Synchronisation of oestrus in dairy cows using prostaglandin F2alpha, gonadotrophin-releasing hormone, and oestradiol cypionate.

An oestrous synchronisation protocol was developed for use in lactating dairy cows using PGF(2alpha), GnRH, and oestradiol cypionate (ECP). In experiment 1, lactating dairy cows received two injections of PGF(2alpha) (on days 0 and 11) (PP; n=10) or two injections of PGF(2alpha) (days 0 and 11) and 100 microg of GnRH on day 3 (PGP; n=10). In experiment 2, cows were treated with PGP (n=7), or PGP and 1 mg of ECP at the same time (PGPE(0); n=7) or 1 day after the second PGF(2alpha) injection (PGPE(1); n=7). In experiment 3, 101 lactating dairy cows in a commercial herd were assigned to one of three treatments; PP, PGP, or PGPE(1). Follicular growth was measured by ultrasound in experiments 1 and 2. Every cow (experiments 1, 2, and 3) was blood sampled at selected intervals for progesterone and oestradiol assays and inseminated at oestrus. In experiment 1, a higher percentage of GnRH-treated cows ovulated after the first PGF(2alpha) injection (90% versus 50%; P<0.05). The GnRH-treated cows tended to have a larger dominant follicle present at the time of the second PGF(2alpha) injection (16.5+/-0.5 mm versus 15.0+/-0.7 mm; P<0.10). The percentage of cows that ovulated after the second PGF(2alpha) injection was similar (60%). In experiment 2, cows treated with ECP had higher peak preovulatory concentrations of oestradiol in plasma (6.99+/-0.63 versus 3.63+/-0.63; P<0.01) following the second PGF(2alpha) injection and a higher percentage ovulated (86% versus 43%; P<0.05). A higher percentage of PGPE(1)-treated cows in experiment 3 were observed in standing oestrus and ovulated after the second PGF(2alpha) injection (standing oestrus, 26.4, 34.3, and 62.6%, P<0.01; ovulated, 56, 63, and 78%, P<0.05; PP, PGP, and PGPE(1), respectively). In conclusion, the PGP protocol increased the number of cows that ovulated after the first PGF(2alpha) injection and produced a more mature dominant follicle at the time of the second PGF(2alpha) injection. Adding ECP to PGP (PGPE(1)) enhanced the expression of oestrus and increased ovulation percentage. The combination of PGP and ECP is potentially a new method to routinely synchronise oestrus and ovulation in dairy cows.

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.

Temporary suppression of pulsatile LH release following a single injection of a GnRH agonist (deslorelin) in ovariectomised Holstein dairy cows.

The objective of the experiment was to investigate the potential for using a single injection of the GnRH agonist [D-Trp(6), Pro(9)-des-Gly(10)-NH(2)] GnRH-ethylamide (deslorelin) to suppress LH secretion in ovariectomised Holstein cows. Each dose of 10, 100 and 1000 microg deslorelin was injected intravenously into each of four ovariectomised cows on day 0. Blood samples were collected hourly on day 0 to profile the induced LH release. Frequent serial blood samples were collected at 10min intervals over 4h on days -3, -1, +2, +4 and +6. The injection of deslorelin induced a surge-like release of LH that begun within 1h in all cows. There was no difference between deslorelin doses in terms of maximum LH concentration, area under the LH curve (AUC) or log(10)(AUC). The average interval from injection to maximum LH concentration was longer for cows receiving 1000 microg than in those receiving 10 microg (3.5 versus 1.5h; P<0.01), though no different to 100 microg (2.8h; P>0.1). This relationship was described by a logarithmic function of deslorelin dose in micrograms (R(2)=73.3%, P<0.01). Pre-treatment smoothed mean LH concentration was significantly correlated with peak LH concentration of the induced surge: max_LH=5.37+9.57 x pre-amplitude (R(2)=33.2%, P=0.05). Similarly, LH pulse amplitude pre-deslorelin was also correlated with peak LH of the induced surge max_LH=0.07+12.9 x pre-amplitude (R(2)=53.7%, P=0.07). Pulsatile release of LH was suppressed only with the 1000 microg dose on day +2. Suppression was characterised by a reduction in mean LH, smoothed mean LH and LH pulse amplitude. By day +4, LH parameters were no different to pre-treatment ones. Pulse frequency was not affected by the treatment, although a small non-significant reduction at day +2 for 1000 microg dose was observed (3.9 versus 2.8, P=0.14). In conclusion, temporary suppression of LH output for at least 48h occurred following a single intravenous injection of 1000 microg of deslorelin, even though there were similar peak LH concentrations were for the three doses.

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.