Variables associated with peripartum traits in dairy cows. V. Hormonal profiles associated with retained fetal membranes

Profiles of certain hormones measured by radioimmunoassay in 41 Holstein cows and heifers with retained fetal membranes (RFM; >12 hr postpartum) were compared to 41 peers without RFM (NRFM). Peers were matched by parity, season of calving, gestation length, dystocia and parturient paresis within prepartum diet group. Linear covariates of natural photoperiod, mean daily temperature, calf birth weight, length of gestation, and age and body weight of cow were included in the leastsquares analyses of data. Plasma profiles of prolactin and estrone were nearly identical from day 8 prepartum to day 2.5 postpartum. Plasma estradiol-17α was approximately one-third higher each day in group RFM (P<.05 across days) but estradiol-17β (Eβ) tended to be lower until day 2 prepartum (not significant). Also, plasma progesterone (P) was higher in group RFM between days 8 to 3 prepartum (p<.05 across days).Relationships between plasma P and Eβ were indicative of subsequent RFM (>24 hr rather than >12 hr), but only on day 6 prepartum. Three of four cases of 12 to 24 hr RFM had P and Eß profiles similar to NRFM. Either a combination of low P (<3.0 ng/ml) and low Eß (<100 pg/ml) or only high P (>7.9 ng/ml) were associated with a ten-fold higher rate of RFM (>24 hr) than when P was intermediate (4 to 8 ng/ml) and Eß exceeded 99 pg/ml. These results are in agreement with prior data wherein RFM were induced at premature births either by ovariectomy during pregnancy or by glucocorticoids.     

Effect of corticoid induced parturition on lactation and on prepartum profiles of serum progesterone and the estrogens among cows retaining and not retaining fetal membranes

Twenty-one mature F1 Brahman-Hereford cows were treated with 25 mg of dexamethasone (DEX) on day 279 or 280 of gestation to induce birth prematurely. Eigth cows were untreated (UT). Blood was sampled on day 279 or 280 of gestation just prior to treatment of cows with DEX (0 hr), at least daily thereafter to calving and within 1 hr postpartum. Concentrations of progesterone (P₄), estrone (E₁) and estradiol-17β (Eβ) and -17α (Eα) in blood serum were measured by radioimmunoassay. Among 21 cows treated with DEX, 16 (76%) calved within 78 hr (52±3 hr). Eleven of the 16 cows retained fetal membranes more than 12 hr (RFM) and five cows did not retain fetal membranes (NRFM). Five cows (24%) treated with DEX calved 266±46 hr later (NOR) on day 290±1 of gestation compared to day 286±2 for cows in group UT. No cow in groups NOR or UT had RFM. Failure of group NOR to calve prematurely appeared due to elevated serum P₄ (P<.05), low serum Eβ (P<.10) and other estrogens (P>.10) pretreatment, and to only a 32% decrease in serum P₄ within 72 hr after treatment. Serum estrogens, especially Eβ, were next lowest pretreatment in group RFM. However, in group RFM, all serum estrogens increased (P<.10 to P<.01) within 48 hr after treatment, reached higher concentrations and peaked later in relation to calving than in other groups (NRFM, NOR and UT). Synchronization of placental maturation and parturition may require a longer period of elevated serum estrogens prior to calving than was observed in group RFM. Treatment of cows prepartum with DEX had no effect on gain of calves, milk yield or yields of fat, total protein and total solids in milk during the first 12 weeks of lactation.     

Control of estrus in the lactating postpartum mare with fluprostenol (ICI-81,008)

During the 1976 breeding season 68 mares (56 Thoroughbred and 12 Quarter Horse) were allotted to 4 treatment groups. On day 7, 8 or 9 post-ovulation or day 6, 7 or 8 after foal heat each of 28 mares was injected intramuscularly with 250 μg of the prostaglandin analogue ICI-81,008 (generic name fluprostenol). In the second group, 32 mares were bred at foal heat. Group 3 consisted of 9 mares, which were passed at foal heat and bred at the second postpartum estrus. In group four, 12 of the mares which had failed to conceive at foal heat were bred at the second estrus. Twenty-four prostaglandin treated mares returned to estrus 4.2±.4 days post-injection. The interestrual interval was shorter (P<.05) for prostaglandin treated mares (11.4±.6 days) than for previously mated second heat control mares (19.2±2.3). Also, the interval between parturition and second estrus was decreased (P<.05) in treated mares (24.5±.8 days) compared to group three (32.8±2.5 days). Duration of the second postpartum estrus was similar for both treated and control mares. Plasma progesterone levels in prostaglandin treated mares as determined by RIA were 7.5±.5 and 6.9±.5 ng/ml before treatment and at l hour post-injection, then dropped precipitously to near undetectable levels at 48 hours after injection. Pregnancy rate at 45 days was significantly higher (P<.05) in prostaglandin treated mares (78%) as compared to foal heat mares (48%) and mares which were passed at foal heat and bred at the second postpartum estrus (44%).     

The determination of the vitamin D metabolites on a single plasma sample: changes during parturition in dairy cows.

Methods have been developed for the precise measurement of the major known vitamin D metabolites in a single sample of cow plasma (~5 ml). The procedure involves initial extraction with methylene chloride-methanol followed by chromatography on Sephadex LH-20. 25-Hydroxyvitamin D₂ and 25-hydroxyvitamin D₃ were determined using high-pressure liquid chromatography and comparing ultraviolet absorption peak height with absorption peak heights of standards. The dihydroxylated metabolites were further purified and resolved by high-pressure liquid chromatography and determined by radioligand binding assays. The assays were employed to measure the total vitamin D metabolite levels in the plasma of paretic and normal dairy cows at parturition. Parturition had no effect on 25-hydroxyvitamin D levels in either group of cows (paretic, 37–44 ng/ml; normal, 35–38 ng/ml). However, normal cows did show lower mean 25-hydroxyvitamin D levels at every sampling period with the lowest levels in both groups occurring at 7 days postpartum. Plasma 25, 26-dihydroxyvitamin D was higher in paretic animals prepartum and at parturition (0.7–1.0 ng/ml) when compared to nonparetic animals (0.4–0.45 ng/ml). Similar levels (0.6 ng/ml) were observed in both groups postpartum. Cows developing parturient paresis showed a significant (P < 0.05) elevation of 1,25-dihydroxyvitamin D at parturition with a maximum level of 350 pg/ml attained at 1 day postpartum compared to prepartum levels of 60 pg/ml. Normal animals also showed a rise in plasma levels of 1,25-dihydroxyvitamin D with a maximum level of 185 pg/ml observed at 1 day postpartum. Plasma 24,25-dihydroxyvitamin D was initially higher in paretic cows (1.9 ng/ml) with a significant (P < 0.05) drop to 1.05 ng/ml occurring at parturition. This level was maintained for 7 days postpartum. The levels of this steroid were maintained at 1.3–1.4 ng/ml in the normal cows throughout the entire sampling period.     

Effect of monensin and suckling on the GnRH induced luteinizing hormone surge and the effect of monensin on the postpartum interval in Brangus cows

Twenty-seven fall calving Brangus cows were randomly allotted to one of four treatment groups: nonsuckled monensin (NSM), suckled monensin (SM), nonsuckled control (NSC), and suckled control (SC). Cows were group fed 1.82 kg/hd/day concentrate and Coastal bermuda grass hay $\text{ad}$$\text{libitum}$. Monensin cows received 200 mg monensin/hd/day in the concentrate. At 0800 hr on day 21 postcalving, the calves were separated from the cows. Suckled monensin and SC cows were allowed to suckle their calves for 30 min at 6-hr intervals. Nonsuckled monensin and NSC cows were not suckled. Calves were given free access to the cows after 1400 hr on day 22 postpartum. At 0800 hr on day 22 postpartum, a blood sample was collected. A 100 μg GnRH challenge was administered IM at 0801 hr. Blood samples were collected at 15-min intervals for 6 hr postinjection. Changes in body weight and body condition from day 21 postpartum to the day of first estrus were not different (P>0.10) by dietary treatment. Monensin cows consumed 10.7% less hay than did the control cows. Serum luteinizing hormone (LH) following GnRH was greater (P<0.005) in suckled than nonsuckled cows. Control cows released more (P<0.005) LH in response to GnRH than did the monensin cows. The postpartum interval (to first estrus) for the monensin cows (92.4±14.7 days) was shorter (P<0.025) than the controls (138.5±9.5 days). A greater proportion (P<0.005) of the monensin cows (8 of 14) exhibited estrus by 90 days postpartum compared to the control cows (0 of 13). Monensin and suckling appear to exert independent and agonistic influences on pituitary function in the postpartum beef cow.     

Radioimmunoassay of cortisol in peripheral blood plasma of buffaloes peripartum

Changes in the concentration of cortisol were observed in the jugular venous plasma of pregnant buffaloes on days 30, 15, 5, 2 and 1 prepartum, at partum, at regular 6-hr intervals up to 72 hr postpartum and on days 4, 6, 10, 18, 34 and 50 postpartum. A radioimmunoassay (RIA) procedure for cortisol standardized in the laboratory was used. Mean plasma cortisol levels showed little fluctuation (P<0.05) between days 30 and 2 prepartum with the values ranging from 1.28 +/- 0.23 to 1.46 +/- 0.13ng/ml. A small (but nonsignificant) rise in the hormone level was observed one day prepartum followed by a sharp increase to a high mean value of 3.78+/-0.36 ng/ml (P<0.05) at parturition. A sharp decline (P<0.05) to a low mean value was recorded within 6 hr postpartum followed by marked fluctuations in the hormone level up to 72 hr postpartum. The hormone levels subsequently varied narrowly between 1.74+/-0.39 and 2.01+/-0.27 ng/ml up to 50 days postpartum.     

The effect of calf removal on estrous response and pregnancy rate of beef cows after SYNCRO-MATE-B treatment

The effect of calf removal on estrous response and pregnancy rate of cows given SYNCRO-MATE-B (SMB) was determined. Two hundred forty three lactating beef cows treated with SMB were allotted to three treatments: treatment 1, no calf removal; treatment 2, 24 hr calf removal and treatment 3, 48 hr calf removal. Calf removal time began with removal of the SMB implant. All cows were artificially inseminated 48 to 54 hr after implant removal. Body condition of cows in each heard was visually appraised as adequate or marginal. At each location, technicians and sires were stratified across all treatments.Estrous response of cows (n=143) was different (P<.01) between treatments which averaged 23, 40 and 77 percent for treatments 1, 2 and 3, respectively. Pregnancy rates of cows (n=243) after the first artificial insemination (AI) were 32, 28 and 46 percent for treatments 1, 2 and 3, respectively. The pregnancy rate was greater (P<.05) for treatment 3 than other treatments. After 25 days of breeding, the pregnancy rates were 59, 58 and 72 percent, respectively, for the three treatments. There was a linear relationship between days postpartum at the time of treatment and estrous response (P<.01) and first service pregnancy rate (P<.05). The partial regression coefficients for estrous response and first service pregnancy rate were 1.2 and .6 percent, respectively.In summary, estrous response and pregnancy rate of lactating beef cows treated with SMB were increased by 48 hr calf removal, compared to no calf removal or 24 hr calf removal, when calf removal time began with removal of the SMB implant.     

Effect of monensin on postpartum interval to first estrus and serum LH response to 0, 1, 2 or 4 mg estradiol-17β at 21 days postpartum

A 2×4 factorial design was used to evaluate the effects of monensin (0 vs 200 mg) and estradiol-17β (E2) dose (0, 1, 2 vs 4 mg) on postpartum interval (PPI) to first estrus and on serum LH release at 21 days postpartum. Forty-eight spring calving Brangus cows were randomly stratified by calving date and sex of calf into two feeding groups within 24 hr of calving. Each group received 2.7 kg/head/day of a milo:cottonseed meal (4:1) mixture containing either 0 or 200 mg monensin. Coastal bermuda grass hay and water were available $\text{ad}$$\text{libitum}$. During the period of E2 treatment and bi-hourly blood sampling, suckling was controlled at 6-hr intervals.Mean cow weight and body condition score within cell changed less than 23 kg and 0.5 points, respectively, from day 1 to day 21 postpartum and were unaffected by treatment (P>0.10). PPI was reduced (P<0.01) and proportion of cows exhibiting estrual behavior by 85 days postpartum was increased (P<0.05) by treatment with 200 mg monensin and unaffected by E2 dose. Monensin fed cows had a longer (P<0.05) interval to LH response (ILH) and to peak LH (ILHP) at the 4 mg E2 dose. Monensin had no effect (P>0.10) on LH variables at 0, 1 or 2 mg E2.     

Plasma and atrial content of atrial natriuretic factor in cardiomyopathic hamsters

Immunoreactive atrial natriuretic factor (IR-ANF) was measured in plasma and atrial extracts from normal and cardiomyopathic Syrian golden hamsters. Plasma IR-ANF was increased from 84.8 ± 9.8 pg/ml(n = 17) to 234 ± 23 (n = 25; P<.0001) in hamsters with moderate failure, and to 1085 ± 321 pg/ml (n = 10; P<.02) in animals with severe failure. Plasma IR-ANF increased with increased atrial hypertrophy. Atrial IR-ANF content was essentially the same in normal animals and in those with moderate heart failure (3.06 ± 0.28 vs 3.17 ± 0.19 μg/100 g body wt., P<.001) and lower in the majority of those with severe failure (1.82 μg/100 g body wt., P<.001). The elevations of IR-ANF in plasma are similar to those seen in patients with congestive heart failure. Our studies do not support bioassay results showing a deficiency of atrial ANF content as being important in the congestive heart failure associated with cardiomyopathy in the hamster.     

Luteinizing hormone,total estrogens and progesterone secretion during lactation and after weaning in sows

Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low (< 1 ng/ml) during lactation and averaged 1.9 ± .3, .6 ± .3 and 1.2 ± .3 on days 1, 3 and 5 after weaning. Estrogens were variable during lactation, averaged 121 ± 36 pg/ml on day 1 after weaning and decreased thereafter. Estrus began on day 3 after weaning in 1 sow and on day 5 in the remaining 10 sows.In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low (< 1 ng/ml) until after ovulation when progesterone increased. Estrus began on day 4 after weaning in all seven sows.Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.     

Effect of feed restriction or feeding high-fibre diet during the rearing period on body composition, serum parameters and productive performance of rabbit does

This study evaluated the effect of different feeding regimes from 11 weeks of age to first parturition on feed intake, leptin, non-esterified fatty acids (NEFA) and total protein serum levels, as well as productive performance in young rabbit does. In addition, body composition was estimated by bioimpedance analysis. Thirty-six 11-week-old does were randomly distributed in three groups. The AL-C group was fed ad libitum a control diet containing 350 g neutral detergent fibre (aNDFom)/kg, 11.6 MJ digestible energy (DE)/kg and 173 g crude protein (CP)/kg, and the does were inseminated at 16 weeks of age. The R-C group was fed 150 g/d of the same diet until 16 weeks of age, one week before artificial insemination (AI) at 17 weeks of age, and then fed ad libitum. The AL-F group was fed a diet containing 475 g aNDFom/kg, 9.4 MJ DE/kg and 174 g CP/kg ad libitum, and was inseminated at 17 weeks of age. During rearing (11-16 weeks), does in the R-C group had the lowest DE (1.54 MJ/d; P<0.003) and digestible protein (DP, 17.9 g/d; P<0.001) intake, as well as the lowest protein (172 g/kg; P<0.05) and energy (5.9 MJ/kg) body contents, leptin concentration at 16 weeks of age (2.48 ng/ml; P<0.001) and fertility (P<0.02) at first AI. Daily feed intake during pregnancy and lactation, as well as prolificacy and litter weight, were similar among groups. The highest percentage of body fat was observed for all the does when were inseminated for the first time (135 g/kg; P<0.001), consistent with the highest leptin (4.48 ng/ml; P<0.001) and total protein serum levels (6.87 g/dl; P<0.001) at this time. Serum NEFA level around parturition was higher (P<0.05) in groups AL-C and R-C (1.11 and 0.85 mmol/l) than in group AL-F (0.71 mmol/l), suggesting a lower lipid mobilization that tended to improve fertility rate for AL-F does on day 11 post-parturition (P<0.09). In conclusion, feed restriction during the rearing period delays reproductive development in young rabbits. In nulliparous does, ad libitum feeding during rearing with a high-fibre diet allows a similar productive performance to that of feeding with a less fibrous diet. Nevertheless, the use of high fibre diets during rearing does not affect feed intake throughout the first pregnancy and lactation.     

Changes in plasma levels of estrone sulfate and estrone in the pregnant ewe around parturition

A method for the extraction, separation and measurement of estrone sulfate and estrone in a single plasma sample is described. The method has been applied to the determination of plasma levels of estrone sulfate and estrone in pregnant ewes over the period 60 hr before to 20 hr after parturition. The study revealed that the plasma levels of estrone sulfate and estrone began to increase about 40 hr before parturition, reached a peak at parturition and then declined rapidly to levels below the sensitivity of the method by 15 hr postpartum. The peak level of estrone sulfate recorded at parturition was 103 pmol (38 ng) per ml of plasma which was approximately 30 times greater than the corresponding peak level of estrone.     

Mycotoxin production in a carbendazim-resistant strain of fusarium sporotrichioides

Mycelial yield and production of three trichothecenes, namely T-2 toxin, diacetoxyscirpenol (DAS) and neosolaniol (NEO) were compared in control (CS) and carbendazim-resistant strains (RS) ofFusarium sporotrichioides. Each strain was exposed to graded concentrations of carbendazim (0, 1, 2, and 4 μg/ml media) for 2, 5 and 7 days under shake-culture conditions at an incubation temperature of 25°C. Mycelial yield was significantly (P<0.001) affected by strain, carbendazim concentration and incubation time. The strain differences in mycelial mass at 2 days (P<0.05) became more pronounced at 5 and 7 days of incubation (P<0.001). However, mycelial growth differences between the two strains were greatest following exposure to carbendazim, with the effects becoming more divergent with time. Combined results for the three incubation times showed dose related effects in carbendazim inhibition of T-2 toxin production by CS isolates. In contrast, RS cultures exposed to the 2 μg/ml addition of carbendazim significantly increased T-2 toxin production (P<0.05 or better). At 1 and 4 μg/ml additions, T-2 toxin inhibition occurred but the effect was less marked than in the CS series. RS yielded more DAS than CS at 5 days (P<0.05) and at 7 days (P<0.01) of incubation. The major component of this strain difference arose from the effects of the 2 μg/ml addition of carbendazim (P<0.01). NEO production was also higher in RS than in CS, with the difference becoming progressively more pronounced from day 5 (P<0.05) to day 7 (P<0.01) of incubation. However, these differences reflected enhanced NEO output with carbendazim addition of 4 μg/ml (P<0.05) in day 5 extracts and of both 2 μg/ml (P<0.01) and 4 μg/ml additions (P<0.05) in day 7 samples. Moreover, the ratio of NEO to T-2 toxin production was affected by an interaction involving incubation time, strain and carbendazim dose (P<0.05 or better). On day 5, this ratio was greater in CS exposed to 2 μg/ml, but at 4 μg/ml, the ratio was higher in RS. It is concluded that carbendazim resistance induced genuine differences in the synthesis of T-2 toxin and NEO. It is suggested that the strain difference may reside in the conversion of NEO to T-2 toxin which may be sensitive to fungicide concentration. This would imply that carbendazim resistance induces changes in the terminal rather than initial phases of trichothecene biosynthesis.     

Running and shipping elevate plasma levels of beta-endorphin-like substance (B-END-LI) in thoroughbred horses

A specific RIA for beta-endorphin (B-END) was developed to measure horse plasma levels of B-END-like material (B-END-LI) during exercises and shipping. Three exercise speeds and durations were: trot at 260-300 m/min for 10 min; slow gallop at 390-420 m/min for 5 min and fast gallop at 700-800 m/min for 2 min. Blood samples were taken from 4 horses before, immediately after, 30 and 60 min after exercise. Trotting increased plasma B-END-LI from a basal level of 109 +/- 7 pg/ml to 172 +/- 22 at the end of exercise and returned to 127 +/- 17 and 107 +/- 10 pg/ml at 30 and 60 min after exercise. Similar results were obtained in slow gallop (121 +/- 6 to 210 +/- 17 then 155 +/- 8 and 131 +/- 11 pg/ml). However, fast gallop caused the greatest increase (352%) in B-END-LI to concentrations of 544 +/- 93 pg/ml and 276 +/- 74 pg/ml at 5 and 30 min after exercise. Plasma B-END-LI returned to 199 +/- 46 pg/ml in 1 hr. Sequential exercises of trot, slow and fast gallop were conducted in 6 horses. Plasma B-END-LI were 116 +/- 19 pg/ml (pre-exercise), 198 +/- 21 (trot), 361 +/- 51 (slow gallop), 500 +/- 57 (fast gallop) and 248 +/- 29, 171 +/- 24, 143 +/- 20 and 139 +/- 21 pg/ml at 0.5, 1, 2 and 3 hr, respectively, following exercises. Transportation in horse trailer also significantly increased plasma levels of B-END-LI from a basal level of 138 +/- 12 to 196 +/- 24 pg/ml within 30 min and this levels were maintained at 45 min (177 +/- 3 pg/ml). Plasma levels of B-END-LI began to decline at 60 min of shipping. These results showed that plasma B-END-LI was increased in all speeds of exercise and by shipping and returned to pre-exercise and pre-shipping level in 30 min except fast gallop which returned to pre-exercise level in 1 hr.     

Mechanism for the increase in plasma renin activity by pentobarbital anesthesia

The mechanism by which pentobarbital anesthesia causes increases in plasma renin activity (PRA) was examined in dogs infused with either propranolol or indomethacin, an inhibitor of prostaglandin synthetase. Infusion of propranolol at 1 mg/kg, (I.V.) followed by 0.6–0.7 mg/kg/hr decreased PRA from 6.98±2.49 ng/m1/hr during control periods to 1.58±0.79 ng/m1/hr 30 minutes after the injection of propranolol (P<0.025). Subsequent induction of anesthesia with sodium pentobarbital caused PRA to rise to 3.87±0.93 ng/m1/hr in 30 minutes. (P<0.01). Plasma potassium concentration decreased from 4.6±0.2 mEq/L to reach 4.0±0.1 mEq/L 30 minutes after induction of anesthesia (P<0.005). Infusion of indomethacin at 5 mg/kg, (I.V.) followed by 1.5 ? 3.1 mg/kg/hr into conscious dogs did not decrease PRA. In contrast to the report by Montgomery et al (Fed. Proc. 36: 989, 1977), we found that the increase in PRA after pentobarbital anesthesia could not be blocked by indomethacin. PRA was 5.3±1.2 ng/m1/hr(M ± SEM) during control periods and was 4.7±1.4 ng/m1/hr 30 minutes after the infusion of indomethacin (P<0.1). PRA increased to 10.9±2.3 ng/m1/hr, 9.2±2.2 ng/m1/hr, and 7.7±1.7 ng/m1/hr at 5, 15 and 30 minutes, respectively, after the administration of pentobarbital (P<0.005, P<0.025, P<0.05). PRA declined to 4.2±1.3 ng/m1/hr 60 minutes after pentobarbital anesthesia (P<0.1). It is concluded that the mechanism by which pentobarbital causes increases in PRA is independent of prostaglandins.     

Serum levels of progesterone, 5 alpha-dihydroprogesterone and hydroxy-5 alpha-pregnanones in the prepartum and postpartum equine.

Blood samples were collected from eight mares for ten days before and two days following parturition. Progesterone, 5 alpha-dihydroprogesterone and hydroxy-5 alpha-pregnanones were extracted from serum, separated by Sephadex LH-20 column chromatography and quantitated by radioimmunoassay. Progesterone levels ranged from 8.5 to 4.1 ng/ml among mares with normal parturition and decreased to 1.2 ng/ml after parturition. One mare with a retained placenta maintained the prepartal levels of progesterone into the postpartum period. 5 alpha-dihydroprogesterone increased to a level of 133 ng/ml at 80 hrs before parturition and began decreasing and reached a level of 9.2 ng/ml in the postpartum period. Levels of hydroxy-5 alpha-pregnanones were variable with a high of 1690 ng/ml and declined to a postpartum level of 60 ng/ml. The timing of the decline varied among the mares. The possible source and significance of these progestins remain speculative.     

A study of prostaglandin F2α as the luteolysin in swine: II characterization and comparison of prostaglandin F, estrogens and progestin concentrations in utero-ovarian vein plasma of nonpregnant and pregnant gilts

Polyvinyl catheters were inserted into the right and left utero-ovarian veins (UOV) and saphenous vein (SV) and artery (SA)_of six nonpregnant (O) and five pregnant (P) gilts on day 11 after onset of estrus. Beginning on day 12, UOV blood samples were collected at 15-min intervals from 0800 to 1100 hr and 2000 to 2300 hr, and single samples were taken at 1200 and 2400 hrs. Peripheral blood (SA or SV) was sampled at 0800, 1200, 2000 and 2400 hr until gilts returned to estrus ( ) or day 24 or pregnancy. UOV plasma PGF concentrations (ng/ml; n = 1929) were measured by RIA. Status (P O) by day interactions were detected (P<.01) but variances among treatments were heterogenous (P<.01). Cuvilinear day trends were detected for PGF in 0 gilts (P<.01) but not P gilts. PGF peaks, defined as concentrations greater than two SD above the mean concentration for each gilt, occurred with greater frequency ((ifχ² = 16.4; P>.01)) in 0 than P gilts; and mean peak levels ( ) were 5.0 ± .27 and 3.84 ± .13 ng/ml, respectively.Progesterone concentrations were maintaiend in pregnant pigs and were indicative of luteal maintenance. Systematic differences in day trends of utero-ovarian venous plasma estradiol were detected between O and P pigs. These differences may be of paramount physiological importance and are discussed.     

Plasma oxytocin concentrations during late pregnancy and parturition in the dog

While oxytocin is widely used in the treatment of dystocia in dogs, there is little information about its secretion before and during normal unassisted whelping. We therefore measured plasma oxytocin concentrations during late pregnancy and the expulsive stage of parturition. Blood samples were collected from eight dogs at 3-min intervals during a 42-min period between the 2nd and 14th day before whelping and during parturition after the birth of 1-3 pups. The litters consisted of 5-15 pups and the progression of the expulsive stage was linear and nearly parallel in the eight bitches. The overall mean (+/-S.D.) plasma oxytocin concentration during late pregnancy was 3.6+/-2.1pg/ml. Mean values in individual dogs ranged from 1.2 to 7.4 pg/ml, but the intra-animal variation was rather small. During the expulsive stage the overall mean (+/-S.D.) plasma oxytocin concentration was 12.9+/-13.9 pg/ml, with mean values in individual dogs ranging from 3.5 to 46 pg/ml. The mean area under the oxytocin curve for parturient dogs was significantly higher (P<0.05) than for pregnant dogs. During the expulsive stage, the peak plasma oxytocin level in individual dogs ranged between 10 and 117 pg/ml. In six of the eight dogs a pup was born during blood collection and in five of these animals the plasma oxytocin concentration increased temporarily during periods of abdominal straining and expulsion. However, straining efforts and expulsion were not consistently associated with a rise in the circulating oxytocin level. It is concluded that in the dog plasma oxytocin levels are higher and more variable during the expulsive stage of parturition than during late pregnancy. Interrelationships between the secretion pattern of oxytocin, the level of uterine contractility, and the progress of fetal expulsion in dogs need further exploration.     

Reproductive studies of Brahman cattle V. The effect of various dose levels of estradiol-17β upon serum luteinizing hormone in ovariectomized Brahman cows

Twelve mature chronically-ovariectomized Brahman cows were randomly assigned to receive three of six different dosages of estradiol-17_b (E2) at three different time periods such that at the termination of the trial six animals received each E2 dosage. The E2 was suspended in 0, 1, 2.5, 5, 10 and 20 milligrams. A two week period was maintained between injections. The cows were bled via coccygeal vessel puncture immediately before E2 injection, every 2 hr from 0 to 18 hr, every hr from 18 to 42 hr and every 2 hr from 42 to 48 hr postinjection. Blood was processed to yield serum and stored at ?20 Celsius. Serum luteinizing hormone (LH) was quantitated by validated radioimmunoassay. An LH surge was defined as a sustained elevation of LH at least two standard deviations above the level of LH prior to the rise and was observed in $\text{0}\text{6}$, $\text{3}\text{6}$, $\text{5}\text{6}$, $\text{5}\text{6}$, $\text{5}\text{6}$, and $\text{6}\text{6}$ cows administered 0, 1, 2.5, 5, 10, and 20 mg of E2, respectively. All animals injected with E2 responded with a significant initial decrease (independent of E2 dosage) in LH that persisted from 2 through 12 hr post E2 injection. No significant decrease in LH levels was recorded in animals injected with the corn oil vehicle. The time to the LH surge differed (P<.05) between 1 mg E2 (10 hr) vs 20 mg E2 (19.5 hr), 1 mg E2 vs 10 mg E2 (16.2 hr), and 2.5 mg E2 (12.4 hr) vs 20 mg estradiol-17_β. Luteinizing hormone concentrations at the onset of the surge did not differ (P>.10) between E2 dosages. The elapsed time from E2 injection to the peak LH value differed (P<.05) between 1 mg E2 (20.3 hr) vs 20 mg E2 (26.8 hr), and 2.5 mg E2 (21.2 hr) vs 20 mg estradiol-17_β. The peak LH value, the area under the LH curve and the duration of the LH surge did not differ (P>.10) with E2 dosage. The time to the end of the LH surge differed (P<.05) between 1 mg E2 (25.3 hr) vs 2.5 mg E2 (31.6 hr), 1 mg E2 vs 5 mg (34.4 hr), 1 mg E2 vs 10 mg E2 (34.8 hr), 1 mg E2 vs 20 mg E2 (37.3 hr), and 2.5 mg E2 vs 20 mg estradiol-17_β. Luteinizing hormone values at the termination of the surge did not differ (P>.10) between dosages nor did the LH values at the termination of the surge differ (P>.10) from LH concentrations observed at the onset of the LH surge.     

Inferences of body energy reserves on conception rate of suckled Zebu beef cows subjected to timed artificial insemination followed by natural mating

The influence of body condition score (BCS), rump fat thickness (RFAT), and live weight (LW), and the changes in these parameters during the interval from 165 of prepartum (i.e., 125 days of prior gestation) to 112 postpartum on first service conception and pregnancy rates were investigated in suckled Zebu (Bos indicus) beef cows (n = 266) subjected to timed artificial insemination (TAI) followed by natural mating. The aforementioned parameters were recorded at 165 ± 14 days (mean ± standard error) prepartum (concurrent with the weaning of previous calf), at parturition, and at 42 ± 7 days (at the onset of the synchronization of ovulation protocol), 82 ± 7 days (30 days after TAI), and 112 ± 7 days (60 days after TAI) postpartum. At the start of the breeding season (BS), cows were subjected to a synchronization of ovulation program for TAI. Bulls were placed with cows 10 days after TAI and remained until the end of the study (112 days postpartum). Cows with the highest BCS at parturition had an increased probability of first service conception rate at 60 days after TAI (P = 0.02) and a reduced probability of occurrence of pregnancy loss (P = 0.05). Also, cows had a greater likelihood of conceiving postpartum if they had greater RFAT and BCS at 165 ± 14 days prepartum (P = 0.01 and P = 0.03, respectively) and at parturition (P = 0.0007 and P = 0.003, respectively). Cows that had an increase in RFAT and BCS during the dry period (i.e., interval from weaning of the previous calf to parturition) also had a greater likelihood of conceiving (P = 0.03 and P = 0.06, respectively) during the BS. Among the different time points, RFAT and BCS at parturition had the largest impact on risk of conception during the BS. The LW was a poor predictor of conception during the BS (P = 0.11–0.68) except for LW at 165 ± 14 days prepartum (P = 0.01). Collectively, the findings indicated that the likelihood of conception during the BS was highest in cows that had an improvement in RFAT and BCS during the dry period. Therefore, assuring a good nutritional status in the dry period (BCS ≥ 3.0 at 165 ± 14 days prepartum and ≥3.25 at parturition) is an important aim to optimize the postpartum conception rate of suckled Zebu beef cows subjected to TAI followed by natural mating.