Greyface Ewes Research Articles

Restoration of ovarian function and natural fertility following the cryopreservation and autotransplantation of whole adult sheep ovaries.

STUDY QUESTIONIs it possible to restore ovarian function and natural fertility following the cryopreservation and autotransplantation of whole ovaries, complete with vascular pedicle, in adult females from a large monovulatory animal model species (i.e. sheep)?SUMMARY ANSWERFull (100%) restoration of acute ovarian function and high rates of natural fertility (pregnancy rate 64%; live birth rate 29%), with multiple live births, were obtained following whole ovary cryopreservation and autotransplantation (WOCP&TP) of adult sheep ovaries utilizing optimized cryopreservation and post-operative anti-coagulant regimes.WHAT IS KNOWN ALREADYFertility preservation by WOCP&TP requires successful cryopreservation of both the ovary and its vascular supply. Previous work has indicated detrimental effects of WOCP&TP on the ovarian follicle population. Recent experiments suggest that these deleterious effects can be attributed to an acute loss of vascular patency due to clot formation induced by damage to ovarian arterial endothelial cells.STUDY DESIGN, SIZE, DURATIONStudy 1 (2010–2011; N = 16) examined the effect of post-thaw perfusion of survival factors (angiogenic, antioxidant, anti-apoptotic; n = 7–8) and treatment with aspirin (pre-operative versus pre- and post-operative (n = 7–9)) on the restoration of ovarian function for 3 months after WOCP&TP. Study 2 (2011–2012; N = 16) examined the effect of cryoprotectant (CPA) perfusion time (10 versus 60 min; n = 16) and pre- and post-operative treatment with aspirin in combination with enoxaparine (Clexane®; n = 8) or eptifibatide (Integrilin®; n = 8) on ovarian function and fertility 11–23 months after WOCP&TP.PARTICIPANTS/MATERIALS, SETTING, METHODSBoth studies utilized mature, parous, Greyface ewes aged 3–6 years and weighing 50–75 kg. Restoration of ovarian function was monitored by bi-weekly blood sampling and display of behavioural oestrus. Blood samples were assayed for gonadotrophins, progesterone, anti-Müllerian Hormone and inhibin A. Fertility restoration in Study 2 was quantified by pregnancy rate after a 3 month fertile mating period and was confirmed by ultrasound, hormonal monitoring and live birth. Ovarian function was assessed at sacrifice by ovarian appearance and vascular patency (Doppler ultrasound) and by follicular histology.MAIN RESULTS AND THE ROLE OF CHANCEIn Study 1, survival factors were found to have no benefit, but the inclusion of pre-operative aspirin resulted in four ewes showing acute restoration of ovarian function within 3 weeks and a further six ewes showing partial restoration. The addition of post-operative aspirin alone had no clear benefit. In Study 2, combination of aspirin with additional post-operative anti-coagulants resulted in total acute restoration of ovarian function in 14/14 ewes within 3 weeks of WOCP&TP, with 9/14 ewes becoming pregnant and 4/14 giving birth to a total of seven normal lambs. There was no difference between anti-coagulants in terms of restoration of reproductive function and fertility. In contrast, the duration of CPA perfusion was highly significant with a 60 min perfusion resulting in ovaries of normal appearance and function with high rates of primordial follicle survival (70%) and an abundant blood supply, whereas ovaries perfused for 10 min had either resorbed completely and were vestigial (7/14) or were markedly smaller (P < 0.01). It is concluded that both the degree of CPA penetration and the maintenance of post-operative vascular patency are critical determinants of the success of WOCP&TP.LIMITATIONS, REASONS FOR CAUTIONBefore application of this technology to fertility preservation patients, it will be critical to optimize the CPA perfusion time for different sized human ovaries, determine the optimum period and level of anti-coagulant therapy, and confirm the normality of offspring derived from this procedure.WIDER IMPLICATIONS OF THE FINDINGSThis technology holds promise for the preservation of fertility in women. It could also potentially be applied to the cryopreservation of other reproductive or even major organs (kidneys) where there are considerable difficulties in storing donated tissue.STUDY FUNDING/COMPETING INTEREST(S)Funding was received from the Medical Research Council, University of Nottingham. The authors confirm that they have no conflict of interest in relation to this work.

Enhanced Thecal Androgen Production Is Prenatally Programmed in an Ovine Model of Polycystic Ovary Syndrome

One of the hallmarks of polycystic ovary syndrome (PCOS) is increased ovarian androgen secretion that contributes to the ovarian, hormonal, and metabolic features of this condition. Thecal cells from women with PCOS have an enhanced capacity for androgen synthesis. To investigate whether this propensity is a potential cause, rather than a consequence, of PCOS, we used an ovine prenatal androgenization model of PCOS and assessed ewes at 11 months of age. Pregnant Scottish Greyface ewes were administered 100 mg testosterone propionate (TP) or vehicle control twice weekly from d 62 to 102 of gestation, and female offspring (TP = 9, control = 5) were studied. Prenatal TP exposure did not alter ovarian morphology or cyclicity, or plasma androgen, estrogen, and gonadotropin concentrations, at this stage. However, follicle function was reprogrammed in vivo with increased proportions of estrogenic follicles (P < 0.05) in the TP-exposed cohort. Furthermore, in vitro the thecal cells of follicles (>4 mm) secreted more LH-stimulated androstenedione after prenatal androgenization (P < 0.05), associated with increased basal expression of thecal StAR (P < 0.01), CYP11A (P < 0.05), HSD3B1 (P < 0.01), CYP17 (P < 0.05), and LHR (P < 0.05). This provides the first evidence of increased thecal androgenic capacity in the absence of a PCOS phenotype, suggesting a thecal defect induced during fetal life.

Are Scottish Blackface ewes more resistant to nematode parasite infection than Greyface ewes?

The extent of periparturient relaxation of immunity (PPRI) to gastrointestinal nematode parasites is sensitive to metabolisable protein (MP) scarcity but also varies between breeds of sheep (Houdijk, 2008). For example, under ad libitum feeding, Scottish Blackface ewes had a lower extent of PPRI than Greyface ewes (Zaralis et al., 2008). Such between-breed variation in PPRI may not necessarily be associated with genetic resistance per se but could arise from a higher nutrient demand of the more productive Greyface ewes (Houdijk, 2008). This experiment was designed to test the hypothesis that if the extent of PPRI has only a nutritional basis, then the sensitivity of PPRI to MP scarcity will not differ between the breeds when MP feeding is adjusted for between-breed differences in MP demand.

Nutritional sensitivity of resistance to Trichostrongylus colubriformis in lactating ewes

It has been suggested that the periparturient breakdown of immunity to parasites has a nutritional basis. Our overall hypothesis is that it results from a prioritized scarce metabolizable protein (MP) allocation to reproductive functions (e.g. milk production) rather than to immune functions. We have earlier shown that the relationship between MP supply, milk production and resistance to the abomasal nematode Teladorsagia circumcincta provides support for this hypothesis. Because nutritional sensitivity of resistance to parasites may differ between parasite species, we used the same nutritional protocol to test the overall hypothesis with a different parasite. Thus, five levels of dietary MP, ranging from 0.60 to 1.2 times assumed requirements, were offered for 4 weeks post-parturition to twin-rearing Greyface ewes, experimentally infected with the small intestinal nematode Trichostrongylus colubriformis. We hypothesized that the initial increments of MP supply would increase milk production without affecting the degree of breakdown of immunity whilst later increments would reduce the degree of breakdown of immunity. Indeed, the data suggest that the first two increments of MP supply increased milk production, whilst final worm burdens were reduced from the second increment onwards. MP supply did not affect mucosal mast cell concentration but increased globule leukocyte concentration. These results support the overall hypothesis that scarce MP allocation is prioritized to milk production over immune functions. In addition, the contrast between effects of MP supply on resistance to T. colubriformis and to T. circumcincta supports the view that periparturient immunity to small intestinal nematodes may be less sensitive to nutrient scarcity than periparturient immunity to abomasal nematodes.

Effects of plane of nutrition during the first month of pregnancy on conception rate, foetal development and lamb output of mature and adolescent ewes

AbstractEmbryo transfer studies have demonstrated that high plane feeding in early pregnancy is detrimental to the successful establishment of pregnancy in adolescent but not mature ewes. To further examine this relationship with ewes that conceive naturally and to investigate its effects on foetal development, 102 Greyface and Texel×Greyface ewes (body condition score (BCS) 3·8) and 114 Texel×Greyface adolescent ewes (BCS 3·3) were allocated to one of three treatments following a synchronized mating. From day 1 to 31 of pregnancy, animals were offered grass nuts (10·2 MJ metabolizable energy (ME) per kg dry matter (DM); 163 g crude protein per kg DM) at one of three levels to supply approximately 2·0 (H); 1·0 (M) and 0·6 (L) of their predicted ME requirements for maintenance. Increasing the post-mating plane of nutrition resulted in significant increases in ewe live weight (P&lt;0·001) and BCS (P&lt;0·001) during the treatment period. When diets were standardized for all animals during mid pregnancy (days 31 to 105), L ewes gained more live weight (P&lt;0·05) and BCS (P&lt;0·001) than H ewes. Early pregnancy nutrition had no effect on the conception rate of mature ewes; however adolescent ewes on the H and M treatments had lower conception rates (P&lt;0·05) than those offered the L diet (0·59, 0·61 and 0·82 respectively). As a result, L adolescent ewes tended to have a higher mean total lamb birth weight per ewe mated (P=0·09) although lamb output at weaning was not influenced by plane of nutrition. Lambs born from adolescent mothers had lower lamb birth weights (P&lt;0·001) and a shorter mean head length, crown-rump length and thoracic girth (P&lt;0·001). Foetuses from H ewes had longer hind legs than those from L ewes on day 83 of gestation (P&lt;0·05) and at term (P&lt;0·05). The results of this study suggest that allowing adolescent but not mature ewes to lose live weight and body condition can increase the proportion of productive ewes following a natural service.

Effect of herbage allowance and concentrate food level offered to ewes in late pregnancy on ewe and lamb performance

AbstractTwo experiments were undertaken to investigate the effect of herbage allowance and concentrate food level offered to twin-bearing ewes in the last 6 weeks of pregnancy on ewe and lamb performance. In each study, 96 twin-bearing Greyface (Border Leicester × Scottish Blackface), Rouge × Greyface and Texel × Greyface ewes were used. In experiment 1, the ewes were allocated to eight treatments consisting of two herbage allowances (1·3 and 2·6 kg herbage dry matter per ewe per day) and four concentrate food levels ranging from zero to 1000 g per day. In experiment 2, ewes were offered four herbage allowances (1·3, 1·75, 2·2 and 2·6 kg herbage dry matter per ewe per day) and zero or 500 g concentrates per day. In experiment 1, herbage allowance and concentrate food level had no significant effect on lamb birth weight, lamb mortality or lamb performance up to weaning. Herbage dry matter intake decreased linearly with increasing concentrate food level with a substitution rate of 18 g of herbage dry matter per 100 g concentrate food level. In experiment 2, lamb birth weight increased with increasing herbage allowance (P&lt; 0·01) and with increasing concentrate food level (P&lt; 0·01). However, lamb performance to weaning was unaffected by late pregnancy nutrition. The satisfactory levels of performance obtained with ewes offered grass-only diets in late pregnancy indicates that grazed grass is a high nutritive value food for twin-bearing ewes in late pregnancy.

Is the allocation of metabolisable protein prioritised to milk production rather than to immune functions in Teladorsagiacircumcincta-infected lactating ewes?

It has been suggested that the periparturient breakdown of immunity to parasites has a nutritional basis. Our overall hypothesis is that it results from a prioritised scarce nutrient allocation to reproductive functions (e.g. milk production) rather than to immune functions. We tested this hypothesis by offering five levels of dietary metabolisable protein, ranging from 0.65 to 1.25 times their assumed requirements, for 4 weeks post-parturition to twin-rearing Greyface ewes, experimentally infected with Teladorsagia circumcincta. We hypothesised that the initial increments of metabolisable protein supply would increase milk production without affecting the degree of breakdown of immunity whilst later increments would reduce the degree of breakdown of immunity. The first two increments of metabolisable protein supply indeed increased milk production and did not affect final worm burdens, but in contrast to the expectation, reduced faecal egg counts and total egg output. The last two increments of metabolisable protein supply did not further affect milk production and egg output, but resulted in reduced final worm burdens. Metabolisable protein supply did not affect plasma IgG and IgE antibody against somatic L 3 antigen but the first three increments reduced plasma pepsinogen and plasma IgA antibody. The last increment did not further reduce plasma pepsinogen but increased plasma IgA. Metabolisable protein supply did not systematically affect abomasal mucosal mast cell, globule leukocyte and eosinophil counts. Our results support the view that the priority of scarce metabolisable protein allocation to milk production over immune functions may be gradual rather than absolute. The contrast between effects of metabolisable protein supply on faecal egg count and final worm burden points towards the possibility that if different effector responses regulate fecundity and worm expulsion, then they would differ in their sensitivity towards changes in the degree of nutrient scarcity.

Can an increased intake of metabolizable protein affect the periparturient relaxation in immunity against Teladorsagia circumcincta in sheep?

Within the overall hypothesis that the periparturient relaxation of immunity (PPRI) to gastrointestinal parasites has a nutritional basis, we studied whether an increased intake of metabolizable protein (MP) could affect the expression of immunity to Teladorsagia ( Ostertagia) circumcincta of twin-bearing and -rearing Greyface ewes. Two sets of iso-energetic diets were formulated to provide either 85% (L-) or 130% (H-) of the MP requirements during the last 6 weeks of pregnancy (-P) and the first 6 weeks of lactation (-L). Thirty ewes were allocated to LP or HP. Six ewes of each group were slaughtered after lambing (S 0); the remaining 24 ewes of each group were allocated to either LL or HL, thus creating four treatment combinations during lactation (LP/LL, LP/HL, HP/LL and HP/HL; n=12). Six ewes of each treatment combination were slaughtered at Week 3 (S 3) or at Week 6 (S 6) in lactation. The HP ewes were heavier at lambing, produced heavier lambs, had lower faecal egg counts (FECs), a lower concentration of plasma pepsinogen, a higher concentration of plasma albumin during late pregnancy and more abomasal globule leukocytes (GLs) but similar worm burdens at S 0 compared to the LP ewes. The LP/HL and HP/HL ewes had a higher calculated milk production than the LP/LL and HP/LL ewes. FECs increased for each treatment combination during the first 3 weeks of lactation. This increase concurred with fewer abomasal GLs at S 3 compared to S 0. The LP/HL and HP/HL ewes had a higher proportion of immature worms and more abomasal GLs than the LP/LL and HP/LL ewes at S 6. The FECs continued to increase during the second 3 weeks of lactation for the LP/LL ewes only, which concurred with an elevated plasma pepsinogen concentration and an absence of abomasal GLs at S 6. The plasma pepsinogen concentration decreased rapidly for the LP/HL ewes during lactation. We conclude that an increased intake of MP could enhance the expression of immunity to T. circumcincta of twin-bearing and -rearing Greyface ewes.

A comparison of sires of Suffolk and Dutch Texel breeds and ewes of Greyface, Suffolk Cheviot and Dutch Texel breeds in terms of food intake, prolificacy and lamb growth rates

AbstractA comparison was made over 2 years of sires of Suffolk and Dutch Texel breeds and ewes of Greyface (Border Leicester × Scottish Blackface), Suffolk Cheviot and Dutch Texel breeds in terms of food intake, prolificacy and lamb growth rates under a grass-based system of production. Suffolk Cheviot ewes consumed significantly more silage dry matter than the Greyface ewes in both years of the study. There was no overall difference between Greyface and Suffolk Cheviot ewes in terms of prolificacy. However lambs from Suffolk Cheviot ewes had a higher growth rate than lambs from Greyface ewes from birth to weaning in year 1 (P &lt; 0·01). In the comparison of the three ewe breeds sired by Dutch Texel rams in year 2, Dutch Texel ewes produced a similar number of lambs to the other genotypes but had a higher incidence of difficult lambings, higher lamb mortality and consequently a lower number of lambs weaned. Purebred Dutch Texel male lambs had lower growth rates than crossbred Dutch Texel lambs (143 compared with 158 glday for lambs from Greyface ewes and 166 (s.e. 13.4) glday for lambs from Suffolk Cheviot ewes in year 1 and 183 compared with 251 and 248 respectively (s.e. 10.9) glday in year 2). Lambs sired by Suffolk rams had higher growth rates than those sired by Dutch Texel rams (252 compared with 224 (s.e. 5.4) glday) in year 2.

Effects of Texel or Rouge de l’Ouest genes in lowland ewes and rams on ewe prolificacy, lamb viability and weaned lamb output

AbstractAn evaluation of the effects of the proportion of Texel or Rouge de l’Ouest (Rouge) genes in ewes (0, 0·5 or 1·0; the remainder being Greyface (Border Leicester × Scottish Blackface)) on prolificacy, lamb viability and lamb output was undertaken. A comparison of Texel and Rouge sires was carried out on Greyface, Texel and Rouge ewes. Prolificacy was higher in Greyface compared with Texel ewes (P = 0·06) but was lower in Greyface compared with Rouge ewes (P &lt; 0·001). Prolificacy was similar in Greyface and Texel × Greyface ewes mated to Texel rams and in Greyface and Rouge × Greyface ewes mated to Rouge rams. The level of dystocia was similar in Greyface and Texel × Greyface ewes but significantly higher in Texel ewes (P &lt; 0·001). The proportion of Rouge genes in the ewe had no effect on the level of dystocia. Litter weight of lambs at birth was significantly heavier in Greyface (P &lt; 0·001) and Texel × Greyface (P &lt; 0·01) ewes compared with Texel ewes. The proportion of Rouge genes in the ewe had no significant effect on litter weight. Lamb mortality (no. of lambs born dead and died birth to weaning) was significantly greater with Rouge ewes compared with the other ewe breed types (P &lt; 0·001). The number of lambs which died from birth to weaning was lower with Texel × Greyface compared with Greyface ewes (P &lt; 0·01). Expressed on a unit metabolic weight basis, Greyface ewes produced a significantly greater weight of lamb compared with Texel (P &lt; 0·05) and Rouge ewes (P &lt; 0·001). Texel × Greyface ewes produced a significantly greater weight of Texel-sired lamb compared with Greyface (P &lt; 0·01) and Texel ewes (P &lt; 0·001).Sire had a significant effect on a number of parameters. The number of productive ewes was significantly lower in ewes mated with Texel sires (P &lt; 0·001). Lamb birth weights and pre-weaning growth rates were greater with Rouge sires (P &lt; 0·05). Number of lambs weaned per ewe lambed was significantly greater with Texel sires (P &lt; 0·01). Overall weight of weaned lamb produced per ewe was not significantly affected by sire breed.

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 4. The effect of seasonal pattern of nitrogen fertilizer application and annual stocking rate

Greyface (Border Leicester × Scottish Blackface) ewes, mated in October, were housed in winter and turned out after lambing in late March to one of four treatments replicated three times on perennial ryegrass (Lolium perenne)‐dominated pastures. On three of the treatments the stocking rate was 12·5 ewes plus lambs ha−1 annum−1 (SR12·5), whereas on the fourth it was 15·0 ewes plus lambs ha−1 annum−1 (SR15·0). There were two levels of applied fertilizer nitrogen (N), 152 kg N ha−1 annum−1 (N152) and 205 kg N ha−1 annum−1 (N205). Three patterns of nitrogen application were used: predominantly in spring (E), predominantly in autumn (L), and mainly in spring and autumn (E + L). Grazed sward surface height was controlled within the range 3·5–5·5 cm during spring and summer, and supplementary feed was offered when sward height was below 3·5 cm.The effects on animal performance, yield of silage and requirement for supplementary feed were measured over 3 years (1986–88). Management of the sward height within the specified limits resulted in similar levels of individual animal performance for all treatments, but treatment SR15·0N205E + L produced a significantly (P &lt; 0·05) greater output of lamb per hectare. There was no evidence to suggest that, by increasing the amount of N fertilizer applied in the autumn, ewe reproductive performance was increased. Neither the treatment with the lower level of N applied in the spring (SR12·5N152L) nor the high stocking rate treatment (SR15·0N205E + L) was self‐sufficient in winter feed (silage) production. SR15·0N205E + L also required more supplementary feed in both the lactation (38·1 kg ewe−1) and the mating (9·1 kg ewe−1) periods. SR12·5N152L required the second greatest amount of supplementary feed during lactation (36·1 kg ewe−1), whereas SR12·5N205E + L required the least supplementary feed over both periods (27·8 kg and 4·8 kg ewe−1). Taking all treatments together, there were significant (P &lt; 0·05) differences between years in lamb weaning weight (kg), lamb output (kg ha−1), yield of silage (kg ewe−1) and supplementary feed required (kg ewe−1), arising mainly from a lower level of herbage production in one year. Treatment SR12·5N152E generated the highest gross margin per hectare.

Suppression of fetal gonadotrophin concentrations by maternal passive immunization to GnRH in sheep.

The hypothalamo-pituitary-gonadal axis matures during fetal life and may be susceptible to adverse effects. Model systems can be used to understand its physiological role. The aim of this study was to determine whether antibodies to GnRH, administered to the mother, can cross the ovine fetal-placental barrier and suppress fetal gonadotrophin secretion. Maternal passive immunization to GnRH in pregnant Greyface ewes (day 103 of gestation) resulted in GnRH antibody titres of from 1:6000 to 1:9000 after 1 day and a suppression of the pulsatile secretion of fetal LH after 2 days. Fetal FSH concentrations declined gradually over the 11 days of the experiment and were only significantly different from control animals immunized against BSA in male fetuses. The slower decrease in fetal FSH concentrations than in LH concentrations shows that the secretion of FSH, unlike that of LH, is not dependent on short term changes in GnRH release. The lack of a suppressive effect of the maternal GnRH immunoneutralization on female fetal FSH secretion may be due to removal of the negative feedback effect of oestradiol and, possibly, inhibin. There was no sexual dimorphism in the effect of maternal GnRH immunoneutralization on fetal GnRH antibody titres or fetal LH secretion. These findings show that maternal passive immunization against GnRH results in GnRH antibodies crossing the fetal-placental barrier and suppressing fetal LH and FSH secretion in males, but only suppressing LH secretion in the females. Although the lack of effect on FSH secretion in the females needs to be investigated further, the present study provides evidence of a non-invasive procedure for blocking fetal gonadotrophin secretion which may be used to investigate hypothalamo-pituitary-gonadal function during early gestation in sheep.

Dietary-induced suppression of pre-ovulatory progesterone concentrations in superovulated ewes impairs the subsequent in vivo and in vitro development of their ova

In the first of three experiments, eight ovariectomised Greyface ewes primed with exogenous progesterone were used to provide quantitative data on the effects of two contrasting feeding levels (0.3 vs. 1.4 × maintenance) on plasma progesterone concentrations. Over the 9 day study period, mean (± SEM) daily progesterone concentrations were 4.3 ± 0.13 and 3.3 ± 0.17 μg l −1 for the low and high feeding regimens, respectively ( P = 0.06), indicating that high feed intake suppressed circulating progesterone levels. The second experiment examined the effect in superovulated Finn-Dorset ewes of a diet supplying either 0.6 (Group L, n = 8) or 2.3 (Group H, n = 8) times their daily energy needs for maintenance, from 1 day before introduction of exogenous progesterone to the time of insemination, on plasma progesterone concentrations and the viability of ova recovered 4 days after insemination. Mean (± SEM) plasma progesterone concentrations were 4.5 ± 0.17 μg l −1 and 2.8 ± 0.16 μg l −1 for L and H ewes, respectively, during the 12 day priming period ( P < 0.001). Eight hours after progesterone withdrawal, levels had fallen to 0.9 ± 0.06 μg l −1 and 0.8 ± 0.07 μg l −1 , respectively, then rose to 17.8 ± 3.01 μg l −1 and 12.9 ± 2.50 μg l −1 ( P > 0.10) at ovum collection. Intervals (mean ± SEM) to oestrous onset (14.5 ± 0.38 h) and the luteinising hormone (LH) surge (27.1 ± 0.98 h) were unaffected by feed intake. Mean (± SEM) ovulation rates (8.1 ± 1.57 vs. 7.8 ± 1.10) and numbers of ova recovered (5.0 ± 1.39 vs. 4.8 ± 1.11) were also similar for each group. However, the proportions of ova considered viable (over 32 cells) at recovery were 0.53 and 0.22 for L and H groups, respectively ( P < 0.005). Following 72 h culture (Tissue Culture Medium-199 (M199) + 10% foetal calf serum (FCS)), 0.55 and 0.27, respectively, had developed to blastocysts ( P < 0.025). Of ova assessed as viable at recovery, similar proportions (0.86 vs. 0.75) from L and H treatments developed to blastocysts, with corresponding nuclei counts (mean ± SEM) of 55 ± 5.2 and 55 ± 13.2. The third experiment used 12 superovulated Greyface ewes, each offered a different feed level within the range 0.6–2.5 × maintenance, to determine the nature of the relationship between feeding level, pre-ovulatory progesterone concentrations and ovum development at Day 2 following insemination and subsequently during 7 day co-culture (M199 + FCS). Increases in feeding level were accompanied by linear decreases in plasma progesterone ( r 2 = 0.79, P < 0.001), the interval to oestrous onset ( r 2 = 0.52, P < 0.01) and timing of the LH surge ( r 2 = 0.32, P < 0.06). Although undetectable at ovum collection, and somewhat equivocal after 4 day culture, high feeding levels prior to ovulation reduced the proportion of ova (0.16 vs. 0.58) developing to or beyond the expanding blastocyst stage after 7 day culture. Quantitative indices of cell division and protein synthesis confirmed this. In conclusion, excessive feeding during follicular recruitment and oocyte maturation in superovulated ewes imparts a legacy of embryonic loss and developmental retardation.

The effect of late pregnancy on the diet selections made by ewes

To test the hypothesis that sheep select a diet that meets their physiological needs (imposed by late pregnancy), four foods were formulated of either a high metabolisable energy (ME) concentration (A, B 12 MJ/kg dry matter (DM)) or a low concentration (C, D 9 MJ/kg DM). The crude protein (CP) concentrations of A and C were high (279 and 191 g/kg DM) relative to B and D (105 and 95 g/kg DM); the ratios of metabolisable protein: ME were 12 g/MJ for foods A and C and 4 g/MJ for foods B and D. Twin bearing and non pregnant Greyface ewes of similar body condition were offered ad lib., A, B and C as single foods and paired choices (A with B) and (C with D). Replication was a minimum of four ewes for single foods and six for the choices. Food intakes by pregnant and non pregnant ewes were similar until parturition was imminent, when the intakes by the pregnant ewes declined rapidly. The majority of pregnant ewes carried twin foetuses to term without problems. When the ME concentration of the food choice was high (A/B) pregnant ewes selected a greater proportion (P < 0.05) of the food of high CP concentration than non pregnant ewes: pregnant 0.57 (se 0.074); non pregnant 0.28 (se 0.105). By contrast when ewes were offered a choice between foods of low ME concentration diet selection was unaffected by state: proportion of the higher CP food, C selected were: 0.70 (se 0.070) and 0.79 (se 0.069) for pregnant and non pregnant ewes respectively. These results show that when the dietary ME concentration of foods given as a choice is high, pregnant ewes select a diet that reflects their enhanced demand for protein in contrast with non pregnant contemporaries. However, when the ME of the foods is low priorities other than physiological state may motivate their diet selection. It is suggested that such a priority is the maintenance of a balanced rumen environment.

Melatonin Treatment of Donor and Recipient Ewes in an Embryo Transfer Programme: Effects on Ovulation Rate and Embryo Survival During Normal Seasonal Anoestrus

Conception rates and litter sizes in ewes are often higher during the peak of the breeding season than at the beginning or end. How much of this is due to seasonal differences in ovulation rate (Montgomery et al 1988) and ram fertility (Colas, 1983) is uncertain. Using laparoscopic intrauterine insemination which virtually eliminates fertilization failure, Aitken et al (1990) obtained estimates of embryo survival for Greyface ewes induced to ovulate in mid-June (mid anoestrus) that were 25, 19 and 13% below the expected values for 2, 3 and 4 ovulations respectively. While this implies that embryos transferred to recipient ewes at an induced oestrus during seasonal anoestrus may have sub-optimal survival rates, it does not identify whether the cause lies solely with the embryo or with the uterine environment or with both. The present study employs reciprocal embryo transfer in conjunction with melatonin treatment to identify the influence of seasonality on the inherent viability of the embryos and the ability of the uterine environment to sustain pregnancy.

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 1. Effects of two annual stocking rates in combination with two sward height profiles

AbstractThe consequences of controlling sward height at two levels, around 5 cm (HS) and around 3·5 cm (LS), during spring and summer by adjusting weekly the proportion of the areas grazed in response to changes in rate of herbage production and utilizing the surplus pasture areas to conserve winter fodder were studied over three complete years for Greyface ewes with their lambs at 15ha−1 (SR15) and 10ha−1 (SR10). The rules used to control grazed sward height resulted in acceptable sward height control in three of four treatments and, by providing supplementary feed when sward height was below target, gave rise to similar levels of individual animal performance. Total output of lamb weaned was greater for the SR15 than for the SR10 flocks (607 vs 477 kg live weight ha−1; P&lt;0·001). Amounts of winter fodder produced were less for the SR15 than for the SR10 flocks [39 vs 213kg dry matter (DM) per ewe; P &lt; 0·001]. Significantly more supplementary feed (10·0 vs 4·4kg DM per ewe; P &lt; 0·01) and hay (13·7 vs 4·0kg DM per ewe; P7lt;0·05) were offered around mating to SR15 flocks than to SR10 flocks. It is concluded that, provided that sward height can be controlled between 3·5 and 5·0cm during the spring and summer and that supplementation is offered when the grazed sward is below 3·5 cm, flock performance will fall within acceptable and predictable limits.

A note on herbage intake by Greyface ewes on perennial ryegrass white clover swards in the autumn

The effects on herbage intake of changes of herbage mass associated with different stocking rates were studied in Greyface (Border Leicester × Scottish Blackface) ewes in the autumn. Intake was measured in 5-day periods in late September (PI), late October (P2) and late November (P3) on two established, perennial ryegrass/white clover swards (SI and S2). Both swards had previously been variably stocked to produce areas with a range in herbage masses, some of which were grazed continuously (G) at stocking rates declining from 18 to 6 ewes per ha.Intake was also measured in P2 and P3 on other areas of the swards which were ungrazed for 6 weeks in September and October (C) and then stocked at 18 ewes per ha. Intakes of dry matter, organic matter and digestible organic matter were 16 g, 10 g and 7·5 g/kg live weight, respectively. Organic matter digestibility was 075 in PI and P2 but declined in P3.Differences in herbage intake and digestibility arose largely because of differences between the swards in herbage mass, sward height and sward density. Ewes in condition scores &gt; 3·00 in early September had lower intakes at all times than did thinner ewes. Changes in sward management associated with different strategies of use had little long-term effect on herbage intake. Keywords: digestibility, herbage, sheep, stocking rate.

Effect of litter size on the milk production, blood metabolite profiles and endocrine status of ewes lambing in January and April

ABSTRACTMilk yields and blood metabolite and hormone profiles of a total of 40 Greyface ewes lambing in January or April and suckling single (S) or twin (T) lambs were determined. Ewes were given a fixed level of feeding throughout the first 10 weeks of lactation. Milk yields were measured weekly. Pooled blood samples (six samples; 20-min intervals), collected at weekly intervals for the first 10 weeks of lactation, were assayed for glucose, non-esterified fatty acids (NEVA), 3β-hydroxybutyrate, urea, albumin, total protein, insulin, growth hormone (GH), cortisol, prolactin, thyroxine (T4) and triiodothyronine (T3). At weeks 2, 4 and 10 of lactation samples were collected at 20-min intervals for 8 h and assayed individually for insulin, GH, cortisol and prolactin. Mean daily milk yield was lower in S than in T ewes in January (1·93v.2·33 kg/day;P&lt; 0·05) and April-lambing ewes (1·95v.2·28 kg/day; P &gt; 0·05). Profiles of NEFA and 3β-hydroxybutyrate indicated that T ewes were mobilizing adipose tissue at a greater rate than S ewes. The higher milk yield and rate of fat mobilization in T ewes compared with S ewes was associated with lower overall mean insulin concentrations (3·37v.5·04 mil per I;P&lt; 0·002) and higher GH (6·29v.2·77 μg/l;P&lt; 0·001) and cortisol (7·04v.3·64 μg/l;P&lt; 0·001) concentrations in the weekly samples. Differences between rearing groups in mean concentrations of T4 and T3 were generally small and not significant. Mean prolactin concentrations were much lower in the January- than in the April-lambing ewes (73·7v.270·2 μ/l;P&lt; 0·001) but this difference was not associated with a difference in milk yield. Substantial increases in insulin and GH concentrations generally followed feeding but the post-prandial profiles were dependent on stage of lactation; while GH concentrations increased following feeding at weeks 2 and 4 of lactation, there was generally a decline in post-prandial concentrations at week 10. It is concluded that the patterns of insulin and GH secretion during the hours following feeding may be an important determinant of the rate of tissue mobilization and milk yield in ewes subject to differences in demand for milk created by differences in litter sizes.

A note on the effect of post-mating stocking rate on reproductive performance of Greyface ewes

Continuously grazed rye grassl clover swards with surface heights of 8 to 10 cm at 5 weeks before a synchronized mating and 7·5 cm at mating were grazed by 151 Greyface ewes stocked at 12 per ha until mating. The effects of two stocking rates (eight and 16 ewes per ha) for 6 weeks over the mating and post-mating period were then studied on live weight, body condition and reproductive peformance. Sward height fell more rapidly post mating when stocked at 16 ewes per ha than at eight ewes per ha, but remained above 3·5 cm until 4 weeks after first mating under both rates. Ewes stocked at 16 per ha became significantly lighter and leaner than ewes stocked at eight per ha. There was no significant effect of post-mating stocking rate on reproductive performance in terms of conception rate and lambing rate to first mating or lambing rate to all matings. Reproductive performance of Greyface ewes is therefore unlikely to be adversely affected by post-mating stocking rate on swards of 7 to 8 cm which do not fall below 3·5 to 4·0 cm until 3 to 4 weeks after mating.

Diurnal profiles of LH, prolactin and progesterone and their inter-relationships in ewes in high or moderate levels of body condition

Relationships between circulating progesterone profiles and those of the luteotrophic hormones luteinising hormone (LH) and prolactin were examined at different times of day in two groups of 19 and 18 Greyface ewes in a high level of body condition (H; condition score ≥3.5) or moderate level of condition (M; condition score 2.5/2.75). These levels of body condition were maintained from 4 weeks before mating at a synchronised oestrus until slaughter at approximately 5 weeks post mating. On day 10 post mating, blood samples were collected at 20-min intervals during two periods of 6 h during the day (10:00–16:00) and night (22:00–04:00). All samples were assayed for progesterone, LH and prolactin. There were no significant effects of level of body condition on mean ovulation rates, pregnancy rates and ova wastage rates or on progesterone, LH and prolactin profiles. Mean progesterone concentrations were lower during the day than at night (3.2 vs. 3.6 ng ml −1; P < 0.001) while LH concentrations were higher (0.74 vs. 0.66 ng ml −1; P < 0.001) and prolactin concentrations were unaffected (12.8 vs. 11.9; NS). There was a higher incidence of progesterone pulses (0.24 vs. 0.17 pulses h −1; P < 0.01) and a lower prolactin pulse frequency (0.22 vs. 0.33 pulses h −1; P < 0.01) during the day than at night. Whereas the LH pulse frequency was similar during the two periods for M ewes (0.21 vs. 0.22 pulses h −1; NS), it was higher during the day in H ewes (0.25 vs. 012 pulses h −1; P < 0.01). LH and progesterone concentrations were significantly correlated but not prolactin and progesterone concentrations. Body condition did not affect the mean magnitude of the increase in progesterone concentrations following LH pulses. We conclude that LH profiles, but not prolactin profiles, directly influence progesterone profiles and that diurnal variations in LH pulse frequency are likely to be associated with diurnal variations in progesterone supply to the uterus and oviduct. We suggest that the nocturnal reduction in LH pulse frequency in H ewes could have detrimental effects on reproductive performance.