the first 21 d (F+, 54.7%; ++, 40.3%). Interpretation of the effects of genotype and ovulation rate on embryo wastage measured on Days 21, 45 and 90 was obscured by significant (P < 0.05) genotype and ovulation rate interactions with the day of slaughter/RUI. The effect of age on embryo loss was not significant (P > 0.05). Reasons for the high rate of wastage observed in this experiment require further study.     

Factors influencing lamb survival in a high fecundity Booroola Merino x South Australian Merino flock

The effects of year of lambing, age of ewe and litter size on lamb survival and birthweight, and the effects of ewe mating weight and pregnancy wastage (ovulation rate minus litter size) on birthweight were examined in Booroola Merino x South Australian Merino ewes. Year of lambing, litter size and their interaction were significant (P<0.001) sources of variation for lamb survival. When birthweight was included as a linear and quadratic covariate for lamb survival, year of lambing and litter size and their interaction remained as statistically significant sources of variation. Year of lambing, litter size and pregnancy wastage contributed significantly (P<0.05) to variation in birthweight. Ewe liveweight at mating was not an important source of variation (P>0.05). Birthweight was significantly (P<0.05) reduced with an increase in pregnancy wastage. Improvement of birthweight of multiple birth lambs has some potential for increasing lamb survival. Other factors influencing lamb survival (year of lambing, litter size, pregnancy wastage) require further study so that strategies for reducing lamb loss in high fecundity Merino flocks can be developed.     

Uterine presensitization and embryo survival and growth in Booroola Merino x South Australian Merino ewes

The fertility enhancing effects of semen were examined following the intra-uterine insemination of killed spermatozoa plus seminal plasma 17 d prior to insemination with viable spermatozoa. Three experiments were conducted: two on 1.5-yr old and 2.5 to 5.5 yr-old Booroola Merino x South Australian Merino ewes in 1986 and one on 1.5 yr-old ewes in 1987. Differences between treatment and control groups for the percentage of ewes exhibiting estrus by Days 21 and 35 following fertile insemination, the percentage of ewes with viable embryos at Day 35, the number and weight of viable embryos per ewe, the nubmer of caruncular implantation sites and the progesterone level were not statistically significant (P>0.05). There were no statistically significant treatment by experiment interactions for any of the variables examined. Inflammation and edema of the endometrial tissue was not observed following the presensitization treatment.     

An assessment of reproductive wastage in sheep

Reproductive wastage was evaluated by relating ovulation rate to lambs born or raised in range finewool ewes over a ten-year period. The results indicate that reproductive losses are of large magnitude and that these losses are concentrated in the period of ovulation to implantation and in death losses of lambs born. In this study, 33.5% of the potential lamb crop was lost in the early period. Multiple ovulating ewes showed the greatest embryonic loss. The data do not deviate from the binomial distribution, thus suggesting that these losses are largely due to chance. Further work is indicated in the first seventeen days after ovulation to examine losses due to fertilization failure, chromosomal abnormalities, and implantation failure. Abortion or absorption of the fetus was indicated in only 4% of the ewes sampled. An average of 16% of the potential lamb crop was lost from birth to weaning, with 73% of these losses occurring in the first few weeks. Management practices need to be developed to reduce these losses, and these would be expected to vary from one producer to the next depending on conditions. Increasing ovulation rate is one possible method of improving reproductive efficiency, as results of this study indicate that for each unit increase in ovulation rate, there is an increase of 0.52, 0.46, 0.33, and 0.23 in the average number of embryos surviving, lambs born, lambs marked and lambs weaned, respectively.     

Genetic variation in Australian Merino sheep

Variation at 22 gene loci was investigated in a flock of Australian Merino sheep using restriction fragment length polymorphism (RFLP) analysis. Polymorphism was observed at 20 loci, including loci for wool keratin, hormone and immunoglobulin light chain genes. Eleven loci yielded unambiguous genotypes suitable for population data analysis. Average heterozygosity, determined from these and two monomorphic loci, was estimated as 0.107 (SE = 0.024). Average heterozygosity excluding all monomorphic data was estimated as 0–377 (SE = 0.031), which is comparable with human RFLP heterozygosities for loci chosen in the same way that we selected sheep loci.     

Erythrocyte oxidized glutathione in Australian Merino sheep

The concentration of GSSG was determined in the erythrocytes of Merino sheep. These sheep were grouped according to erythrocyte potassium type, haemoglobin type, and GSH type. It was found that haemoglobin and potassium type were not correlated with GSSG concentration; however, GSSG concentration was found to be significantly correlated with GSH concentration. This relationship may explain previously reported differences in ATPase activity and may reflect further metabolic differences in the erythrocytes of GSH-high and GSH-low type Merino sheep.     

Erythrocyte oxidized glutathione in Australian Merino sheep.

The concentration of GSSG was determined in the erythrocytes of Merino sheep. These sheep were grouped according to erythrocyte potassium type, haemoglobin type, and GSH type. It was found that haemoglobin and potassium type were not correlated with GSSG concentration; however, GSSG concentration was found to be significantly correlated with GSH concentration. This relationship may explain previously reported differences in ATPase activity and may reflect further metabolic differences in the erythrocytes of GSH-high and GSH-low type Merino sheep.     

Transcervical artificial insemination of Australian Merino ewes with frozen-thawed semen

We compared conventional methods for laparoscopic and cervical artificial insemination (AI) to a transcervical AI procedure (Guelph System for Transcervical AI; GST-AI) for use with frozen semen in Merino ewes. The GST-AI procedure was performed by an experienced operator in Experiment 1 (771 ewes) and by 2 inexperienced operators in Experiment 2 (555 ewes). In Experiment 1, intrauterine insemination by GST-AI was achieved in 76% of the ewes. The pregnancy rate at Day 70 for ewes inseminated by laparoscopy (48%, 120 251 ) was higher (P<0.01) than for ewes inseminated by either intrauterine GST-AI (32%, 64 201 ) or cervical AI (9%, 24 256 ). The overall (intrauterine and intracervical) pregnancy rate for GST-AI was 26% (68 264 ) and was unaffected by depth of insemination within the cervix. Pregnancy rates were unaffected by ram or day of insemination. In Experiment 2, the operators achieved intrauterine inseminations by GST-AI in 43% (78 182 ) of the ewes, with a significant operator effect (P<0.01) on depth of cervical penetration. The pregnancy rate to intrauterine GST-AI (40%, 31 78 ) did not differ from that to laparoscopic insemination. The total pregnancy rate for GST-AI in Experiment 2 (19%, 34 182 ) was lower (P<0.05) than that for laparoscopic AI (39%, 72 187 ) but superior (P<0.05) to that for cervical AI (1%, 1 186 ). The GST-AI pregnancy rates were affected by depth of AI (P<0.01) and by operator (P<0.05). It is concluded that GST-AI is superior to cervical AI, and may have application in Merinos if cervical penetration rates can be improved.     

Effect of nutrition during pregnancy on fetal growth and survival in Fec(B) Booroola x South Australian Merino ewes

The effect of nutritional manipulation during mid and late pregnancy on fetal growth and survival in high fecundity (Fec(B) Fec(+)) Merino ewes was examined. A total of 4 treatment groups was utilized in each of 3 years (1987, 1988 and 1989); and 2 groups were given low nutrition during mid pregnancy while 2 groups received high nutrition during this period. One group from each of these treatments subsequently received a high protein diet 1 to 2 weeks prior to term. Differential feeding during mid pregnancy resulted in the high and low treatment groups varying by 7.5 and 5.0 kg liveweight at Days 100 and 135 of pregnancy, respectively. Fetal survival was not improved by variation in nutritional intake during mid pregnancy (P>0.05) and neither were placental and fetal growth (P>0.05), as indicated by observations on cotyledon diameter and fetal head width, respectively. However, fetal survival during late pregnancy was reduced by a high level of nutrition during both mid and late pregnancy (P<0.05).     

Polyploid cells in blastocysts and early fetuses from Australian Merino sheep

Cytogenetic examination was made of 103 13-14-day-old blastocysts and 116 24-32-day-old fetuses from untreated and androstenedione-7-HSA-immunized Merino ewes. There were no differences in the chromosome composition of blastocysts or fetuses from treated or untreated ewes and so the data were combined. At Days 13-14 a 1N/2N mosaic and a 2N - 1/2N/4N mosaic embryo were observed. In addition, 52 of the blastocysts were 2N/4N mosaics, with 8 of these also containing 8N cells, and one blastocyst was a 2N/8N mosaic. No aneuploid fetuses were observed, but 80 of the 116 fetuses contained polyploid cells, including 4N, 6N and 8N cells. The polyploid cells observed in the blastocysts and fetuses should not be considered as abnormal cells as they appear to be a normal part of the developmental processes leading to trophoblast formation and fetal differentiation.     

Some effects of epidermal growth factor on reproductive function in Merino sheep

During the i.v. infusion of a depilatory dose (100 micrograms/kg bodyweight) of mouse epidermal growth factor (EGF) into ovariectomized Merino ewes the frequency of pulsatile LH release was significantly reduced. However, the amplitude of pulses of LH secretion, either those naturally occurring or those induced by LHRH injection, was unchanged or only slightly reduced. Similar infusions of mouse EGF were made in progestagen-treated anoestrous Merino ewes in which LH secretion was maintained by injections of LHRH. These ewes did not experience oestrus or ovulate in response to PMSG injected 1 day after mouse EGF treatment (2 days before progestagen withdrawal); both responses occurred in controls. The EGF-treated ewes experienced oestrus and ovulated following progestagen-PMSG treatment 6 weeks later. These results suggest that mouse EGF inhibits the hypothalamic pulse generator responsible for LH release in the ewe but has little if any effect on pituitary sensitivity to LHRH; and mouse EGF apparently has a direct effect on the ovaries, temporarily impairing their ability to ovulate in response to exogenous gonadotrophin.     

Livestock production in central Mali: Reproductive performance and reproductive wastage in ruminants in the agro-pastoral system

Results of a 7-yr field study and a 3-yr slaughterhouse study into reproductive performance and reproductive wastage of ruminants in central Mali are reported. Cattle had delayed age at first puberty (40), long calving intervals (644) and produced few young (3.02) per lifetime. Goats and sheep first conceived at about 11 mo, had shorter parturition intervals (298 and 280 d) but also produced few young (2.64 and 1.92) per lifetime. Conceptions showed a strong seasonality in cattle and mainly occurred during and shortly after the short rainy season. Seasonality was less marked in small ruminants, but most females conceived before the rains. However, maximum litter sizes were associated with late-rain and post-rain conceptions. Early embryonic wastage did not appear to be a major problem but abortions, stillbirths and heavy preweaning mortality were sources of loss of reproductive potential. Additionally at a secondary (government controlled) abattoir, 15.0 % of cows, 31.7 % of goats and 20.0 % of sheep that were slaughtered were found to be pregnant.     

A study of the relationship between chromosome anomalies and reproductive wastage in domestic animals

A cytogenetic survey was carried out on a partially unselected group of aborted foetuses, stillbirths/neonatal deaths and congenital defects originating from various domestic animals such as the feline, porcine, ovine, canine and bovine species. Chromosomes were analysed largely from fibroblast cultures of somatic tissue specimens received from different sources. Both fibroblast and lymphocyte cultures were simultaneously initiated whenever possible (e.g. from liveborns that had to be subjected to suthanasia as a result of debilitating phenotypic malformations).Forty-three and eight-tenths percent of the specimens cultured (i.e., 46 out of 105 specimens) could be adequately karyotyped. The overall incidence of chromosome anomalies was 8.7%, with mosaicism being the predominant observation. Because no gross chromosome abnormalities such as trisomy or polyploidy were found, it was concluded that any grossly abnormal foetuses might have already been selectively eliminated before the gestational stage at which this investigation was undertaken. The relatively low incidence of chromosome anomalies observed so far in various studies of domestic animals is discussed and compared to corresponding studies in humans.     

Effect of zinc supplementation on the reproductive performance of grazing Merino ewes

Two experiments were carried out in Western Australia to investigate the effect of zinc supplementation, on the reproductive performance of grazing Merino ewes. We found that supplemental zinc, when provided prior to mating and throughout pregnancy, increased the number of lambs produced by 14% (P<0.05) in both experiments. An intermediate zinc treatment, when supplementation was begun later in pregnancy gave a 9% (P<0.01) increase in the number of lambs in one experiment and no increase in the second. Lamb birth weights were increased by zinc supplementation in Experiment 1 and in Experiment 2, 12–20-week-old lambs from zinc supplemented ewes were 2.1 kg heavier than those from nonsupplemented controls. Plasma zince levels decreased significantly during pregnancy and lactation, but were increased at some sampling dates by 20–25% by zinc supplementation.