Texel Ewes Research Articles

Effects of progesterone treatment on ovarian and estrous activity and on LH pulsatility and PGF 2α concentration in suckling and non-suckling Texel ewes

Two experiments investigated the effects of low amounts of exogenous progesterone (P 4) on the resumption of estrous and ovarian activity and on luteinizing hormone (LH) pulsatility and prostaglandin F 2α (measured as 13,14-dihydro-15-keto-PGF 2α, PGFM) concentrations in postpartum Texel ewes early after lambing. In Expt. 1, six single-suckling ewes received intravaginal devices containing 210 mg of native P 4, from d 4 ± 2 to d 16 ± 2 after parturition during the breeding season, and six others served as controls. The P 4 supplementation induced earlier return to estrus in single-suckling ewes (23 ± 7 vs. 37 ± 3 d, P < 0.01) and was not associated with subsequent inadequate luteal function. Duration of the first luteal function was shorter in three of the six control ewes. LH pulse frequency (per 6 h) was decreased during the period of P 4 supplementation and increased 1 d after removal of P 4 devices ( P < 0.01). Concentrations of PGFM were lower in P 4-treated ewes than in the control group ( P < 0.01). In Expt. 2, ewes either suckled one lamb or weaned soon after parturition and received intravaginal devices containing 210 mg of native P 4 from d 16 ± 3 to d 28 ± 3 post partum. The incidence of estrous behavior after P 4 supplementation was lower in suckling than in dry ewes ( P < 0.01), while ovarian activity resumed to the same extent in both groups and was not associated with inadequate luteal function as in Expt. 1. The P 4 treatment raised circulating P 4 to higher levels in weaned than suckling ewes ( P < 0.01). In both categories, LH pulse frequency was suppressed during the P 4 treatment and increased 1 d after the P 4 withdrawal ( P < 0.01). Weaning reduced significantly plasma PGFM concentrations ( P < 0.01). These results indicate that the positive effect of P 4 on the re-establishment of hypothalamo-pituitary functions prevents the premature regression of the CL after lambing. They strongly suggest that P 4 treatment reduces the interval between parturition and return to estrus and is more effective in dry than in suckling ewes.

The effect of subclinical intestinal nematode infection on the diet selection of growing sheep.

To test the hypothesis that subclinical gastrointestinal parasitism, associated with an impairment in N digestion and metabolism and a reduction in the voluntary feed intake (VFI), could affect the diet selection of sheep given a choice between two feeds that differed in their crude protein (CP) content, twenty-four Texel x Scottish Blackface ewe lambs growing from 28 to 48 kg live weight (LWT) were given a daily dose of 2500 larvae of the intestinal nematode Trichostrongylus colubriformis; twenty-four similar lambs were used as uninfected controls. Six infected and six control lambs were given a free choice between two pelleted feeds (10.4 MJ metabolizable energy/kg), with different CP contents (90 (L) and 214 (H) g CP/kg fresh feed respectively). In addition, eighteen parasitized and eighteen control sheep were given access ad lib. to either feed L, or feed H, or their mixture M (164 g CP/kg; twelve per feed), in order to quantify the effects of the feeds when offered alone, and to test for any interactions between feed CP content and parasitism on the performance of the lambs. Intestinal parasitism reduced significantly (P < 0.001) both the rates of LWT gain (by 30%) and VFI (by 10%). The adult and developing parasitic forms took 4 weeks to establish and develop to a significant adult worm population (as judged by the faecal egg counts and blood variables) and until then there was no effect of parasitism on the performance of the lambs. The diet selection of the lambs given a choice between two feeds was similar between the two groups in the first 4 weeks of the experiment, but differed significantly (P < 0.05) in the second part of the experiment (4th week to the end). Thus, while parasitized lambs had a reduced rate of feed intake, by changing their diet selection they achieved a daily rate of CP intake similar to the control ones. However, since the parasitized lambs had a reduced rate of LWT gain, they also consumed a higher total amount of CP to reach the same LWT. It is concluded that sheep infected daily with a small number of larvae of T. colubriformis and given a choice between two feeds that differ in their protein contents are able to modify their diet selection in order to meet the increased protein requirements resulting from such an infection.

Comparison of MOET in Texel ewe lambs and yearling ewes

Combined multiple ovulation and embryo transfer (MOET) from ewe lambs could significantly increase the rate of genetic progress in sheep improvement programmes (Smith, 1986). The benefits arise from a combination of an increased number of progeny from superior females and a reduction in the generation interval. Maximum success requires that the procedures are carried out in ewe lambs at six to seven months of age to produce offspring when the donors are one year old. Previous studies suggest that embryo quality and survival rates are naturally lower in ewe lambs and are likely to limit the success of MOET in this class of animal (Quirke and Hanrahan, 1977; McMillan and McDonald, 1985). The present study was undertaken to evaluate the potential of recently developed superovulatory procedures for application to ewe lambs.

Effects of hormonal manipulation on the resumption of postpartum reproductive activity in Texel ewes

Three experiments were conducted on Texel ewes to study the influence of prostaglandin F 2α (PGF 2α), prolactin (PRL), estradiol (E 2), and gonadotrophin releasing hormone (GnRH) on postpartum reproductive activity. In Experiment 1, oral administration of indomethacin (25 to 50 mg/day/ewe) from Day 3 post partum to the first detected estrus inhibited plasma 13, 14-dihydro-15-keto, PGF 2α (PGFM) concentrations (P < 0.0001). This treatment resulted in an earlier rise in the frequency and amplitude of luteinizing hormone (LH) pulses and a resumption of estrous behavior (P < 0.05), while ovarian activity estimated by progesterone (P 4) concentrations resumed to the same extent in treated ewes and controls. Bromocriptine treatment (2.5 mg/day/ewe) reduced plasma PRL levels (P < 0.0001) but had no effect on ovarian activity as evidenced by P 4 and resumption of estrus or on either the frequency or amplitude of the LH pulse. In Experiment 2, a single injection of GnRH agonist (42 mcg of buserelin/ewe) on Day 16 post partum resulted in an abrupt elevation of plasma LH concentrations; mean LH values were 18 to 27 times higher when compared with those of the control ewes. Two days after this treatment, ovulations occurred in 5 of the treated ewes and in 2 of the control ewes. This induced ovarian activity was not associated with estrous behavior; however, after an adequate subsequent luteal phase all the treated ewes displayed estrus, the resumption of estrus thus being earlier in treated than in control ewes (P < 0.01). In Experiment 3, E 2 supplementation from Day 16 to Day 28 post partum increased the number of LH pulses per 6 hours in suckling ewes (P < 0.05) and induced earlier resumption of estrus in dry ewes but not in suckling ewes (P < 0.01). Luteal function was detected about 5 and 8 days after the insertion of E 2 implants in 4 dry ewes and in 2 suckling ewes, respectively.

Lung compliance, lung volume and transfer factor for carbon monoxide in anaesthetised sheep: normal values and reproducibility of measurements

Measurements of quasistatic compliance ( C qst), effective alveolar volume ( VA,eff) and single-breath transfer factor for carbon monoxide ( T L, CO , ‘sb’) were completed in 16 normal, anaesthetised, adult Texel ewes. Regression equations were computed for these variables as a function of bodyweight and the optimal equations selected. The 95 per cent prediction intervals for the equations were calculated such that normal lung function in similar sheep could be accurately predicted. The long term reproducibility of these measurements was assessed in nine sheep, measured at monthly intervals over a period of five months. Although measurements made in individual sheep were often highly variable, the variation between repeated measurements on the separate days for the group was insignificant.

Milk yield and milk composition of Flemish milksheep, Suffolk and Texel ewes and their crossbreds

Milk production (MP) and milk composition (MC) were investigated in 72 ewes of West European sheep breeds: Flemish Milksheep, Suffolk and Texel and their crossbreds, during the first 45 days of lactation and related to postnatal growth of their lambs. Without correction for significant influences, mean daily MP was 1.35 ± 0.47 kg and milk fat, protein and lactose contents were 9.00 ± 1.29, 4.85 ± 0.36, and 5.62 ± 0.25%, respectively. Breed, age of ewe and number of lambs suckled influenced MP significantly ( P < 0.05). Flemish Milksheep ewes had the highest average daily MP (3.33 ± 0.29 kg), while Texel ewes produced the lowest amount (1.10 ± 0.15 kg). The other genotypes had 1.5 kg MP. Two-year old ewes produced 200 g/day more milk than one-year olds. Ewes rearing twins had a higher MP of 400 g/day compared to ewes suckling singles. MC was not significantly influenced by genetic and physiological effects. MP and MC did not vary with circadian rhythms, i.e. a.m. vs. p.m. Significant correlations ( P < 0.0001) indicated that ewes with a high MP in early lactation also continued for a good performance at 45 d postpartum. Early postnatal growth of lambs was dependent on genotype of lamb, birth weight and number of lambs suckled ( P < 0.05). Purebred Milksheep lambs realized a high growth rate (306 ± 37 g/d). Crossbred lambs approximated Milk-sheep, while purebred Texel lambs showed the slowest weight gain. These results were associated with milk uptake and conversion by lambs. Twin lambs grew slower than singles. Regression analyses showed that lambs had to have a chance to suck at least five times/d after 4 h of separation before a good estimation of the realized MP was obtained.

Effects of suckling mode on endocrine control of reproductive activity resumption in Texel ewes lambing in July or November

To study the effects of the overlapping of seasonal and lactation anestrus and the influence of the suckling mode on the resumption of reproductive activity in Texel ewes, two experiments were carried out after the July and November lambings. The frequency and the duration of suckling decreased with the age of the lambs, and the suckling intensity in the lambs that were allowed to suck unrestrictedly was three times higher than in lambs restricted to sucking three times a day. The overlapping of seasonal anestrus and lactation delayed the resumption of ovarian and estrus activity, but no difference was observed between dams suckling single lambs and twins. The resumption of ovarian and estrus activity was much earlier after the November lambing than after the July lambing. Weaning after the November lambing shortened the interval between parturition to first estrus but not to the first luteal function. The reduction of suckling intensity by suckling management had no effect on the resumption of ovarian and estrus activity. In early postpartum, suckling inhibited the luteinizing hormone (LH) pulsatile secretion and consequently the first LH discharge. However, the earlier restoration of gonadotropin stimulation in dry ewes was not immediately followed by ovarian activity. The suckling inhibition may be due to a temporary disturbance in hormonal balance, the rise in prolactin (PRL) and cortisol secretions. Plasma estradiol 17β (E2) concentrations were higher in dry than in suckling ewes in early postpartum. Follicle stimulating hormone (FSH) secretion was not involved in the process of delaying the resumption of reproductive activity after lambing.

Daily variations in suckling behaviour and relationship between suckling intensity and lactation anestrus in Texel ewes

A study was carried out on nine ewes suckling single (five) or twin (four) lambs, born in July, to observe the changes in daily distribution of suckling behaviour during lactation, and to determine whether suckling intensity influenced the time taken for Texel ewes to return to estrus. Nine other ewes, which had lambed in March and from which lambs were removed at the beginning of July, served as controls for the occurrence of estrus. Recording suckling behaviour during a 24-h period weekly, from the first to the ninth week, allowed us to conclude that: (1) sucklings were more frequent during the day than during the night ( P<0.01) with a trend to increase in the morning; (2) the frequency and the duration of suckling decreased with age of the lambs; (3) the frequency of suckling did not differ among single and twin lambs, but the mean and total duration of suckling were higher within twin lambs; (4) suckling delayed the return to estrus for 14 days ( P<0.01), but no difference was observed between dams suckling singles and twins. The suckling intensity and the duration of post-partum anestrus were not linked. The inhibitory effect of suckling on the resumption of estrus is thus not related to the intensity of the stimuli.

Fetal blood flow velocity waveforms in relation to changing peripheral vascular resistance

In an acute experiment in Texel ewes, Doppler flow velocity waveforms from the fetal descending aorta were related to peripheral vascular resistance as calculated from perfusion pressure divided by electromagnetically measured volume flow in the descending aorta. Vascular resistance was increased by stepwise embolization of the peripheral circulation via repeated bolus administration of Sephadex G-25 microspheres. A rise in peripheral vascular resistance was associated with a reduction in peak and end-diastolic flow velocity and an increase in Pulsatility Index. Clinically, if similar changes are observed in growth retarded fetuses, the findings are usually interpreted to represent ‘uteroplacental insufficiency’. Present data provide direct evidence that raised peripheral vascular resistance does indeed produce such waveform changes.

Development of a synthetic dam line in a reciprocal cross between Finnish Landrace and Ile de France in The Netherlands

The profitability of a three breed cross with Texel, Finnish Landrace (FL) and Ile de France (IdF) was investigated in a crossbreeding experiment. FL and IdF were used as dam breeds for the production of crossbred ewes and the Texel as terminal sire breed. The reciprocal crossbred ewes demonstrated both good prolificacy and pregnancy rates in an 8-month lambing system without artificial oestrus induction. The crossbred ewe doubled on average the lamb production per ewe per year (2.6 vs. 1.3) compared with the traditional system with Texel ewes. A 3-way cross is difficult to organise within the small scale sheep farming structure of The Netherlands. The development of a synthetic dam line was therefore favored because of the simplicity of the organisation at farm level, despite the expected loss of considerable maternal heterosis in the synthetic ewe. Although the development is not yet complete, there is no apparant loss in reproduction traits in the synthetic ewes compared with F 1 ewes.

Sexual dimorphism in immunoneutralization of bioactivity of rat and ovine inhibin.

Inhibin was partially purified from bovine follicular fluid using chromatography on immobilized Procion Red 3B and anion-exchange chromatography. Ovariectomized Texel ewes were immunized against the inhibin-containing fraction from the Procion Red 3B column and the immune response was subsequently boosted with similar fractions or with the preparation obtained from the anion-exchange column. The potencies of the resulting antisera were evaluated in an in-vitro bioassay system for estimating inhibin activity, using dispersed rat pituitary cells. The antisera were found to inhibit the bioactivity of inhibin preparations from ovarian follicular fluid of bovine, porcine, ovine or human origin, as well as inhibin activity in ovine testicular lymph and rete testis fluid, in culture media from rat granulosa and rat Sertoli cells and in homogenates of rat ovaries and testes. These results indicate that the inhibin molecules from several species contain a common bioactive moiety. The results also showed that the antiserum was more effective in neutralizing inhibin activity from ovarian than from testicular sources in both sheep and rat, indicating a sex-related difference in the inhibin molecules within a species.

Comportement alimentaire, rumination, fermentations réticulo-ruminales et acides gras volatils plasmatiques, comparés chez la chèvre et le mouton ; influence du régime

Two-year old Alpine she-goats (n = 3) and Texel ewes (n = 3) were compared as to eating behaviour, rumination and volatile fatty acids (VFA) in rumen and blood. The animals were fed once daily with two different proportions (20 and 80%) of barley and hay. Dry matter intake was fixed at 48 g D.M/kg P0.75 per day. In similar feeding and environmental conditions, eating behaviour and rumination of goats and sheep did not differ much: the goats tended to eat faster and there were more rumination periods in the sheep. Latency time, mean duration of rumination periods, daily rumination time and circadian pattern of rumination did not differ significantly between the two species (fig. 1). With both diets we observed a higher VFA concentration and a lower acetate/propionate ratio in the rumen of the ewes; however, rumen pH was lower only in those eating the 80% barley ration (fig. 2). Blood VFA in the jugular vein did not differ between sheep and goats (fig. 3). The proportion of cereals and hay in the diets affected rumen fermentation and rumination pattern in both species. With a higher concentrate/roughage ratio, rumen and plasma VFA increased, while the pH and acetate/propionate ratio in the lumen juice, the number of rumination periods and daily rumination time decreased. When the animals were fed the 80% barley ration, there was practically no rumination in the first 9 h after the single meal. During this time, rumen pH was minimal and VFA levels in the rumen and blood were maximal.

Inhibition of lactation and ovarian function: a possible animal experimental model for humans

Lactating Texel ewes are hyperprolactinemic. Hyperprolactinemia persists for at least the first 50 h after weaning, when the udder is swollen and tender. Oral administration of bromocriptine lowers hyperprolactinemia dramatically within 4 h, correlated with ‘shrinking’ of the udder. During lowering of hyperprolactinemia there is no immediate increase in LH.

Die circadiane rhythmik einiger blutbestandteile bei schafen mit erblicher mikrophthalmie und bei intakten vergleichstieren

Abstract [Circadian Rhythm of Blood Components in Sheep with Congenital Microphthalmus and in Intact Controls] Blood samples were drawn via indwelling vena jugularis catheters at 08:00, 12:00, 16:00, 24:00 and 04:00 h from a group of 10 Texel ewes suffering from congenital microphthalmus and from 10 intact controls. All animals were of the same age. The samples were analyzed for 11‐hydroxycorticosteroids, butanol‐extractable iodine, thyroxine, glucose and potassium content, in addition the hematocrit was measured and the eosinophils were counted. The results were evaluated by the least squares method for the factors: group (intact controls versus animals suffering from microphthalmus), day of investigation (1–3) and time of sampling. After eliminating all but one effect animals with microphthalmus and the intact controls showed only small differences in the parameters with the exception of a highly significant difference in the potassium concentration. When comparing the 24‐h profiles of the two groups, however, significant differences were seen, particularly in the concentration patterns of potassium, 11‐hydroxycorticosteroids and glucose and in the hematocrit. The day of investigation had a highly significant influence on the hematocrit value and a somewhat lesser pronounced effect on the concentrations of glucose and thyroxine. All parameters analyzed were — in tendency — influenced by the sampling time. The maximal values for 11‐hydroxycortico‐steroids, the hematocrit, the butanol‐extractable iodine and for thyroxine were obtained during the day, the minima at‐night. The opposite was true for the eosinophil count and the concentration of glucose and potassium. Significant differences of the time‐dependent variations from the estimated mean μ were established for the concentrations of 11‐hydroxycorticosteroids, glucose, potassium, butanol‐extractable iodine and for the hematocrit.

Repeatability of the duration of oestrus and breed differences in the relationship between druation of oestrus and ovulation rate of sheep.

The duration of oestrus and the time interval from removal of progestagen-impregnated pessaries to the onset and end of oestrus were examined in Texel, Finnish Landrace, Galway and Fingalway (Finnish Landrace X Galway) ewes. The differences among the breeds in the relationship between these variables and ovulation rate at the controlled oestrus were also investigated. Breed differences were significant for all traits except the interval from pessary withdrawal to the onset of oestrus. The relationship between ovulation rate and both the interval from pessary withdrawal to the onset of oestrus and the duration of oestrus differed significantly among the breeds. The repeatability of the duration of oestrus was significant for Texel and Rambouillet ewes (mean = 0.5) and for pooled data from ewe lambs of various breeds. It was concluded that, in view of the breed differences in the relationship between ovulation rate and duration of oestrus and other traits, generalizations should not be made from among-breed to within-breed relationships. The high repeatability for the duration of oestrus may mean substantial heritabilities for the physiological determinants of oestrus duration.