Use of a long-acting oxytetracycline preparation in respiratory disease in young beef bulls.
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Age Factors↗
Biomedical subjects
A R Peters
Publications and source records attributed to A R Peters.
Studies of hormone patterns during the oestrous cycle of beef cows.
Hormone patterns in blood plasma were examined in relation to the bovine oestrous cycle in two experiments. During the luteal phase LH pulse frequency was low (2-3 pulses per 8 h). There were no consistent correlations between LH, FSH and progesterone concentrations. During luteolysis, falling progesterone concentrations were accompanied by an increase in oestradiol-17 beta concentrations, LH concentrations and LH pulse frequency, the latter being almost one pulse per hour on the day before the preovulatory surge.
Animals↗
Plasma LH and FSH responses and ovarian activity in prepubertal heifers treated with repeated injections of low doses of GnRH for 72 h.
Twelve 5-month-old Hereford X Friesian heifers were injected i.v. with 2.0 micrograms GnRH at 2-h intervals for 72 h. Blood samples were collected at 15-min intervals from 24 h before the start until 8 h after the end of the GnRH treatment period. Over the 24-h pretreatment period, mean LH concentrations ranged from 0.4 to 2.2 ng/ml and FSH concentrations from 14.1 to 157.4 ng/ml; LH episodes (2-6 episodes/24 h) were evident in all animals. Each injection of GnRH resulted in a distinct episode-like response in LH, but not FSH. Mean LH, but not FSH, concentrations were significantly increased by GnRH treatment. The GnRH-induced LH episodes were of greater magnitude than naturally-occurring episodes (mean maximum concentration 6.7 +/- 0.5 and 4.9 +/- 0.6 ng/ml respectively). Preovulatory LH surges occurred between 17.0 and 58.8 h after the start of treatment in 9/12 heifers, with a coincident FSH surge in 8 of these animals. This was not followed by normal luteal function. There were no apparent correlations between pretreatment hormone concentrations, and either the pituitary response to GnRH or the occurrence of preovulatory gonadotrophin release.
Animals↗
Hormone responses to exogenous GnRH pulses in post-partum dairy cows.
Nine Friesian dairy cows were treated with 2.5 micrograms GnRH i.v. at 2-h intervals for 48 h commencing between Days 3 and 8 post partum. Hormone concentrations were measured in jugular venous plasma. An episodic pattern of LH release was induced in all animals and there was no significant change in amplitude during treatment. However, cows treated between Days 7 and 8 ('late') showed higher LH episode peaks than did those treated between Days 3 and 6 ('early'). Plasma FSH concentrations showed a less clear episodic pattern in response to GnRH injection. The mean height of FSH responses to GnRH tended to be higher in the 'early' group than in the 'late' group, as did mean FSH concentrations during the pretreatment sampling period. Although clear episodic changes were not observed, GnRH treatment induced a rapid sustained rise in plasma oestradiol-17 beta concentrations, indicating the responsiveness of ovarian follicles to gonadotrophin stimulation early in the post-partum period. There was no difference in oestradiol-17 beta concentrations between the 'early' and 'late' groups during the treatment period. Only one cow exhibited preovulatory-type LH, FSH and oestradiol-17 beta surges during the 96-h post-treatment sampling period. It is concluded that: (1) responsiveness to GnRH pulses increases significantly and FSH responsiveness tends to decrease with time post partum, (2) ovarian follicles are able to secrete oestradiol-17 beta in response to GnRH-induced LH and FSH release during the early post-partum period and there is no time-dependent change in responsiveness; and (3) the lack of preovulatory surges, except in one cow, may reflect a temporary defect in the positive-feedback mechanism by which high concentrations of oestradiol-17 beta induce preovulatory gonadotrophin release.
Animals↗
Plasma progesterone and gonadotrophin concentrations following norgestomet treatment with and without cloprostenol in beef cows.
Twelve Hereford cross Friesian cows received subcutaneous implants containing 6 mg norgestomet and intramuscular injections of 5 mg oestradiol valerate and 3 mg norgestomet. Six of the cows also received 0.5 mg cloprostenol eight days later and all implants were removed on day 9. When treatment was commenced between days 3 and 5 of the ovarian cycle, luteal function was not prevented although the luteal phase was shortened in some cases. When treatment was commenced between days 8 and 14 of the cycle progesterone concentrations remained above basal levels for five to seven days. Cows with corpora lutea that were given cloprostenol underwent rapid luteolysis. It is concluded that oestradiol valerate does not control luteal function adequately, particularly if administered early in the cycle, and this may explain failure of oestrus synchronisation in some cases. Administration of prostaglandin 24 hours before norgestomet implant removal may improve the degree of oestrus synchronisation in groups of cyclic cows.
Animals↗
Luteolysis in cows using the prostaglandin F2 alpha analogue, tiaprost, and the effect of mode of administration.
Thirteen cows received 0.75 mg tiaprost by subcutaneous injection during the mid-luteal phase of the ovarian cycle. Twelve underwent rapid luteolytic and continued to cycle normally as determined by milk or plasma progesterone concentrations. The other cow underwent only a transient decrease in progesterone concentrations. A further 15 cows received either a subcutaneous osmotic mini-pump containing 30 mg tiaprost , calibrated to release 0.75 mg over a 24 hour period (group 1); a subcutaneous injection of 0.375 mg tiaprost (group 2), or a subcutaneous injection of 0.375 mg tiaprost plus the osmotic mini pump (group 3). Treatment caused luteolysis in zero and one cows in groups 1 and 3 respectively. However all six cows in group 2 underwent rapid luteolysis. Although the standard therapeutic dose of tiaprost (0.75 mg) appears to be a highly effective luteolytic agent it is concluded that there may be scope for development of longer acting formulations of this compound.
Animals↗
Effects of exogenous growth hormone on mammary function in lactating goats.
The galactopoietic effect of daily injections, for five day periods, of growth hormone was examined by measuring milk yield, mammary blood flow and arteriovenous differences of glucose and amino acids on 12 occasions in four goats. In 10 periods there were marked increases (mean 18.1%) in mammary blood flow (8 statistically significant) and less-marked increases (mean 8.0%) in milk yield (6 statistically significant). On 8 of the occasions on which it was measured the maximum blood plasma growth hormone concentration was increased to more than 8 ng/ml. There were no statistically significant changes in mammary arteriovenous concentration differences of glucose or amino acids in response to growth hormone injections. It is suggested that, contrary to the usual situation in which the rate of mammary blood flow appears to be regulated by the metabolic activity of the gland, the galactopoietic response to growth hormone may be a consequence of elevated blood flow, which increases the supply to the gland of rate-limiting metabolic substrates.
Amino Acids↗
Plasma LH and FSH concentrations in prepubertal beef heifers before and in response to repeated injections of low doses of Gn-RH.
Blood samples were taken at 15-min intervals from prepubertal beef heifers, 6 aged 4 months and 6 aged 10 months, to determine plasma LH and FSH concentrations. Two animals of each age group were then subjected to 9 consecutive injections of 0.5, 2.0 or 5.0 micrograms Gn-RH at 2-h intervals. LH episodes were evident in all animals before treatment, and in 11/12 heifers occurred at a rate of between 1 and 4 per 24 h. One 10-month old heifer, later detected in oestrus, displayed 10 episodes/24 h. Mean FSH concentrations did not differ significantly between age groups. In all animals, Gn-RH injections induced an episodic pattern of LH secretion which was significantly different between Gn-RH doses, but not between age groups. A distinct episode-like response in FSH concentrations occurred to each Gn-RH injection in only one heifer. These results provide further evidence that the prepubertal period is associated with a lack of pituitary stimulation, rather than an inability to respond to Gn-RH.
Animals↗
Effect of exogenous oestradiol-17 beta on gonadotrophin secretion in post-partum beef cows.
Twelve cows between Days 10 and 17 post partum received one or two silicone rubber implants, each containing 45 mg oestradiol-17 beta. Plasma oestradiol concentrations increased from 4.25 +/- 0.51 pg/ml before implant insertion to 16.57 +/- 3.66 pg/ml (one implant) and 37.10 +/- 9.1 pg/ml (two implants) during the 5 days of implant treatment. Preovulatory-type LH and FSH surges were induced in 11/12 cows between 15 and 79 h after implant insertion. There were no relationships amongst plasma oestradiol concentrations, LH pulse frequency, pretreatment FSH concentrations, timing of the LH surge or time to first rise in milk progesterone concentration. There was a negative correlation (r = -0.58; P less than 0.05) between the stage post partum and the timing of the peak of the LH surge after implant insertion. Although the positive feedback mechanism was functional in most cows, the data may reflect a continuing recovery of the responsiveness of the hypothalamo-pituitary axis to the positive feedback effects of oestradiol-17 beta between Days 10 and 17 post partum.
Animals↗
Serological survey on the prevalence of bovine herpesvirus 1 antibodies in pedigree beef bulls.
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Animals↗
Calving intervals of beef cows treated with either gonadotrophin releasing hormone or a progesterone releasing intravaginal device.
Over a two year period, 436 suckling beef cows were treated either with a progesterone releasing intravaginal device (PRID) for 10 days, or two injections of 0.25 mg gonadotrophin releasing (gn-RH) at an interval of 10 days, or left as controls. Treatment commenced between days 20 and 40 post partum and cows were subsequently mated naturally at oestrus. PRID treated cows showed a more synchronous onset of oestrus than the control or Gn-RH treated cows. There was no overall significant effect of either treatment on the mean calving interval, although in the first year PRID treatment before day 30 post partum reduced the mean calving interval by 12.8 days compared to the controls (P less than 0.05). Neither bodyweight nor body condition score had a significant effect on the calving interval.
Animals↗
Plasma gonadotrophin responses in beef cows two progesterone plus prostaglandin treatment.
Progesterone Releasing Intravaginal Devices (Prids) were inserted into six post-partum beef cows for nine days and 0.5 mg cloprostenol was injected i m on day eight. Blood samples were taken via jugular venous catheters at frequent intervals for seven days after Prid removal and assayed for LH, FSH and progesterone. The induced pre-ovulatory type LH and FSH surges occurred between 35 and 123h after Prid withdrawal in five of the cows. In four cows which underwent surges during the time of most intensive sampling, LH levels were significantly higher during the 30h period prior to the LH surge than during the 30h period after the surge. FSH values were low for the 30h period preceding and the 14h period following the time of maximum FSH/LH concentrations. 16 - 30h after the FSH and LH surges, FSH values were again significantly raised compared with the period immediately after the surge. Despite the success of this Prid/PG regime in inducing ovulation, the variability in time between progestagen withdrawal and the LH surge and ovulation is such that the use of fixed time artificial insemination may give poor results.
Journal Article↗
A comparison of plasma LH concentrations in milked and suckling post-partum cows.
Plasma samples were taken every 10 min for periods of 8 h on 3 occasions during the post-partum period from 8 cows milked twice daily (Groups M1 and M2) and from 4 cows each suckling 4 calves (Group S). All samples were assayed for LH, and ovarian activity was monitored by measurement of milk progesterone. Three of the Group M1 cows had a delayed return to ovarian activity after calving (greater than 70 days) whereas all 4 Group M2 cows resumed ovarian cycles by 25.25 +/- 3.35 days post partum. Three Group S cows resumed cycles by a mean of 47.7 days post partum while the fourth had not done so by Day 100. Mean plasma LH concentrations were low pre partum (0.67 +/- 0.05 ng/ml) and up to day 5 post partum (0.80 +/- 0.03 ng/ml, Group S; 0.90 +/- 0.12 ng/ml, Group M1; 0.80 +/- 0.25 ng/ml, Group M2). Concentrations then increased up to Day 12 (1.23 +/- 0.20, 1.66 +/- 0.16 and 1.67 +/- 0.21 ng/ml in Groups S, M1 and M2 respectively). Between Days 13 and 20 a distinct pulsatile pattern was seen in the profiles of milked but not of suckling cows. The pulse frequency was lower (approximately 2/8 h) in those milked cows in which ovarian activity was delayed and varied from 4 to 10 episodes/8 h in milked cows that commenced ovarian activity early in the post-partum period. It is suggested that the pulsatile LH pattern is a prerequisite for the onset of ovarian cycles.
Animals↗
Induction of pulsatile LH release, FSH release and ovulation in post-partum acyclic beef cows by repeated small doses of Gn-RH.
Five acyclic spring-calving beef cows (20-40 days post partum) were bled every 15 min for 60 h and thereafter every 6 h for 5 days. Gn-RH (5 micrograms) was injected every 2 h for 48 h, starting 12 h after sampling began. Pulsatile patterns of LH release occurred synchronously in response to injection and 4 of the 5 treated animals subsequently ovulated and completed at least one full ovarian cycle. Four of 6 similar control cows were bled every 10 min for 8-h periods at equivalent times post partum. Pulses of LH were seen after approximately Day 25 post partum with a mean pulse frequency of 0.5 per h. There was little evidence of a discrete pulsatile mode of FSH release in any of the treated or control cows. The time to the first significant progesterone rise in the 4 treated and ovulating cows (34.5 +/- 5.6 days post partum) was significantly shorter (P less than 0.05) than in the 6 control animals (66.3 +/- 11.4 days).
Animals↗
Endocrine patterns of the post-partum cow.
Milked dairy cows generally have a shorter post-partum interval to ovarian cyclicity than suckling dairy or beef cows. In milked and suckling cows, there is a strong seasonal influence with spring-calving cows remaining anoestrous longer. Increasing the suckling intensity further delays the onset of ovarian cyclicity, probably by increasing the frequency or strength of its inhibitory influence on hypothalamic activity. Plasma FSH levels rise in most cows 5-10 days after calving and thereafter the random changes observed have little relationship to the onset of cycles. Recovery of FSH release therefore occurs earlier post partum than recovery of LH release. Hyperprolactinaemia is not a cause of reproductive failure in milked or suckling cows because there is no correlation between plasma prolactin levels and the onset of ovarian cycles. Plasma LH concentrations undergo significant changes directly related to the initiation of ovarian cycles, with low plasma levels immediately post partum, followed by an increase in basal secretion and the development of clear LH episodes. This pulsatile pattern appears earlier in dairy than in beef cows and is further delayed by suckling compared to milking. Before the first ovulation there is an increased frequency and peak height of LH episodes leading to a rise in plasma LH levels and eventually to a preovulatory-type LH surge which results in the first ovulation. These changes in the pattern of LH release appear definitive in the initiation of ovarian activity in post-partum cows.
Animals↗
Milk progesterone profiles and the double injection of cloprostenol in post partum beef cows.
The time to resumption of ovarian cycles was determined in 27 post partum beef suckler cows by twice weekly milk progesterone analysis and was 24.5 +/ 1.6 (SEM) days. Treatment of 87 cows with a double injection of 500 micrograms cloprostenol at an interval of 11 days resulted in 55 cows (63.2 per cent) responding by a fall in progesterone levels and ovulation. Thirty-eight of these cows (43.7 per cent of total) subsequently conceived to a timed double insemination. Eight (9.2 per cent) had high progesterone levels at the second injection had failed to respond; three (3.4 per cent) had a prolonged period of low progesterone levels after the first injection which were still low when the second was given. A further 21 cows (24.1 per cent) had low progesterone levels at the time of the second injection but could not be categorised further with certainty because of lack of previous samples. These cows were treated at a significantly earlier stage post partum than the rest and in fact were treated earlier than the recommended day 42. However, four of the 21 cows conceived to the timed insemination resulting in a total conception rate of 48.3 per cent.
Animals↗
Short-term relationships between plasma LH, FSH and progesterone concentrations in post-partum dairy cows and the effect of Gn-RH injection.
Jugular venous blood samples were obtained from 7 dairy cows every 10 min for 10-19 h during the early- or mid-luteal phase of the oestrous cycle, and each cow was given 1 or 2 i.v. injections of 100 micrograms synthetic Gn-RH. Four of these cows were also sampled in a different cycle with no treatment being administered. Peaks of plasma LH, FHS and progesterone were detected in each animal in the absence of treatment; those of LH and progesterone often occurred in parallel. Injection of Gn-RH was always followed by a significant increase in plasma LH and progesterone concentrations and in most cases by a significant FSH increase. There was a significant temporal relationship between the peaks of all 3 hormones. A further 8 cows were sampled during the first 10 days post partum when the mean plasma progesterone concentration was low. An i.v. injection of 200 micrograms synthetic Gn-RH was given to each animal and this resulted in a significant increase in plasma LH and FSH concentrations, but in only one cow was the Gn-RH injection followed by a significant increase in plasma progesterone concentration. The LH response to Gn-RH injection was significantly less in cows injected on or before Day 5 post partum than in cows injected on Days 7-10 post partum.
Animals↗
Effects of increased supply of essential amino acids on the metabolism of the isolated perfused guinea-pig mammary gland.
The effects of high rates of infusion of essential amino acids on amino acid uptake by the isolated perfused guinea-pig mammary gland were studied. Infusion of methionine, tyrosine, phenylalanine, histidine and tryptophan (designated group 1) resulted in significant increases in the uptakes of tyrosine, phenylalanine and histidine. Methionine, tryptophan and other essential amino acids were not significantly affected. Infusion of threonine, valine, isoleucine, leucine, lysine and arginine (designated group 2) resulted in significant increases in uptake of all these amino acids. Group 1 amino acid uptake was not significantly affected. Infusion of all the essential amino acids (i.e. groups 1 and 2 together) resulted in significant increases in all their uptakes. Using as index 'the predicted rate of protein synthesis', infusion of group 1 and 2 together led to an apparent 27% increase in protein synthesis. The above results are discussed in relation to the control of milk protein synthesis by limiting essential amino acids.
Alanine↗