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.     

Progesterone clearance rate in lactating dairy cows with two levels of dry matter and metabolisable energy intakes

The aim of these studies was to determine the effect of levels of dry matter (DM) and metabolisable energy (ME) intakes on clearance rate of progesterone (P4) in dairy cows. Thirty-two lactating Holstein-Friesian cows were selected for the study and were fed indoors in individual stalls for a period of 5 weeks. They were individually offered a diet of combinations of pasture, hay and pelleted cereal grain to achieve two different levels of DM and ME. In the first trial, 16 cows were allocated to two groups: (i) high DM (HDM), and (ii) low DM (LDM) intakes, while the amount of ME intake was constant. In the second trial, 16 cows were allocated to two groups: (i) high ME, and (ii) low ME intakes with similar amount of DM intake. A GnRH-agonist (deslorelin) was initially implanted in the ear of each cow to block endogenous P4 secretion. Then 3 weeks later, a CIDR device was inserted into the vagina of each cow and left in place for 11 days. Chromic oxide (Cr(2)O(3)) capsules were administered to allow daily faecal output (FO) to be estimated. Daily blood, faecal and milk samples were taken during the period of the experiment for P4 and faecal P4 metabolites analyses. Trial 1: The average milk yield was similar among cows in high and LDM intake groups (26.7 versus 25.0 l per day, P = 0.2). The average daily FO was 7.8 kg DM in the HDM and 5.7 in the LDM cows (P < 0.0001). Average daily DM intakes were 17.3 kg and 15.4 kg in the HDM and LDM groups, respectively (P < 0.0001). The average plasma P4 concentrations were similar between the two groups (1.56 versus 1.60 ng/ml, P = 0.7) but milk P4 concentrations were higher in LDM cows (4.6 versus 3.6 ng/ml, P = 0.02). The average daily excretion rate of P4 into the milk was higher in LDM cows (122.3 versus 88.5 microg, P = 0.002). The concentrations of faecal P4 metabolites (FP4M) were not influenced by the level of daily DM intake (2.85 versus 2.90 microg/g, P = 0.6). The average daily yields of FP4M were higher among cows in the HDM group (23.2 versus 16.3mg, P = 0.01).Trial 2: The average milk yield was 31.2l per day in HME cows compared to 25.0l per day in LME cows (P < 0.0001). The average daily FO was 7.8 kg DM in LME and 5.8 kg DM in HME cows (P < 0.0001), and the average DM content of faeces was higher in LME cows (15.8 versus 12.7%, P = 0.01). The average daily ME intake was 213MJ per day in HME group compared to 183MJ per day in LME group (P<0.0001). The average plasma and milk P4 concentrations were similar between the two groups (plasma P4 = 1.54 versus 1.56 ng/ml, P = 0.4; milk P4: 3.7 versus 3.6 ng/ml, P = 0.6). The average daily excretion rate of P4 into the milk was higher in HME cows (114 versus 88.5 microg, P = 0.03). Concentrations of FP4M were not influenced by the level of daily ME intake (2.5 versus 2.85 micro g/g, P = 0.08). However, daily yields of FP4M were greater in the LME group (23.2 versus 14.4 mg, P = 0.01).In conclusion, this study was unable to establish a relationship between the level of DM and ME in the diet with the excretion rates of FP4M metabolites and plasma P4 concentrations.     

Effects of level of feeding and progesterone dose on plasma and faecal progesterone in ovariectomised cows

The effects of two levels of feeding and two doses of progesterone (P4) on plasma and faecal progesterone metabolites (FP4M) were studied using a total of 24 ovariectomised (OVX), non-lactating, Holstein-Friesian cows. Cows were grazed on improved ryegrass/white clover pastures and allowed ad libitum access to pasture or were restricted to grazing for a total of 4 h per day in two 2 h periods. Progesterone (P4) was administered as one or two, simultaneous, intravaginal progesterone devices (CIDR). The cows were adapted to their pasture supply for 2 weeks before the start of the progesterone treatments. The progesterone devices were administered for 11 days and the cows were dosed with slow release chromic oxide capsules during the P4 treatment to allow faecal output (FO) to be estimated. Daily blood samples for P4 assay and weekly samples for blood metabolite assay were collected. Faecal samples were collected per rectum daily and assayed for pregnanes containing a 20-oxo-, 20alpha- or a 20beta-OH group by enzyme immunoassay (EIA). Daily FO was higher (P < 0.001) for ad libitum than pasture restricted cows (6.3 vs 4.1 kg DM) but was similar for both doses of P4. The average mass of P4 released from a CIDR device over a 11-day period was higher for cows allowed ad libitum pasture compared with those on restricted pasture (0.64 vs 0.60 g; P = 0.04). Plasma P4 concentrations, however, were higher in restricted than ad libitum fed cows (1x CIDR: 1.81 vs 1.41 ng/ml; 2x CIDR: 4.10 vs 3.46 ng/ml). Increasing the progesterone dose significantly (P < 0.001) increased both the concentrations and daily totals of the faecal pregnanes assayed and total FP4M. Restricted pasture cows had higher (P < 0.001) pregnanes and FP4M concentrations than cows fed ad libitum. Daily total faecal pregnane and FP4M did not differ between feeding levels except for faecal 20alpha-pregnane which was highest for ad libitum fed cows (P < 0.05). These results showed that the plasma concentrations of P4 in CIDR-treated OVX cows were negatively associated with the level of feeding. Level of feeding and dose of P4 affected the concentrations of FP4M, but the daily excretion rate of FP4M was not positively influenced by the level of feeding.     

The effect of level of feed intake on progesterone clearance rate by measuring faecal progesterone metabolites in grazing dairy cows

The objective of the present study was to determine the effect of level of feed intake of pasture on P4 clearance rates in dairy cows. Twelve non-lactating Holstein-Friesian cows aged 4-9 years were randomly allocated to a restricted or ad libitum group. The ad libitum group had unrestricted access to irrigated pasture, whereas the restricted group had access for only 2h per day. Each animal was drenched orally twice daily with a chromic oxide capsule to allow daily feed intake to be estimated from faecal output (FO). Endogenous progesterone (P4) production was eliminated by subcutanously implanting a capsule containing 6 mg of a potent GnRH-agonist (deslorelin) into the ear of each animal 3 weeks before inserting a CIDR device containing 1.9 g P4 into the vagina. Two luteolytic PGF2alpha were given 10 days later. Each device was removed after 11 days and residual P4 measured. Daily plasma samples were assayed for P4. Faecal samples were also taken daily and assayed for pregnanes (FP4M) containing a 20-oxo-, a 20alpha- or a 20beta-OH group with EIAs. The average daily dry matter (DM) intake of pasture was higher for cows in the ad libitum group (15.9 versus 6.3 kg DM, P=0.001). Their plasma P4 concentrations were lower (1.08 versus 1.71 ng/ml, P=0.05), even though the average residual P4 content of the used CIDR devices was not affected by feed intake (1.20 versus 1.25 g, P>0.05). The concentrations of FP4M were not affected by level of feed intake (20-oxo-: 3.3 versus 1.7, 20alpha-: 3.5 versus 3.7, 20beta-: 2.1 versus 3.2 microg/g DM). Daily excretion rates of 20-oxo- and 20alpha- were higher in ad libitum cows (20-oxo-: 17.8 versus 4.3mg per day, P=0.05; 20alpha-: 18.2 versus 8.9 mg per day, P=0.001), but daily yield of faecal 20beta- was not affected by feed intake (11.9 versus 8.6 mg per day, P=0.5). These results show that there was a negative relationship between feed intake and plasma P4 concentrations in these CIDR-treated GnRH-downregulated Holstein cows. Concentrations of FP4M were not affected by level of feed intake or FO, but daily excretion rate of FP4M was associated with the volume of faeces.     

Progesterone concentration, follicular development and induction of cyclicity in dairy cows receiving intravaginal progesterone inserts

Objectives were to evaluate progesterone concentrations after cows had initiated estrous cycles following calving and induction of estrous cycles in postpartum anovular high-producing Holstein dairy cows treated with controlled internal drug releasing (CIDR). In experiment 1 (EXP1), 62 cows that had initiated estrous cycles received a new CIDR (NCIDR) containing 1.38 g of progesterone or a 7-d used autoclaved CIDR (UCIDR) 48h after luteolysis for 7 d. Ovaries were examined by ultrasonography, and plasma analyzed for concentrations of progesterone. In experiment 2 (EXP2), 515 cows diagnosed as anestrus were randomly assigned to untreated control, NCIDR or UCIDR for 6d. Plasma was analyzed for concentration of progesterone 12 d after CIDR removal to determine ovulation. In EXP1, milk yield and body condition did not influence progesterone concentrations. Concentration of progesterone tended to increase faster (P=0.10) in cows receiving UCIDR than NCIDR, but both treatments reached a plateau at 90min. Cows receiving the NCIDR had greater (P=0.04) concentrations of progesterone during the 7-d treatment, but they were mostly subluteal (<1.0 ng/mL) after d 2. After removal, concentrations of progesterone were greater for NCIDR than UCIDR for the first 45 min, and were similar thereafter. Multiparous cows had lesser (P=0.004) concentrations than primiparous cows throughout the study. The pattern of ovarian follicular development was not affected by treatment. In EXP2, induction of onset of estrous cycles increased (P<0.01) with progesterone treatments, but was similar between NCIDR and UCIDR. Proportion of cows experiencing shorter than typical length estrous cycles after first AI tended to be greater (P=0.09) for control cows than those receiving the CIDR, and for cows remaining anestrous than those in which onset of estrous cycles was induced. Pregnancy per AI and pregnancy loss were similar among treatments. Cows that resumed estrous cyclicity prior to first AI had greater (P=0.01) pregnancy per AI. Treatment of high-producing Holstein cows that had previously initiated onset of estrous cycles with CIDR resulted in subluteal concentrations of progesterone, but in anestrous high-producing cows increased induction of estrous cycles with no effect on fertility at first insemination.     

Body condition influences maintenance of a persistent first wave dominant follicle in dairy cattle

The objective of this study was to determine whether plasma concentrations of progesterone (P4) from a controlled internal drug releasing (CIDR) device (approximately 2 ng/ml) were adequate to sustain a persistent first wave dominant follicle (FWDF) in low body condition (LBC, body condition score [BCS] 1 = lean, 5 = fat [2.3 +/- 0.72, n = 4]) compared with high body condition (HBC, BCS = 4.4 +/- 0.12, n = 4) nonlactating dairy cows. On Day 7 of the estrous cycle (Day 0 = estrus), cows were treated with PGF2 alpha (25 mg i.m. Lutalyse, P.M., and Day 8 A.M.) and a used CIDR device containing P4 (1.2 g) was inserted into the vagina until ovulation or Day 16. Plasma was collected for P4 and estradiol (E2) analyses from Day 5 to Day 18 (or ovulation), and ovarian follicles were monitored daily by ultrasonography. Mean concentrations of plasma P4 were greater in HBC than LBC cows between Days 5 and 7 (4.6 > 3.4 +/- 0.37 ng/ml; P < 0.04). All LBC cows maintained the first wave dominant follicle and ovulated after removal of the CIDR device (18.3 +/- 0.3 d, n = 3; Cow 4 lost the CIDR device on Day 11 and ovulated on Day 15), whereas in the HBC cows ovulation occurred during the period of CIDR exposure (11.3 +/- 0.3 d; n = 3; a fourth cow developed a luteinized first wave dominant follicle that did not ovulate during the experimental protocol on Day 19). Mean day of estrus was 17 +/- 0.4 for LBC (n = 3) and 10 +/- 0.4 for HBC (n = 3) cows. Sustained concentrations of plasma E2 (12.9 +/- 2.8 pg/ml; Days 8 to 17) in LBC cows reflected presence of an active persistent first wave dominant follicle. The differential effect of BCS on concentrations of plasma P4 (y = ng/ml) was reflected by the difference (P < 0.01) in regressions: yLBC = 19.9 - 3.49x + 0.166x2 vs yHBC = 37.3 - 7.04x + 0.340x2 (x = day of cycle, Days 7 to 12). Although P4 concentration was greater for HBC cows prior to Day 8, a greater clearance of plasma P4 released from the CIDR device in the absence of a CL altered follicular dynamics, leading to premature ovulation in the HBC cows. A greater basal concentration of P4 was sustained in LBC cows that permitted maintenance of a persistent first wave dominant follicle.     

Improved conception in timed-artificial insemination using a progesterone-releasing intravaginal device and Ovsynch protocol in postpartum suckled Japanese Black beef cows

The primary objective was to determine the effect of supplemental progesterone, administered via an intravaginal device (CIDR), on conception rates to timed-artificial insemination (timed-AI) in postpartum suckled Japanese Black beef cows treated with the Ovsynch protocol. A secondary objective was to compare the effects of treatments on plasma concentrations of progesterone and estradiol. Cows in the control group (Ovsynch, n=38) received a standard Ovsynch protocol (100 microg GnRH analogue on Day 0, 500 microg PGF2alpha analogue on Day 7, and 100 microg GnRH analogue on Day 9), with AI on Day 10, approximately 20 h after the second GnRH treatment. Cows in the treatment group (Ovsynch+CIDR; n=40) received a standard Ovsynch protocol plus a CIDR for 7 days (starting on Day 0). Plasma progesterone concentrations were determined on Days 0, 1, 7, 9, 10, and 17 and plasma estradiol-17beta concentrations were determined on Days 7, 9, 10, and 17. The odds ratio for likelihood of conception was 3.29 times greater (P=0.02) in the Ovsynch+CIDR group compared to Ovsynch group. The conception rate was greater (P=0.03) in the Ovsynch+CIDR group than in the Ovsynch group (72.5% versus 47.7%). Insertion of a CIDR device significantly increased plasma progesterone concentrations only on Days 1 and 7 (P<0.001 and P=0.05, respectively), but had no significant effect on plasma estradiol-17beta concentrations. Including a CIDR with the Ovsynch protocol significantly improved conception rates in postpartum suckled Japanese Black beef cows.     

Post-insemination milk progesterone concentration and embryo survival in dairy cows

Logistic regression analysis was used to evaluate the relationship between post-insemination milk progesterone concentration and embryo survival, and between milk yield and milk progesterone concentration. Milk samples were collected on Days 1, 4, 5, 6, and 7 (insemination=Day 0) following 871 inseminations in spring-calving dairy cows. Milk progesterone concentrations were measured by enzyme-immunoassay and pregnancy diagnosis was conducted with transrectal ultrasonography at approximately Day 30. There was a negative linear relationship (P<0.01) between milk progesterone concentration on Day 4 and embryo survival while, in contrast, there was a positive linear and quadratic relationship between milk progesterone concentration on Days 5, 6 and 7 (P<0.05) and also between the rate of change in progesterone concentrations between Days 4 and 7 inclusive and embryo survival (P<0.05). There was a weak negative linear relationship between average daily milk yield at the time of insemination and milk progesterone concentrations (P<0.001). There was no association between many production parameters, including liveweight and body condition score measured at various stages between calving and insemination, and milk progesterone concentration between Days 4 and 7 inclusive (P>0.05). In conclusion, low progesterone during Days 5-7 (after insemination) was associated with low fertility in dairy cows and there were indications of a range of progesterone concentrations within which embryo survival was maximal.     

Progesterone metabolism in ovariectomised non-lactating Holstein-Friesian cows treated with progesterone with two levels of feed intake

The goal of this study was to measure the effects of level of feeding and the form of progesterone (P4) administration on the concentrations and yields of faecal P4 metabolites relative to differences in plasma P4 concentrations in non-lactating cows. Six non-lactating Holstein-Friesian cows were ovariectomised (OVX) and allocated to two groups: (i) P4 by subcutaneous injection (P4-s.c., n=3); and (ii) P4 administration per vaginum (P4-p.v., n=3). Each cow in the P4-s.c. group was injected subcutaneously once daily with 200mg P4. Each cow in the P4-p.v. group had a CIDR device inserted for 11 days when it was removed and replaced with a second device for further 11 days. Cows were fed a ration containing lucerne (33%) and oaten (66%) chaff at a maintenance level (M) in two portions in the first period of the study, and at a half-maintenance (1/2M) level during the second period. Chromic oxide capsules (Cr(2)O(3)) were administered twice daily to allow faecal output (FO) to be estimated. Plasma P4 and faecal P4 metabolites (FP4M; 20-oxo-pregnanes, 20alpha- and 20beta-OH-pregnanes) were measured during the treatment period. Daily FO declined after reducing the M diet to 1/2M (4.77 versus 2.61kg; P<0.01), whereas plasma P4 concentrations increased in the P4-s.c. group (4.2 versus 6.2ng/ml; P<0.05), but not in the P4-p.v. group (0.9 versus 1.0ng/ml; P>0.2). The mass of P4 released from a CIDR device during each 11-day period (M or 1/2M) was similar (0.66 versus 0.63g). Faecal 20-oxo-pregnanes (20-oxo-) concentrations were not affected by day or level of feeding, whereas faecal 20alpha-OH (20alpha-) and 20beta-OH (20beta-) concentrations were increased with the 1/2M diet in the P4-s.c. group (4.3 versus 5.6 microg/gDM; 2.2 versus 5.6 microg/gDM, respectively; P<0.05), but not in the P4-p.v. group (2.3 versus 2.7 microg/gDM; 1.7 versus 3.04 microg/gDM P>0.05). These changes in concentration only partly compensated for the reduced FO with the 1/2M diets as daily yields of FP4M (20-oxo- and 20alpha-) were greater during the M diet period (20-oxo-: 6.9 versus 4.1 microg/gDM; 2.7 versus 1.5 microg/gDM, for P4-s.c. and P4-p.v. groups, respectively; P<0.05, 20alpha-: 19.9 versus 13.6 microg/gDM; 10.9 versus 6.6 microg/gDM for P4-s.c. and P4-p.v. groups, respectively; P<0.05). The level of feeding and the route of P4 administration had key roles in controlling P4 concentrations in blood and daily FP4M yield.     

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.     

Metabolic variables and plasma leptin concentrations in dairy cows exhibiting reproductive cycle abnormalities identified through milk progesterone monitoring during the post partum period

We have used milk progesterone analysis to monitor reproductive function in lactating dairy cows and have then related this reproductive function to a variety of metabolic variables. Monitoring of cows (n = 41) during the period of onset of luteal function (first milk progesterone reading>5 ng/ml) revealed that delayed onset was associated with increased milk yield and greater loss of body weight and body condition but was not related to plasma metabolite or leptin concentrations. Further monitoring of reproductive function in these 41 cows and an additional 33 cows (total n = 74) during the mating period (from weeks 6 to 14 post partum) identified reproductive cycle abnormalities in 29 (39.2% of animals). The occurrence of cycle abnormalities was associated with increased milk yield (P < 0.05), elevated plasma beta hydroxybutyrate (P < 0.05) and reduced plasma leptin (P < 0.01) concentrations as well as a lower (P < 0.05) rate of gain of body weight and condition score but was not associated with plasma urea or glucose concentrations. Furthermore, cows exhibiting cycle abnormalities had a longer (P < 0.01) interval to first service and a smaller percentage had conceived by 100 days post partum (34.5% versus 66.7%; P < 0.01). These results provide further evidence that impaired reproductive function during the post partum period in dairy cows is caused by a poor energy status and not elevated urea concentrations. Reduced plasma leptin concentrations in animals suffering reproductive dysfunction further supports this view.     

Effect of treatment with progesterone and oestradiol benzoate on ovarian follicular turnover in postpartum anoestrous cows and cows which have resumed oestrous cycles.

Two experiments were carried out to determine the effect of a low dose of progesterone (P) with and without the addition of an injection of oestradiol benzoate (ODB) on ovarian follicle dynamics, oestradiol production and LH pulsatility in postpartum anoestrous cows, compared with cows which had resumed oestrous cycles (cycling cows). In the first experiment, anoestrous Jersey cows were treated with (AN+P, n=8) or without (AN-3, n=3) a previously used intravaginal progesterone releasing (CIDR) device for 10 days, commencing 3 or 4 days after emergence of a new dominant follicle (DF1) as determined by transrectal ultrasonography. Contemporary cycling cows (CYC+P, n=8) were similarly treated with used CIDR devices and injected with prostaglandin F(2alpha) (PGF) at the time of device insertion. Follicle turnover was monitored by daily ultrasonography and pulsatile release of LH was measured on the ninth day after device insertion. During the period of CIDR device insertion, a second dominant follicle emerged in 4/8 of the CYC+P group and 7/8 of the AN+P group (P=0.14). Maximum diameter of DF1 was greater in cows in the CYC+P compared with the AN+P group (P=0.02), but did not differ between cows in the AN+P and AN-P groups (P>0.1). Frequency of LH pulses was greater in cows in the CYC+P than AN+P group (P=0.06), and in cows in the AN+P than AN-P group (P=0.02).In the second experiment, anoestrous (n=20) and cycling (n=11) Friesian cows were treated with a new CIDR device for 6 days commencing 3 days after emergence of a new dominant follicle (DF1). Cycling cows were also injected with PGF on the day of device insertion. Half of the cows in each group were injected with 2mg ODB on the day of device insertion. Daily ultrasonography was used to monitor follicular dynamics throughout the experimental period. Follicular turnover was increased by ODB in cycling (5/5 versus 1/6; P<0.05), but not anoestrous cows (5/9 versus 4/11). Persistence of DF1 was reduced by ODB treatment in both cycling and anoestrous cows (P<0.001). Maximum diameter of DF1 was influenced by ODB treatment and reproductive status (P<0.05). In anoestrous cows in which a second dominant follicle did not emerge during the period of device insertion, the interval from emergence of DF1 to emergence of a second dominant follicle was significantly delayed by treatment with ODB (P=0.04).In conclusion, P treatment of anoestrous cows increased pulsatile release of LH, but did not induce the development of persistent follicles. Injection of ODB in association with P treatment reduced the persistence of dominant follicles in both cycling and anoestrous cows, but delayed subsequent follicular development in a proportion of anoestrous cows.     

The excretion of prostaglandin F-2ALPHA in milk of cows.

Prostaglandin F-2ALPHA (PGF-2ALPHA) was measured by immunoassay in plasma and milk of four cows (six experiments). After 30 mg PGF-2ALPHA im, plasma PGF-2ALPHA peaked at 15 minutes (2.4 plus or minus 0.7 ng/ml) and declined toward basal values by 3 hours; maxiumum milk PGF-2ALPHA (0.91 plus or minus 0.12 ng/ml) occurred at 1 hour. The average excretion rate in milk was 2.9 mu-g/day 0.9 mu-g (0.003%) of which was due to the 30 mg PGF-2ALPHA injected. In six nonpregnant control cows, daily changes of milk PGF-2ALPHA and progesterone were not consistently related.     

Progesterone and follicular changes in postpartum noncyclic dairy cows after treatment with progesterone and estradiol or with progesterone, GnRH, PGF2alpha, and estradiol

A previous study showed that noncyclic dairy cows treated with 10 microg of GnRH and a progesterone-releasing CIDR insert on Day 0, 25 mg of PGF2alpha and CIDR removal on Day 7, followed by 1 mg estradiol benzoate on Day 9 for those cows that still had not shown estrus (CGPE program) had higher conception rate (47% vs. 29%) than cows treated only with CIDR and estradiol benzoate as above (CE program). This study was to investigate the mechanisms by which the CGPE program improved conception rate compared with the CE program. Sixteen noncyclic Holstein-Friesian cows were randomly assigned to 2 groups balanced for the size and growth pattern of the dominant follicles, which were determined by ultrasonography over a 3-d period. One group received the above CGPE treatment, and the other group received the CE treatment. Follicular and luteal development were monitored by daily ultrasonography. Blood samples were collected daily from Day -2 to Day 11, and thereafter milk samples were collected thrice weekly for a further 24 d. Blood and milk samples were analyzed for progesterone. The GnRH treatment induced ovulation in 7 of 8 cows, resulting in elevated (P<0.05) progesterone concentrations between Days 4 and 7 for cows in the CGPE group. All induced CL underwent luteolysis by 24 h after PGF2alpha treatment. Within 5 d of CIDR removal, 7 of 8 cows in both the CE and CGPE groups ovulated. The interval from emergence of the ovulatory follicle to ovulation was similar (P=0.32) but less (P<0.05) variable for the CGPE group (9.0+/-0.3 d) compared with the CE group (10.3+/-1.2 d). Progesterone concentration in milk samples was similar between the two groups up to 10 d after ovulation. In summary, the GnRH treatment induced ovulation or turnover of dominant follicles, induced a synchronized initiation of a new follicular wave, and increased the progesterone concentration from 4 d after treatment. These could be the reasons for the increased conception rate of cows treated with the CGPE program.     

Restoring ovulation in beef donor cows with ovarian cysts by progesterone-releasing intravaginal silastic devices.

The objective of this study was to determine the efficacy of a progesterone-releasing intravaginal silastic device (Controlled Internal Drug Release: CIDR) for inducing ovulation in beef cows with persistent ovarian cysts. Fifteen cows with cysts and abnormal cycles for over 40 days were randomly assigned to receive either a single CIDR (CIDR group, n=9), or a CIDR containing no progesterone (blank CIDR) (BLANK group, n=6) for about 14 days. Determination of plasma progesterone levels at the beginning of CIDR treatment indicated 4 of 6 BLANK cows with non-luteinized cysts and 5 of 9 CIDR cows with non-luteinized cysts. In 5 of 6 BLANK cows, one follicular wave appeared and newly emerged dominant follicles increased in size up to 20 mm in diameter and persisted during the experiment, while one cow experienced estrus with spontaneous ovulation. In contrast, during CIDR treatment, 2 or 3 waves, in which dominant follicles were from 7 to 15 mm in diameter, appeared approximately at 7-day intervals. Within 3 days after CIDR removal, estrous behavior was detected followed by ovulation of the dominant follicle in the last wave. All CIDR cows resumed normal cyclicity with 2 follicular waves for over 2 months. Insertion of a CIDR caused a rapid increase of about 2 ng/mL in plasma progesterone. The levels were greater than 1.3 ng/mL until removal of a CIDR, then dropped under 0.3 ng/mL. Concentrations of plasma estradiol in BLANK cows increased during growth of the cystic follicles, with high levels greater than 10 pg/mL for over 10 days. In 4 of 5 cows with non-luteinized cysts, with high plasma estradiol on the day of CIDR insertion, CIDR treatment resulted in rapid decline of estradiol levels. During placement of the CIDR, estradiol levels showed no increase in the growth phase of a newly appeared dominant follicle. After CIDR removal, however, estradiol significantly increased associated with the growth of ovulatory follicles in all 9 cows. A transient increase in plasma FSH levels preceded detection of each follicular or cyst wave in both BLANK and CIDR cows. Pulse frequency and mean concentration of LH in cows with non-luteinized cysts showed values corresponding to those in normal follicular phase. However, throughout CIDR treatment, these parameters reduced to levels found in the normal luteal phase. In cows with luteinized cysts, parameters of LH secretion were as low as in the normal luteal phase before and during CIDR treatment, then increased significantly after CIDR removal. Present results indicate that treatment with CIDR proved effective in restoring ovulation and reestablishing normal cyclicity in beef donor cows with cysts persistent for a long period. The CIDR reduced and maintained LH secretion at normal luteal levels, thereby, inducing atresia of estrogen-active cysts and preventing formation of cysts from the newly emerged follicles.     

Iodine and selenium carry over in milk and cheese in dairy cows: effect of diet supplementation and milk yield

Iodine and selenium are essential trace elements involved in the regulation of thyroid metabolism and antioxidant status. Two experiments were undertaken on lactating cows to determine the milk concentrations of iodine and selenium, carry over (CO) in milk, the fraction in curdle portion and how milk yield affects the milk iodine and selenium concentrations and CO. Sources of elements were potassium iodide and sodium selenite. In Experiment 1, 12 cows were randomly allotted to three diet groups in a completely randomized design: control group (CTR) - total mixed ration (TMR) containing 1.71 and 0.08 mg/kg dry matter (DM); Group 1 (T1) - TMR plus 23.8 and 2.2 mg; Group 2 (T2) - TMR plus 45.5 and 4.3 mg, respectively, for iodine and selenium. In Experiment 2, 30 cows were allotted to three groups according to milk yield: high (H), average (A) and low (L). Within each group, cows were randomly assigned two levels of iodine and selenium: Level 1: TMR containing 1.55 and 0.15 mg/kg DM; Level 2: TMR plus 47.2 mg and 8.0 mg, respectively, iodine and selenium. In both experiments, individual milk samples were collected and analyzed for iodine and selenium contents. In Experiment 1, Grana Padano cheese was obtained at lab scale and the iodine and selenium fractions in the curd were measured. In Experiment 1, the iodine intake increased (P < 0.001) the concentration and total excretion in milk. The CO increased (P < 0.05) from 16 (CTR) to 27 (T1) and 26% (T2); the sampling time was significant (P < 0.05) with no interaction with treatments. Concentration of selenium in milk was increased (P < 0.05) by treatment and CO decreased (P < 0.01) from 26 (CTR) to 12 (T1) and 9% (T2). The iodine showed a mild enrichment factor in the curdle (about 1.7-fold), whereas selenium enriched five- to sevenfold. In Experiment 2, the level of iodine supplementation affected (P < 0.05) the concentration and total excretion in milk. No effects on milk iodine concentration were related to milk yield or milk yield × treatment interaction; however, the iodine excretion in milk was major (P < 0.05) in higher yielding groups. The iodine CO was affected (P < 0.05) by the milk yield in supplemented groups. The selenium milk concentration and excretion were affected (P < 0.01) by the milk yield, whereas the CO was affected (P < 0.05) by the milk yield and selenium supplementation. Results highlight the possibility of fortification with iodine in milk and selenium in cheese through animal feeding.     

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.     

Ovarian responses to progesterone and oestradiol benzoate administered intravaginally during dioestrus in cattle

This study examined the effects of administering progesterone and oestradiol benzoate (ODB) during mid-dioestrus, on ovarian follicular dynamics in cattle. Twelve cycling cows were used in a 4 x 4 latin square design, with the 4 treatments being initiated on Day 13 of the cycle (oestrus = Day 0) and comprising intravaginal insertion for 5 days of: (i) a progesterone releasing device (CIDR; 'P4'); (ii) a CIDR device with a gelatin capsule containing 10 mg ODB and 1 g lactose (CIDIROL; 'P4/ODB') attached; (iii) a placebo CIDR device with the 10 mg ODB capsule (ODB); and, (iv) a placebo CIDR device alone (CTRL). The ovaries of each cow were examined daily by transrectal ultrasonography from Day 7 of the cycle until subsequent ovulation. Blood samples were collected daily from Day 11, and at intervals of 2-4 h during the 24 h period either side of treatment initiation. The second dominant follicle (DF2) emerged on Day 10.7 +/- 0.2 (mean +/- SEM), and was 8.5 +/- 0.2 mm in diameter by Day 13. The DF2 developed through to ovulation (2-wave cycles) in half of the animals in the CTRL group; while in the other half of cases, the ovulatory follicle originated from the third follicle wave that emerged on Day 17.2 +/- 0.4. Administration of a CIDR device alone (P4 group) did not alter the 1:1 ratio of 2 and 3-wave cycles, but the third dominant follicle (DF3) in those cows with 3-wave cycles emerged earlier on Day 15.6 +/- 0.2. In contrast, the DF2 of every animal in the ODB and P4/ODB groups became atretic and was replaced by a DF3 which emerged 4.0 +/- 0.3 days later. The effects of ODB on luteal function were limited to an earlier decline in plasma progesterone concentrations from 2 to 4 days after device insertion and a reduction in diameter of the corpus luteum when administered concurrently with progesterone. Intravaginal administration of 10 mg ODB on Day 13 of the oestrous cycle, with or without progesterone, was effective in promoting follicle wave turnover. In the absence of ODB, progesterone administration alone (P4 group) did not alter the ratio of animals with 2 or 3-wave cycles from that observed in animals in the CTRL group, but did advance the timing of subsequent follicle wave emergence in those animals with 3-wave cycles.     

Hormonal and ovarian responses to a 5-day progesterone treatment in anoestrous dairy cows in the third week post-partum

Primiparous cows with low body condition at calving have an extended anovulatory period. Induction of ovulation and oestrus is possible with progesterone treatment but the response to this treatment differs between Friesian and Jersey breeds. The objective of this study was to describe changes in pulsatile LH secretion and the synchrony of developing ovarian follicles that occur during a progesterone treatment period of 5 days in primiparous anovulatory cows. The experimental model compared the progesterone treatment with spontaneous post-partum changes as well as a breed comparison in a factorial design.Thirty-six cows (Jersey n=19 and Friesian n=17) were managed to calve with a low body condition score (BCS<4. 5). Daily changes in ovarian follicle size were observed with transrectal ultrasonography in each cow from 8 days post-partum. Thirty of these cows were diagnosed to be anovulatory at 12-18 days post-partum (day 0) and allocated to a treatment (n=16) or a control group (n=14), balanced for breed. Each treated cow had a progesterone-releasing controlled internal drug-releasing (CIDR) device inserted vaginally for 5 days while control cows were left untreated. Changes in plasma LH concentrations were measured with intensive blood sampling over 8 h on days -1, 1, and 4. Blood samples were also collected daily (06:00 h) for determination of plasma progesterone as well as oestradiol concentrations on days 6 and 8.Treatment with progesterone was associated with a transient initial decrease (day 1) in both LH pulse frequency and mean LH concentrations after device insertion, but both had returned to pre-treatment levels by day 4. Jersey cows had a greater pulse frequency, but there was no breed difference in mean LH concentrations. Patterns of ovarian follicle growth were affected by progesterone treatment with an increase in diameter of the dominant follicle (DF) identified after treatment initiation. This followed an earlier emergence of a new DF after device insertion. Follicular response to progesterone was dependent on the diameter of the DF present at treatment initiation. Those follicles >/=9 mm were replaced by a new DF during treatment such that the DF observed at the time of device removal was large (>/=9 mm) and growing in 13/16 cases.Progesterone was not effective for the induction of an LH surge, ovulation and oestrus in anovulatory cows with a low BCS. However, treatment was associated with synchronous development of a DF so that it was large and growing at the end of the treatment period in most cases. This synchronous development may be due to the transient suppression of LH and the presence of an LH-dependent DF.     

Effect of an implant containing the GnRH agonist deslorelin on secretion of LH, ovarian activity and milk yield of postpartum dairy cows

Prevention of high plasma progesterone concentrations in the early postpartum period may improve fertility. Our objective was to determine whether a Deslorelin implant (DESL; 2100 microg, s.c.) would reduce secretion of LH and alter follicle dynamics, plasma concentrations of progesterone, estradiol and PGF2alpha metabolite (PGFM) in postpartum dairy cows. Cows received DESL on Day 7 postpartum (Day 7, n=8) or were untreated (Control, n=9). All cows were injected with GnRH (100 microg, i.m.) on Day 14 to assess LH response. A protocol for synchronization of ovulation with timed AI was initiated on Day 60 (GnRH [Day 60], CIDR [Day 60 to Day 67], PGF2alpha [Day 67, 25 mg and Day 68, 15 mg], GnRH [Day 69] , AI [Day 70]). The LH response to injection of GnRH on Day 14 was blocked in animals treated with DESL. Numbers of Class 1 (<6 mm) follicles were unaffected (P > 0.05) whereas numbers of Class 2 (6 to 9 mm) (P < 0.01) and Class 3 (>9 mm) follicles were less (P < 0.01) in DESL cows between Day 7 and Day 21. From Day 22 to Day 60, DESL-treated cows had more of Class 1 follicles and less Class 2 (P < 0.01) and Class 3 (P < 0.01) follicles, and lower plasma concentrations of progesterone and estradiol (P < 0.01). Concentrations of PGFM between Day 7 and Day 42 were not affected by treatment (P > 0.05). All cows ovulated in response to GnRH on Day 69. Subsequent luteal phase increases in plasma progesterone concentrations (Day 70 to Day 84) did not differ. The use of the DESL implant associated with PGF2alpha given 14 days later suppressed ovarian activity and caused plasma progesterone concentrations to remain < 1 ng/mL between Day 22 and Day 51. The DESL implant did not affect milk production.