Blackface Ewes Research Articles

Effect of suppression of plasma prolactin on ovulation, plasma gonadotrophins and corpus luteum function in LH-RH-treated anoestrous ewes

Nineteen Scottish Blackface ewes were given LH-RH (3 X 30 micrograms i.v., 90-min intervals) during anoestrus when prolactin levels were elevated. Plasma levels of prolactin were suppressed with CB 154 (twice daily, i.m.) on Days -5 to 0 (N = 5), 0 to +5 (N = 5) or -5 to +5 (N = 5) around the day of LH-RH treatment (Day 0). Control animals (N = 4) received saline on Days -5 to +5. Nine animals ovulated forming corpora lutea as judged by laparoscopy on Day +7. No difference in FSH or LH levels was found between treatments and ovulations occurred equally in all treatment groups. Progesterone levels were less than ng/ml in all animals up to Day 14. It is concluded that short-term suppression of prolactin does not affect the incidence of ovulation or corpus luteum progesterone production in LH-RH-treated anoestrous ewes.

Concentrations of free amino acids in maternal and fetal plasma from conscious catheterised ewes during the last five weeks of pregnancy

Concentrations of amino acids, urea, glucose, fructose and corticosteroids were measured in maternal and fetal plasma from nine Scottish Blackface ewes during the last 35 days of pregnancy. During this period maternal plasma levels of most amino acids did not change significantly. In fetal plasma the concentrations of most amino acids decreased or remained relatively constant until about 20 days before birth (day -20) and then increased as term approached. Glucose levels in plasma from both sources did not change, but urea concentrations rose to maximum values about day -20. Except for valine and isoleucine, the concentrations of amino acids in fetal plasma varied independently of levels in maternal plasma up to day -20, but thereafter 10 amino acids, including seven essential amino acids, showed a significant positive correlation with maternal values. Possible causes of the observed variations in fetal plasma composition are discussed.

Lactation pattern in Scottish Blackface and East Friesland × Scottish Blackface cross-bred ewes

SummaryMilk yield of 2-year-old Scottish Blackface and of East Friesland × Scottish Blackface ewes rearing single or twin lambs was estimated by the oxytocin method on 1 day each week up to the 14th week of lactation. Both groups of ewes had been reared from birth under good nutritional conditions. They were housed in individual pens from mid-pregnancy and offered a liberal ration of a pelleted concentrate food until parturition. Similar food was offered ad libitum during lactation.The cross-bred ewes rearing singles or twins produced significantly more milk in the first 12 weeks (181 and 258 kg respectively) than did pure Blackface ewes in the same period (144 and 208 kg respectively). The pattern of lactation differed between breeds. Cross-bred ewes attained higher maximum yields between the second and sixth weeks (2·37 and 3·32 kg/day, respectively, for single- and twin-suckled ewes) than did the Blackface ewes (1·97 and 2·88 kg/day). The yield from the cross-breds was sustained at a higher level throughout lactation. In the third 4-week period cross-bred ewes rearing single and twin lambs produced 116 and 92%, respectively, of their yield in the first 4 weeks whilst Blackface ewes produced 87 and 65%, respectively.In the sixth week of lactation the milk produced by the two breed groups was similar in quality (mean value of solids-not-fat 11·04% and fat 5·48%) but by the 11th week the fat percentage of milk produced by Blackface ewes had increased significantly to 7·34% whereas that of the cross-breds had remained almost unchanged.Single-suckled ewes gained weight throughout lactation but twin-suckled ewes remained relatively constant. Lambs reared as singles by cross-bred or Blackface ewes reached a mean live weight of 36·2 and 35·0 kg at 102 days of age, respectively, compared with 33·6 and 30·1 kg for twin lambs. Food intake of all ewes increased until the fifth or sixth week of lactation.

A consideration of the techniques for estimation of milk yield by suckled sheep and a comparison of estimates obtained by two methods in relation to the effect of breed, level of production and stage of lactation

SummaryThree techniques, lamb-suckling and test-weighing, hand- or machine-milking following administration of oxytocin, and measurements of body-water turnover, used for the estimation of milk yield in suckled sheep are discussed in relation to sources of error and comparability of estimates.Results are presented from an experiment in which the lamb-suckling and the oxytocin techniques were compared. The mean daily milk production of Scottish Blackface and East Friesland × Scottish Blackface ewes suckling single and twin lambs was measured by both methods at weekly intervals for 6 weeks. All ewes were well nourished to ensure full expression of milking capacity. Additional information from a similar experiment on Merino ewes is also presented.The oxytocin method gave higher estimates of mean daily milk yield in the first week of lactation, especially in the groups of ewes rearing single lambs and in the Blackface breed. By the second week in most groups and the third week in all groups there were no significant differences between estimates made by the two methods and the relative values of the estimates were not affected by level of milk production, number of lambs suckled or genotype of ewe and lamb.

The relationship in ewes between voluntary food intake during pregnancy and forage intake during lactation and after weaning

ABSTRACT(1) Voluntary intake of forage was measured in 31 Scottish Blackface ewes for the last 14 weeks of pregnancy, throughout lactation, and 15 weeks subsequently. During pregnancy 15 ewes were given hay and 16 dried grass (apparent dry-matter digestibilities in vitro were 51 and 69·6% respectively). All ewes were given the same dried grass during lactation and after weaning (digestibilities 75 and 73% respectively). Body fat was estimated from tritiated water space.(2) Pregnant ewes consumed twice as much digestible dry matter from dried grass (1028 g) as from hay (502 g). Intakes of ewes with twin and single foetuses were similar.(3) During lactation the mean daily intakes of dried grass were 2278, 2610,2612 and 2722 g dry matter respectively, for ewes that had been given dried grass in pregnancy and had single and twin lambs, and for those that had been given hay and had singles and twins. Differences between dried grass and hay were consistently significant (P < 0·01).(4) After weaning the intakes declined rapidly but their ranking remained similar.(5) Lamb birth weights were affected by nutrition during pregnancy, lamb growth rates within twins or singles were not influenced by maternal nutrition during pregnancy or lactation. Differences in ewe intakes during lactation were reflected in ewe body-weight changes.(6) For all ewes, up to 64% of the variation in intake during lactation could be related to factors prevailing before and at lambing (pregnancy diet, ewe weight and fat content) and during lactation (lamb gain and ewe weight change).

ACTIVE IMMUNIZATION OF EWES AGAINST LUTEINIZING HORMONE RELEASING HORMONE, AND ITS EFFECTS ON OVULATION AND GONADOTROPHIN, PROLACTIN AND OVARIAN STEROID SECRETION

Three Scottish Blackface ewes were immunized against luteinizing hormone releasing hormone (LH-RH) conjugated to bovine serum albumin (BSA) and three control ewes were immunized against BSA alone. When the antibody titre to LH-RH became raised the treated animals failed to show oestrus or ovulate; they had significantly lower levels of plasma luteinizing hormone (LH) and higher levels of prolactin than the controls, whereas the levels of follicle-stimulating hormone (FSH) were unaltered. The integrity of the hypothalamus-pituitary-gonadal system of these animals was then challenged by the injection of a highly active analogue of LH-RH and by ovariectomy. An i.v. injection of 5 microgram D-serine-t-butyl 6 des-glycine-NH2 10 LH-RH ethylamide raised plasma LH and FSH. Ovariectomy caused an eight- and ninefold rise in plasma levels of LH and FSH respectively in controls, but failed to increase plasma levels of LH and FSH in the LH-RH-immunized ewes. Plasma prolactin concentrations in the LH-RH-immunized ewes were significantly reduced by ovariectomy.

Reproductive performance of ewes mated to rams heterozygous for the Massey I (t1) centric fusion (Robertsonian) translocation.

One hundred Scottish Blackface ewes were mated to New Zealand Romney rams heterozygous for the Massey I (t1) centric fusion (Robertsonian) translocation. The lambing percentage of ewes lambed was 131 and the segregation of normal to balanced heterozygous lambs was 1:1. No chromosomally unbalanced lambs were born. Nine heterozygous females were mated to a heterozygous male and produced two homozygous, three heterozygous and seven normal lambs. The homozygous male had hypoplastic testes. The results indicate that there is no significant reduced fertility with 53XYt1 rams but that fertility of 52XYt1t1 rams should be further investigated.

Oestradiol levels in sheep plasma during the oestrous cycle.

The concentration of oestradiol was measured by radioimmunoassay in ovarian venous plasma collected from ewes of three breeds (Finnish Landrace, Scottish Blackface and Tasmanian Merino) on Day 9 of the oestrous cycle and in jugular venous plasma collected daily around oestrus in two of these breeds. The mean +/- s.e.m. concentration in the ovarian venous plasma of the Merino (44.1 +/- 7.6 pg/ml) was lower than that in Blackface (72.2 +/- 10.2 pg/ml) and Finn ewes (66.8 +/- 10.2 pg/ml). The overall fitted mean concentration in peripheral venous plasma was 1.7 pg oestradiol-17beta/ml, with no difference between the Finn and Blackface ewes, in which the highest preovulatory values were 3.9 +/- 0.5 and 3.4 +/- 0.5 pg/ml respectively.

Pattern of intake of three roughage diets by non-pregnant, non-lactating Scottish Blackface ewes over a long period and the effects of previous nutritional history on current intake

ABSTRACTThe voluntary intake of two hays and one dried grass by 48 mature non-pregnant Blackface ewes was measured for 33 weeks. The apparent dry-matter digestibility coefficients of the diets in vitro were 59, 61 and 77% respectively for the hays and the dried grass. At the end of the first phase of the experiment each group of 16 ewes was split into two subgroups of five animals, each of which was subsequently given one of the other diets, and one subgroup of six animals which remained on the same diet. Food intake was measured for a further 8 weeks. Body fat was estimated at intervals from tritiated water space.The amount of variation in voluntary food intake that could be attributed to variation in live weight and fatness of the animals and in apparent dry-matter digestibility and cell wall constituents of the diet was calculated for various periods.The range of live weight and fatness increased during the experiment. Initially, and after the change in diets, variation in apparent dry-matter digestibility had an important positive effect on intake, but at the end of the 33-week phase its influence was negligible or, when fat weight was not considered, negative. The negative effect of fat weight on intake increased during the experiment.Within individual diets during short periods of time (1 to 5 weeks) the highest proportions of the variation in intake that could be attributed to variation in live weight and fatness of the ewes were 50, 94 and 65% respectively for the hays and the dried grass. Taking all three diets together all the variables considered could explain 75% of the variation for a few weeks at a time, but for longer periods seasonal influences, and other factors not included among the independent variables, probably operated.

Relationships between energy intake, nutritional state and lamb birth weight in Greyface ewes

SummaryIndividual feed intakes of housed mature Greyface (Border Leicester × Scottish Blackface) ewes were adjusted weekly to maintain plasma 3-hydroxybutyrate concentrations during the final 6 weeks of pregnancy at the following values: treatment 1 (adequately nourished; 17 ewes) less than 0·7 mmol/1; treatment 2 (moderately undernourished; 15 ewes) at about 1·1 mmol/1; treatment 3 (severely undernourished; 15 ewes) at about 1·6 mmol/1.The mean energy intakes (MJ metabolizable energy (ME)/day) required to maintain the prescribed nutritional states in single- and twin-bearing ewes were: treatment 1, 14·3 and 16·3; treatment 2, 10·6 and 11·6; treatment 3, 8·1 and 10·0 respectively.The moderate degree of undernourishment had no significant effect on the birth weight of single lambs, but reduced the birth weight of twins by 8·2%, while the more severe undernourishment reduced the birth weights of singles and twins by 21·5 and 25·8% respectively.Foetal energy requirements, estimated by regression analysis, appeared to decrease from more than 2 MJ ME/kg/24 h at 35 days prepartum to 1·54 MJ ME/kg/24 h in the week before parturition.The amounts of energy required to sustain the nutritional states of treatments 1–3 in non-pregnant ewes were calculated to be 348, 271 and 231 kJ ME/kg0.75/24 h, compared with a maintenance requirement, determined in this experiment, of 344 kJ ME/kg0.75/24h.It is concluded that in individually fed ewes a nutritional state characterized by plasma 3-hydroxybutyrate concentrations of 1·1 mmol/1 would constitute an acceptable compromise between an uneconomically high energy input and an excessive reduction in lamb birth weight.

The relative susceptibility of Soay and Blackface sheep to natural infection with Dictyocaulus filaria

Simultaneous studies by faecal larval counts on a mixed flock of Blackface and Soay ewes, yearlings and lambs suggested that the Soay animals were less able to develop resistance to Dictyocaulus filaria. This susceptibility resulted in a greater proportion of the Soay ewes developing heavy burdens of these lung worms, and in a greater proportion of the yearlings and ewes excreting D filaria larvae in their faeces.

The effects of two nutritional environments from 6 weeks pre partum to 12 months of age on lifetime performance and reproductive potential of Scottish Blackface ewes in two adult environments

SUMMARYIn one experiment, 227 female sheep in two age groups were reared on low (107 sheep) and high (120 sheep) levels of nutrition from birth to 12 mo of age after their dams had been given low and high levels of nutrition during the last 6 weeks of pregnancy. From 12 mo, 47 of the low-level sheep and 51 of the high were grazed on poor hill pasture to provide a low-level adult nutritional environment while 46 of the low level and 52 of the high were grazed on good quality pasture to provide a high-level adult nutritional environment. These treatments were continued for 5 production years for one age group and 4 production years for the other.Live-weight differences associated with rearing treatment persisted throughout the experiment in both adult environments. Lifetime lamb production was significantly affected by both rearing and adult treatments.The effects of these treatments on reproductive potential were examined in a second experiment by determination of ovulation rate when the sheep were brought into uniform good body condition at mating after the end of the first experiment. Potential ovulation rate was significantly affected by rearing treatment but not by adult treatment, although live weight and body size were affected by both.It is concluded that while reproductive potential is related to body size it may also be influenced by the pattern of early growth during unidentified developmental stages.

Seasonal variation in oestrus and ovarian activity of Finnish Landrace, Tasmanian Merino and Scottish Blackface ewes

SUMMARYThe patterns of seasonal variation in reproductive activity were observed over a period of 15 mo for approximately 15 females of each of three breeds: Finnish Landrace (Finn), Tasmanian Merino (Merino) and Scottish Blackface (Blackface). The incidence of oestrus was measured by teasing with vasectomized rams, and the incidence and rate of ovulation were determined frequently by laparoscopy. Luteal function was assessed from peripheral venous blood progesterone concentration on days 7 and 11 of the oestrous cycle. Nutritional status was monitored by recording body weight and plasma-free fatty acid levels throughout the study.The breeding seasons differed significantly: Finn, October to May; Merino, September to February; and Blackface, October to February. Variation in the incidence of ovulation was similar to that in the incidence of oestrus for each breed. The incidence of silent ovulation varied with the breed, being greatest in the Merino and least in the Finn. The ovulation rate varied among breeds (Finn, 2·99; Merino, 1·08 and Blackface, 1·30), and during the breeding season (e.g. Finn: November, 3·5; March, 2·6). Follicles were observed in each breed throughout the period of study.The pattern of variation in progesterone concentration was similar for each breed despite their different breeding seasons. In addition to breed differences in ovulation rate and in onset and end of the breeding season, the sensitivity to oestrogen was apparently such that, with the Finn if oestrogen secretion was high enough to stimulate ovulation it would usually also stimulate oestrus, whereas with the Merino ovulation often occurred without oestrus; this suggests that in the Merino the centres controlling ovulation are more sensitive to oestrogen than those controlling behaviour.

The reproductive performance of Finnish Landrace × Dorset Horn and Border Leicester × Scottish Blackface ewes mated three times in 2 years

SUMMARYThe reproductive performance of 51 Finnish Landrace × Dorset Horn (FD) ewes was compared with that of 50 Border Leicester × Scottish Blackface or Greyface (GF) ewes. Ewes were mated without hormone synchronization in November 1973 and with hormone synchronization in August 1974 and again in February 1975. Conception rates at the three matings were 88, 82 and 73% respectively in FD ewes and 96, 56 and 26% respectively in GF ewes. Mean litter size over three lambings was 2·34 in FD ewes and 2·15 in GF ewes. Stillbirths accounted for 12·0 and 10·2% of all lambs respectively and further lamb deaths during and after birth were 15·2 and 4·3% respectively; 11·6% of live FD lambs and 7·7% of GF lambs were fostered or reared artificially. The losses resulted in mean numbers of lambs weaned per ewe lambing of 1·75 from FD ewes and 1·85 from GF ewes (including lambs from those ewes that were artificially reared). Annual productivity was 2·13 and 1·67 lambs respectively.

The survival of embryos transferred in large groups to sheep of breeds with different ovulation rates

SUMMARYThe possibility that embryo survival in a breed of sheep may be related to the number of embryos normally present after natural mating was investigated by transferring large numbers of embryos to sheep of breeds with an approximately two-fold difference in ovulation rate. When the same number of embryos (14) was transferred to each of 12 Scottish Blackface and 11 Finnish Landrace ewes survival was greater in the Finn ewes (10%) than in the Black-faces (4%). The survival of 28% of embryos when transferred in groups of 7 to each of 14 Scottish Blackface ewes indicated that survival was not similar in the two breeds when the number of embryos present was a similar multiple of their natural ovulation rates. When the number of embryos transferred to Scottish Black-face ewes increased from 7 to 14 the decline in survival rate was so great that the number of lambs born also declined, indicating an intermediate optimum ovulation rate for maximum litter size.

Effects of starvation, surgery and infusion of adrenocorticotrophin on plasma amino acid concentrations in the pregnant ewe

Total plasma amino acid concentrations (TAA) in 12 Scottish Blackface ewes between 80 and 140 days of pregnancy were unaltered by two days of starvation, but concentrations of essential amino acids (EAA) increased and non-essential amino acid (NAA) levels decreased. These trends were more pronounced later in pregnancy. Ewes fasted before surgery to implant fetal catheters showed marked reductions in mean TAA levels (--26 per cent, n-5) on the day after operation (day+ 1). Half of this decrease was accounted for by glycine. Mean concentrations of NAA increased after day +1 but by day +6 were still 15 per cent below baseline values. In contrast mean plasma concentrations of EAA were 31 per cent above prestarvation levels on day +6 and maximal on day +4(+39 per cent). Following a two-day fast, sheep given half rations and simultaneously infused with adrenocorticotrophin showed changes in plasma-free amino acid composition like those observed during the two days after operation. Disturbances to plasma amino acid concetrations persisted for up to 12 days after operation and are attributed to the preoperative starvation and the combined effects of irregular feeding patterns and elevated plasma corticosteroid levels during and after operation.

Cytogenetic examination of pre-implantation blastocysts of ewes mated to rams heterozygous for the Massey I (t1) translocation.

One hundred-and-two 13- to 18-day blastocysts were collected from 98 Scottish Blackface ewes mated to one of four New Zealand Romney rams heterozygous for the Massey I (t1) translocation. The karyotype of 75 blastocysts was established, of which 22 were 54,XY, 18 were 54,XX, 20 were 53,XY,t1, and 15 were 53,XX,t1. It is suggested that these results indicated that there was no increase in embryonic loss in ewes mated to rams heterozygous for the Massey I (t1) translocation and that the unbalanced secondary spermatocytes in heterozygous males probably did not mature to spermatozoa.

A comparison of the sown swards of perennial ryegrass S. 24 and Italian ryegrass RvP in a two-year lamb production system, with different breeds of sheep

SummaryA comparison was made between an intensive system of lamb production based on Italian ryegrass RvP and one based on perennial ryegrass S. 24, over 2 years, each at three stocking rates (14, 17, 20 ewes/ha). More grass was grown in the first year than in the second when the yield of RvP was particularly reduced. The ewes and lambs ate more RvP than S. 24 but there was no difference in lamb growth rate. The lambs grew faster at the low stocking rate from 0 to 18 weeks and from 0 to slaughter than at the medium and high stocking rates, in both years. Ewe intake and lamb growth rate were higher in the second year than the first. The Masham ewes with two lambs ate significantly more grass per unit of body weight than the Finnish Landrace × Scottish Halfbred and Finnish Landrace × Scottish Blackface ewes, and their lambs grew significantly faster. It was concluded that for an intensive system of lamb production from grass, S. 24 was more suitable than RvP.

A note on immunoglobulin concentrations in Scottish Blackface lambs born to 1- or 2-yr-old ewes

SUMMARYThe concentrations of maternal immunoglobulin in 2-day-old lambs born to Scottish Blackface ewes which had been mated when 6 to 7 mo old were significantly lower than in lambs born to these ewes a year later. But the mortality rates were almost identical. The concentrations in lambs born to the same ewes in successive years were significantly more highly correlated than the concentrations in lambs born to older females in successive years, examined in a previous study.

The sensitivity of the ovulation rate of Finnish Landrace and Blackface ewes to exogenous oestrogen.

Variation in ovulation rate among different sheep breeds or crosses has been found to be related to the characteristics of the preovulatory discharge of LH, but there is no marked association with the concentration of LH during the oestrous cycle (Land, Pelletier, Thimonier & Mauléon, 1973). Studies of the oestrogen-induced discharge of LH in ovariectomized ewes indicated that breeds with high ovulation rates may be less sensitive to the positive and negative feed-back effects of oestrogen than are those with low ovulation rates. It was postulated that a low sensitivity of gonadotrophin release to the inhibitory effects of gonadal steroids may enable ewes which normally shed large numbers of eggs to tolerate higher concentrations of plasma oestrogen before the release of gonadotrophins is reduced (Land, Wheeler & Carr, 1976). Breed differences in follicular development and ovulation rate would therefore be compatible with similar LH concentrations. Alternatively, animals of a high-ovulation breed might catabolize the steroid produced more rapidly, or might produce less per follicle, than those of a breed in which fewer follicles developed; Bindon, Blanc, Pelletier, Terqui & Thimonier (1975) found no differences in the peripheral plasma oestrogen concentrations of ewes of breeds with differing ovulation rates.