Plasma prolactin concentrations during the oestrous cycle of sows

Plasma prolactin levels were measured in 7 sows during the oestrous cycle after the 1st farrow. Blood samples were taken 4 times during the day (07:00, 11:00, 14:00 and 19:00 h). The prolactin concentration was determined by a double-antibody radioimmunoassay method. There was an increase in plasma prolactin at the second oestrus after weaning, with a peak of prolactin 4 days before oestrus, regardless of the length of the cycle.     

Peripheral plasma concentrations of oestradiol, progesterone, cortisol, LH and prolactin during the oestrous cycle in the cow, with emphasis on the peri-oestrous period

Interrelationships of circulating hormone levels and their implications for follicular development were studied throughout the oestrous cycle with emphasis on the perioestrous period in heifers and cows. The oestradiol level showed a major peak (45 pmol/1) before and coinciding with oestrus, and a second peak (27 pmol/1) around day 5–6 (day 0: day of first standing oestrus); it was low during the luteal phase of the cycle when progesterone was higher than 14 nmol/1 from day −12 to day −2. Large antral follicles, which had developed during the luteal phase, did not secrete significant amounts of oestradiol, degenerated after luteolysis, and were replaced by a newly developing follicle which became preovulatory. Parallel with this development the oestradiol level increased from the onset of luteolysis to reach a plateau about 26 h before the onset of oestrus. The interval between the onset of luteolysis and the onset of oestrus was 58 h; luteolysis proceeded at a slower rate in heifers than in cows. At 4.6 h after the onset of oestrus the maximum of the LH surge was recorded; the LH surge appeared to be postponed in the period October–December in comparison to the period August–September. The maximum of the LH surge was higher in heifers (45 μg/l) than in cows (30 μg/l), but its duration was similar (8.0 h). The oestradiol level decreased significantly from 6 h after the maximum of the LH surge, and standing oestrus (duration 18 h) was terminated almost at the same time as the return to basal values of oestradiol. Cortisol and prolactin levels did not show a peak during the peri-oestrus period. Cortisol fluctuated irrespective of the stage of the oestrus cycle and prolactin was significantly higher during the luteal phase.

The results of this study indicate that development of the preovulatory follicle starts in the cow at the onset of luteolysis, about 2.5 days before the preovulatory LH surge, and that oestradiol secretion by this follicle is possibly inhibited by the LH surge.     

The effect of prolonged stress on the oestrous cycles and prolactin secretion in sheep

The effect of repeated and prolonged stimuli on the release of luteinizing hormone (LH) and the course of oestrous cycles was studied in sheep. Weak electric footshocks were administered in different phases of the cycle in a programmed schedule for 9 h daily during 3–4 days. The enduring and repetitive character of the stimuli was supposed to induce some emotional state which approximated to the so-called management stress. Plasma prolactin concentration was also determined in the pro-oestrous phase of the cycle to follow the interrelationship between the pre-ovulatory release of LH and this hormone.Five out of 26 ewes stimulated in different phases of the oestrous cycle showed inhibition in the release of LH and disturbances in the function of the ovaries (cystic or inactive ovaries). The disturbances of the oestrous cycles appeared not only in the course of the current cycle (in which stimulation was applied), but also in the subsequent ones.Increased plasma prolactin levels after stimulation seem not to have an inhibitory action on the pre-ovulatory LH release. The other cause of the observed disturbances in the course of the oestrous cycle, i.e. the impairment of neuro-hormonal regulation, is discussed.     

Peripheral plasma prolactin and progesterone levels in pseudopregnant goats during bromocryptine treatment

Persistence of luteal function and accumulation of fluid within the uterus (hydrometra) are characteristics of pseudopregnancy in goats. To study the luteotrophic role of prolactin in this condition, seven seudopregnant goats were treated with bromocryptine (1 mg subcutaneously, twice daily) for 6 to 10 d. Plasma progesterone (P4) and prolactin (PRL) were measured by radioimmunoassay (RIA) in samples taken twice daily by venipuncture. Ultrasound scanning took place at regular intervals to visualize the presence of fluid within the uterus. Bromocryptine treatment effectively reduced the plasma PRL concentration in six goats. In all seven goats, a gradual decrease of the plasma P4 concentration to levels < 1.8 ng/ml occured during treatment. After bromocryptine treatment, P4 concentrations reached basal levels (<0.1 ng/ml) in two animals. In four goats, P4 concentrations remained close to 1.0 ng/ml, or even temporarily rose above the 2.0 ng/ml level. Spontaneous discharge of uterine fluid took place during (two goats) or within 4 d after bromocryptine treatment (three goats). These results indicate that prolactin plays an important luteotrophic role during pseudopregnancy in goats.     

The influence of male contact on plasma cortisol concentrations in the prepubertal gilt

Large White X (Large White X Landrace) prepubertal gilts, 165 days of age, were fitted with indwelling venous catheters and housed in modified metabolism crates. After a period of acclimatization, frequent blood samples were taken at regular intervals before, during and after the 7 gilts were exposed to various degrees of contact with male pigs. The plasma samples were assayed for cortisol concentration using a competitive protein-binding radioassay. Significantly elevated concentrations of plasma cortisol (P less than 0.001) occurred only when full physical contact between the boar and the gilts was allowed. Boar exposure without full physical contact induced only minor changes in plasma cortisol concentrations of gilts. Plasma cortisol concentrations have been shown to constitute a reliable indicator of a stress response in pigs, and so the results of this study suggest that tactile stimulation from a male pig induces a stress response in the recipient prepubertal gilt. This stress response in the gilt may be involved in the stimulation of puberty onset by contact with a mature boar (i.e. the 'boar effect').     

Peripheral plasma levels of certain mineral elements in primitive African goats

Changes in blood plasma calcium, inorganic phosphorus, magnesium, zinc, iron, copper, sodium and potassium concentrations over a 3-year period were investigated in primitive goats. Blood plasma mineral concentrations were determined by atomic absorption and a colorimetric method. Changes in Zn and Ca concentrations are season dependent, potassium levels show only a long-term change tendency, and magnesium and inorganic phosphorus had constant levels throughout the investigation period. Iron, copper and sodium showed both long-term change tendencies and more or less marked season related changes.     

Synchronization of oestrous cycles in sable antelope

Techniques for manipulating the oestrous cycle of sable antelope, Hippotragus niger, were evaluated in a captive population of 24 females maintained at the Smithsonian Institution's Conservation and Research Center in Front Royal, VA, USA. A secondary objective was to demonstrate the effectiveness of fecal steroid monitoring techniques as a non-invasive method of tracking experimental manipulations. Controlled Internal Drug Releasing (CIDR) devices designed for cattle (type B, reduced in length by 5 cm to fit the sable antelope's smaller reproductive tract) were more effective than CIDR devices designed for goats (type G) at delivering progesterone into circulation, and maintained serum progesterone at levels up to 86.1+/-7.8% of normal luteal concentrations in females whose spontaneous ovarian activity had been inhibited with melengestrol acetate. Serum progesterone and fecal progestagen measurements were highly correlated (P<0.05). Synchronization treatments of prostaglandin (PG) F2alpha alone and in combination with modified CIDR-B devices (12-day insertion interval) were both effective in inducing synchronized ovulation, however the PGF2alpha/modified CIDR-B treatment resulted in more precise synchrony and a shorter latency to ovulation than did PGF2alpha alone. In a separate experiment to characterize the temporal relationship between synchronization treatment, behavioral oestrus and ovulation, onset of behavioral oestrus occurred 34.1+/-5.7 h following PGF2alpha/modified CIDR-B treatment. Mean duration of the induced oestrus was 24.9+/-4.3 h. The first detectable rise in fecal progestagens occurred 5.1+/-1.0 and 4.1+/-1.0 days following PGF2alpha/modified CIDR-B treatment in groups of females housed with and without an adult male, respectively, indicating that the presence of a male did not accelerate the onset of the induced cycle.     

Cortisol and prolactin concentrations during three different seasons in relocated Brahman and Hereford bulls

The objective of this study was to evaluate seasonal changes of cortisol and prolactin (PRL) concentrations in Brahman and Hereford bulls moved to locations that differ in geographical and environmental conditions. Postpubertal Hereford bulls from Montana (n = 15) and Nebraska (n = 15) and Brahman bulls from Texas (n = 18) were located in or relocated to Montana, Nebraska or Texas so that each location had 5 Montana Herefords, 5 Nebraska Herefords and 6 Texas Brahman bulls. Blood samples were collected at 20-minute intervals for 8 hours in November (Fall 1), April (Spring) and November (Fall 2) of the next year. These dates corresponded to 6, 12 and 18 months, respectively, after relocation in May of the first year. Cortisol concentrations were higher (P<0.05) in Fall 1 than in Fall 2 and were higher (P<0.05) for bulls in Montana than for bulls in Texas. The decrease in cortisol concentrations from Fall 1 to Fall 2 was negatively related (P<0.05) to age and weight. There was a three-way interaction (P<0.05) of breed-type origin, location and season for PRL concentrations. Seasonal patterns of PRL concentrations differed between relocated Texas Brahman and Hereford bulls, and patterns for relocated bulls differed from those of the nonrelocated bulls. Seasonal patterns of PRL were influenced to a greater extent by relocation in Texas Brahman bulls than in Hereford bulls.     

Remote temperature sensing of oestrous cycles in cattle

Radio transmission of deep-body temperature changes in cattle was found to be a feasible method of collecting information for husbandry decisions. Oestrous cycles were plotted and ovulations detected so that cattle were effectively bred artificially. Abnormalities of the cycle pattern accurately indicated abnormal reproductive phenomena. The presence of febrile illness was also detectable. The occurrence of silent oestrus was clearly demonstrated.     

Changes in plasma leptin concentration during different types of exercises performed by horses

Leptin is a tissue-derivative adipokine that regulates appetite, food intake and energy expenditure. It is still not clear how exercise affects plasma leptin concentration in horses. The aim of this study was to evaluate the influence of exercise intensity and duration on plasma leptin levels in working horses. A total of 38 horses were prospectively included in the study and grouped according to the type of exercise they performed: dressage (six stallions, group D), jumping (12 stallions, group J), race (12 Thoroughbred horses, six stallions and six mares, group R) and harness (10 light draft stallions, group H). Blood samples were taken both before and after routine exercise (immediately after the exercise, 30 min and 24 h after). Blood lactic acid (LA) and plasma concentration of leptin, cortisol, uric acid, triacylglycerols, glycerol and free fatty acids were determined. Immediately after exercise, group R had the highest level of LA, whereas groups D and J had the lowest levels. A significant increase in plasma leptin concentration was stated only in group H in samples taken immediately after the end of the exercise period and 30 min after the exercise period, as compared with the values obtained at rest. A significant increase in plasma cortisol concentration was found immediately after the end of the exercise period in groups R and H. Leptin exercise-to-rest ratio was significantly correlated with cortisol exercise-to-rest ratio (r=0.64; P<0.001). The increase in plasma leptin concentration in exercised horses was related to the increased plasma cortisol concentration and took place only during long-lasting exercise, which was not intensive.     

Plasma,milk and faecal progesterone concentrations during the oestrous cycle of lactating dairy cows with different milk yields

The hypotheses tested in this study were that neither average progesterone (P4) concentrations in plasma and milk nor average progesterone metabolites concentrations in faeces would differ during an oestrous cycle in two groups of cows with differing daily milk yields. High producing (HP = 8) and low producing (LP = 8) dairy cows were selected randomly for the study. Their oestrous cycles were initially synchronised using P4 and prostaglandin F2alpha. Chromic oxide capsules were administered twice daily to measure total faecal output. Samples of blood, faeces and milk were taken daily throughout one oestrous cycle, plasma and milk P4, and faecal progesterone metabolites (FP4M) assayed. The average daily milk yields in the two groups were 30.8 and 21.9l per day, respectively (P < 0.0001), although daily faecal output was similar in both the groups (HP, 7.7 versus LP, 6.9 kg DM; P = 0.24). Mean plasma and milk P4 concentrations were similar in both the groups (plasma P4, 4.12 versus 4.05 ng/ml; P = 0.3; milk P4, 8.2 versus 8.3; P = 0.9) during dioestrus. Average daily excretion of P4 to the milk was greater in HP than LP cows (252 versus 185 microg, P = 0.04). Neither concentration nor the daily yield of FP4Ms was affected by level of milk yield (concentration: 12.2 versus 11.5 microg/g; daily yield: 89.1 versus 82.9 mg per day; P > 0.05). These data showed that the concentrations of P4 in plasma and milk, and the concentrations and daily yields of FP4M were not affected by the level of daily milk yields which differed by about 41% of the LP average of 21.9l.     

Short-term inhibition of prolactin secretion by naloxone treatment in the pregnant gilt

The involvement of endogenous opioids in modulation of prolactin (PRL) secretion during pregnancy in the pig was studied. Twenty-four crossbred pregnant gilts (150 ± 10 kg) were cannulated via the cephalic vein 24–48 h before treatment with 1 mg kg⁻¹ body weight of naloxone (NAL) or 3 ml of saline (CONT) i.v. at Day 40 (NAL, n = 6; CONT, n = 6) or Day 70 (NAL, n = 6; CONT, n = 6) of pregnancy. Blood plasma was collected at 15 min intervals from 1 h before to 3 h after treatment with NAL or saline. At Day 40 of pregnancy, administration of NAL caused a decrease in mean plasma PRL concentrations at 60 min, 120 min and 180 min post-treatment (NAL, 19.1 ± 1.3 ng ml⁻¹, P < 0.05; 15.8 ± 0.6 ng ml⁻¹, P < 0.001; 14.6 ± 0.7 ng ml⁻¹, P < 0.001, respectively) when compared with the CONT group (22.9 ± 0.7 ng ml⁻¹, 21.6 ± 0.6 ng ml⁻¹ and 22.4 ± 0.5 ng ml⁻¹, respectively). Mean plasma estradiol concentration was higher (P < 0.01) in the NAL group during the second and third hour post-treatment than in the CONT group. At Day 70 of pregnancy, infusion of NAL also decreased (P < 0.001) plasma PRL concentrations at 60 min, 120 min and 180 min after treatment (20.1 ± 1.6 ng ml⁻¹, 16.2 ± 1.5 ng ml⁻¹ and 14.8 ± 0.4 ng ml⁻¹, respectively) compared with the CONT group (33.4 ± 1.7 ng ml⁻¹, 34.1 ± 1.3 ng ml⁻¹ and 29.1 ± 0.9 ng ml⁻¹, respectively). Estradiol concentrations were not different (P > 0.05) between groups in this stage of gestation. Mean concentrations of progesterone were similar during the pre- and post-treatment periods in both stages of pregnancy.These data would suggest a possible role of the opioids in modulation of PRL secretion at these stages of pregnancy in the pig.