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Biomedical subjects

C B Gow

Publications and source records attributed to C B Gow.

28 records · Page 2Linked to original sources
PubMed1987

Comparisons of time intervals and plasma LH concentrations during the ovulatory cycle of broiler breeder hens maintained under either a 24 h light:dark cycle or continuous light.

The possibility that egg production in broiler breeder hens may be increased by selection for reduced oviposition interval under continuous light was investigated by comparing the pattern of pre-ovulatory releases of plasma luteinising hormone (LH) and the associated ovipositions in the same broiler hens maintained under normal cycles (15.25 h light/d) or continuous light. The lighting conditions had no effect on plasma concentrations of LH before and at the pre-ovulatory LH peak in first, mid-sequence or terminal ovulatory cycles. Plasma LH concentrations were similar during first, mid-sequence and terminal ovulatory cycles. Mid-sequence oviposition intervals and the interval between a mid-sequence LH peak and its associated oviposition were longer under continuous light than under normal lighting. Pre-ovulatory releases of LH occurred during a restricted period of day in both lighting conditions. Under continuous lighting they were probably entrained by the daily pattern of restricted feeding. Any selection programme for reduced oviposition interval under continuous lighting in broiler breeder hens should take into account the entraining effects of the daily pattern of feeding.

Animals↗
PubMed1986

Plasma concentrations of luteinising hormone during the ovulatory cycle in hens selected for reduced oviposition interval and maintained in continuous light or a 24 h light:dark cycle.

Plasma luteinising hormone (LH) concentrations were measured during the ovulatory cycle in lines of Australorps and White Leghorns selected for reduced oviposition interval and maintained under continuous light and noise. Selection significantly increased plasma LH concentrations in mid-sequence ovulatory cycles of Australorps but not in the White Leg-horns. Selection in the Australorps apparently increased the rate of ovarian follicular maturation, resulting in more frequent LH peaks. The effect of selection on plasma LH concentrations is a function of the lighting condition to which the hens are exposed.

Animals↗
PubMed1985

Effects of selection for reduced oviposition interval on plasma concentrations of luteinising hormone during the ovulatory cycle in hens on a 24 h lighting cycle.

The effects of selection under continuous light for reduced oviposition interval within a sequence of eggs on plasma luteinising hormone (LH) concentrations during the ovulatory cycle were investigated in lines of Australorps and White Leghorns maintained on a 24-h light:dark cycle. Selection did not significantly alter LH concentrations during mid-sequence cycles in either breed. In the control lines, concentrations were higher in the Australorps than in the White Leghorns before and at peak in mid-sequence cycles. The increase in egg production resulting from selection was associated with an advance in the mean time of lay of mid-sequence eggs in both breeds and, in the Australorps, with more pre-ovulatory LH peaks being initiated at the beginning of the open period of the ovulatory cycle. Selection reduced the time an egg spends in the oviduct and, in the Australorps, significantly reduced the interval between a pre-ovulatory LH peak and the oviposition of the egg currently in the shell gland. We suggest that selection under continuous light for reduced oviposition interval increased the rate of ovarian follicular maturation by a mechanism which did not involve an increase in pre-ovulatory concentration of plasma LH in a 24-h light-dark cycle.

Animals↗
PubMed1983

The importance of prolactin for initiation of lactation in the pregnant ewe.

A single injection of ergocryptine (0.5 mg/kg liveweight) given to ewes 0.5-20 days prepartum or two injections (0.5 mg/kg liveweight per injection) given c. 30 and 10 days prepartum reduced concentrations of plasma prolactin to negligible (less than 5 ng/ml) values for 4 weeks after parturition, but did not affect concentrations of growth hormone and placental lactogen. Milking of treated ewes had no effect on concentrations of plasma prolactin during the first 4 weeks of lactation, but concentrations of growth hormone were increased during the 10-20 min period after milking. The half-life of prolactin in plasma was estimated as 21 min. In spite of the dramatic effect of ergocryptine on plasma prolactin all treated ewes secreted copious quantities of milk of normal composition. Mean daily yields of ewes treated with ergocryptine were not significantly different (P greater than 0.05) from those of untreated control ewes, but the mean +/- s.e.m. of total milk production over the first 3 weeks of lactation for ergocryptine-treated ewes was significantly lower (P less than 0.05) than that of control ewes (9.5 +/- 1.11 v. 14.1 +/- 1.20 kg milk). The results suggest that prolactin is not an essential component of the lactogenic and galactopoietic complexes of hormones in the ewe.

Animals↗
PubMed1981

Comparison of glucose biokinetics in parturient ewes and ewes induced to lactate artificially.

Glucose biokinetics of six normal pregnant/lactating ewes during the periparturient period were compared with those of five non-pregnant ewes induced to lactate artificially by treatment with oestrogen and progesterone, followed by a series of infusions of oxytocin. Normal ewes produced large amounts of milk (800-900 g/day) on day 1, and yields remained relatively constant until day 8 post partum. Milk production of induced ewes, however, was negligible on day 1 (30 g/day) but increased progressively until day 8 (540 g/day) after the start of milking. The glucose irreversible loss per minute 2-8 days before (6.4 v. 5.6 mg per kilogram body weight 0.75), and 2 days after the onset of lactation (9.1 v. 5.5 mg/min per kg0.75) was significantly greater (P less than 0.05) in normal pregnant/lactating ewes than in ewes induced to lactate artificially. By the eighth day of lactation rates of glucose irreversible loss per minute (7.4 v. 6.4 mg per kilogram body weight 0.75) were not significantly different (P greater than 0.05). The data were consistent with the hypothesis that glucose supply is rate limiting for milk production for several days after the initiation of lactation in non-pregnant, hormone-treated ewes. In parturient ewes, the rate of glucose irreversible loss was significantly increased 1-2 days post partum.

Animals↗
PubMed1981

Control of gluconeogenesis in the lactating sheep.

Ewes which had been lactating for 3--4 weeks and which had been milked by hand from the day of parturition were subjected to food restriction for 4 days. One group of three ewes was fed ad libitum and a second group of four ewes was fed to meet calculated requirements for maintenance and milk production. Over 4 days food intake was reduced by 80% in both groups of ewes. In response to food restriction, milk yields and body weight decreased. Blood amino acids, plasma glucose, glucose pool size, glucose irreversible loss, insulin, thyroxine and the insulin: glucagon molar ratio decreased. In contrast, plasma glucagon remained relatively unaffected and plasma free fatty acids and growth hormone increased. These changes were similar for both groups of ewes and were reversed when food intake was restored. The results suggest that the hormonal control of gluconeogenesis in the ruminant is similar to that in the non-ruminant.

Amino Acids↗
PubMed1980

Investigations of ultradian and circadian rhythms in the concentration of cortisol and prolactin in the plasma of dairy cattle.

This experiment analysed the circadian and ultradian pattern of secretion of cortisol and prolactin in cattle, and from this a meaningful sampling technique for these hormones has been suggested. Two Friesian and two Jersey heifers, non-pregnant and 18 months of age, were bled (2 ml blood) every 10 min for 24 h via an indwelling jugular cannula inserted 6 h before sampling commenced. The concentration of cortisol in plasma showed an ultradian rhythm with an amplitude of approximately 30 ng/ml and a frequency of about 0.6 cycles/h. Elimination of the ultradian component of variation, by taking the mean of the rolling means (last three values) for individual heifers, indicated a diurnal variation in cortisol concentration which was high between midnight and midmorning and low in the afternoon. There were frequent sporadic "bursts' of prolactin secretion but these were inconsistent. There was no evidence of diurnal variation in prolactin concentration, or of a temporal relationship between cortisol and prolactin secretion.

Animals↗
PubMed1979

Responses to post-ruminal infusions of casein and arginine, and to dietary protein supplements in lactating goats.

1. In Expt 1 a study was made in goats of responses in terms of milk production, nitrogen utilization and plasma amino acids to abomasas infusions of casein (45 g/d) in goats given 2.5 kg/d of a ration containing crude protein (N x 6.25) at 109 (L1) or 146 (H1) g/kg. 2. In Expt 2 a study was made in goats of responses in terms of milk production, nitrogen utilization, plasma amino acids and growth hormone levels to abomasal infusions of casein (45 g/d) or arginine (25 g/d) in goats given 2.3 kg/d of a ration containing crude protein (N x 6.25) at 104 g/kg (L2). These observations were made also in goats given a ration containing crude protein at 136 g/kg (H2). 3. Milk production in Expt 1 was 2.75, 2.45 and 2.76 kg/d on L1+casein, H1 and H1+casein treatments respectively, the response to casein infusion being significant (P less than 0.05). Milk production in Expt 2 was 1.90, 2.04, 1.96 and 1.96 kg/d on L1, L2+casein, L2+arginine and H2 treatments respectively, and the differences were not significant. 4. Total N intake in Expt 1 was 49, 58 and 64 g/d on L1+casein, H1 and H1+casein treatments respectively. Faecal N was similar on the three treatments (14 g/d), urinary N was 15, 23 and 30 g/d and milk N was 14, 12 and 14 g/d on the respective treatments. Total N intake in Expt 2 was 33, 40, 43 and 44 g/d on L2, L2+casein, L2+arginine and H2 treatments respectively. Faecal N was similar on the four treatments (12 g/d), urinary N was 7, 10, 13 and 14 g/d and milk N was 9, 9, 8 and 8 g/d on the respective treatments. 5. The concentration of indispensable amino acids in plasma was increased by casein infusion in both experiments. It was 1279, 825 and 1133 micrometers/l on L1+casein, H1 and H1+casein treatments respectively in Expt 1, and 1081, 1582, 1055 and 1163 micrometers/l on L2, L2+casein, L2+arginine and H2 treatments respectively in Expt 2. 6. The concentration of arginine in plasma was doubled 1 h after the onset of arginine infusion in Expt 2, Growth hormone levels in plasma were not increased when arginine levels rose following arginine infusion. and did not differ between treatments. 7. The results of the two experiments showed that the stimulatory effect on milk production of intra-abomasal infusion of casein was not reproduced by increasing the dietary intake of protein or by infusing arginine. The results of the second experiment showed that abomasal infusion of arginine did not stimulate production of growth hormone and that growth hormone apparently was not implicated in the effects of casein infusion on milk production.

Abomasum↗
PubMedDate not supplied

Effects of indomethacin on epidermal growth factor-induced renal responses in sheep.

1. The effects of indomethacin (an inhibitor of prostaglandin synthesis) on the renal responses to epidermal growth factor (EGF) were investigated in conscious sheep. 2. Ewes (n = 5 per group) received an i.v. saline infusion (150 mL/day) for days 1-8, followed by either vehicle control, 15 micrograms/h EGF, 2 mg/kg per day indomethacin or 15 micrograms/h EGF with 2 mg/kg per day indomethacin in 150 mL/day saline, i.v., over days 9-12. All ewes subsequently received an i.v. saline infusion (150 mL/day) over days 13-20. 3. Polydipsia, diuresis, transient natriuresis and reduced urine osmolality occurred during EGF treatment alone. There was no effect of EGF on fluid balance, plasma electrolyte or hormone concentrations, plasma osmolality or haematocrit or on the urinary excretion of potassium. 4. Simultaneous infusion of indomethacin with EGF attenuated (P < 0.05) the stimulatory effects of EGF infusion alone on urine volume, water intake, natriuresis and urine osmolality. 5. We conclude that prostaglandins may be involved in the diuretic/natriuretic effects of EGF, but may not be the sole mechanism involved.

Animals↗