Fertility Of Ewes Research Articles

Genetic evaluation of crossbred lamb production. 1. Breed and fixed effects for birth and weaning weight of first-cross lambs, gestation length, and reproduction of base ewes

This is the first paper in a series that reports on a national maternal sire central progeny test program (MCPT) to evaluate the genetic variation for economically important production traits in first- and second-cross progeny of maternal and dual purpose (meat and wool) sires and the scope for genetic improvement. The MCPT program also provides direct linkages between breeds that will contribute information for across-breed genetic evaluation. Crossbred progeny by 91 sires from more than 7 maternal breeds (including Border Leicester, East Friesian, Finnsheep, Coopworth, White Suffolk, Corriedale, and Booroola Leicester) at 3 sites over 3 years with 3 link sires in common at each site and year were evaluated in this study. National estimated breeding values for the sires that were entered by industry breeders indicated that there was some selection for weight, but not other traits and the sires were generally representative of the maternal genetics available to the industry. There were 8377 base Merino and Corriedale ewes artificially inseminated with thawed-frozen semen from the 91 sires and 8193 crossbred lambs born and 6117 lambs weaned. Mixed model analyses of birth and weaning weight, lamb survival, and gestation length as well as fertility, litter size, and lamb weaning rate of the base ewes are reported. Sire breed was significant for birth weight (with a range of 4.0–4.4 kg at an average litter size of 1.8) and weaning weight (19.6–22.5 kg), as well as lamb survival (70–79%) and gestation length (147.1–150.3 days). Birth/rearing type was significant for all traits. Males were significantly heavier than females at birth and weaning, although there was no sex difference for lamb survival or gestation length when birthweight was included in the model. Pregnancy rate from the artificially inseminated base ewes varied from 40 to 84% at the 3 locations in the various years. Sire breed was significant for the number of lambs weaned per ewe lambing, but not for fetal number or litter size born. There were also significant differences in performance due to the source of the base ewes at each site.

Effect of progestagen and PMSG on oestrous synchronization and fertility in Dorper ewes during the transition period

An oestrous synchronization study was conducted on 202 Dorper ewes kept under extensive veld conditions of South Africa, during the transition period from the natural breeding to the anoestrus season. Two types of intravaginal progestagen sponges, namely MAP (60 mg) ( n=102) and FGA (40 mg) ( n=100), three times of PMSG administration relative to sponge withdrawal (24 h before ( n=59), at ( n=56) or 24 h after ( n=57)) and two routes of PMSG administration (intramuscular ( n=87) or subcutaneous ( n=85)) were compared regarding synchronization efficiency (oestrous response, time to onset of oestrus and duration of oestrus) and fertility (pregnancy, lambing, and fecundity rates) following AI with 0.1 ml fresh diluted semen. There were no significant differences in terms of oestrous response, time to onset of oestrus and the duration of induced oestrus due to differences in the type of progestagen sponges or time and route of PMSG administration. The overall pregnancy, lambing, and fecundity rates were 72.3, 91.1, and 126.0%, respectively. There were no significant differences in pregnancy, lambing, and fecundity rates between ewes treated with MAP and FGA sponges (70.6, 85.3, and 120.8% versus 74.0, 97.0, and 131.1%, respectively). However, within treatment, pregnancy, lambing, and fecundity rates were significantly ( P<0.01) higher in ewes administered 300 IU PMSG 24 h prior to (78.0, 115.3, and 147.8%, respectively) or at sponge withdrawal (75.0, 94.6, and 126.2%, respectively), compared to those administered 24 h after sponge withdrawal (70.2, 73.7, and 105.0%, respectively) or those not injected with PMSG (60.0, 70.0, and 116.7%, respectively). Both MAP and FGA sponges could be used to synchronize oestrus in Dorper ewes during the transition period from breeding to anoestrus. Administration of 300 IU PMSG preferably 24 h prior to or at progestagen sponge withdrawal is essential to obtain better fertility rates at the induced oestrus and following AI. The subcutaneous administration of PMSG is preferable to intramuscular administration as it resulted in higher fertility rates and litter sizes.

The effects of ram exposure during progestagen oestrus synchronisation and time of ram introduction post progestagen withdrawal on fertility in ewes

Three experiments were undertaken to investigate the effect of a pre-mating ram exposure during progestagen synchronisation treatment on time of breeding, ovulation rate, embryo quality and fertility and any interaction with time of ram introduction for breeding post sponge withdrawal. Crossbred ewes in experiment 1a ( n = 348), 1b (mule; n = 133) and 2 ( n = 58) underwent a 12–14 days synchronisation protocol. Three days prior to sponge withdrawal ewes were divided into Control (ewes in continued isolation from rams) or +Ram (ram-exposed) groups. Rams were introduced to +Ram ewes and remained with ewes until sponge withdrawal. Ewes in experiments 1a and 2 received eCG at sponge withdrawal and were reintroduced to rams at either 36 or 48 h post sponge removal (PSR). In experiment 1b, ewes did not receive eCG and were reintroduced to rams at 24 h PSR. In experiments 1a and 1b time of breeding, date of lambing and litter size were recorded. In experiment 2, ewes were slaughtered 5 days post breeding, reproductive tracts flushed and corpora lutea, ova and embryos assessed. Fewer +Ram ewes were mated by 96 h PSR ( P < 0.001) than Control ewes in experiment 1a but not when rams were introduced earlier in experiment 1b. In experiment 1a, ram introduction at 36 h PSR improved conception to first service compared to introduction at 48 h PSR ( P < 0.01) in both +Ram and Control groups. In experiments 1a and 1b, +Ram ewes had reduced litter size caused by more single births (1a; P < 0.001, 1b; P < 0.01). In experiment 2, +Ram ewes had fewer corpora lutea than Control ewes ( P < 0.001) but embryo quality was similar. However, more good embryos were produced when rams were introduced for breeding at 36 h compared to 48 h PSR ( P < 0.001). We conclude that a pre-mating ram exposure during the synchronisation treatment reduced the number of ewes mated at and conceiving to the first service. This was partially overcome by introducing rams for breeding earlier (24 or 36 h compared to 48 h PSR) but the most dramatic decrease in fertility was due to a reduction in ovulation rate in the ram-exposed ewes.

Sperm survival and heterogeneity are correlated with fertility after intrauterine insemination in superovulated ewes

Efficient animal production involves accurate estimations of fertilizing ability. One key factor is the plasma membrane of the sperm cell, which is actively involved in the cascade of events before oocyte fusion. Many methods are used to analyze the characteristics of this membrane, including partition in aqueous two-phase systems which is an efficient method to analyze sperm surface changes accounting for loss of viability and different functional states. Centrifugal countercurrent distribution (CCCD) analysis can also be used in an aqueous two-phase system to determine the relationship between sperm parameters and in vivo fertility in ewes. In a previous work, we found a significant correlation between two post-CCCD parameters (heterogeneity and recovered viability) and field fertility when the same sample was used after cervical AI. The present study was intended to find out whether the control of several external factors that affect reproductive efficiency is able to increase the correlation coefficient between post-CCCD parameters and fertility. Thus, 90 Rasa aragonesa ewes were controlled on the same farm and received intrauterine inseminations using the same technical equipment. The fertilizing ability of the raw semen and sperm samples selected by a dextran/swim-up process was compared using a low number of spermatozoa per insemination (7 × 10 7) to enhance possible fertility differences. A new post-CCCD parameter was considered; the loss of viability (LV) occurred during the CCCD process. This variable denotes the sperm surviving ability and corresponds to the difference between the total number of viable cells loaded and recovered after the CCCD run. The mean fertility of eight sperm control samples was 60% (range: 25–76%), and there was no significant correlation between standard parameters and in vivo fertility. LV ranged from 2 to 69% (average 27%) and was negatively correlated with fertility ( r = −0.914, P < 0.01). Ejaculate heterogeneity (H) ranged from 20 to 47% and was positively, but not significantly, correlated with fertility ( r = 0.391). A predictive equation for fertility was deduced by multiple analysis with a very high correlation coefficient ( r = 0.967), and level of significance ( P < 0.005): predictive fertility PF = 52.546 − 0.594 LV + 0.665 H. The mean fertility of 13 swim-up selected samples was 63% (range: 25–86%). Again, only parameters derived from the CCCD analysis were highly correlated with fertility, especially LV and H ( P < 0.05).

Inheritance of fecal egg count and packed cell volume and their relationship with production traits in sheep infected with Haemonchus contortus.

This study describes responses to artificial infection with Haemonchus contortus in ewes and lambs of 50% Dorset, 25% Rambouillet, and 25% Finn-sheep ancestry and provides estimates of genetic parameters for measures of parasite resistance. One hundred ninety-eight ewes out of 64 sires, and 386 lambs out of 25 sires were evaluated in autumn and spring of 2 yr. Ewes were dewormed shortly after weaning their lambs and lambs were dewormed at about 120 d of age. One week after deworming, ewes and lambs were dosed with approximately 10,000 infective larvae of H. contortus. After infection, BW, fecal egg counts (FEC), and packed cell volume (PCV) were measured weekly for 7 wk in lambs kept in drylot and fortnightly for 11 wk in ewes on pasture. Summary traits were defined as initial PCV, mean BW across all times, and means for PCV (MPCV) and log-transformed FEC (MLFEC) at wk 3 to 7 after infection for lambs and wk 3 to 11 after infection for ewes. Ewes and lambs did not lose weight overall in any year or season, but there was no consistent effect of year or lambing season on mean LFEC or mean PCV during infection in either ewes or lambs. Yearling ewes were less resistant to infection than older ewes, with lower PCV (P < 0.05) and higher LFEC (P < 0.05). During infection, PCV was positively correlated with BW and negatively correlated with LFEC in both ewes and lambs. In lambs, heritabilities were 0.39 (P < 0.01) for PCV, 0.10 (P < 0.05) for LFEC across all measurement times, and 0.19 (P < 0.01) for three measures of LFEC taken at the peak of infection. Heritability estimates for ewes were 0.15 (P < 0.05) for PCV and 0.31 (P < 0.01) for LFEC. Repeatabilities for LFEC and PCV across measurement times were moderate in ewes and lambs. Correlations between dam and lamb records for MLFEC were generally low, suggesting different mechanisms of resistance in lambs and nonlactating ewes. Ewes with higher genetic merit for growth as lambs were less resistant to infection as adults, but genetic merit for fertility and prolificacy were not related to parasite resistance. Lambs with higher genetic merit for body weight were more resistant to infection. Selection for resistance to H. contortus is therefore possible and should not adversely affect growth of lambs and fertility of ewes in this production environment.

The production characteristics of the indigenous Imroz and Kivircik sheep breeds in Turkey

SummaryThis study was carried out to investigate the fertility, milk production and body weight of ewes and the survival and growth characteristics of lambs of the indigenous Imroz and Kivircik sheep breeds. The Imroz and Kivircik sheep breeds are included among the genetic resources in the project for the conservation of the indigenous breeds in Turkey.Conception rates for Imroz and Kivircik ewes were 57.6% and 81.7% respectively, litter sizes were 1.2 and 1.2 respectively, milk yields were 89 kg and 62 kg respectively and average live weights (2–7 years of age) were 43 kg and 55 kg, respectively. Imroz and Kivircik lambs had survival rates at weaning (90th day) of 98% and 96%, birth weights of 3.3 kg and 4.1 kg and weaning weights of 19.8 kg and 28.0 kg, respectively.The results showed that the Kivircik sheep were heavier and the lambs had a better growth rate until weaning than the Imroz breed. However, the milk production of the Imroz ewes was higher than that of Kivircik. The lambs of both breeds had a satisfactory survival and growth rates until weaning and these results might be regarded as a desired adaptation of the Imroz and Kivircik lambs to the environmental conditions of the Marmara Region.

Functional and Molecular Characterization of Naturally Occurring Mutations in the Oocyte-secreted Factors Bone Morphogenetic Protein-15 and Growth and Differentiation Factor-9

Bone morphogenetic protein-15 (BMP-15) and growth and differentiation factor-9 (GDF-9) are oocyte-secreted factors that are critical local regulators of ovarian physiology. Recent studies have identified a number of mutations in these genes that cause increased fertility and infertility in heterozygous or homozygous ewes carrying the mutations, respectively. Interestingly, heterozygous ewes with a mutation in both BMP-15 and GDF-9 exhibit higher fertility than those having mutation in only one of the genes. Here, we have produced recombinant human BMP-15 and GDF-9 that carry the mutations identified in those sheep, i.e. I31D and S99I in BMP-15 and S77F in GDF-9. We found that when individually expressed, both BMP-15 mutations had no effect on the processing, secretion, and dimerization of the mature proteins or on the biological activity of the molecules. However, when mutant BMP-15 was co-expressed with wild-type GDF-9, the secretion of BMP-15 and GDF-9 was significantly reduced, suggesting that the mechanisms by which the BMP-15 mutations affect sheep fertility occurs at the level of protein secretion rather than dimerization and biological activity. Moreover, when mutant GDF-9 was co-expressed with mutant BMP-15, the secretion levels of both proteins were significantly lower than those of cells co-expressing wildtype GDF-9 and mutant BMP-15, suggesting a possible mechanism for the extreme fertility observed in the compound heterozygous mutant sheep.

Recovery of natural fertility after grafting of cryopreserved germinative tissue in ewes subjected to radiotherapy

Objective To recover natural fertility of ewes that were subjected to ovarian failure induced by radiotherapy with an autologous orthotopic graft of cryopreserved germinative tissue. Design Experimental surgery study. Setting University hospital unit. Animal(s) Adult ewes. Intervention(s) Four ewes were submitted to right oophorectomy and posterior dissecting and freezing of the germinative tissue. Afterward, they were administered radiotherapy to induce infertility on the remaining left ovary. Later, two of the ewes had the thawed fragments of the right ovary injected inside the cortex of the irradiated left ovary in a “sowing” procedure that eliminated the need for sutures. Main outcome measure(s) Recovery of fertility in ewes after transplantation of germinative tissue into the ovary destroyed by radiotherapy. Result(s) The ewes were housed with fertile rams. Six months following the grafting, the rams impregnated the transplanted ewes. More than 2 years after radiotherapy, the nongrafted (control) ewes have not become pregnant. Conclusion(s) Intracortical grafting of the germinative tissue circumvents the obstacle of vascular anastomosis with autologous ovarian implants. Patients could benefit from the subcortical grafting of germinative tissue in one of the ovaries, recovering fertility after radiotherapy treatment for malignancy.

MIXED FARMING SYSTEMS IN TRANSITION: THE CASE OF FIVE VILLAGES ALONG A RAINFALL GRADIENT IN NORTH-WEST SYRIA

The changes taking place in the mixed farming systems of northwest Syria were examined by re-visiting, in 1996 and 2000, five villages along a rainfall gradient. The villages had been surveyed first in 1977–79. In those villages with moderate rainfall, intensification of crop production, namely a trend towards cereal monoculture and the planting of tree crops, did not lead to specialization in cropping at the expense of sheep ownership. In contrast, households in the areas too dry for most rainfed crops except barley (Hordeum vulgare) were more likely to sell their sheep because they depended heavily on off-farm income. Increases in crop yields were found but these only benefited the families in villages in the higher rainfall zones. Conversely, with the exception of ewe fertility, there was little evidence of improvements in sheep productivity. The mixed farming systems in the five villages sampled are still passing through a period of transition, and the cropping component will undoubtedly continue to change. This is less likely to happen to the small ruminant component in the near future unless the sector is given higher priority in national policy. As a strategy to increase feed production and balance the crop rotations, the prospects for closer crop/livestock integration at the farm level are limited by the many difficulties associated with the introduction of leguminous pasture and forage crops.

Effect of nutrition in early pregnancy on the periparturient relaxation of immunity to gastro-intestinal parasitism in prolific ewes

AbstractThe rôle of body reserves stored during early pregnancy on the periparturient breakdown of resistance to nematode parasites was investigated. From the 35th day of pregnancy, 46 ewes were distributed in four groups and given access to a lucerne pelleted diet. Two groups were given food at maintenance (M and C) and the other two were offered food either ad libitum (H) or at 0·70 their maintenance requirements (L) in order to achieve three well differentiated levels of body reserves by the 90th day of pregnancy when backfat thickness reached a mean value of 10·6, 7·5, 7·4 and 5·0 mm for H, M, C, and L treatments respectively. After the 90th day of pregnancy all animals were given food at 50 g/kg live weight per day. All ewes in groups H, M and L received 5000 infective larvae per week (40% Teladorsagia circumcincta, 40% Trichostrongylus colubriformis, 20% Haemonchus contortus) from 5 weeks before to 3 weeks after lambing. The animals in group C remained as uninfected controls.Host resistance, as measured by faecal egg counts, was significantly affected by the nutritional treatment established during early pregnancy, showing a mean excretion of 546, 766 and 1007 eggs per gram (e.p.g. ) for H, M, and L treatments, respectively, until 3 weeks post lambing. This response was accompanied by a significant effect on circulating eosinophils and better fed ewes showed a higher concentration with a maximum mean value of 10·1, 6·9, 5·5 and 4·0 cells per mm3 for H, M, L and C treatments, respectively, 2 weeks post infection. The effect of the worm infection per se was evident in that the lambs of the M treatment ewes grew at 0·90 of the rate of those in the control treatment (189 v. 213 g/day). Ad libitum feeding in early pregnancy appeared to sufficiently compensate for this depressive effect, with the H ewes producing lambs that grew at a rate similar to those of the C ewes (213 v. 213 g/day).The results support the view that fat mass stored by ewes in early pregnancy is involved in the expression of immunity against gastro-intestinal nematode infection around parturition. Furthermore, the depressive effect of ewes’ infection on lambs’ growth rate can be overcome by increasing the plane of nutrition of their dams. These results have clear implications for grazing animals, particularly their nutritional management in early pregnancy and provide a simple management strategy in sustainable management systems.

Effects of dosage of FSH, vehicle and time of treatment on ovulation rate and prolificacy in ewes during the anestrous season

The effects of dosage of follicle stimulating hormone (FSH), vehicle and time of injection on ovulation rate and prolificacy were evaluated during the anestrous season. Ewes on four farms ( n=445) were treated with a CIDR-G ® device for 5 days and exposed to rams upon removal of the insert (CRRI, day 0). A 3×2×2 factorial arrangement tested effects of dosage of FSH (Folltropin ®; 0, 42 or 68 mg NIH-FSH-P1), vehicle (saline:propylene glycol 1:4, v/v [PGL], or 50% polyvinylpyrrolidone K 29–32 [PVP]) and time of injection (12 or 36 h before CRRI). Follicular growth was monitored by ultrasonography in four ewes per treatment at injection of FSH, at CRRI, and on days 1–3 post-CRRI. All ewes were examined by ultrasonography on days 10–14 for ovulation rate, and on days 26–31 and 46–51 for pregnancy and number of embryos. The largest follicle (F 1) increased in diameter (mm) between FSH injection (5.3±0.1) and day 1 (6.1±0.1; P<0.01). The F 1 was larger at CRRI ( P≤0.05) in ewes receiving 42 than 0 mg FSH, and 68 than 42 mg FSH. The F 2 increased in diameter ( P<0.05) from FSH injection (4.7±0.2) to CRRI (5.2±0.2) and to day 1 (5.8±0.2), but was not affected by treatment. Number of small follicles (≤4 mm) did not differ with time or treatment. Number of medium follicles (5 mm) declined ( P<0.05) between FSH (1.5±0.2) and days 1 (0.8±0.2), 2 (0.9±0.2), and 3 (0.5±0.2). Number of large follicles (≥6 mm) increased from FSH (0.6±0.3) to CRRI (1.4±0.3; P<0.05), and day 1 (2.3±0.3; P<0.05), then declined by day 3 (0.6±0.3; P<0.05). There were more large follicles at CRRI ( P<0.05) with 68 mg (2.1±0.3) or 42 mg (1.6±0.2) than 0 mg (0.5±0.4) FSH. Ovulation rate (mean 2.12±0.05) increased with FSH given 12 h, but not 36 h before CRRI (dosage × time, P<0.05). Estrous response, conception rate, percentage of ewes lambing or prolificacy did not differ. However, number of corpora lutea not represented by embryos increased with dosage of FSH ( P<0.01; 0.25±0.14, 0.55±0.09, 0.71±0.09 for ewes treated with 0, 42, and 68 mg FSH, respectively).

Evaluation of melatonin receptor 1a as a candidate gene influencing reproduction in an autumn-lambing sheep flock.

The effect of the melatonin receptor 1a (MTNR1A) gene on fertility and litter size in autumn lambing was studied with 373 ewes from a population of sheep selected for 10 yr for fertility in May and June matings. Animals were from a composite line of 50% Dorset, 25% Rambouillet, and 25% Finnsheep. Two restriction fragment length polymorphisms were present in the population, with allelic frequencies of 0.42 and 0.58 for an MnII polymorphism (alleles M and m, respectively) and of 0.34 and 0.66 for an RsaI polymorphism (alleles R and r, respectively). Genotypic frequencies for the polymorphisms were not independent, suggesting an association between them in foundation animals. Effects of MTNR1A genotype on fertility and litter size were evaluated using mixed linear model or REML procedures, but were not significant for matings involving ewes of all ages. However, in adult ewes (3 yr old and older), fertility of ewes of genotype mm was 10.0 (mixed model; P < 0.09) to 11.2% (REML; P = 0.03) less than that of other ewes. Genotypic effects associated with MTNR1A in adult ewes accounted for 23.8% of the estimated total additive genetic variance in fertility. Litter size was not significantly associated with MTNR1A genotype; adult ewes of genotype mm had approximately 0.11 fewer lambs per ewe lambing than ewes of other genotypes. Fertility in autumn lambing is lowly heritable, expressed only in females, and manifested relatively late in life and only in some management systems. Access to genetic markers would thus be advantageous in selection programs.

Effect of digestible undegradable protein (DUP) concentration of concentrates offered to ewes on grass-based diets in late pregnancy on colostrum production and lamb performance

Nutrition of ewes during late pregnancy is a key factor influencing lamb survival and subsequent lamb growth and performance. Results from on-farm trials indicate that the superior lamb output from highly prolific compared with moderately prolific ewe breed types is less in grass-based compared with indoor lambing systems (Carson and Dawson, 2002). This is as a result of higher mortality rates of triplet lambs in outdoor systems with lower levels of intervention. Feeding and management strategies to maximise lamb viability for multiple births are required for grass-based lambing systems. Protein nutrition is likely to be a key factor, particularly considering that energy intakes in late pregnancy in triplet-bearing ewes are unlikely to meet requirements (Robinson, 1983). At sub-optimal energy intakes the supply of rumen undegraded protein is a major determinant of colostrum production and lamb birth weight. The objectives of this experiment were to investigate the effect of supplementing grass-based diets with concentrates with a range of digestible undegradable protein concentrations on colostrum production and lamb output.

Comparison of the productivity of Texel and Rouge de l’Ouest ewes and their crosses

AbstractAn experiment was undertaken to compare the productivity of crossbred ewes, produced by crossing Texel sires with Rouge de l’Ouest (Rouge) dams and Rouge sires with Texel dams, relative to purebred Texel and Rouge ewes. The purebred and crossbred ewes were crossed with Rouge and Texel sires. The proportion of productive ewes was similar in the purebred and crossbred ewes with an average figure of 0·92. Irrespective of crossing sire, Rouge ewes produced 0·48 more lambs per ewe lambed than Texel ewes (P &lt; 0·001). The two crossbred ewe types (Texel ✕ Rouge and Rouge ✕ Texel) each produced similar numbers of lambs (on average 1·92 lambs per ewe lambed). Individual heterosis values for ewe fertility and prolificacy were small and not significant (–1·67 for the proportion of productive ewes and –3·14 for the number of lambs born per ewe lambed). Maternal heterosis values were also not significant but were of larger magnitude (6·26 for ewe fertility and 3·12 for prolificacy). Lamb mortality (number of lambs born dead per ewe lambed) at birth was similar for purebred Rouge (0·44) and Texel (0·30) ewes and was significantly reduced by crossbred matings and mating the crossbred ewes (individual heterosis –30·68, P &lt; 0·10; maternal heterosis –80·23, P &lt; 0·001). Individual and maternal heterosis values for lamb growth rate from birth to six weeks were 8 (P &lt; 0·05) and 4 (P &gt; 0·05) respectively. Lamb growth rate from birth to weaning was significantly lower in lambs from Texel ewes compared with those from the other genotypes (P &lt; 0·05). Individual and maternal heterosis values for live-weight gain from birth to weaning were 5 (P &lt; 0·10) and 5 (P &lt; 0·01). The results of the current study demonstrate the superior performance of purebred Rouge ewes compared with purebred Texel ewes in terms of prolificacy and lamb growth rate from birth to weaning. However, both breeds had high lamb mortality at birth. Crossbreeding led to the production of hybrid ewes which had relatively high prolificacy with low levels of dystocia and lamb mortality.

Rumen digesta kinetics in cold exposed prolific sheep: impact on protein evaluation

In vivo measurements of the changes over time in rumen degraded and undegraded protein fractions were used to study effects of midwinter shearing of prolific ewes on effective rumen degradability of dietary protein (EPD). Values were compared to EPD estimated with the standard method of in situ feed characteristics and an assumed rumen passage rate. The effect of the experimental treatments (unshorn and shorn) was investigated in ewes during three years ( n=11). Rumens of the sheep were emptied and sampled 1, 2, 4, 8 and 12 h after feeding to monitor rumen contents of dry matter (DM), crude protein-free organic matter (OM-CP) and nitrogen (N). The degraded and undegraded fractions of DM, OM-CP and N in rumen contents were measured by in situ rumen incubation of rumen content samples. Protein evaluation based on EPD estimated from changes in rumen digesta volume with time had more variation and 10% more digestible protein in the small intestine (DVE) than the commonly used EPD. Midwinter shearing of crossbred ewes increased the extent of degradation of DM and OM-CP in the rumen. The extent of degradation of protein tended to be higher in shorn ewes. These differences did not result in different DVE yields with an assumption of an unchanged efficiency of microbial protein growth during cold exposure. While the commonly used EPD is more suitable for routine techniques than EPD based on changes in rumen digesta volume over time, the commonly used EPD may result in an underestimation of the DVE value of feeds for prolific ewes. Protein evaluation should take account of differences in efficiency of microbial production between unshorn and shorn ewes to avoid underestimation of the DVE value of feeds.

Genetic parameters of testicular measurements in Merino rams and the influence of scrotal circumference on total flock fertility

Genetic parameter estimates for scrotal circumference (SC), testis diameter (TD) and two-tooth liveweight (LW) were obtained for 1380 two-tooth Merino rams born from 1986 to 1998 on the Tygerhoek Experimental Farm. The effect of SC of service sires (n = 263) on ewe fertility was also investigated. Year of birth, selection group and LW were significant sources of variation for both SC and TD. SC had a significant effect on ewe fertility. Heritability estimates ranged from 0.29 to 0.40, 0.25 to 0.38 and from 0.49 to 0.52 for SC, TD and LW, respectively. Adjustment for LW decreased heritability estimates of SC and TD and the genetic correlations between the latter traits. Rams with an unadjusted SC of less than 30 cm should not be used. South African Journal of Animal Science Vol.32(2) 2002: 76-82

Fertility of Estrus-Induced Ewes during the Non-Breeding Season and Artificially Inseminated with Frozen Semen Imported from New Zealand.

The present study was conducted to investigate fertility of estrus-induced ewes during the non-breeding season, artificially inseminated with frozen semen imported from New Zealand. A total of 122 Suffolk and Suffolk-crossed ewes in three different sheep farms (T, S, M) were treated with an intravaginal progesterone release device (CIDR-G) for 12 days, and an intramuscular injection of 500 IU equine chorionic gonadotropin one day before CIDR removal. Effects of intrauterine insemination doses (0.2 and 0.4 ml per head) and two rams on fertility were compared at Farm T using 75 ewes. At the other two farms (S and M), 0.1 to 0.2 ml doses were inseminated into the uteri on the fixed-time basis. The lambing rates of ewes inseminated with 0.2 and 0.4 ml doses were 68.4 and 59.5%, and the lambing rates of ewes inseminated with the two rams were 61.3 and 65.9%. No significant differences were found between any of the factors. The lambing rates on Farms S and M were 54.2% and 47.8%, respectively. Overall, there was no significant difference in the lambing rates (58.3% and 59.5%) and prolificacy (2.03 and 1.61) between the two rams. These results indicate that the fertility of ewes inseminated during the non-breeding season with frozen-thawed semen imported from New Zealand is acceptable and that new blood lines of Suffolk sires and dams can be produced on Japanese sheep farms.

Prediction of stage of pregnancy in prolific sheep using ultrasound measurement of fetal bones.

The use of ultrasound to estimate stage of pregnancy was assessed in 32 ewes of a prolific genotype carrying 7 singleton fetuses and 9 twin, 10 triplet and 6 quadruplet litters that were scanned on six occasions from 60 to 120 days of gestation. At least one ultrasound measurement per ewe of fetal metacarpal bone length (MCL), biparietal diameter (BPD), or of both bones was made on over 90% of attempts (n = 152). Measurement of MCL was made on 78% of attempts (n = 371), of BPD on 73% of attempts, and of both bones on 62% of attempts. The equation developed from BPD (mean absolute error (MAE) = 3.2 days) was similar to that developed from measurement of MCL (MAE = 3.3 days) in its capacity to predict stage of pregnancy. Accuracy of prediction was improved using equations that included mean values within litters for BPD (MAE = 2.5 days) and MCL (MAE = 2.6 days). Further improvement in predictive capacity was achieved using multiple regression equations developed from measurement of both bones (individual fetuses: MAE = 2.6 days; equations including mean values within litters: MAE = 2.2 days). The results demonstrate that ultrasound can be used to estimate stage of pregnancy in prolific ewes, and that the use of mean values for bone measurements from different fetuses within litters and/or measurement of bones with different growth allometry can increase the reliability of estimates. The utility of the procedure depends on the number of fetuses measured per ewe, the number of bones measured per fetus and, hence, the time required to measure bones and the degree of accuracy required.

Ovulation of aged follicles does not affect embryo quality or fertility after a 14-day progestagen estrus synchronization protocol in ewes

The aim was to examine the effect of ovulation of aged follicles on embryo quality and fertility in ewes. In Experiment 1, ewes (n = 39) received a prostaglandin analogue on Day 6 of the cycle and then received either a progestagen sponge from Day 6 to 20 after estrus (Single sponge) or a progestagen sponge on Day 6 that was replaced on Day 11 and 16 and removed on Day 20 (Multiple sponges). In a subgroup of ewes, the growth of ovarian follicles was characterised using ultrasonography. Fertile rams were introduced 48 hours after sponge withdrawal; we slaughtered the ewes on Day 5 of pregnancy and recovered the embryos. The mean age of the ovulatory follicles was greater in ewes that received a single sponge compared with multiple sponges (8.7±0.8 days, range 4 to 14, versus 4.5±0.7 days, range 3 to 6; P<0.05). However, the groups did not differ (P>0.05) in ovulation rate (2.4±0.3 corporal lutea per ewe) or the proportion of good quality embryos recovered (71 to 82%; developed to the early morula stage or further). In Experiment 2, ewes (570 in total) received treatments similar to those in Experiment 1 but were kept until lambing. Ewes that received a single sponge came into heat earlier (P<0.05) than those that received multiple sponges, but ≥97% of ewes in all groups (P>0.05) were bred by 48 to 72 hours after ram introduction. There was no difference (P>0.05) between groups for the proportion of ewes that lambed to first service (80 to 86%) or the number of lambs per ewe (1.94±0.08 lambs). We conclude that when luteolysis occurs at the beginning of progestagen synchronisation, ewes will ovulate aged follicles, but that compared to shorter duration follicles, these follicles produce oocytes that are equally competent to be fertilised and develop into good quality embryos and full-term lambs.

Weaning and the ram-effect on fertility, serum luteinizing hormone and prolactin levels in spring rebreeding of postpartum Awassi ewes

Spring rebreeding activity was investigated in 44 multiparous Awassi ewes allocated to one of three treatments. The first treatment entailed ewes suckling lambs for 45 days and then continuously exposed to fertile rams (Group 1); ewes of the second group were weaned at 14 days of age and then were either exposed continuously (Group 2) or intermittently (Group 3) to rams. Time of weaning and type of exposure to the ram did not influence the reproductive performance in terms of fertility and prolificacy in postpartum Awassi ewes. Time of weaning did not influence serum LH concentrations monitored at 3 h intervals in Groups 1 and 2. However, serum prolactin (PRL) concentrations were significantly higher in Group 1, compared to Group 2 of ewes. Serum LH levels at weaning were significantly higher in ewes that conceived and lambed, compared to ewes that did not. It was concluded that spring rebreeding of postpartum Awassi ewes did not respond to ram presence and/or early weaning in terms of improved reproductive performance. The lack of reproductive response was further reflected in LH and PRL profiles.