Romney Ewes Research Articles

Active immunisation of Romney ewes with an androstenedione–protein conjugate

Abstract Romney ewes were immunised on one occasion with androstenedione-6-hemisuccinate-bovine serum albumin during mid-anoestrus (December). The onset of seasonal oestrous activity, the number of animals displaying oestrous behaviour, and the number of ovulations per ewe were recorded during the following breeding season. The results were compared with those from untreated (control) animals and from animals treated with pregnant mare serum gonadotrophin (PMSG). The immunised animals showed a small but highly significant increase (P< 0.001) in the mean ovulation rate (1.43 ovulations per ewe) relative to control (1.08 ovulations per ewe). The increased ovulation rate in the immunised ewes was comparable with that achieved in the animals treated with PMSG (1.37 ovulations per ewe). None of the animals that were immunised with the androstenedione-protein conjugate ovulated more than two follicles, and all but one showed oestrous activity. Many of the animals with low antibody titres against androstenedione had an increase in ovulation rate (11 ewes with titres less than 1:5000 had 1.55 ovulations per ewe), whereas those with high antibody titres more commonly had low ovulation rates (11 ewes with titres greater than 1:5000 had 1.27 ovulations per ewe). A possible interference in behavioural oestrous activity appeared to be associated with high antibody titres. If further studies can show an increased number of live births per ewe mated, a single-injection procedure with an androstenedione-protein conjugate may be of practical importance in enhancing the fecundity of New Zealand Romney ewes.

Corpus luteum function in ewes stimulated by rams

In late February Dorset rams were introduced (day = 0) to 40 mature Romney ewes that were observed by laparoscopy to be anovular. The ovaries of 20 of these ewes were examined by laparoscopy every second day while the remaining 20 ewes served as unoperated controls. Jugular blood samples were taken daily and plasma progesterone concentrations assayed to provide information on the functional status of any corpora lutea (CL) arising from ovulations stimulated by introduction of the rams. Eighty-five percent (-17/20) of the ewes that were repeatedly laparoscoped had ovulated within 4 days of ram introduction and premature regression of the CL had occurred between days 4 and 8 in 8 ewes and days 6 to 10 in 2 ewes. A second ovulation was observed after or during the premature regression of the first CL and this subsequent CL was maintained for the normal duration. The prematurely regressing CL produced a small peak in progesterone concentration on days 4 to 5 but the concentrations declined on days 6 to 7. In the unoperated ewes 50% (-10/20) appeared, from the progesterone profiles, to have ovulated by day 4 and half of these appeared to have premature CL regression. The interval from introduction of the ram to first oestrus was 23 days in ewes with premature regression of the CL and 19 days in ewes ovulating within 4 days but having no premature regression. From the results it was concluded that the premature regression of the CL is the cause of the delayed interval from ram introduction to first oestrus in Romney ewes and is a major factor contributing to the two peaks of oestrous activity observed after ram introduction.

Haemoglobin types, blood parameters and erythrocyte glutathione in the New Zealand Romney and other breeds.

Abstract From a study of approximately 1000 New Zealand Romney ewes from different areas of New Zealand it was found that the mean packed cell volume of sheep of haemoglobin type B Hb B was significantly lower than for haemoglobin type A (Hb A) sheep. The mean Hb A gene frequency was 0.60. The concentrations of reduced glutathione (GSH) in the erythrocytes of these Romneys followed a normal distribution, the mean being 67.1 ± 12.4 mg GSH per 100 ml erythrocytes. The concentration of GSH in selenium deficient sheep was significantly higher than for selenium adequate sheep. The concentrations of the selenium-containing enzyme, glutathione peroxidase in the erythrocytes and of copper in the plasma of Hb B sheep were significantly higher than for Hb A sheep. When different breeds of sheep on Mana Island were compared, the Finnish Landrace had significantly less ferroxidase in their plasma than did other breeds.

Effects of PMSG and the prostaglandin F-2 alpha analogue, cloprostenol, on superovulation, fertilization and egg transport in the ewe.

Romney ewes were artificially inseminated at the oestrus after treatment with PMSG on Day 12 of the cycle, Cloprostenol on Day 14, or both. PMSG resulted in increased numbers of ovulations and large follicles but Cloprostenol had no effect alone or with PMSG, PMSG and Cloprostenol alone led to reduced proportions of eggs fertilized, and PMSG also reduced the proportion of ewes with fertilized eggs. The distribution of eggs in the reproductive tract indicated more rapid egg transport in ewes treated with PMSG. A greater proportion of eggs was recovered from the uterus in ewes in which oestrus was first detected at night. Cloprostenol, as administered to PMSG-treated ewes in this trial, offered no advantage for the preparation of donor ewes for egg transfer.

Responses to abomasal infusions of casein plus methionine in lactating ewes fed fresh pasture

Abstract Twin-bearing Romney ewes were fed fresh pasture of 80% organic matter digestibility (11.4 MJ ME per kg DM) and 3.5% N ad libitum for 6 weeks during early lactation. Eight of the 18 ewes were given a daily abomasal infusion of 95 g sodium caseinate and 2 g l-methionine. Voluntary pasture DM intake did not significantly differ between control and infused ewes. The infusions had no effect on milk secretion at peak lactation (week 1), but the decline in net rates of protein and fat secretion as lactation progressed was less for infused than for control ewes. Wool production rates were low, and were unaffected by the infusion treatment. The quantity of amino acid N estimated to have been absorbed from the small intestine was respectively 85% and 110% of that required to sustain the levels of milk and wool production that were actually recorded in control and infused ewes. The absence of a difference in milk production between the two groups of ewes at peak lactation may have been due to greater mobilisation of body protein reserves by the control ewes. The higher plasma concentration of growth hormone observed in the infused ewes was probably implicated in their improved lactation persistency.

Onset of mating activity in Romney ewes after short periods of teasing

Abstract In 1½-and 2½-year-old Romney ewes teased with vasectomised Dorset rams for 24h in a 0.1 ha paddock, mean interval to first mating was 2.5 days shorter than in isolated ewes. Teasing for 14days in 7- to 10-hapaddocks reduced the interval by 5.4 days. Teasing 2½-and 3½-year-old Romney ewes with entire Dorset rams for 48 hin a 0.1 ha paddock, and with vasectomised Dorset rams for 17 days in 7-to 10-ha paddocks, were equally effective at stimulating the onset ofmating activity: 30 and 34% respectively ofewes were mated in the first 14 days of entire joining compared with 18% of isolated ewes. The earlier onset of mating activity of teased ewes was only partially reflected in the lambing pattern because ofthe lower conception rates in the first 14 days of entire joining in teased (49% and 63%) than in isolated ewes (76%). Apart from a small negative correlation (r = -0.13) in 1½-year-old ewes between pre-joining live weight and interval to first mating, neither pre-joining live weight in mature ewes n...

Source of ram pheromones that stimulate ovulation in the ewe

The wool and wax collected from entire Dorset rams contained odoriferous substances (pheromones) that stimulated 48% of a group of Romney ewes to ovulate in 5 days. The response was similar to that obtained in ewes running with Dorset rams. Only 7% of the ewes isolated from rams ovulated in the same period. Ram urine was not found to be a major source of the pheromone.

EFFECTS OF AZAPERONE AND ACETYLPROMAZINE ON SOCIAL AND ENVIRONMENTAL BEHAVIOUR IN SHEEP

1 Acetylpromazine (Acp, 0.05, 0.1 and 0.5 mg/kg) and azaperone (Azp, 1.0, 1.25 and 1.5 mg/kg) were given by intramuscular injection to separate groups of seven familiar Romney ewes. Thirty minutes after injection the sheep were led into a featureless arena and spatial distribution, activity and shade preference were monitored for 20 min by overhead photography. 2 Behavioural response was complex with both stimulant and depressant effects being seen. The response trends with increasing time for all three measures were significantly different for the two drugs. In particular, Azp tended to increase animal dispersion and Acp to decrease it, in agreement with earlier predictions. 3 The dosage range for Azp was adequate for reduction of individual movement and inter-animal distance but steady state effect was not reached in the time period studied. All doses of Azp initially caused disorientation, as measured by shade preference,, but this improved as sedation deepened. 4 The highest dose of Acp (0.5 mg/kg) achieved steady state effect on individual movement within the study period. The three doses of ACp caused either no change or a slight increase in inter-animal distance. Disorientation with Acp was less and briefer than that seen with Azp.

Reproductive performance of ewes grazing red clover (Grasslands Pawera) or white clover—grass pasture at mating

Abstract One hundred 3½ to 4½-year-old Romney ewes grazed a pure sward of ‘Grasslands Pawera’ red clover from 8 days before to 17 days after the beginning of mating; a similar group of ewes (Controls) grazed white clover-grass pastures. The formononetin content of the leaf material (dry matter basis) of Pawera at the start and end of grazing was 1.2% and 0.8% respectively. Compared with controls, fewer of the ewes grazing Pawera were mated during the first cycle (80% v. 100%). Over three cycles of mating, 66% of ewes that grazed Pawera returned to service at least once compared with 22% of Control ewes. Mean ovulation rates on day 18 of mating were lower for ewes grazing Pawera than Control ewes (0.79 v. 1.55 ovulations/ewe examined). Of the ewes grazing Pawera 24 were anovular. Lambing performances reflected mating records, with 25% of Pawera ewes lambing to the first cycle of mating (lambs born/ewe lambing (LB/EL) = 1.00); in comparison, 75% of Control ewes lambed to the first cycle of mating (LB/EL = 1.52). These results are consistent with other published work on the effect on ewes of exposure to large amounts of exogenous oestrogens at mating.

Fat content of heavy-weight lamb carcasses of several breeds and crosses

Abstract Southdown, Dorset Down, Poll Dorset, Suffolk, Coopworth, and Romney rams were mated to Romney, Coopworth, and Border-Corriedale ewes, and the lambs taken to carcass weights in the range 16–20 kg. Fat thickness and carcass composition measurements were made. At 18 kg carcass weight fat thickness over the eye muscle varied from 7.0 mm in the Southdown cross lambs to 4.4 mm in those by the Poll Dorset and Suffolk, and at 12th rib 11 cm from mid-line from 12.8 mm (Southdown) to 9.7 mm in the Poll Dorset and Suffolk. Fat varied from 36.7% in the Southdown to 32.8% in the Coopworth and Romney and to 28.8% in the heavy Down breeds at 18 kg. Even the best breed combination exceeded the optimum fat level and thus emphasises the problem of producing heavy-weight lambs which are lean.

Lactation performance, growth, and carcass composition of sheep

Abstract Milk production of Romney, Corriedale, Dorset, Romney × Dorset, and Dorset × Romney ewes was measured in relation to lamb growth in experiments carried out over 3 years (1972–74). Single- and twin-suckled Dorset ewes produced 26–63% and 35–88% more milk (125–132 kg and 133–220 kg respectively) than single- and twin-suckled Romneys during the initial 9 weeks of lactation. Over the same lactation period, milk production in twin-suckled Corriedale ewes was intermediate (117 kg) between Dorsets and Romneys rearing twins during the 1972 season. Crossbred ewes suckling single lambs showed lev('ls of heterosis for milk production ranging from 6% to 15%. Ewe breed differences in lamb growth performance were less evident than those for milk yields, although by weaning (12 weeks old) twin lambs reared by Dorset ewes were up to 20% heavier (31.6 kg) than twin lambs reared by Romneys (26.3 kg). The correlation between lamb live weight and milk yield over 9 weeks of lactation ranged from 0.53 to 0.70 and 0.17 to 0.51 for single- and twin-suckled lambs respectively. The milk components of protein and solids-not-fat were significantly correlated with lamb live weights. Ewe live weights were generally greatest for Dorsets, with the exception of the 1972 experiment; crossbred ewes showed 4% to 7% heterosis.

Relationship between plasma progesterone in late gestation and the incidence of dystocia in romney ewes

Thirty-eight percent ( 6 16 ) of the ewes with a previous history of dystocia and 15% ( 2 13 ) of the ewes with no dystocia in 4 lambings, had difficult births in 1976. Despite large variations in plasma progesterone concentrations among ewes at the same stage of gestation there were no differences in the progesterone concentration during the last 30 days of gestation for both single- and twin-bearing ewes with or without a history of dystocia, nor for single-bearing ewes with or without a dystocia. The progesterone concentrations declined during the last 10 days before parturition in ewes with and without dystocia. The lambs from single-bearing ewes with a dystocia did not have heavier birth weights than the lambs from single-bearing ewes without a dystocia.

Studies on dystocia in sheep II: Pelvic measurements of ewes with histories of dystocia and eutocia

Abstract Three groups of mature Romney ewes (⪖ 4 years of age), with different histories of lambing performance, were radiographed to obtain measurements of pelvic dimensions. The ewes in Group I had all been assisted to lamb at least once (group mean 2.3), whereas the ewes of Groups II and III had histories of freedom from dystocia. Group II ewes were selected from a commercial flock and the Group III ewes from a closed flock that had been unshepherded at lambing for approximately 40 years. Pelvic inlet area (conjugate diameter × transverse diameter) differed between groups such that Groups II and III had larger pelvic areas than Group I ewes (p<0.01). Size of the pelvic inlet in relation to birth weight of the lambs also differed between groups, and Group III ewes had the largest, and Group I ewes the smallest, relative pelvic inlet area. Significant correlations were recorded between a number of internal and external pelvic measurements, but were not considered high enough to be of use in predicting internal pelvic dimensions from external measurements. Differences were observed in correlations between internal and external measurements of different groups of mature ewes. Similarly, differences in correlations between internal and external pelvic measurements were found in different age groups, when an additional two groups of 2 and 3-year-old ewes were obtained from the Group III flock, and compared with the mature ewes of that flock. It was concluded that an incompatibility in size between the maternal pelvis and the lamb at birth is largely responsible for the need for repeated assistance at birth. Selection for large pelvic-inlet area by using external measurements (as a means of reducing the incidence of dystocia in the flock) was shown to be impracticable. Furthermore, such a policy ignores the importance of birth weight. Selective breeding for freedom from dystocia in both ewes and rams appears to be a more effective way of overcoming the problem of lambing difficulties.

Genetic and phenotypic parameters in New Zealand Romney sheep

Genetic and phenotypic parameters were estimated from 4 annual lamb drops in an experimental flock of 1050 Romney ewes. Progeny were sired by 133 different rams drawn initially from a wide range of industry sources and subsequently selected at random from within the flock. Traits analysed were: growth from weaning (3 months) to 16 months of age, fleece weights of lambs (4 months) and of hoggets (13 months), and number of hogget oestrus occurrences. Relevant records were available on all live progeny as well as on parents born in the flock in the first 2 years. Within years, the principal environmental sources of variation for live weights and fleece weights were age (birth date), birth—rearing rank, and age of dam, all of whose effects diminished as animals grew older; and sex-management group, whose effects increased markedly with age. Of these factors, only date of birth significantly influenced number of hogget oestruses. Interactions among environmental factors were of little importance. For genetic analyses, records were first adjusted for environmental effects. Heritabilities of live weights increased up to about 10 months of age (0.34) and thereafter declined. Likewise, they were about twice as high for hogget as for lamb fleece weights.The estimates were comparable with previous published New Zealand findings except for higher values for hogget fleece weight (0.29) and lower values for weaning weight (0.08), hogget live weight (0.27), and live-weight gain (range 0–0.19). The number of hogget oestruses showed a heritability of 0.31. A striking and consistent finding was the higher heritability estimates for female than male progeny. For July (10 month) live weight the values were 0.46 and 0.21 respectively; corresponding estimates for hogget fleece weight were 0.41 and 0.27. Higher environmental and lower genetic variances among males were implicated. Heritabilities calculated from offspring–sire regression agreed with those from paternal half-sib analyses, whereas offspring—dam regression estimates were substantially higher for most live weights but similar for hogget fleece weight. Both phenotypic and genetic correlations among live weights and number of hogget oestruses were lower than in a previous New Zealand study. Phenotypic and genetic (paternal half-sib) correlations between fleece weight and post-weaning live weights were in the range 0.38–0.52, but genetic correlations estimated from offspring—parent relationships were much lower. Lamb and hogget fleece weights showed a strong genetic correlation (0.80). The results are discussed in relation to the expected genetic progress from direct and indirect selection and two-stage selection. To improve weaning weight, more progress per generation can be expected by selecting on yearling weight than weaning weight itself. Two-stage selection, with preliminary selection at weaning and final selection at the yearling stage, is expected to lead to the same genetic progress as selection on yearling weight alone and may be more acceptable in practice.

The ovarian and hormonal response of the ewe to stimulation by the ram early in the breeding season

The introduction of Dorset rams to Romney ewes at the beginning of the breeding season (February 14 to March 1) stimulated 39% to 70% of the non-cycling ewes to ovulate. Most of the ewes that ovulated did so within 65 to 72 hours of ram introduction. The ovulations were preceded by LH peaks, the mean onset of which was 35.0±4.8 (SE) hours after ram introduction. The mean oestradiol-17β concentration per ewe ranged from 0.3 to 14.9 pg/ml plasma and there were large fluctuations among the samples collected every 3 hours. All ewes, irrespective of treatment, had similar mean concentrations of oestradiol-17β and ovarian follicular activity, and there were no changes in oestradiol-17β concentration that could be attributed to the presence of the rams.

Testosterone levels in Dorset and Romney rams and the effectiveness of these breeds in stimulating early onset of estrus in Romney ewes

Groups of Romney ewes were joined with either Dorset or Romney rams on December 24 1975 and further groups joined on January 30 1976. A control group was subjected to laparotomy and joined with Romney rams after first ovulation was observed. Matings were recorded daily in all groups. At weekly intervals rams were separated from ewes and bled every 10 minutes for one hour. The plasma was radioimmunoassayed for testosterone. Ewes run with rams showed their first estrus of the breeding season earlier than controls and their onset was more synchronised. The time of ram joining did not affect the time of first estrus but ewes joined with Dorsets showed their first estrus earlier than those with Romneys. Romney rams had significantly higher mean testosterone levels than Dorsets on 5 of the 11 weekly bleedings throughout summer. The testosterone level decreased significantly over the seven consecutive bleedings of the hourly sampling period in five weeks and a significant interaction between breed of ram and testosterone level of consecutive bleedings was observed in three weeks. The results show that testosterone levels in Dorset and Romney rams during summer do not reflect the effectiveness of the breeds in inducing the early onset of estrus in Romney ewes.

Comparison of lamb carcasses sired by Southdown with those sired by Dorset Down or Suffolk rams mated to Romney ewes

Abstract Ten progeny were examined from each of five Southdown sires, three Suffolk sires, and two Dorset Down sires all mated to Romney ewes. The lambs sired by Suffolks and Dorset Down rams grew faster than those sired by Southdown rams. The Suffolk cross lamb carcasses contained more meat and less fat than those of the other breeds.

Flock mating in sheep

Abstract Romney rams were joined with Romney ewes in two experiments. When groups of two-tooth and six-tooth rams were joined with either 200 or 400 ewes, ram age had no effect on numbers of ewes mated. Fertility of ewes mated by rams of each age group was similar. In a second experiment groups of 4 two-tooth rams were compared with groups of 4 six-tooth rams when joined with either 240 or 720 ewes. Two-tooth rams each mated with a lower percentage of the total number of ewes in oestrus than did each of the six-tooth rams (P < 0.01). Fertility of ewes mated with rams of each age group was similar. During 8 h continuous observation sexual activity differed little between the ram age groups when run with 14 oestrous spayed ewes, but six-tooth rams were more active when run with 42 such ewes. In a 24 h period almost all of the 42 ewes were marked by both ram age groups, although two-tooth rams each marked a lower number of ewes than the six-tooth rams (20.4 v. 29.9 respectively. P < 0.01). Most rams were capable of at least 10 services in 8 h (range 0–30).

Wool production of different breeds of mixed-age ewes on hill country

Abstract Greasy fleece weight, staple length, quality number, character, and severity of staple unsoundness and cotting were recorded from Romney, Coopworth, Perendale, Cheviot, and Dorset-Romney ewes over 7 years. All breeds were grazed together except during mating. Romney had the heaviest fleece weight followed by Coopworth, Perendale, Dorset-Romney and Cheviot. Fleece weights increased to 3 or 4 years of age and declined to 5 years of age, Coopworth and Perendale showing the greatest decline. All breeds except Romney showed a decline in fleece weight associated with fertility status, dry ewes having the heaviest fleeces. Romney ewes rearing their own single lamb had higher fleece weights than dry ewes. The subjectively assessed fleece characteristics were not influenced by fertility status. Romney and Coopworth had a higher proportion of cotted fleeces than the other breeds and Cheviot had the highest proportion of fleeces with staple unsoundness. Increased staple unsoundness was associated with lower fleece weights for all breeds, but only Romney and Coopworth showed a decline in fleece weight with increased cotting.

THE EFFECT OF PASTURE ALLOWANCE ON THE PERFORMANCE OF DIFFERENT BREEDS OF SHEEP

In a trial conducted at Ruakura over 5 years, mixed-age flocks of Coopworth, Perendale, High Fertility Romney and Control Romney ewes were run on separate farmlets stocked at 26, 21 or 16 ewes/ha. At any given pasture allowance the Coopworth ate more pasture than the other breeds. Lambing performance, weight of lamb weaned and fleece weight were curvilinearly related to allowance. Lamb production per ewe tended to level out at a DM allowance of 4 kg/ewe/day for the Perendale and about 5 kg/ewe/day for the other breeds. Pasture allowance accounted for an appreciable amount of variation in animal production between years and stocking rates; litter size, 38 to 90%; lambs weaned/ewes mated. 29 to 71'%; weight of lamb weaned/ewe mated, 26 to 62%; and fleece weight, 25 to 49%. Pasture allowance accounted for the least variation in all variables in the Perendale compared with the other breeds.