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Biomedical subjects

H Dobson

Publications and source records attributed to H Dobson.

At least 109 records · Page 6Linked to original sources
PubMed1990

A technique for transcervical intrauterine insemination of ewes.

In commercial artificial insemination (AI) of sheep, fresh extended semen is deposited into the vagina or cervical os, or fresh extended or frozen semen is placed laparoscopically into the uterus. Transcervical intrauterine insemination of the ewe is not used commercially. In this study, methods of restraint and instrumentation for AI were evaluated and modified to produce a transcervical intrauterine technique suitable for commercial application. Four methods of restraint, four vaginal specula, three forceps and four instruments suitable for transcervical passage were compared. From these comparisons a technique was developed in which the ewes were positioned in dorsal recumbency with their hindquarters elevated. The vagina was dilated using a duck-billed speculum, the cervix was grasped and retracted using forceps, and an inseminating instrument was introduced into the cervical opening and manipulated through the cervical canal. The technique was repeated on 89 mature, multiparous ewes: the difficulty in locating the cervical opening, the force required to retract the cervix and the time required to penetrate into the uterus were recorded. Uterine penetration was achieved in 82% of the ewes. This technique has the potential to be applied in commercial artificial insemination programs of sheep.

Journal Article↗
PubMed1990

Investigations into the effect of two sedatives on the stress response in cattle.

The effects of the sedatives acepromazine (an alpha-adrenergic antagonist) and xylazine (an alpha 2-adrenergic agonist) on plasma indicators of stress in cows were assessed after intramuscular injection and transport. After blood samples had been taken for baseline values, nine cows were given an intramuscular injection of saline (2.5 ml), acepromazine (0.05 mg/kg in 2.5 ml) or xylazine (0.05 mg/kg in 2.5 ml) on different occasions at least 1 week apart. The animals were then transported for 5 min by truck to a different environment and blood sampled for a further 1-3 h. There was a significant increase in plasma cortisol concentration (3.29 +/- 1.59 x baseline) after the injection of saline and transport. The injection of acepromazine also resulted in a significant increase in cortisol concentration (2.84 +/- 0.84 x baseline). There was no similar increase after injection of xylazine. This suggests that alpha 2-adrenergic receptors are involved in the response of plasma cortisol concentrations to stressors. An hyperglycaemic response occurred after xylazine (1.66 +/- 0.49 x baseline) and saline (1.20 +/- 0.1 x baseline) but not after acepromazine. Both sedatives produced a metabolic alkalosis (1.13 +/- 0.01 x baseline pH after xylazine and 1.034 +/- 0.02 x baseline pH after acepromazine). A greater decrease in haematocrit was seen after both sedatives (0.88 +/- 0.04 x baseline after xylazine, 0.81 +/- 0.08 x baseline after acepromazine) than after the injection of saline (0.97 +/- 0.06 x baseline).

Acepromazine↗
PubMed1990

Relationship between an increase in plasma cortisol during transport-induced stress and failure of oestradiol to induce a luteinising hormone surge in dairy cows.

This study investigated whether the stress associated with a 30-minute journey in a truck could distort the oestradiol-induced surge of luteinising hormone (LH) in dairy cows. Altogether 20 journeys were monitored, 16 to 18 hours after intramuscular administration of 1 mg oestradiol benzoate (OE2). Plasma cortisol concentration was elevated (P less than 0.001) within 30 minutes of the start of each journey, even when the journey was repeated at about weekly intervals, indicating a lack of habituation. The LH surge in response to 11 OE2 treatments in nine non-cycling cows within 30 days after calving was either absent (one cow) or significantly delayed, of shorter duration or of lesser amplitude following transport, compared with untransported OE2-treated controls. However, in six cycling cows, 58 days or more after calving, transport affected the LH surge only once. Even in these cows, the LH surge did not start until the cortisol concentration returned to normal, which may suggest a transient postponement of the LH surge by transport. In conclusion, transport impaired the LH surge in early post partum cows with little or no effect after ovarian cyclicity was resumed. It is hypothesised that endocrine events leading to the onset of the LH surge are more vulnerable to stressors in early post partum cows and in the natural situation this might be responsible for the occurrence of anovulation and cystic ovarian disease.

Animals↗
PubMed1989

Associations between types of lameness and fertility.

Four hundred and twenty-seven cases of first-reported foot lameness were recorded in 17 dairy herds in Somerset during the winter housing period. Lameness was classified into three categories: sole ulceration, digital disease (white line abscess, foreign bodies in the sole and pricked or punctured sole), and interdigital disease (lesions of the skin between claws and heel including foul in the foot, interdigital fibroma and dermatitis). In addition, a 'clinical effect score' was calculated to take account of the severity of lameness, the structures involved and the time for which the cows were clinically affected. The fertility records of lame cows were compared with those of the healthy cows nearest in parity and stage of lactation. In the lame cows the interval from calving to first service was four days longer, and the interval from calving to conception was 14 days longer than in the control cows, the pregnancy rate to first service was 46 per cent (controls 56 per cent), 2.14 services were required per conception (controls 1.72) and 16 per cent of lame cows were culled (controls 5 per cent). Lameness, first reported in the period 36 to 70 days after calving, was associated with a significant (P less than 0.01) increase in the interval from calving to first service of eight days; and sole ulceration, in the period 71 to 120 days after calving, was associated with an increase of 11 days (P less than 0.05). Lameness in all periods up to 120 days after calving was associated with significantly increased intervals from calving to conception (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Oestrus during pregnancy in the cow.

Forty-three oestruses were observed in 35 pregnant cows in one beef suckler herd and 17 dairy herds; at each oestrus the pregnant cow stood willingly to be mounted by another cow or bull. Such oestruses were observed at all stages of pregnancy, although more often between 121 and 240 days, occurred more than once per pregnancy and were also seen in successive pregnancies. On one farm where the dairy cows were observed for four 30 minute periods daily, oestrus was recorded in 5.7 per cent of pregnant cows. The behavioural signs associated with oestrus during pregnancy were indistinguishable from those of true oestrus in non-pregnant animals and although its duration was shorter (mean 5.6 hours), its intensity was comparable to that of the true oestrus. Pregnant cows showing oestrus were usually seen interacting with other oestrous cows in the sexually active group. Pregnant cows showing oestrus had a higher mean condition score (3.9 +/- 0.64) than control pregnant cows (3.0 +/- 0.36). Physiological changes in the genital tract normally associated with true oestrus were not observed in pregnant cows showing oestrus. There was no ovulation or metoestrous bleeding. The characteristics of cervical mucus, including ferning patterns, were similar to those of pregnant cows at the same stage of pregnancy. Hormonal changes associated with oestrus in non-pregnant cows were not observed in the pregnant cows exhibiting oestrus. Seven of nine pregnant cows at oestrus stood willingly to be mounted by a bull. On seven occasions, bulls exposed only to cervical mucus from pregnant cows showing oestrus did not display flehmen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Periparturient diseases and their effect on reproductive performance in five dairy herds.

The incidence of periparturient diseases and their effects on the calving to first service interval, the calving to conception interval and the mean number of services per conception were recorded in five Friesian-Holstein herds in the United Kingdom. The incidence rates of milk fever, milk fever followed by endometritis, retained fetal membranes, endometritis after retained fetal membranes, endometritis, or ovarian cysts, were 7.5, 1.4, 1.3, 3.3, 10.1 and 6.7 per cent, respectively, and the affected cows had significantly (P less than 0.05) extended calving to conception intervals (13, 66, 25, 51, 31 and 64 days, respectively) compared with herd-mates. Calving to first service intervals and services per conception were also adversely affected. In spite of treatment, milk fever, endometritis and ovarian cysts had a considerable impact on fertility. Improved methods of treatment and, or, prevention are clearly required.

Animals↗
PubMed1989

Electrolytes and reproductive hormone concentrations in maternal plasma and fetal fluids of dairy cows with hydrops.

Electrolytes, metabolites, cortisol and reproductive hormones were measured in maternal plasma taken at least twice daily from three cases of bovine hydrops before, during and after parturition induced by dexamethasone or prostaglandin. Caesarean operations were required for two of the cases. Maternal plasma electrolytes remained within the normal range, but average potassium and creatinine concentrations were higher (9.2 and 0.68 mmol/litre, respectively) than normal (4.7 and 0.42 mmol/litre) in samples of amniotic fluid obtained at calving. Sodium (100 mmol/litre) and chloride (67 mmol/litre) in allantoic fluid were also higher than normal (53 and 20 mmol/litre, respectively). Conversely, creatinine concentrations were lower than normal in allantoic fluid (2.2 vs 13.8 mmol/litre). Oestradiol concentrations were lower than normal in maternal plasma (ranges: less than 20 to 140 pg/ml vs 30 to 440 pg/ml); maximum prostaglandin F metabolite (PGFM) concentrations were slightly elevated (ranges 1.1 to 2.0 ng/ml vs 0.4 to 0.9 ng/ml). Progesterone and cortisol concentrations remained within the normal range; the latter hormone increased markedly in parallel with raised PGFM concentrations. In two cases, the concentrations of reproductive hormones tended to be lower in the amniotic fluid than in the allantoic fluid. For example, progesterone concentrations were 42.8 and 14.9 ng/ml in the amniotic fluids vs 64.2 and 29.8 ng/ml in the allantoic fluids of the two cows; PGFM concentrations were 27.7 and 4.3 ng/ml vs 34.6 and 5.0 ng/ml, and oestradiol concentrations were 1.5 and 3.5 ng/ml vs 1.1 and 6.4 ng/ml in the two fluids, respectively.

Animals↗
PubMed1989

Effect of dose and route of administration of ACTH1-24 on plasma cortisol concentrations in ewes.

Doses of 0.005-1.0 mg of ACTH1-24 given intravenously, intramuscularly or as an intramuscular depot injection caused increases in cortisol concentrations within 15 min in the plasma of ewes. There was, however, considerable animal-to-animal variation in maximum concentrations achieved. A curvilinear dose-response relationship to ACTH1-24 was obtained which was similar for each route of administration when expressed in terms of maximum cortisol concentrations. However, for a given dose, more prolonged release of cortisol occurred after i.m. injection compared to i.v., with maximum concentrations occurring 6 h after the depot formulation injection. Five repeated daily doses of 1.0 mg depot ACTH1-24 resulted in no diminution of cortisol response indicating considerable synthesizing capacity of the adrenals in clinically normal ewes. Comparison of cortisol concentrations after an acute stressor (shearing) suggests that doses of ACTH1-24 greater than 0.25 mg are excessive for simulation of stress-induced adrenal activity.

Animals↗
PubMed1989

Opioid modulation of tonic luteinizing hormone release in ovariectomized dairy cows.

A possible role of endogenous opioid peptides (EOP) in regulating the release of luteinizing hormone (LH) in the absence of ovarian influence was investigated. Experiments were conducted on three lactating Holstein-Friesian dairy cows, 20-27 days after ovariectomy. The cows were bled before and after a single intravenous (i.v.) injection of either 250 mg of naloxone (EOP antagonist) or 300 mg of morphine (EOP agonist) or a combination of the two in Experiments 1, 2 and 3, respectively. The mean and basal LH concentrations and the LH pulse frequency and amplitude were compared before and after each treatment in each cow. Naloxone induced an immediate rise in LH concentration by 60-300% above the preceding baseline values. This rise lasted for 15-30 min in each cow, after which the normal rhythmic LH release continued. One cow (A) suffered discomfort and respiratory distress 15-25 min after naloxone administration and the mean and basal LH concentration dropped significantly. Morphine significantly reduced the mean LH concentration by decreasing the number and amplitude of LH pulses and the basal LH values in two cows, although the decrease in one was not significant. The mean LH concentration in each cow remained unaffected by the combined treatment of morphine and naloxone. In conclusion, the elevation of LH concentration by naloxone, the suppression of LH release by morphine and the reversal by morphine and naloxone of each other's effects suggest that EOP could be involved in the control of LH release in cows in the absence of ovarian influence.

Animals↗
PubMed1989

Effects of naloxone on the oestradiol-induced LH surge and cortisol release in transported cows.

Four control cows released a normal LH surge in response to 1 mg oestradiol benzoate i.m. Compared to controls, 30 min transport of 5 cows 16-18 h after oestradiol significantly delayed the onset (P less than 0.05), suppressed the amplitude (P less than 0.01) and reduced the total LH release (P less than 0.001) in 4 cows and totally blocked the surge in the 5th cow. Just before the onset of transport, 5 cows were given 250 mg naloxone i.v. In 3 cows, the LH surge was delayed and reduced in amplitude and duration and was totally blocked in the other two, i.e. naloxone did not avert the detrimental effects of transport. Transport stimulated cortisol release in cows. Cows given naloxone + transport released significantly more (P less than 0.001) cortisol than did those subjected to transport alone. In conclusion, naloxone appeared to have further stimulated the hypothalamopituitary-adrenal axis of cows under stress.

Animals↗
PubMed1988

Retrospective analysis of the efficacy of different hormone treatments of cystic ovarian disease in cattle.

Cystic ovarian disease in cows was treated either with a single intramuscular injection of 500 micrograms cloprostenol, a prostaglandin F2 alpha analogue, in 77 cases of luteal cysts or with 500 micrograms gonadorelin or 20 micrograms buserelin, gonadotrophin releasing hormone or its analogue (GnRH), in 116 cases of follicular cysts. Recovery was defined as the absence of cysts and the formation of a corpus luteum either with or without observed oestrus within 10 days after treatment with cloprostenol and 15 days after treatment with GnRH. Recovery occurred in 65 per cent and 52.6 per cent of cases, respectively, in average times of 4.9 and 19 days. Fifteen days after treatment with GnRH, 20 cows with luteinised cysts were treated with cloprostenol and 15 recovered in a mean of 20.4 days, while 10 which still had follicular cysts, were given GnRH and one recovered 31 days after the beginning of treatment. Another 27 cows, in which cysts became luteinised, were treated with cloprostenol seven days after treatment with GnRH to give quicker (average 11.5 days) but poor (48 per cent) recovery and with a higher rate (33 per cent) of recurrence of cysts. A progesterone releasing intrauterine device was used in 25 cases of cystic ovarian disease, some of which had been previously treated. Sixty-eight per cent recovered in an average of 15 days. The proportions of cows becoming pregnant to one to three inseminations after the different methods of treatment were similar (77 to 94 per cent).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Increased collagenase activity is not detectable in cervical softening in the ewe.

Cervical tissue from ewes at various stages of pregnancy was examined for evidence that collagenase is involved in the process of cervical softening. Collagenase activity was detected in medium after 2-3 days culture of ovine cervical explants, but there was no significant difference in total enzymic activity produced by explants from non-pregnant, early pregnant or late pregnant animals when expressed as units/mg wet weight of tissue over five days in culture. Oestradiol infusion into ewes prior to parturition did not alter the enzyme activity subsequently produced in explant culture. However, the DNA concentration, and hence the number of cells per unit volume, decreased significantly with length of pregnancy, this effect being due to expansion of cervical tissue which occurs late in pregnancy. Thus, if collagenase activity is expressed relative to DNA and hence cell number, there is evidence for increased production per cell in order to keep the tissue concentration constant. However, as the concentration of collagen in cervix remains constant during pregnancy, the ratio of collagenase activity to collagen is also constant. It is therefore concluded that there is no evidence of a role for increased collagenase activity in cervical softening in the ewe.

Animals↗
PubMed1988

Collagenase inhibitor concentration in cultured cervical tissue of sheep is increased in late pregnancy.

An inhibitor of collagenase was released from cultured cervical tissue of sheep and the amounts released were greatest from tissue in late pregnancy (145-146 days). The molecular weights of material with inhibitory activity, estimated by gel filtration of extracted inhibitor, at different stages of pregnancy were different, i.e. 20,000 from extracts of late-pregnant and post-partum samples and 29,000 from extracts of non-pregnant samples. Inhibitor from culture supernatants had a molecular weight of 42,000. We conclude that the inhibitor has binding characteristics and molecular weights similar to those of the tissue inhibitor of metalloproteinase.

Animals↗
PubMed1988

Effect of endogenous and exogenous progesterone on the oestradiol-induced LH surge in dairy cows.

Four cows released an LH surge after 1.0 mg oestradiol benzoate administered i.m. during the post-partum anoestrous period with continuing low plasma progesterone. A similar response occurred in the early follicular phase when plasma progesterone concentration at the time of injection was less than 0.5 ng/ml. Cows treated with a progesterone-releasing intravaginal device (PRID) for 8 days were injected with cloprostenol on the 5th day to remove any endogenous source of progesterone. Oestradiol was injected on the 7th day when the plasma progesterone concentration from the PRID was between 0.7 and 1.5 ng/ml. No LH surge occurred. Similarly, oestradiol benzoate injected in the luteal phase of 3 cows (0.9-2.1 ng progesterone/ml plasma) did not provoke an LH surge. An oestradiol challenge given to 3 cows 6 days after ovariectomy induced a normal LH surge in each cow. However, when oestradiol treatment was repeated on the 7th day of PRID treatment, none released LH. It is concluded that ovaries are not necessary for progesterone to inhibit the release of LH, and cows with plasma progesterone concentrations greater than 0.5 ng/ml, whether endogenous or exogenous, did not release LH in response to oestradiol.

Anestrus↗
PubMed1988

Suppression of LH response to gonadotrophin-releasing hormone or oestradiol by ACTH(1-24) treatment in anoestrous ewes.

Stress is known to result in lowered female reproductive efficiency. The objective of this study was to examine how increased pituitary-adrenal activity may influence gonadotrophin release in anoestrous ewes. Various doses (0.06-1.0 mg) of a synthetic adrenocorticotrophic hormone (ACTH(1-24)) preparation were injected into ewes 30 min or 3 h before an i.v. injection of 500 ng gonadotrophin-releasing hormone (GnRH). The LH response to GnRH given 30 min after ACTH(1-24) was similar to that after GnRH alone, whereas the response 3 h after ACTH(1-24) was significantly lower, irrespective of the dose of ACTH(1-24). At 30 min and 3 h after ACTH(1-24) the concentrations of cortisol exceeded 50 nmol/l compared with baseline values of less than 10 nmol/l. The effect of ACTH(1-24) on oestradiol-induced LH release was also examined. Those ewes receiving 0.8 mg ACTH(1-24) depot and 50 micrograms oestradiol benzoate simultaneously had a preovulatory-type increase in LH 14-20 h later, similar to when oestradiol benzoate was given alone. None of the ewes receiving an additional 0.8 mg ACTH(1-24) depot 10 h after oestradiol benzoate had increases in LH concentration. The cortisol concentrations in all ewes receiving either one or two injections of ACTH(1-24) were greater than 35 nmol/l at 10 h after the oestradiol injection. However, concentrations of progesterone increased from 0.9 +/- 0.3 (S.E.M.) nmol/l at the time of the second ACTH(1-24) injection to 2.1 +/- 0.3 nmol/l after 2 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗
PubMed1987

Preliminary results of treatment and endocrinology of chronic endometritis in the dairy cow.

Cows with chronic endometritis were treated by using uterine irrigation, prostaglandin or oestradiol benzoate. An attempt was made to relate the success of treatment to the nature of the discharge. No statistically significant differences were demonstrated between the different treatments, nor did the severity of the disease as judged by the amount of pus in the discharge affect the success of treatment. Progesterone and in some cases a metabolite of prostaglandin were measured in a milk sample taken at the time of treatment. Increased prostaglandin concentrations were found in 69 of 71 samples examined but they were not correlated with the progesterone concentrations. These measurements from cases of endometritis were higher than those from normal cows in the immediate post partum period and during established oestrous cycles. Treatment with prostaglandin when the concentration of progesterone was high was not more effective than when progesterone concentrations were low. Treatment had less influence on the subsequent fertility of the cow than other factors investigated; in particular, the sooner after calving the cow was treated the greater was the chance of success. This was thought to be due, at least in part, to the high rate of spontaneous recovery. Before treatment can be evaluated effectively a method must be found to identify persistent cases.

Animals↗