Dry Ewes Research Articles

Incidence risk and aetiology of mammary abnormalities in dry ewes in 10 flocks in Southern Greece

In a field investigation of 10 flocks in Southern Greece, 3367 dairy ewes were examined twice, in order to estimate the incidence risk and the aetiology of mammary abnormalities during the dry-period. Abnormal secretion, lumps, nodules, diffuse hardness, abscesses and cysts were the abnormalities detected. The cumulative incidence of mammary abnormalities during the dry-period was 5.1% (95% confidence interval: 4.4–5.8%); 47% of the cases detected developed during the first three weeks after cessation of lactation. Despite variation in the flock size, there was no between-flock variation in the risk of a ewe developing mammary abnormalities. Staphylococci ( Staphylococcus aureus and coagulase-negative isolates) were the most frequently isolated bacteria from mammary samples; Actinomyces pyogenes, Clostridium perfringens, streptococci and Escherichia coli were also isolated. Resistance was encountered among the staphylococcal isolates.

Expression of surface antigens on blood and mammary leukocytes in lactating and dry ewes

Flow cytometry was used to study the expression of CD4, CD8, CD14, CD18, WC1, MHCII, B-cell and l-selectin on CD45+ leukocytes in ovine blood and mammary secretions from lactating and dry ewes. The proportion of CD4+ lymphocytes was significantly lower and the proportion of CD8+ lymphocytes significantly higher in mammary secretions than in blood. This suggests that a selective migration to or retention of CD8+ cells in favour of CD4+ cells occurs in the mammary gland. l-selectin staining intensity on lymphocytes and neutrophils was lower in mammary secretions than in blood. In contrast, CD18 staining intensity was higher on leukocytes in milk, but not in dry secretions, than on corresponding cells in blood. These changes in adhesion molecules are in accord with shedding of l-selectin and up-regulation of CD18 during transendothelial migration. Expression of leukocyte antigens differed with lactational status mainly in mammary secretions. In milk, the staining intensity of CD18+ lymphocytes and neutrophils was higher than in dry secretions and more milk neutrophils expressed l-selectin. In contrast, greater numbers of IL-2R+ and MHCII+ lymphocytes and CD14+ leukocytes were observed in dry secretions. An increased proportion of these subpopulations could lead to increased immunological responsiveness of the udder during the dry period.

How degree of selectivity modifies foraging behaviour of dry ewes on reproductive compared to vegetative sward structure

This study was conducted to investigate the effect of sward phenological stage in interaction with the degree of selectivity for green leaves on foraging behaviour of dry ewes. We tested the hypothesis that dry matter (DM) intake per bite, intake rate and intake were determined by the amount of preferred food items (green leaves) per unit area, and that the relationships did not vary with the phenological stage of the sward nor the degree of selectivity of the animal. Two sward structures were compared: V=vegetative, and R=reproductive (fully emerged inflorescence stage, 15% reproductive tillers). They were compared under rotational grazing by 11 ewes, with 6 ewes of variable degree of selectivity studied in detail. Measurements of foraging behaviour were made during the progressive grazing down of the paddocks. Green leaf mass per ha (GLM) was the variable most strongly correlated with intake per bite in both sward structures, but inclusion of the variable stem mass per ha (STEM) in the model resulted in slight, but significant improvement in the prediction of intake per bite. The coefficient of the variable STEM in the multiple regression varied among animals ( P<0.05) and was related to faecal nitrogen concentration, an indicator of animal's degree of selectivity. Time per bite increased linearly with intake per bite, the increase being greater on the reproductive than on the vegetative sward structure. Consequently, parameters of the predictive models of intake rate and digestible intake rate varied with sward phenological stage. On the reproductive sward, slope of the regression of time per bite on intake per bite and parameters of the predictive models of intake rate were linearly related to the animal's degree of selectivity. These results emphasize the importance of inter-individual variation in the trade-off between quality of the diet selected and intake rate. For a given green leaf mass, grazing time was higher on R than V. Grazing time, daily dry matter (DM) intake and digestible daily DM intake were not related to the degree of selectivity of the animals.

Feeding station behaviour of ewes in response to forage availability and sward phenological stage

This study was undertaken to examine the changes in the feeding station (FS) behaviour of sheep during the grazing down of swards, and the effect of the phenological stage of grass on grazing within and moving between FSs. Two cocksfoot sward structures, vegetative and reproductive, were compared under rotational grazing of 0.12-ha paddocks by 11 dry ewes with 4 studied in detail. We determined the changes in FS behaviour with resource depletion and tested the hypothesis that selective grazing on a `heterogeneous' reproductive sward, compared to a `homogeneous' vegetative sward, increased foraging costs, in both bite selection within the station and FS selection within the paddock. On both swards, ewes adjusted their foraging behaviour to resource depletion by decreasing the time spent grazing and the number of bites per FS. They also reduced the time spent moving between FSs, as a result of fewer steps taken and a higher walking speed, and grazed longer per day. For a given green leaf mass, selectivity was increased on reproductive compared to vegetative sward, between FSs (longer distance walked to select a new FS) and within FSs (fewer bites taken for a given FS grazing time). The ewes partly compensated for the extra time costs due to selective grazing by walking faster between FSs and grazing longer per day.

Development of a methodology for studying feeding station behaviour of grazing ewes

A test apparatus was developed to study feeding station (FS) use and abandonment by sheep, by controlling FS number, characteristics and distance between FS. It consists of a rectangular pen with openings in one of the long sides through which the animal can extend its head to graze. The aims of this experiment were (i) to study FS behaviour of ewes according to the number of FS offered, at two sward heights, and so (ii) to determine the test conditions (FS number, test duration, sward height) most conducive to grazing. Eight dry ewes were offered four grazing treatments (two FS numbers (8 vs. 12) × two sward heights (7 vs. 15 cm)), during four 3-day periods. The ewes were fasted for 17 h and then tested individually for 15 min. A 34-session preliminary training period was necessary to select suitable animals. Behaviour at FS was independent of the FS number, until min 10, when idling increased, particularly for 8 FS and on short sward. A test limited to 10 minutes using an 8-station device seems practical, subject to a sufficiently motivating sward height. FS behaviour was closely related to sward height: grazing time per FS was longer on tall than short swards, which was consistent with field observations and optimal foraging predictions. However, grazing times per FS were much longer in test than in field conditions, which may partly be explained by the absence of fellow animals, a long fast, and constraints of the device.

Effect of condensed tannins on the production of wool and on its processing characteristics in sheep grazing Lotus corniculatus

The effect of condensed tannins (CT) in Lotus corniculatus upon voluntary feed intake (VFI), concentration of rumen and plasma metabolites, production of wool, and wool processing characteristics was measured in grazing ewes restricted to maintenance feeding for 125 days during summer. A rotational grazing system with restricted feed allowance with 40 mixed aged dry ewes (54±1·0 kg) was used. Half of the ewes were selected randomly for twice-daily oral polyethylene glycol (PEG; MW 3500) supplementation (CT-inactivated), with the remainder being CT-acting animals. Measurements of the diet selected, VFI, wool production, and wool processing characteristics were made. The concentration of ammonia in rumen fluid and the concentrations of methionine, cysteine, and urea in blood plasma were also measured. The diet selected contained 32 g total nitrogen (N) and 28 g total CT/kg dry matter (DM) and had an in vitro organic matter digestibility of 0·70. Action of CT reduced rumen ammonia concentration (256 v. 302 mg N/L), reduced blood plasma urea concentration (7·3 v. 8·9 µM), and increased blood plasma cysteine concentration (30 v. 27 µM) compared with sheep receiving PEG supplementation. CT had no effect on VFI but increased clean fleece weight (2·53 v. 2·28 kg/ewe) and staple length (7·7 v. 6·9 cm), but did not affect liveweight gain (54 v 67 g/day). The CT reduced dag weight and tended to reduce wool yellowness relative to sheep receiving PEG. There were no signifiant effects of CT on fibre diameter, staple strength, bulk density, and wool resilience. It was concluded that action of CT in sheep fed L. corniculatus reduced the degradation of forage protein in the rumen and the principal effect of this was to increase the efficiency of wool production, with more wool being produced at the same feed intake and the wool being of reduced yellowness.

Decrease of response to social separation in preparturient ewes

The response to social isolation was compared in multiparous non-pregnant (controls) and periparturient (experimental) Rambouillet ewes over three tests performed at times corresponding to 111±31 h prepartum (148 days of pregnancy), 3.1±1.2 h prepartum (after onset of labour) and 1.3±0.2 h postpartum for the experimental group. Twenty-four and 15 ewes (test 1), 16 and 12 (test 2) and 7 and 10 (test 3) were tested in control and experimental groups respectively. Each test lasted 10 min (5 min in presence of conspecifics, 5 min in their absence). High-pitched bleats, locomotor activity, attempts at jumping out of the testing pen, eliminations and latency out of the pen were recorded. In both groups and in all tests there was a significant increase of agitation following removal of the conspecifics. Few differences were encountered between groups in the first test. On the other hand, in the second and third tests the agitation induced by social separation was significantly higher in dry ewes for the great majority of behaviours. We conclude that the reduction of response to social separation previously reported in postparturient ewes is not totally due to the maternal bonding to the neonate, but that before parturition, some physiological factors internal to the mother already reduce gregariousness.

Peri-parturient rise in faecal strongyle egg counts of different genotypes of sheep in North Sumatra, Indonesia

Faecal strongyle egg counts were monitored in peri-parturient ewes and dry ewes grazing in a rubber plantation in North Sumatra, Indonesia. A significant rise in faecal egg counts was observed during the post-parturient period. Haemonchus contortus was the dominant species in the faecal cultures of the lactating ewes. The intensity of the peri-parturient rise was affected by the genotype of the sheep, which were the local Sumatra and its F1 crosses with St. Croix, Barbados Blackbelly and Java Fat-tail. The peri-parturient rise in egg counts was highest in Sumatra and lowest in the Barbados Blackbelly X Sumatra cross. A significant effect of litter size on the peri-parturient rise was also demonstrated. These findings are discussed in relation to the epidemiology and control of gastrointestinal nematodes in the humid tropics.

Leukocyte and cytokine accumulation in the ovine teat and udder during endotoxin-induced inflammation.

The accumulation of leukocytes, ovine serum albumin and the cytokines interleukin-1 beta(IL-1 beta), tumour necrosis factor-alpha(TNF-alpha), interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma(IFN-gamma) was studied during endotoxin-induced inflammation in lactating and dry ovine udders, and in the teat cisterns of dry ewes after surgical closure of the passage between the teat and udder cisterns. Samples were taken before infusion and hourly up to 10 h after infusion of 0.1, 1 or 10 micrograms of endotoxin, or infusion of pyrogen-free saline (PFS) as a control. Rectal temperatures were measured. A significant dose- and time-dependent accumulation of leukocytes, mainly neutrophils, was observed in the lactating udders and in the teat cisterns. In the dry udders, the leukocyte accumulation was significant for time but not for dose. Peak numbers of cells were reached at 3-4 h in the dry udders and in the teat cisterns, but not until 10 h after infusion in the lactating udders. The changes in the ovine serum albumin concentrations mostly paralleled changes in leukocyte numbers. A role was indicated for TNF-alpha, IL-8 and GM-CSF, but not for IL-1 beta and IFN-gamma, during endotoxin-induced inflammation in the ovine udder. Release of TNF-alpha, IL-8 and GM-CSF was most prominent in lactating udders, peaking at 2 or 3 h after infusion, but was also detected in dry udders and teat cisterns. Detectable levels of IL-1 beta and IFN-gamma were occasionally found in all three groups.

The effect of a high‐magnesium perennial ryegrass variety on the magnesium status of sheep

AbstractAn early‐heading variety of perennial ryegrass (Ramore) bred for high magnesium (Mg) content was compared with an early control variety (Frances) for its ability to increase Mg intake, Mg utilization and blood Mg concentration in sheep, and so reduce the incidence of hypomagnesaemic tetany. Swards of the two varieties were established and each was grazed by ewes suckling twin lambs from turn‐out to weaning and thereafter by dry ewes. In early and late season herbage from a proportion of each sward was cut daily and fed fresh to ewes housed indoors in metabolism crates.Under grazing conditions herbage from Ramore swards had, over the 1992 and 1993 grazing seasons, a higher Mg concentration than Frances (2.35 g kg−1 vs. 2.18 g kg−1; s.e.m. 0.019, P&lt; 0.001). During the spring period there was a higher (P 0.001, s.e.m. 0.0074) Mg concentration in the blood of ewes grazing Ramore (0.854 m mol 1−l) swards compared with those grazing Frances (0.793 m mol 1 −1) whereas during the autumn period blood Mg concentrations were higher in ewes grazing Frances. Ewe and lamb liveweight gains, recorded in 1992 only, were higher on Ramore swards than on Frances swards, although the difference was not significant.Indoor feeding studies showed that Mg intake was significantly higher (P&lt; 0.001, s.e.m. 0.026) in ewes offered Ramore (1.98 g d−1) herbage compared with those offered Frances (1.74 g d−1) herbage with no significant difference in dry‐matter intake between the two varieties. Apparent availability and retention of Mg were higher for animals fed Ramore during the spring feeding periods than those fed Frances, but during the autumn feeding periods the reverse was true. Under indoor feeding conditions, variety had no significant effect on blood Mg concentrations.It was concluded that under grazing conditions a high Mg variety could provide an effective means of reducing the incidence of hypomagnesaemic tetany.

Cytokine-induced inflammation in the ovine teat and udder

The inflammatory response, as measured by the accumulation of leukocytes and ovine serum albumin, induced by interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α), interleukin-8 (IL-8), and granulocyte-macrophage colony stimulating factor (GM-CSF) was studied in lactating ovine udders, and in teat cisterns of dry ewes after surgical closure of the passage between the teat and udder cisterns. In the lactating udders, IL-1β and TNF-α, but not IL-8 and GM-CSF, induced significant accumulation of cells. In the teat cisterns, all four cytokines IL-1β, TNF-α, IL-8, and GM-CSF induced significant cell accumulation, IL-1β was the most potent cytokine. A slight increase in serum albumin, paralleling the changes in leukocyte numbers, was observed after infusion of IL-1β and, to some extent, TNF-α. The cell accumulation induced by IL-1β or TNF-α was dose and time dependent in lactating udders, and time-dependent in teat cisterns. The cell numbers were considerably higher in lactating udders than in teat cisterns after infusion with IL-1β. The first influx of cells was observed earlier, and the cell numbers peaked earlier in the teat cisterns than in the lactating udders. IL-8 and GM-CSF induced dose and time dependent cell accumulation in teat cisterns only. The differences between lactating udders and teat cisterns may be attributable to the differences in tissue area involved and the number of receptors available, or to dilution of cytokines in milk, or to presence of inhibitory factors. Differences between cytokines in their inflammatory effects may be explained by their modes of action. IL-1β and TNF-α have a wide range of cellular functions enabling them to induce a more prominent response than IL-8 and GM-CSF. Furthermore, receptors for IL-1β and TNF-α are present on a larger number of cell types. Finally, the results indicated that the teat cisterns, being the port of entry for udder infections, as well as the lactating udders are capable of a diversified inflammatory response which is important in the defence against udder infections.

Inter-breed variation in the postpartum ewe response to continuous low dose infusion of GnRH

During the nonbreeding season the pituitary and ovarian responses to a subcutaneous GnRH infusion were investigated in acyclic, lactating Mule ewes which exhibit a deep seasonal anestrus and in Finn x Dorset ewes in which seasonal anestrus is ill-defined. Each breed received 10 d of progestagen priming before being subdivided into 3 groups. In Group L + G, 5 lactating ewes received GnRH (250 ng/h sc) for 96 h; in Group D + G, 5 dry ewes received GnRH (250 ng/h sc) for 96 h; in Group L, 5 lactating ewes received saline vehicle for 96 h. The infusions began when lactating and dry ewes were approximately 28 d and 120 d post partum, respectively. Blood samples were collected for LH, progesterone and estradiol analysis. Estrous behavior was monitored between Day −4 and Day +7. On Day +7 the reproductive tract was also examined. In the Mule ewes the mean plasma LH concentration increased (P < 0.05) following minipump insertion in each treatment group, although mean LH levels were greater (P < 0.05) in Group D + G, than in either Group L + G or Group L. Following the GnRH infusion, mean plasma estradiol levels increased (P < 0.05) in Group D + G but not in Group L + G. A preovulatory LH surge and subsequent ovulation occurred in 5 5 , 2 5 and 0 5 ewes from Group D + G, L + G and L, respectively, and estrus was recorded in 5 5 , 1 5 and 0 5 of these ewes, respectively. The LH surges began earlier (P < 0.05) (43.2 ± 6.8 h vs 77.0 ± 1.0 h) and the ovulation rate was greater (2.2 ± 0.37 vs 1.00 ± 0.00) in Group D + G than Group L + G. In the Finn x Dorset ewes mean LH concentrations increased (P < 0.05), to a similar level following minipump insertion in Groups D + G and L + G, but not Group L. The elevated LH levels were accompanied by increased (P < 0.05) plasma estradiol levels in Group D + G, but not in Group L + G. The GnRH infusion culminated in an LH surge and estrous behavior in 5 5 , 1 5 and 0 5 ewes from Groups D + G, L + D and L, respectively. The interval to the LH surge was similar between Group D + G (48.4 ± 6.6 h) and Group L + G (46.0 h). Ovulation was evident in those ewes which exhibited an LH surge plus one additional ewe from Group L + G. The mean ovulation rate was greater in Group D + G (4.00 ± 1.05) than in Group L + G (1.5 ± 0.50). These data show that continuous GnRH infusion can consistently induce out of season breeding in the nonlactating Mule and Finn x Dorset ewe but can not break combined seasonal and lactational anestrous in these breeds. Further, between-breed differences are evident in the site along the hypothalamic-pituitary-ovarian axis at which reproduction is compromised in ewes at the same chronological stage post partum.

Responses to feeding canola meal or lupin seed to pregnant, lactating, and dry ewes

Responses in wool production, ewe liveweight, lamb birth weight, and growth were compared when the major source of protein in the diet was either lupin seed or canola meal. The diets were fed to ewes during the final 3 weeks of pregnancy and first 3 weeks of lactation, and for a similar period of time to a group of dry ewes. All ewes were fed to maintain conceptus-free liveweight. The diet containing canola meal increased (P &lt; 0.001) wool growth in the reproducing ewes (50-63%) and the dry ewes (12.5-20%) during, and for 3 weeks after, the treatment period. Fibre diameter of wool grown during the treatment period was increased (P &lt; 0.025) by 0.5-1.5 pm in the ewes fed canola meal compared with ewes fed lupins. The ewes fed canola meal gained slightly (P = 0.06) more weight during the experiment than the ewes fed lupins. Lambs from the ewes fed canola meal were lighter (P &lt; 0.05) at birth (480 g) than lambs from ewes fed lupins. The reproducing ewes had lower fleece weights, average fibre diameters, and staple strengths and lengths than the dry ewes. These fleece characteristics were not significantly affected by diet. Canola meal is partially protected from rumen degradation and is less expensive than other sources of similar proteins and may therefore provide a practical option for commercial sheep producers.

The response of lactating and dry ewes to energy intake and protein source in the diet

In this lactation experiment, 40 Rasa Aragonesa ewes rearing two lambs were distributed to four treatments to study two levels of metabolizable energy restriction, 80% (E 1) and 70% (E 2) of the requirements, and two protein sources in the concentrate (soybean cake or fish meal) on milk yield and lamb growth. At weaning on Day 67 after lambing the ewes were allocated to four treatments to study the effect of the level of energy restriction in lactation and of the amount of barley grain (fresh matter) offered from weaning until 70 days later (250 and 500 g per ewe per day) on the recovery of body reserves. Ewes which were fed fishmeal produced milk with higher protein content (4.98 vs. 4.69%; P < 0.05) and had greater output of protein in milk than the ewes fed soybean cake (62 vs. 55 g day −1; P < 0.001). Lambs suckling ewes fed fishmeal had higher daily gains (194 vs. 163 g day −1), greater total weight increase (6.97 vs. 5.88 kg) and lower conversion of the milk than lambs from ewes fed soybean cake ( P < 0.05). Difference in body condition score (BC) between Treatments E 1 and E 2 at beginning of the recovery period was eliminated during the 70 days. Amount of barley offered affected change in BC (0.64 vs. 0.48 points; P < 0.001) and final BC ( P < 0.01). Total live weight and BC increases were higher in animals with larger amounts of barley during the recovery period ( P < 0.01 and P < 0.001, respectively). In conclusion, the level of feeding after weaning had greater effects on total recovery of reserves than the level of energy restriction during lactation.

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.

Consequences of reproduction on the liveweight, fat depth, wool growth, and intake of grazing Merino ewes in the short and long term

Effects of the current and previous year's reproductive performance on liveweight, fat depth, pasture intake, and wool growth were estimated in breeding Merino ewes in each of 2 years and in 4 seasons corresponding with stages of the annual reproductive cycle. Ewes bearing multiple lambs were heavier in early pregnancy (autumn, by 1.5 kg) and in late pregnancy (winter, by 2.5 kg) than single-bearing ewes, with both being heavier than nonpregnant (dry) ewes in winter (by 1.7-4.2 kg). Pregnancy had no effect on fat depth or intake in autumn or winter. Lactating ewes were leaner (by 1.0-1.7 mm), had lower liveweights (by 6.4-8.6 kg), and had substantially higher intakes [by 286-348 g digestible organic matter intake (DOMI)/day] than non-lactating ewes. From summer to winter, ewes that had previously reared a lamb, or lambs, to weaning weighed less, were leaner, and had higher intakes than ewes that were previously dry. Pregnant ewes grew significantly less clean wool and grew it less efficiently (g wool/kg DOMI) in autumn (7-9% less) and winter (11-18% less) than non-pregnant ewes. Similarly, lactating ewes grew less wool (by 23-30%) less efficiently than ewes not suckling, the effect being greater in ewes with multiple lambs. Post-weaning, however, ewes that had reared a lamb to weaning grew significantly more wool (by 6-15%) up to 4 months post-weaning, although efficiency of wool growth was still impaired. The effects of reproductive status on the fibre diameter of wool reflected those for wool growth. Effects of reproduction on productivity are long term and recovery may not be achieved before the next reproductive cycle.

Diet Preference of Sheep: Effects of Recent Diet, Physiological State and Species Abundance

The preference of sheep for two temperate grassland species, ryegrass and white clover, was tested by releasing flocks (of three ewes) onto swards (0.25 ha) that contained adjacent monocultures of grass and clover, and observing their intake behaviour over 6 days. The test paddocks contained either 20, 50, or 80% clover by ground area to distinguish partial preference from indifference. To test whether recent diet affected preference, separate groups of dry (non-pregnant, non-lactating) ewes grazed prior to testing on one of three diet «back-grounds»: an all-grass sward, an all-clover sward, or a 50:50 grass/clover sward by area. To consider the effects of physiological state on preference, a further group of lactating ewes, also from a 50:50 grass/clover «background», were tested

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.

Grazing trials with sheep on kikuyu(Pennisetum clandestinumChiov.) foggage in the eastern Transvaal highveld

Abstract Sheep performance and patterns of herbage utilization were determined in two grazing trials involving different amounts and quality of kikuyu foggage. In both trials each paddock of a series of paddocks of each foggage type was grazed successively. Amounts of leaf and stem, and the digestible organic matter and crude protein contents of these components, were determined at the start and end of grazing in each paddock. In one trial, wether lambs maintained livemass whereas, in the other, dry ewes and wether lambs both lost 8–10% of their initial mass, irrespective of differences in foggage quality. Grazing capacity was proportional to the yield of foggage. Although the percentage leaf in the foggage in the different treatments varied from 72 to 89, only some 50% of the total herbage was utilized. The estimates of quality indicated that a higher level of utilization would have resulted in poorer sheep performance.

Decision rules for controlling the sward height of continuously grazed experimental pastures

AbstractTwo contrasting decision rules for adjusting stock density to control the sward height of continuously grazed grass swards were tested and developed. One rule calculated the adjustment as a percentage of the existing stock density (Percentage Rule); the other related the adjustment to estimates of the bulk density of the grazed horizon and individual animal intake (Absolute Rule). Both decision rules related the adjustments to the change in sward height over the previous week and to the deviation from the target value. The decision rules were tested by continuously grazing lactating ewes and then dry ewes after weaning with a target sward height of 4 cm on 0·33‐ha plots with stock density adjusted by varying animal numbers. The Percentage Rule failed to increase the stock density sufficiently rapidly when grass growth was accelerating, leading to increasing deviation in sward height from a 4 cm target value. The Absolute Rule succeeded in controlling sward height once the bulk density term had been correctly adjusted. Pre‐emptive adjustment of stock density in anticipation of a change in grass growth rate marginally improved the control that was achieved by the Absolute Rule.