Effect of exogenous FSH on estrus, ovulation and endogenous hormone release in dairy cows

Fifteen lactating Holstein cows were randomly allotted to receive either 0 mg (group 0), 32 mg (group 1) or 50 mg (group 2) porcine follicle stimulating hormone (FSH-P) injected in 10 fractions at 12 hr intervals beginning on day 9 of the estrous cycle. All cows received 25 mg prostaglandin (PG) on day 11. Jugular blood samples were collected from cows in all groups at 6 hr intervals beginning on day 7 and continuing through expression of estrus. Mean duration to occurrence of estrus and preovulatory LH surge after PG injection was reduced (P<.05) by injection of FSH-P. Mean number of ovulations increased (P<.05) progressively with increased dose of FSH-P. Mean peripheral progesterone declined more uniformly in FSH-P treated cows after PG and increased earlier (P<.05) after estrus in group 2 cows compared to group 0 and 1 cows. Mean plasma estradiol-17beta elevated (P<.05) after PG injection in both FSH-P-treated groups compared to group 0 cows. Both LH and FSH increased (P<.05) for 36 hr after initiation of FSH-P injection in groups 1 and 2, then declined until after PG injection. Peak LH and FSH occurred more uniformly following PG in treated cows. Results indicate that FSH-P increased endogenous gonadotropin release, estradiol-17beta, ovulation rate and reduced duration to estrus and preovulatory gonadotropin release after PG. Injection of 50 mg FSH-P increased plasma estradiol-17beta and ovulation rate compared to injection of 32 mg FSH-P.     

Levels of circulating and urinary oestrogens during pregnancy in the marmoset monkey (Callithrix jacchus)

The levels of immunoreactive oestrone, oestradiol-17 beta and oestriol in plasma and urine were measured during early, mid- and late pregnancy in the marmoset monkey. In plasma, unconjugated oestrone remained less than 2% of total (conjugated plus unconjugated) oestrone throughout gestation, whereas unconjugated oestradiol-17 beta increased from 3% of the total value in early and mid-pregnancy to 35% in late pregnancy. The reversal in the unconjugated oestrone: oestradiol-17 beta concentration ratio from early (12:1) to late (0 . 15:1) pregnancy occurred despite the continuing predominance of oestrone in terms of total hormone. Total oestriol was measurable but in relatively low concentrations. Oestradiol conjugate was the predominant urinary oestrogen metabolite measured at each stage of pregnancy. The pattern of urinary oestrone and oestradiol-17 beta reflected plasma levels of total hormone, rather than unconjugated hormone, showing no further increase after mid-pregnancy. In contrast, oestriol increased throughout pregnancy and to a proportionately greater extent than oestrone or oestradiol-17 beta, but at lower absolute levels. High-pressure liquid chromatography of urine extract indicated the presence of considerable amounts of oestrogen immunoreactivity not accounted for by oestrone, oestradiol-17 beta and oestriol and with a retention time similar to that of 16 alpha-hydroxyoestrone. Gas chromatography and mass spectroscopy provided further evidence to suggest that 16 alpha-hydroxyoestrone is an abundant urinary oestrogen metabolite during pregnancy in the marmoset monkey.     

Metabolism of glucose,pyruvate, and glutamine during the maturation of oocytes derived from pre‐pubertal and adult cows

The aim of the study was to compare the energy metabolism of oocytes from pre‐pubertal (2 to 3 months) and adult cows during maturation, to identify the cause of poor developmental potential in many pre‐pubertal oocytes. The metabolism of [5‐³H] glucose, [2‐¹⁴C] pyruvate, and [G‐³H] glutamine was measured at 0 hr, 12 hr, and 24 hr maturation. Oxidative metabolism was important during maturation of oocytes from both pre‐pubertal and adult cows, with pyruvate metabolism peaking at 12 hr and glutamine metabolism increasing linearly and peaking at 24 hr. Peak oxidative metabolism was significantly lower in oocytes from pre‐pubertal animals, for both pyruvate and glutamine (P < 0.05). Glucose metabolism increased significantly during oocyte maturation in both groups (0hr to 24 hr). Glucose metabolism was significantly lower in oocytes from pre‐pubertal cows at 12 hr (P < 0.05). Oocytes from pre‐pubertal animals were significantly smaller than oocytes from adult cows at 0 hr, 12 hr, and 24 hr maturation (P < 0.05). When metabolic rates were corrected for oocyte volume, there were no significant differences in substrate metabolism between oocytes from pre‐pubertal and adult cows. There was however, a delay in the increase in glucose metabolism in pre‐pubertal oocytes 0 hr to 12 hr maturation. Germinal vesicle breakdown was slower in oocytes from pre‐pubertal animals with more oocytes still at the germinal vesicle stage approximately 5 hr post‐aspiration, compared to oocytes from adult cows (P < 0.05). By 24 hr, development to metaphase II was equivalent for pre‐pubertal and adult oocytes. This study identified differences in energy metabolism, oocyte size, and meiotic progression between the oocytes from pre‐pubertal and adult cows that may account for the poor developmental potential of many pre‐pubertal oocytes. Mol. Reprod. Dev. 54:92–101, 1999. © 1999 Wiley‐Liss, Inc.     

Fertility in postpartum dairy cows in winter or summer following estrus synchronization and fixed time AI after the induction of an LH surge with GnRH or hCG

In this study, the fertility of postpartum dairy cows after a sequence of treatments with GnRH (Day 0), PGF2alpha (Day 7) and GnRH (Day 9) (GnRH group; n = 164) or hCG (Day 0), PGF2alpha (Day 7) and hCG (Day 9) (group hCG; n = 166) was investigated in summer and winter seasons. All cows were artificially inseminated without estrus detection, 16-18 h after the end of treatment. Control cows (CONT; n = 226) were not treated and were inseminated at natural estrus. The pregnancy rates at Day 90 (46% versus 33%; P < 0.05) and at Day 135 (76% versus 62%; P < 0.05) postpartum were significantly lower in CONT cows in summer compared to winter months but this effect was not observed in the two treated groups. The number of days from calving to conception was significantly lower in GnRH and hCG treatment groups compared to CONT cows in cold months (102 +/- 3.2, 106 +/- 4.2, 126 +/- 3.1, respectively; P < 0.001) and in hot months (112 +/- 3.2, 114 +/- 4.2, 139 +/- 3.1, respectively; P < 0.001). The concentration of insulin was significantly higher in winter (P < 0.001). There were no differences in average plasma concentration of glucose (P = 0.474), GH (P = 0.441) or IGF-I (P = 0.190). In conclusion, we have shown that veterinary supervision combined with a program of estrous synchronization and fixed time insemination can improve fertility of cows suffering heat stress.     

Restoration of LH output and 17beta-oestradiol responsiveness in acutely ovariectomised holstein dairy cows pre-treated with a GnRH agonist (deslorelin) for 10 days

The objectives of the study were firstly to identify the role of the ovary in maintaining plasma luteinising hormone (LH) concentrations in cows treated with an implant of a potent GnRH agonist (deslorelin), and secondly to characterise the changes in LH following ovariectomy (OVX) in the same animals. Oestrus was synchronised in mature Holstein dairy cows and deslorelin implants were inserted 17 days later into two-third of the cows. A further 10 days later (day 0) all cows had bilateral OVX performed. A control group (CON; n=4) received no treatment and had blood samples collected at 15-min intervals for 8h on the day prior to OVX (day -1) and similarly on days 4 and 10. One group (DES_IN; n=4) had implants in place for the duration of the study while another group had implants removed (DES_OUT; n=4) at the time of OVX. DES_IN cows were sampled hourly at each sampling session (days -1, +4 and +10), whereas DES_OUT cows were sampled similarly to CON except on day -1 when hourly samples were collected.Predictable post-operative increases in mean LH (0.61 ng/ml versus 1.79 ng/ml; P<0.01) and LH pulse amplitude (0.66 ng/ml versus 1.56 ng/ml; day -1 versus day +10; P<0.01) occurred after CON cows were ovariectomised. Smoothed LH means showed a delayed effect of time compared to arithmetic means. Pulse frequency was unchanged following OVX in CON cows. A comparison of all cows that had been treated with deslorelin from day -1 showed a significant elevation of smoothed mean LH compared to untreated cows (0.80 ng/ml versus 0.34 ng/ml; DES_IN and DES_OUT versus CON; P<0.05). DES_IN cows had a 54% reduction in mean LH from day -1 to +4 following OVX (1.05 ng/ml versus 0.48 ng/ml; P<0.01) indicating the probable involvement of the ovary in the maintenance of elevated basal LH. No further reduction was detected by day +10. The LH response to an intramuscular (IM) injection of 500 microg 17beta-oestradiol (E2) on day +11 varied significantly between treatment groups (P<0.01). CON cows showed a typical LH surge, reaching maximum concentrations (10.3 ng/ml) at 17.3h post-injection. Even though low amplitude LH pulsatility had been restored in DES_OUT cows by day +4, there was an inconsistent response to E2 on day +12; one cow had an apparently normal surge yet, others showed only attenuated responses. Pulse amplitude in DES_OUT cows was lower at days +4 and +10 compared to CON (P<0.05). DES_IN cows did not produce any surge after E2. Mean LH prior to OVX (day -1) remained unchanged following the 500 microg oestradiol injection (0.38 ng/ml versus 0.45 ng/ml pre-E2 versus post-E2 compared to 1.05 ng/ml pre-OVX).The results of this experiment implicated ovarian involvement in maintaining elevated basal LH output in cows that were chronically treated with a GnRH agonist. Individual cows varied in their LH surge response to exogenous E2 given 12 days after implant removal, even though LH pulse amplitude and frequency had been restored.     

Pregnancy rate following GnRH + PGF 2alpha treatment of low body condition, anestrous Bos taurus by Bos indicus crossbred cows during the summer months in a tropical environment

Anestrous and lactating Bos taurus by Bos indicus crossbred cows with minimum body condition were studied to determine the efficacy of GnRH+PGF 2alpha combinations for induction of estrus and/or ovulation on pregnancy rate during the months of the year when temperatures are greater. On day 0 (start of treatment), cows were assigned randomly to either treatment or control groups. Treated cows (n = 74) received i.m. 200 microg of GnRH on day 0 and 150 microg of PGF 2alpha 7 days later (day 7). On day 7, treated cows were equally distributed to each of three protocols: (1) Select Synch (n = 25), artificial insemination (AI) 12 h after exhibiting estrus from day 7 (PGF 2alpha injection) until day 12; (2) Ovsynch (n = 24), 200 microg of GnRH at 48 h after PGF 2alpha (day 9) + timed-AI (TAI) 16-20 h later; (3) CO-Synch (n = 25), 200 microg of GnRH + TAI at 48 h after PGF 2alpha (day 9). Control cows (n = 25) received no treatment + AI 12 h after exhibiting estrus from days 0 to 12. Detection of estrus was performed daily during the early morning and evening hours from days 0 to 7 in all the cows, and from days 7 to 12 in the cows treated with Select Synch and in the control group, with the aid of a sterilized bull. Palpation per rectum and transrectal ultrasonography were used on days -30, -20, -10 and 0 to confirm anestrus (absence of CL and no signs of estrus at each evaluation) but with ovarian follicles > or = 10 mm on day 0. Pregnancy rate was 0% for Select Synch, 21% for Ovsynch and 28% for CO-Synch (P < 0.05). In conclusion, the Ovsynch and CO-Synch protocols resulted in greater pregnancy rates compared with the Select Synch protocol in Bos taurus/Bos indicus cows with minimum body condition that were anestrous and lactating during the summer months in a tropical environment.     

Steroid levels after intramuscular injection of radioactive estradiol-17beta, estrone, progesterone and testosterone in the bovine

Eight 2 year old Hereford cows from days 8 to 12 of the estrous cycle were injected intramuscularly with 5 ml of corn oil containing 5 mg of estradiol-17beta (two cows), estrone (two cows), progesterone (two cows) or testosterone (two cows). Each cow treated with estradiol received 494 microc of estradiol-17beta-6, 7 H3 and each cow treated with estrone received 492 microc of estrone-6, 7 H3. Each cow treated with progesterone or testosterone received 400 muc of H3 compound labeled in the 7 position. Total urine was collected by urethral catheterization of the cows treated with estrogens. Blood samples for plasma and serum were collected via jugular cannulae. Blood and urine samples from estrogen-treated cows were collected hourly for the first 24 hr, at 2 hr intervals for the next 26 hr, at 4 hr intervals for the next 12 hr and at 12 hr intervals until background was reached. Blood samples were collected hourly from 1 to 8 hr after injection from progesterone or testosterone-treated cows. Plasma and serum levels of radioactive estradiol-17beta, estrone, progesterone and testosterone were similar. Blood levels of radioactivity peaked at 2 hr post-injection in cows receiving estradiol-17beta and at 3 hr in cows receiving estrone. Blood levels of labeled estradiol-17beta and estrone were nondetectable by 54 hr and 83 hr, respectively. Peak urinary excretion of radioactivity was reached at 7 hr for estradiol-17beta and at 14 hr for estrone and nondetectable levels were reached by 95 hr for estradiol-17beta and 14 hr for estrone. At these times, 15.5% of the total dose of radioactive estradiol-17beta and 17.5% of the injected estrone had been excreted in the urine. Peak blood and urinary excretion levels were reached earlier for radioactive estradiol-17beta than for estrone, and excretion of estradiol-17beta was completed more rapidly. No difference was found in plasma and serum levels for any steroid studies; thus, endogenous steroid titers in blood plasma and serum are not different in the cow.     

Effects of dietary soybean meal and photoperiod cycle on osmoregulation following seawater exposure in Atlantic salmon smolts

Atlantic salmon Salmo salar juveniles were fed either fishmeal-based diets (FM) or diets in which soybean meal (SBM) partly replaced the FM from first feeding on. The fish were kept at continuous daylight during the juvenile stage. During the last 3 weeks before reaching 100 g body mass, all fish were subjected to 12L:12D. Starting at 100 g body mass, groups of 60 fish from each feeding background were subjected to continuous light for 12 weeks (short winter), or a square-wave photoperiod cycle to stimulate parr to smolt transformation with 8L:16D during the first 6 weeks, and then continuous light during the last 6 weeks (long winter). After the 12 weeks, 20 fish from each treatment were subjected to 0, 24 or 96 h seawater exposure at a water salinity of 34. Hypo-osmoregulatory ability at seawater exposure was assessed by mortality, intestinal pathology, plasma ion concentrations and osmolality, gill Na⁺/K⁺-ATPase activity and element concentrations in the cytoplasm of distal intestinal enterocytes using X-ray microanalysis. The hypo-osmoregulatory capacity was higher in fish kept at short winter than at long winter, apparently due to more rapid development of gill Na⁺/K⁺-ATPase activity. Fish fed SBM suffered typical soybean meal-induced histological alterations of the distal intestine and apparent reductions in digestive function in the more proximal gastrointestinal regions. The net osmoregulatory capacity of these fish was maintained, as indicated by higher gill Na⁺/K⁺-ATPase activity and lower plasma Na⁺, Ca²⁺ and osmolality compared to the FM-fed fish. Thus, feeding SBM did not impair the hypo-osmoregulatory ability of the Atlantic salmon following seawater exposure.     

Synchronization of ovulation in beef cows (Bos indicus) using GnRH, PGF2alpha and estradiol benzoate

The objective of this study was to evaluate protocols for synchronizing ovulation in beef cattle. In Experiment 1, Nelore cows (Bos indicus) at random stages of the estrous cycle were assigned to 1 of the following treatments: Group GP controls (nonlactating, n=7) received GnRH agonist (Day 0) and PGF2alpha (Day 7); while Groups GPG (nonlactating, n=8) and GPG-L (lactating, n=9) cows were given GnRH (Day 0), PGF2alpha (Day 7) and GnRH again (Day 8, 30 h after PGF2alpha). A new follicular wave was observed 1.79+/-0.34 d after GnRH in 19/24 cows. After PGF2alpha, ovulation occurred in 19/24 cows (6/7 GP, 6/8 GPG, 7/9 GPG-L). Most cows (83.3%) exhibited a dominant follicle just before PGF2alpha, and 17/19 ovulatory follicles were from a new follicular wave. There was a more precise synchrony of ovulation (within 12 h) in cows that received a second dose of GnRH (GPG and GPG-L) than controls (GP, ovulation within 48 h; P<0.01). In Experiment 2, lactating Nelore cows with a visible corpus luteum (CL) by ultrasonography were allocated to 2 treatments: Group GPE (n=10) received GnRH agonist (Day 0), PGF2alpha (Day 7) and estradiol benzoate (EB; Day 8, 24 h after PGF2alpha); while Group EPE (n=11), received EB (Day 0), PGF2alpha (Day 9) and EB (Day 10, 24 h after PGF2alpha). Emergence of a new follicular wave was observed 1.6+/-0.31 d after GnRH (Group GPE). After EB injection (Day 8) ovulation was observed at 45.38+/-2.03 h in 7/10 cows within 12 h. In Group EPE the emergence of a new follicular wave was observed later (4.36+/-0.31 d) than in Group GEP (1.6+/-0.31 d; P<0.001). After the second EB injection (Day 10) ovulation was observed at 44.16+/-2.21 h within 12 (7/11 cows) or 18 h (8/11 cows). All 3 treatments were effective in synchronizing ovulation in beef cows. However, GPE and, particularly, EPE treatments offer a promising alternative to the GPG protocol in timed artificial insemination of beef cattle, due to the low cost of EB compared with GnRH agonists.     

Vertical distribution and movements of brown bullhead (Ameiurus nebulosusLesueur 1819) in Motuoapa Bay,southern Lake Taupo,New Zealand

Ultrasonic telemetry was used to determine the swimming depths of brown bullhead (Ameiurus nebulosus) in Motuoapa Bay at the southern end of Lake Taupo, New Zealand. Sonic transmitters equipped with a pressure sensor were surgically implanted in 12 adult fish (295–345 mm FL). Three automatic receivers recorded a total of 61335 data points on swimming depth between 26 November 1998 and 7 November 1999. Brown bullheads swam in water from 0 to 17 m deep but showed some seasonal variations. They were more active at night when they used shallow water extensively, especially during the winter months. They were most mobile in spring when they left Motuoapa Bay, suggesting migratory behaviour. During winter the fish remained more stationary, only moving around inside the bay. The results of this study provide guidance for establishing a brown bullhead control program should it become necessary.     

Auxins, Inhibitors and Phenolics in Bambarranut Seeds (Voandzeia subterranea Thouars) in Relation to Loss of Viability During Storage

Studies were made on seeds of bambarra groundnut (Voandzeiasubterranea Thouars) after 0, 6, 12, 18 and 24 months of storage. Germinability of the seeds was not adversely affected up to12 months of storage but it rapidly declined and after 24 monthsstorage no germination occurred. Growth of seedlings starteddecreasing in seeds stored for 12 months or more. Closely coincidingwith this, there was an increase in the contents of total phenoland inhibitory phenolic acids (p-hydroxybenzoic, p-coumaric,feruhc and vanillic acids) and a decrease in synergistic phenolicacids (chlorogenic, sinapic and protocatechuic acids). Auxincontent decreased in seeds stored for 18 months or more whilegrowth inhibitors appeared after 12 months of storage and increasedthereafter. Non-viable bambarranut seeds contained larger amounts of totalphenol, inhibitory phenolic acids and other growth inhibitorsand lower amounts of auxin and synergistic phenolic acids comparedwith the viable ones. Voandzeia subterranea Thouars, bambarranut, seed storage, germination, viability, auxins, inhibitors, phenol, phenolic acids     

Absorbable deslorelin implants (Ovuplant) prolong postpartum anestrus in early ovulating dairy cows

Two experiments were conducted to investigate the use of a bioabsorbable implant of the GnRH agonist deslorelin to temporarily delay the resumption of postpartum ovulatory cycles in Holstein cows. In Experiment 1, recently calved cows were paired and received either a single implant (Ovuplant); Peptech Animal Health, Sydney, NSW, Australia) within 48 h of parturition (OVP; n=17), or remained as untreated controls (CON; n=17). Blood samples were collected for plasma progesterone assay three times weekly for 6 weeks to profile the pattern of resumption of ovulatory cycles. In Experiment 2, there were 15 CON and 15 OVP cows initially treated as for Experiment 1 as well as 15 OVP+SYNCH cows. Each cow in the CON and OVP+SYNCH groups received a progesterone vaginal insert (CIDR); Genetics Australia, Bacchus Marsh, Vic., Australia) for 7 days at 23 days postpartum (23 dpp) to synchronise estrus in cycling animals or to induce an ovulation with estrus in anestrus animals. Blood samples were collected weekly until removal of the CIDR insert, and then twice weekly until 56 dpp to monitor plasma P4 for retrospective determination of ovulation. Milk yield was monitored by twice daily electronic volume measurements and milk composition with once weekly milk composition analysis.In Experiment 1, CON cows began ovulating from 9 dpp; 15 of 17 had ovulated by the end of blood sampling at 42 dpp. None of the OVP cows ovulated until at least 24 dpp, and only 6 of 17 had ovulated by 42 dpp. The average day of first ovulation was extended from 22.4+/-2.7 dpp to 39.3+/-2.7 dpp (P<0.05). In Experiment 2, ovulation had occurred in 8 of 15 CON cows at the time of CIDR insertion (23 dpp), 0 of 15 OVP cows and 1 of 15 OVP+SYNCH cows. By 40 dpp (or 10 days following removal of the CIDR insert) every CON cow (15/15) had ovulated, but only 2 of 15 OVP+SYNCH cows and 1 of 15 OVP cows. None of these effects of treatment was associated with any changes in milk yield or composition in either experiment.In conclusion, inserting a bioabsorbable implant of deslorelin within 48 postpartum extended the interval to first ovulation to at least 24 dpp in 46 of 47 cows. Recovery periods were highly variable. This variability was not reduced by using a form of intravaginal progesterone supplementation that did produce a synchronised estrus with ovulation in anestrus animals that had not been treated with deslorelin.     

Ovarian follicular wave synchronization and induction of ovulation in postpartum beef cows

An experiment was designed to evaluate a) the effect of a progesterone-estradiol combined treatment on ovarian follicular dynamics in postpartum beef cows, and b) ovulation and the subsequent luteal activity after short-term calf removal and GnRH agonist treatment. Multiparous Angus cows (25 to 40 d after calving) were assigned to the following treatments: untreated (Control, n = 9); short term calf removal (CR, n = 8); progesterone (CIDR, n = 9) and progesterone plus estradiol-17 beta (CIDR + E-17 beta, n = 9). Progesterone treatment (CIDR) lasted 8 d and the day of device insertion was considered as Day 0. Cows in the CIDR + E-17 beta group also received an i.m. injection of 5 mg of E-17 beta on Day 1. On Day 8, calves were removed for 48 h (CR, CIDR and CIDR + E-17 beta groups) and 6 h before the end of calf removal these cows also received an i.m. injection of 8 micrograms of Busereline (GnRH). Anestrus was confirmed in all cows by the absence of luteal tissue and progesterone concentrations below 1 ng ml-1 at the beginning of the experiment. Although mean (+/- SEM) interval from the beginning of the experiment (Day 0) to wave emergence did not differ (P > 0.05) among treatment groups (Control, 1.9 +/- 1.0, range -2 to 7 d; CR, 3.9 +/- 0.7, range 0 to 6 d; CIDR, 2.8 +/- 0.5, range 0 to 4 d and CIDR + E-17 beta, 4.1 +/- 0.2, range 3 to 5), the variability was less (P < 0.05) in the CIDR + E-17 beta group. The proportion of cows ovulating 24 to 48 h after GnRH administration tended (P = 0.08) to be higher in cows from CIDR + E-17 beta group (8/9) than in those of CR (5/8) or CIDR (6/9) groups, respectively and was associated with a higher proportion (P < 0.05) of CIDR + E-17 beta treated cows (9/9) that had a dominant follicle in the growing/early static phase at the time of GnRH treatment compared to the other GnRH treated groups (5/8, and 4/9 for CR and CIDR groups, respectively). Two CR cows ovulated 0-24 h after GnRH and only one Control cow ovulated the day before the time of GnRH administration. Cows pretreated with progesterone had longer (P < 0.05) luteal lifespan (CIDR, 14.5 +/- 0.7, CIDR + E-17 beta, 13.9 +/- 0.6 d) than those not treated with CIDR (Control, 5, CR, 4.0 +/- 0.4). We conclude that progesterone plus estradiol treatment results in tightly synchronized wave emergence and high GnRH-induced ovulation rate with normal luteal activity in postpartum beef cattle.     

Effects of infusion of GnRH pulses and level of body condition on ovarian function in postpartum beef cows

An experiment was conducted to test the hypothesis that postpartum anoestrus in beef cows is prolonged in cows in low body condition (BC) because they have a reduced LH pulse frequency compared with cows in high BC. Thirty-six multiparous Blue-Grey (White Shorthorn × Galloway) cows were fed so that they calved in either low (L) (BC score 2.07; SE 0.05; n = 24) or high (H) (BC score 2.81; SE 0.08; n = 12) body condition. They were then fed to maintain BC after calving. Twelve L cows were infused (i.v.) with 2 μg GnRH in 2 ml saline every 2 h from 5 to 7 weeks postpartum (LG) while the remaining L cows and all H cows were infused with saline only (LS and HS). Ovulations, as indicated by the presence of a morphologically normal corpus luteum, were recorded in one, one and ten of the cows of the LS, HS and LG groups, respectively. Mean LH concentrations and pulse frequencies were not affected by either GnRH treatment or BC but mean LH pulse amplitudes were lower (P < 0.05) in LG and LS cows than in HS cows at Week 5 and in LG cows at Week 6. At Week 7 postpartum, the numbers of small (3–7.9 mm diameter) and large (≥ 8 mm diameter) ovarian follicles, mean granulosa cell numbers per follicle and mean concentrations of LH receptors (pg per mg thecal and granulosa tissue) were not affected by GnRH treatment or BC. Granulosa cells from oestrogen active follicles of HS and LG cows secreted more oestradiol in vitro (P < 0.01) than cells from LS cows. However, there were no significant differences with treatment in the intrafollicular concentrations of oestradiol, testosterone or insulin-like growth factor-1. It was concluded that, since infusion of GnRH pulses enhanced both follicular steroidogenesis and the incidence of ovulation in low BC cows, the frequency of GnRH pulses is one determinant of follicle development in the postpartum cow. While H cows also exhibited a degree of enhancement of oestradiol synthesis by the granulosa cells of oestrogenic follicles, compared with L cows there was no difference in the LH pulse frequency or in the incidence of ovulation. It is concluded that there may be a threshold level of oestrogen synthesis by granulosa cells below which the final stages of follicle maturation and ovulation cannot be initiated, or that a high rate of oestradiol synthesis by this tissue is not the only factor mediating the effects of body condition on follicle development in the postpartum cow.     

Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows

We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples for glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N were collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks. Blood samples were collected for progesterone analysis and cows were palpated three times per week until 11 weeks to assess ovarian status. Propylene glycol did not affect dry matter intake (DMI), milk yield or energy balance in treatment cows. After drenching, propylene glycol increased (P<0.01) plasma glucose and insulin and decreased (P<0.01) NEFA; plasma urea N of the treatment group tended (P=0.07) to be higher than that of the control group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first insemination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurred earlier than that of control cows (32.3 versus 44.5 days, P=0.06) and the length of the first luteal phase was longer in treated cows (13.1 versus 7.3 days, P<0.05). These data are consistent with the hypothesis that insulin is important for normal ovarian function. During negative energy balance, treatment with propylene glycol, which induced small increases in plasma concentrations of insulin, prevented the short luteal phase characteristic of the first estrous cycle in control cows.     

Steroid-binding proteins in follicular fluid and peripheral plasma from pigs, cows and sheep

No unusual steroid-binding proteins that might react with the oocyte or its investments could be detected in follicular fluid. Corticosteroid-binding globulin occurred in follicular fluid from pigs, sheep and cows, and sex hormone-binding globulin occurred in follicular fluid from sheep and cows. The bulk of the steroid in follicular fluid is bound to albumin with low affinity, indicating that steroid molecules can readily be released, and oestrogen can react with the oocyte and granulosa cells in a manner analogous to that demonstrated for target cells bathed with interstitial fluid. Pigs lack a sex-hormone binding globulin in blood plasma and, hence, in follicular fluid. Because no proteins exist in follicular fluid that would compete with antibodies to bind steroids, direct radioimmunoassay of follicular steroids appears to be a valid technique.     

Ovarian follicular and corpus luteum changes, progesterone concentrations, estrus and ovulation following estradiol benzoate/progesterone based treatment protocol in cross-bred cows

The objectives of the present study were to investigate the effects of the stage of the estrous cycle at the start of an estradiol benzoate (EB) and progesterone (P) based treatment protocol on new follicular wave emergence, subsequent estrus and ovulation. The experiment was conducted using a crossover design with each cow (five cross-bred cows) being assigned to one of three groups at 3-month intervals within a 1-year period. Estrous cycle stage in individual cows was initially synchronized with prostaglandin F(2)alpha. After detection of estrus, each cow was injected intramuscularly (i.m.) with 2 mg EB and 200 mg P (EB/P) on day 5, 12 or 17 of the estrous cycle (estrus=day 0), followed by 1 mg EB i.m. 12 days after the EB/P treatment. Ovarian ultrasonographic examinations showed that the emergence of a new follicular wave occurred after EB/P treatment in all groups and the mean interval from EB/P treatment to wave emergence did not differ among the groups (3.2-3.8 days). All cows in each group exhibited behavioral estrus and ovulated the newly formed dominant follicle. However, cows in the day-17 group exhibited estrus 1-3 days before the second EB injection. The concentrations of progesterone showed faster reduction, during the treatment period, in the day-12 and -17 groups compared to the day-5 group. These results indicate that the EB/P treatment induces an emergence of a new follicular wave, irrespective of the estrous cycle stage at the start of treatment, but the effect of EB/P protocol on estrous/ovulation synchronization is influenced by the stage of the estrous cycle.     

Effects of Glucose Availability on Expression of the Key Genes Involved in Synthesis of Milk Fat,Lactose and Glucose Metabolism in Bovine Mammary Epithelial Cells

As the main precursor for lactose synthesis, large amounts of glucose are required by lactating dairy cows. Milk yield greatly depends on mammary lactose synthesis due to its osmoregulatory property for mammary uptake of water. Thus, glucose availability to the mammary gland could be a potential regulator of milk production. In the present study, the effect of glucose availability on expression of the key genes involved in synthesis of milk fat, lactose and glucose metabolism in vitro was investigated. Bovine mammary epithelial cells (BMEC) were treated for 12 h with various concentrations of glucose (2.5, 5, 10 or 20 mmol/L). The higher concentrations of glucose (10–20 mmol/L) did not affect the mRNA expression of acetyl-CoA carboxylase, diacyl glycerol acyl transferase, glycerol-3 phosphate acyl transferase and α-lactalbumin, whereas fatty acid synthase, sterol regulatory element binding protein-1 and beta-1, 4-galactosyl transferase mRNA expression increased at 10 mmol/L and then decreased at 20 mmol/L. The content of lactose synthase increased with increasing concentration of glucose, with addition of highest value at 20 mmol/L of glucose. Moreover, the increased glucose concentration stimulated the activities of pyruvate kinase and glucose-6-phosphate dehydrogenase, and elevated the energy status of the BMEC. Therefore, it was deduced that after increasing glucose availability, the extra absorbed glucose was partitioned to entering the synthesis of milk fat and lactose by the regulation of the mRNA expression of key genes, promoting glucose metabolism by glycolysis and pentose phosphate pathway as well as energy status. These results indicated that the sufficient availability of glucose in BMEC may promote glucose metabolism, and affect the synthesis of milk composition.     

The effects of GnRH treatment at the time of AI and 12 days later on reproductive performance of high producing dairy cows during the warm season in northeastern Spain

It was hypothesized that gonadotropin-releasing hormone (GnRH) treatment at the time of insemination and 12 days later increases conception rates. The aim of the present study was to evaluate the effects of GnRH treatment at the time of insemination or at the time of insemination and 12 days later on reproductive performance during the warm season in high producing dairy cows. The effect of GnRH treatment on the incidence of subsequent twin pregnancies and pregnancy losses was also evaluated. Data were analyzed using logistic regression methods. Of the entire series of 1289 AI, 373 (29%) resulted in pregnancy. Three study groups were established to evaluate the effects of treatment on the conception rate: control (untreated cows, n=431), GnRH-0 (cows receiving GnRH at AI, n=429) or GnRH-0+12 (cows receiving GnRH at AI and at AI+12 days, n=429). Conception rates were 20.6% (89/431), 30.8% (132/429) and 35.4% (152/429) for animals receiving no treatment, GnRH at AI, and GnRH at AI and 12 days later, respectively. Based on the odds ratio, the probability of pregnancy was 0.80 and 0.46 times less likely for cows receiving treatment GnRH-0 and no treatment, respectively, than for cows receiving treatment GnRH-0+12 (reference). Of the 373 pregnant animals, 326 (87.4%) bore singletons and 47 (12.6%) carried twins. The effects of treatment on the dependent variables: twin pregnancy, additional corpus luteum and pregnancy loss were analyzed. Pregnancy loss between 38 and 90 days after insemination was registered in 30 (8%) cows: 17 (5.2%) in single and 13 (27.7%) in twin pregnancies. Fifty-six (15%) cows had an additional corpus luteum. No pregnancy losses were recorded in these cows. Treatment had no effect on the twin pregnancy rate. The treatment GnRH at AI and 12 days later increased the chances of an additional corpus luteum by a factor 3.7 (using the control group as reference). In conclusion, our results support the hypothesis that GnRH treatment at the time of insemination and 12 days later increases the conception rate in high producing dairy cows during the warm season. Although lower than double treatment, strong benefits were also registered following a single GnRH treatment at insemination. Under these conditions, treatment fails to affect the twin pregnancy rate yet increases the incidence of an additional corpus luteum in pregnant cows.     

Estrus synchronization in cattle using estradiol, melengestrol acetate and PGF

In Experiment 1, all cattle were fed MGA (0.5 mg/head/d) for 7 d (designated Days 0 to 6) and given PGF on Day 6. One-half were administered estradiol valerate (EV; 5 mg, im) on Day 0. At Location 1, a higher proportion (P < 0.005) of EV-treated heifers were detected in estrus and bred by AI between Days 7 and 13 than control heifers not receiving EV (27 of 33 versus 15 of 32), but the number of pregnancies (12 vs 10) was not significantly different. Eighty-three of 104 EV-treated and 89 of 106 control cows were inseminated, resulting in 50 and 45 pregnancies, respectively (not significant). At Location 2, cattle were similarly treated and exposed to bulls on Days 7 to 49. Fall pregnancy rate was higher (P < 0.015) for EV-treated than control heifers (44 of 48 vs 33 of 46), but was not significantly different for cows (22 of 26 vs 19 of 23). In Experiment 2, estradiol 17beta (E17beta; 5 mg, im) and progesterone (100 mg, im) were administered on Day 0 (instead of EV). In a third group (designated the PGF group), cattle were bred on Days 0 to 6, and PGF was administered on Day 6 to those not yet bred. For 213 cows, the percentage pregnant to a synchronized estrus was greater in the PGF group (72%) than in either the control group treated with MGA (49%; P = 0.005) or the group receiving MGA and E17beta (54%; P < 0.025). Fall pregnancy rates were 91, 89, and 96% for the 213 cows (not significant) and 89, 93, and 98% for 131 heifers (not significant) in the PGF, MGA and E17beta groups, respectively. In cattle without a functional CL, the average diameter of the largest follicle at Day 6 was 1 to 2 mm smaller in the E17beta + MGA group than in the MGA group (difference significant only in cows at Location 1). Combined for both locations, the synchronized pregnancy rate in heifers without a functional CL on Day 6 was higher (P < 0.05) in the E17beta + MGA group than in the MGA group (11 of 21, 52% versus 4 of 20, 20%). Estrogen treatment caused regression of ovarian follicles with emergence of a new follicular wave. Including estrogen in an estrus synchronization program utilizing MGA and PGF significantly increased fall pregnancy rate in heifers (at 1 location) and the synchronized pregnancy rate of heifers without a functional CL at the time of PGF treatment (combined for both locations).