Embryo survival in dairy cows managed under pastoral conditions

Efficient pasture-based milk production systems require a compact calving pattern aligned to the onset of the grazing season, a 365-day calving interval and low culling rates for infertility. Achievement of these targets requires high herd reproductive performance. While high genetic merit Holstein cows produce more milk in grass-based systems their fertility is compromised. Management of the modern high genetic merit Holstein dairy cow presents a major challenge in pasture-based systems of production. It appears that the extent of early embryo loss is greater (up to 20% points greater) in the modern high-producing dairy cow and that a much higher proportion of the embryos die before day 7 following insemination in contrast to heifers and lower yielding cows. About 7-8% of pregnancies are lost between days 30 and 90 of gestation with no evidence that loss rate is related to cow genetic merit, parity or level of production. Systemic concentrations of progesterone during both the cycle preceding and following insemination affect embryo survival rate with evidence that too low or indeed too high a concentration of progesterone been negatively associated with embryo survival rate. Peripheral concentrations of both progesterone and oestradiol are lowered by increased plane of feed intake due to increased metabolic clearance rate of the steroids, which is related to liver blood flow. It appears that high producing dairy cows have an increased risk of embryo death as a result of lowered peripheral concentrations of progesterone as a consequence of increased hepatic metabolism of progesterone. Uterine expression of mRNA for progesterone receptor, oestradiol receptor and retinol binding protein mRNA appears to be sensitive to changes in peripheral concentrations of progesterone during the first week after AI. It would appear that energy balance and dry matter intake during the 4 weeks, immediately after calving are critically important in determining conception rate when cows are inseminated at 70-100 days post-calving. Concentrate supplementation of cows at pasture during the breeding period has minimal affects on conception rates though sudden reduction in dietary intake should be avoided. For pasture-based systems of milk production more balanced breeding strategies, with greater emphasis on fertility and feed intake must be developed.     

Relationships between maternal hormone secretion and embryo development on day 5 of pregnancy in dairy cows

In cattle, increasing early embryonic losses are associated with inadequate progesterone concentrations within the first three weeks of pregnancy. The aim of this study was to investigate the complex relationship between early maternal progesterone concentration and embryo development early within the first week of pregnancy, specifically, on day 5 post-oestrus in dairy cows. Twenty Holstein-Friesian cows at the end of lactation were inseminated at oestrus (day 0) and on day 5 post-oestrus cows were slaughtered and the reproductive tract flushed to determine the presence and stage of embryo development. Three cows that had failed to synchronise correctly were excluded from analysis while in the remaining 17 cows 11 (65%) were pregnant with embryos at the morula (n = 3), 9-16 (n = 3) and 8-cell (n = 5) stages of development. No differences in day 5 plasma progesterone concentrations or corpus luteum (CL) size or progesterone content were observed between pregnant (n = 11) and non-pregnant (n = 6) cows. In cows with embryos beyond the 8-cell stage of development (n = 6) plasma progesterone concentration (P < 0.001) and CL weight (P < 0.01) were higher and plasma insulin concentrations lower (P < 0.001) than in cows with 8-cell embryos (n = 5). In addition there was a negative relationship between plasma progesterone and plasma insulin in pregnant cows (R(2) = 0.65; P < 0.005). In cows with an embryo present in the oviduct, oviductal glucose concentrations were lower (P < 0.05) than in cows with no embryo present. These results confirm progesterone is not only directly associated with embryo development, but that it may indirectly modulate embryo development via changes in the oviductal environment. In summary, the association between maternal progesterone concentration and embryo development exists as early as day 5 of pregnancy in dairy cows.     

Bovine endometrial epithelium ultrastructure 6 and 7 days post-breeding

An electron microscopic study of the bovine endometrial epithelium 6 and 7 days post-breeding was carried out. Both scanning and transmission electron microscopy were used and the ultrastructural characteristics of the epithelial cells were described. The average number of ciliated cells found in the luminal surface of repeat-breeder cows (RB) was lower than that of cows with normal fertility history (NB), although the differences were not highly significant (P < 0.1). There were no other major differences in the endometrial epithelium between RB and NB, regardless of whether a normal or abnormal embryo was found.     

Superovulatory responses in dairy cows following ovulation of the dominant follicle of the first wave

In the present study we investigated the effect of hCG administration on Day 7 (Day 0 = day of standing estrus) to ovulate the dominant follicle of the first wave and the associated increase in progesterone concentration on subsequent superovulatory response in dairy cows. Twenty cyclic lactating cows were allocated at random to 2 groups: control (n = 10) and hCG-treated (n = 10). The ovaries of each cow were scanned using an ultrasound scanner on Day 7, to confirm the presence of the dominant follicle and thereafter every other day until embryo recovery. All cows received a total dose of 400 mg Folltropin-V in decreasing amounts for 5 days (Days 9 to 13) and 35 mg PGF(2alpha) on Day 12. In addition, the treated cows received 1000 IU hCG on Day 7. All cows were inseminated twice during estrus, and the embryos were collected 7 days later by a nonsurgical procedure. Blood smaples were taken at different times of the treatment period for progesterone determination. All cows possessed a dominant follicle at Day 7, and all but one of the hCG-treated cows ovulated the dominant follicle and formed an accessory corpus luteum. Plasma progesterone concentrations were significantly higher (P<0.01) in hCG-treated cows than control cows on the first day of Folltropin treatment and on the day of PGF(2alpha) injection. The mean number of follicles at estrus, the number of ovulations, the total number of embryos and the number of transferable embryos were not different (P>0.05) between control and hCG-treated cows.     

Fertility of dairy cattle treated with human chorionic gonadotropin (hCG) to stimulate progesterone secretion

Two experiments were conducted to determine if progesterone secretion and fertility would be affected by administration of human chorionic gonadotropin (hCG) before or after the first insemination. In Experiment 1, 48 Holstein heifers received 1000 IU of hCG or 1 ml of saline on Days 2, 3, and 4 of an estrous cycle. They were inseminated at the subsequent estrus. In Experiment 2, 110 Jersey and 105 Holstein cows received a single injection of 5000 IU of hCG or 5 ml of saline on Day 3 after estrus. These cows were first inseminated either at the estrus immediately preceding treatment or at the subsequent estrus. In both experiments, blood samples for determination of progesterone were collected thrice weekly for 3 to 4 wk following treatment. In Experiment 1, progesterone concentrations during mid-cycle were higher in hCG-treated heifers than in saline-treated controls. Treatment with hCG resulted in an 11% increase in the first service conception rate (P < 0.48). In Experiment 2, hCG-treated cows displayed higher progesterone secretion during mid-cycle than saline-treated herdmates. The conception rate of cows inseminated prior to hCG-treatment was not affected by treatment, but cows inseminated after treatment had a marginally lower fertility rate. The conception rate of cows receiving a repeat insemination following hCG treatment was higher than for the controls. We conclude that treatment with hCG did not improve the conception rate at the first insemination, but it may be beneficial for cows that require a repeat service.     

Induction of lactation in cattle with estradiol 17-beta and progesterone primed with progesterone

Five parous non-pregnant, non-lactating cows were injected (sc) with progesterone (50 mg/day for 7 consecutive days) followed by estradiol (0.1 mg) plus progesterone (0.25 mg) per kg body wt/day on day 12 to 14 and with reserpine / 2 mg twice a day on day 19 to 22. All the 5 cows were successfully induced into lactation. Animals exhibiting estrus following hormonal therapy were artificially inseminated and one cow became pregnant and exhibited normal parturition. Jugular blood collected was used for estimation of progesterone by RIA technique and considerable individual variation was observed in progesterone concentration.     

Improved embryo yield and condition of donor ovaries in cows after PMSG superovulation with monoclonal anti-PMSG administered shortly after the preovulatory LH peak

Nonlactating Dutch-Friesian cows were selected from a local slaughterhouse and synchronized with Syncro-Mate B. Cows with a normal progesterone pattern were treated with PMSG (3,000 I.U. i.m.) on Day 10 followed by PG (Prosolvin 22.5 mg) 48 h later. Blood samples were collected daily and at hourly intervals from 30 h after PG. Monoclonal anti-PMSG (Neutra-PMSG) was administered i.v. at 5.8 h after the LH peak in 16 cows; controls (n = 16) did not receive Neutra-PMSG. For comparison, 16 additional cows were superovulated with FSH-P in decreasing doses, twice a day (total 32 mg), starting at Day 10. All cows were inseminated at 10 h after the LH peak. Embryos were evaluated on Days 6 and 7 after flushing upon slaughter (recovery 87%). The number of corpora lutea and follicles on the donor ovaries were counted. No significant differences in the concentrations of progesterone and LH were observed between the three superovulation groups. Upon Neutra-PMSG, PMSG in blood was completely neutralized, it was decreased to < 0.5 ug/l at AI from 7.0 ug/l at the LH peak. The number of transferable embryos was significantly higher after Neutra-PMSG (9.1 per cow) than without Neutra-PMSG (5.3). or upon FSH-superovulation (4.6). The number of cysts on the ovaries of Neutra-PMSG-treated cows was reduced similarly to that after FSH-superovulation. Treatment with Neutra-PMSG shortly after the LH peak positively affects final follicular maturation in PMSG-superovulated cows and results in a nearly two-fold increase of transferable embryos.     

Inducing ovulation with hCG improves the fertility of dairy cows during the warm season

This study was designed to assess the effects of human chorionic gonadotrophin (hCG), given within a timed artificial insemination program, on plasma progesterone concentrations and subsequent fertility in lactating dairy cows during the warm and cold seasons of the year. Cows were treated intramuscularly with GnRH-agonist (Day 0) and PGF₂ (Day 7) followed by either GnRH-agonist (GPG treatment; 60 animals) or hCG (GPH treatment; 60 animals) on Day 9. All cows were fixed-time inseminated (TAI) 16–22 h after the end of treatment. To determine plasma progesterone levels, blood was withdrawn from all animals on Days 3, 6, 9, 12 and 15 after TAI. During the warm period, the pregnancy rate recorded at TAI was similar for the GPG and GPH groups (20% vs. 23%) while the cumulative pregnancy rate within 30 days of TAI was lower (P < 0.05) for the GPG than the GPH group (36% vs. 63%). No differences were observed during the cold period. During the warm period, embryo losses between Days 28 and 45 after TAI were greater (P < 0.05) for the GPG group compared to the GPH group (36% vs. 5%) while again no differences emerged during the cold period. Mean plasma progesterone levels were higher (P < 0.05) in the GPH group than GPG group on Days 3, 6 and 9 post-insemination. Our findings indicate that the use of hCG to induce ovulation in a timed artificial insemination protocol increases plasma progesterone levels and improves fertility in dairy cows during the warmer period of the year.     

Influence of summer heat stress on pregnancy rates of lactating dairy cattle following embryo transfer or artificial insemination

Lactating Holstein cows were used to determine if pregnancy rate from embryo transfer (n = 113) differed from contemporary control cows (n = 524) that were artificially inseminated (AI). Holstein heifers (n = 55) were superovulated with FSH-P (32 mg total) and inseminated artificially during estrus and subsequently managed under shade structures. On Day 7 post estrus, embryos were recovered, and primarily excellent to good quality embryos (90.3%) were transferred to estrus-synchronized lactating cows. Cows were managed under conditions of exposure to summer heat stress. Pregnancy status was determined by milk progesterone concentrations at Day 21 and palpation per rectum at 45 to 60 d post estrus. Pregnancy rates of cows presented for AI (Day 21, 18.0%; Days 45 to 60, 13.5%) were typical for lactating cows inseminated during periods of summer heat stress in Florida. Pregnancy rates of embryo recipient cows were higher (P<0.001) than those of control cows (Day 21, 47.6%; Days 45 to 60, 29.2%). Summer heat stress had no adverse effect on heifer superovulatory response, but it increased (P<0.05) the incidence of retarded embryos (相似文献   

Development of a persistent ovarian follicle and associated elevated concentrations of 17beta-estradiol preceding ovulation does not alter the pregnancy rate after embryo transfer in cattle

It was hypothesized that prolonged elevation in 17beta-estradiol (E(2)) preceding ovulation as a result of a persistent ovarian follicle would have a detrimental effect on pregnancy rate after Day 7 (behavioral estrus = Day 0) of the estrous cycle. Cows were either treated with exogenous progesterone (P(4)) for 10 d or remained untreated (CON; n = 76). Cows were treated with 1 of 2 doses of P(4) from Day 6 to 16 which was intended to result in either elevated E(2) (EE(2); n = 76) or normal E(2) (NE(2); n = 76) concentration in the circulation. At the initiation of P(4) treatment, cows received prostaglandin F(2alpha) (PGF(2alpha)) to eliminate the endogenous source of P(4). On Day 16, the exogenous source of P(4) was removed from treated cows, while cows in the CON group received PGF(2alpha). A single embryo was transferred into each cow 7 days after observation of behavioral estrus. Blood samples were taken on alternating days during the treatment period to determine concentrations of P(4) and E(2). The pregnancy rate was determined by ultrasonographic examination 25 to 32 d after embryo transfer. There was a treatment-by-day interaction (P < 0.0001) on E(2) concentrations in the plasma during the 10-d treatment period. Cows in the EE(2) group had a higher concentration of E(2) by Day 8 (6.1 +/- 0.5 pg/ml) and this concentration remained elevated until PRID removal compared with that of cows in the NE(2) (2 +/- 0.2 pg/ml) and CON (2.0 +/- 0.3 pg/ml) groups, which had concentrations of E(2) similar to those at the initiation of treatment. Pregnancy rates after embryo transfer did not differ (P = 0.56; X(2) = 1.1) among cows in the EE(2) (30.7%), NE(2) (36.2%) and CON (32.9%) groups. Prolonged elevation of E(2) concentrations associated with the development of a persistent ovarian follicle preceding ovulation did not affect the pregnancy rate to embryo transfer after Day 7 of the estrous cycle in cows.     

Measurement of EPF for detection of cow pregnancy using rosette inhibition test

Early embryonic death of calves due to sub-fertility in cows is of great economic concern to dairy industry. Early pregnancy factor (EPF) is a secretory protein with pregnancy associated immunosuppressive properties. Rosette inhibition test (RIT) was used to detect EPF in inseminated dairy cows. Blood samples were collected at two intervals, 1-3 and 5-7 days after insemination from 23 inseminated and 18 non-inseminated control cows for RIT and pregnancy diagnosis performed between 42 and 45 days on palpation. The study indicates that RIT (P<0.05) has the potential to distinguish pregnant from non-pregnant dairy cows in the first week of pregnancy.     

The effect of strain of Holstein-Friesian cow on size of ovarian structures, periovulatory circulating steroid concentrations, and embryo quality following superovulation

When managed under grass-based systems of production, the New Zealand (NZ) strain of Holstein-Friesian cow has superior reproductive performance compared to the North American (NA) strain despite having similar solids-corrected milk (SCM) yields. This study compared the ontogeny of early pregnancy events in NZ and NA cows. Ten NZ and 10 NA cows were submitted to a superovulation protocol on three occasions. Blood samples were collected daily from every cow from days -3 to +7 relative to a synchronized oestrus during each superovulation protocol. Pre-ovulatory oestradiol concentrations, follicle diameter, post-ovulatory progesterone concentrations, corpus luteum (CL) diameter, and circulating insulin-like growth factor-I concentrations did not differ between the two strains. Uteri were non-surgically flushed 7 days post-AI, embryos were isolated and graded. The proportion of transferable embryos recovered was higher (P<0.01) in the NZ cows compared with the NA cows. A greater (P=0.01) proportion of the recovered structures were at the blastocyst stage in the NZ cows. Peak SCM yield and body condition score (BCS) at the time of peak SCM yield were not different between strains. However, during the experimental period the NA cows maintained significantly higher daily SCM yields, whereas the NZ cows replenished significantly greater levels of BCS. The results indicate that differences in periovulatory steroid concentrations and size of ovarian structures do not explain the differences in embryo quality between the two strains. However, strain differences in nutrient partitioning from the time of peak SCM yield through late lactation may provide the key signals responsible for superior embryo quality in NZ cows.     

Superovulatory response, embryo quality and fertility after treatment with different gonadotrophins in native cattle

We studied native Mertolengo cattle to evaluate superovulatory (SOV) treatments, subsequent fertility of donors and pregnancy rate of recovered embryos. In Experiment 1 we compared superovulatory response (SR), embryo quality and plasma progesterone (P4) levels between donors treated with eCG (10 cows and 5 heifers) vs. FSH (pure, FSH-1, n=10 cows and crude, FSH-2, n=10 cows), during progestagenic impregnation. We also compared fertilization rates and embryo quality of bred and inseminated eCG and FSH-1 donors. Significantly more viable embryos were yielded by FSH than by eCG treated donors. Less FSH-1 than FSH-2-treated donors showed SR, but the response was identical in responder donors of both groups. Fertilization rates were significantly higher in bred than in inseminated donors. Plasma P4 levels were only significantly different (higher) between responder and non-responder donors on the day of embryo recovery. Experiment 2 compared FSH treatments (FSH-2, crude, n=11 cows and FSH-3, pure, n=10 cows) started at the midluteal phase. The mean number of viable embryos was significantly higher in FSH-3 than in FSH-2 treated donors. Both FSH treatments exerted a similar luteotrophic effect upon injection. The FSH-2 donors treated during the midluteal phase yielded more ova and showed significantly higher plasma P4 levels at all sampling days than those treated during progestagenic impregnation. The pregnancy rates of recipient cows were 67% and 46% for fresh and frozen-thawed embryos respectively. In Experiment 3, the fertility of donors (n=20) after SOV treatments was compared with that of untreated cows (n=40). Time to conception of donors, after mating with a bull 14 days after embryo recovery, was identical to that of control cows. There was some delay to conception in eCG-treated cows, but the difference was not significant. These preliminary results suggest that response to SOV treatments in Mertolengo cattle might be affected by the type of gonadotrophin and by the treatment protocol. The fertility of a traditional breeding season after SOV treatments was not impaired. Cryopreserved embryo banking can be used to preserve the breed.     

Evaluation of timed insemination during summer heat stress in lactating dairy cattle

We wished to compare the effect of summer heat stress on pregnancy rate in cows that were inseminated at a set interval associated with a synchronized ovulation vs those inseminated upon routine estrus detection. The study was carried out on a commercial dairy farm in Florida from May to September 1995. Lactating dairy cows were given PGF2 alpha (25 mg i.m.) at 30 + 3 d postpartum and randomly assigned to be inseminated at a set time (Timed group) or when estrus was detected (Control group). Cows in the Timed group were synchronized by sequential administration of Buserelin (8 micrograms i.m.) on Day 0 at 1600 h, PGF2 alpha (25 mg i.m.) on Day 7 at 1600 h and Buserelin (8 micrograms i.m.) on Day 9 at 1600 h. They were inseminated on Day 10 between 0800 and 0900 h (Day 9 + 16 h). Cows in the Control group were given PGF2 alpha at 57 + 3 d postpartum and inseminated when detected in estrus. Estrus detection or insemination rate for control insemination cows was 18.1 +/- 2.5% versus 100% for time inseminated cows (P < 0.01). Mean interval from PGF2 alpha to insemination was shorter for time inseminated cows (3 +/- 2.1 d < 35.5 +/- 1.9 d; P < 0.01). Pregnancy rate was greater for time inseminated cows (13.9 +/- 2.6 > 4.8 +/- 2.5%; P < 0.01) as was overall pregnancy rate by 120 d postpartum (27.0 +/- 3.6 > 16.5 +/- 3.5%; P < 0.05). Number of days open for cows conceiving by 120 d postpartum was less for time inseminated cows (77.6 +/- 3.8 < 90.0 +/- 4.2 d; P < 0.05), as was interval to first service (58.7 +/- 2.1 < 91.0 +/- 1.9 d; P < 0.01). Services per conception were greater for time inseminated cows (1.63 +/- 0.10 > 1.27 +/- 0.11; P < 0.05). The timed insemination program did improve group reproductive performance. However, the timed insemination program will not protect the embryo from temperature-induced embryonic mortality, but management limitations induced by heat stress on estrus detection are eliminated. An economical evaluation of the timed insemination program indicates an increase in net revenue per cow with implementation of timed insemination for first service during the summer months.     

Use of the prostaglandin F2α analog cloprostenol (ICI 80, 996) in dairy cattle with unobserved estrus

Two field trials were designed to evaluate use of the prostaglandin F_2α analog cloprostenol (CP) in dairy cattle with unobserved estrus and a palpably mature corpus luteum (CL). In Trial 1, 98 cows were treated with CP (500 μg IM) and 83 were given saline. Cows in both groups were assigned to be inseminated based on observed signs of estrus. Cows treated with CP were inseminated sooner than controls although heat detection still presented some difficulty. Conception rates were the same for both groups. In Trial 2, 154 cows were treated with CP for unobserved estrus and were assigned to be inseminated at estrus (78 cows) or were inseminated twice by appointment at 72 and 96 hours after treatment (76 cows). Appointment breeding eliminated problems associated with detection of estrus so nearly all cows were inseminated soon after treatment. In addition, cows bred twice by appointment had a higher conception rate than those bred based on signs of estrus. Induction of luteolysis with the prostaglandin F_2α analog CP in cows with unobserved estrus and a CL should prove to be a very effective addition to reproductive herd health programs. Successful use of CP for this purpose is dependent upon accurate diagnosis of the presence of a mature CL. In these trials 83 (92.4%) of 90 cows sampled had blood serum progesterone concentrations indicative (≥ 2.0 ng/ml) of significant luteal tissue activity.     

Endocrine profiles and embryo quality in the PMSG-PGF2alpha treated cow

Plasma progesterone and LH concentrations around estrus were determined for both PMSG treated (experimental animals) and non-treated (control animals) dairy cows and heifers of the Holstein Friesian and Jersey breeds, and these hormone profiles were related to the embryo quality. Most experimental animals experienced an increase in progesterone concentrations following PMSG treatment and an abrupt decrease to values below 3 nmol/l after PG injection. The mean (+/-SE) intervals from prostaglandin treatment to estrus were 46.9+/-1.8 h and 64.5+/-4.8 h for experimental and control animals, respectively. At the onset of heat the progesterone concentration in experimental animals with optimal embryo quality (group I) was significantly lower (p<0.01) than in experimental animals which yielded unfertilized eggs (group II) (1.2+/-0.1 versus 3.9+/-0.8 nmol/l) and significantly higher than the level in the control group (0.6+/-0.1 nmol/l). Following estrus the progesterone profiles in all 3 groups were studied and the length of the superovulatory cycle was measured to 26.0+/-4.8 days. The preovulatory LH surge occurred sooner after prostaglandin injection in experimental (41 h) than in control animals (65 h). The LH surge in group I occurred within a narrow range and reached a higher average level than group II (24.2+/-2.2 ng/ml and 16.3+/-3.7 ng/ml, respectively). The control group attained an even higher LH surge (31.8+/-8.8 ng/ml) than did the experimental animals. The data presented in this experiment indicate that plasma levels of progesterone and LH in PMSG-PGF(2)alpha treated animals are related to embryo or egg quality.     

Factors affecting retention of early pregnancy in dairy cattle

Potential factors affecting retention of pregnancy during weeks 5-9 of gestation were studied in dairy cows and heifers (N = 211) on two farms. Cows were examined by ultrasonography for presence of a viable embryo, and sizes of the corpus luteum (CL) and of follicles > or = 5mm were recorded. Blood samples were taken at each examination and assayed for progesterone and estradiol. Overall pregnancy loss was 11.4%. Cows with two CL did not have greater concentrations of progesterone than cows with one CL and they retained fewer pregnancies (P < 0.01; 73% versus 91%). Pregnancy retention was associated positively with concentrations of progesterone and estradiol during week 5 (P < 0.05). Embryos that were lost apparently died before CL regression. Retention of pregnancy declined in cows with high body condition and as age of the cow increased. Pregnancy retention was lower in cows bred to one of four frequently-used service sires (P < 0.05). Days postpartum, milk production, parity, service number, inseminator, synchronization of estrus, diameter of follicles and size of CL did not affect pregnancy retention. In conclusion, retention of pregnancy during placentation varied with concentrations of progesterone and estradiol, age of cow, body condition and service sire.     

Conception rates in dairy cows after timed-insemination and simultaneous treatment with gonadotrophin releasing hormone and/or prostaglandin F2 alpha

This study was designed to determine conception rates in dairy cows after timed-insemination and simultaneous treatment with gonadotrophin releasing hormone (GnRH) and/or prostaglandin F2 alpha (PGF2alpha). A total of 2352 cows was randomly assigned to six groups. Cows in Groups 1 to 5 were palpated per rectum to determine the presence of a corpus luteum (CL) on the ovary, and blood samples were obtained for the determination of plasma progesterone (P4) concentrations. Cows with a CL and P4 concentrations >1 ng/ml were treated (Day 0) with PGF2alpha (25 mg, i.m.) and were observed for estrus. Cows in estrus prior to 72 hours after treatment (Group 5, n = 106) were bred, but were not treated. Cows not observed in estrus by 72 hours were divided into four remaining groups, were bred between 72 and 80 hours and were assigned as follows: Cows in Group 1 (n = 203) were not treated; Cows in Group 2 (n = 200) were treated with GnRH (100 ug, i.m.); Cows in Group 3 (n = 201) were treated with PGF2alpha (25 mg, i.m.); and cows in Group 4 (n = 202) were treated with both GnRH and PGF2alpha. Cows in Group 6 (n = 1440) were not treated with PGF2alpha on Day 0 and were estrual cows that were bred on days when cows in Groups 1 to 5 were time-inseminated. The percentage of cows in all groups pregnant at 45 to 50 days after one insemination was compared using analysis of variance (P<0.05). The conception rate of cows in Group 2 was significantly higher than that of cows in Groups 1 to 4. There was a significant group-by-season interaction. Cows treated with GnRH during the spring had a higher conception rate than at other times of the year. Conception rates of cows in Groups 1 to 4 that were inseminated during the summer were low and not significantly different from each other. Conception rates of cows in Groups 5 and 6 inseminated during the summer were not significantly different from each other, but were significantly higher than that of cows in Groups 1 to 4 that were inseminated during the summer.     

Associations between milk progesterone concentration on different days and with embryo survival during the early luteal phase in dairy cows

The relationships between the concentration of milk progesterone and early embryo survival on Days 4-8 inclusive and between the concentration of progesterone on different days from Days 0-8 inclusive following ovulation and insemination were examined in dairy cows. The relationships were examined following 77 randomly chosen artificial inseminations to cows in standing oestrus. There was a significant (P < 0.05) linear and quadratic relationship between the concentration of milk progesterone on each of Days 4-6 after ovulation and the probability of embryo survival. There was no association (P > 0.05) between milk progesterone concentration and probability of embryo survival on Days 7 and 8 after ovulation. There were no associations between milk progesterone concentration on Days 0-2 and the concentrations on Days 4-7, however, progesterone concentrations on Days 4 and 5 were highly predictive of the concentration on Days 6 and 7, respectively. Overall, the results indicate that suboptimal progesterone support during the early luteal phase is likely to deleteriously affect embryo viability and in addition, that it is possible to predict milk progesterone concentrations during the early luteal phase based on earlier stage concentrations and thus identify cows at risk of early embryo loss.     

Effect of climate on the response to three oestrous synchronisation techniques in lactating dairy cows

The reproductive efficiency of Friesian dairy cows was investigated in a three (oestrous synchronisation technique) x two (seasons of the year) factorial design. The 90 primiparous and multiparous cows (winter, n=42; summer, n=48) were allocated at random to three synchronisation treatments (n=30 cows per treatment). In treatment 1 (GPG), the cows were administered 15 mg PGF(2alpha) i.m. at 30 +/- 3 days postpartum, 100 microg GnRH i.m. at 51 +/- 3 days and 15 mg PGF(2alpha) 7 days later. A second 100 microg dose of GnRH was given after, further 2 days and fixed time AI occurred 16-20 h later. In treatment 2 (PG-PG), 15 mg PGF(2alpha) was administered i.m. to each cow on three occasions at successive 14 days interval starting at 30 +/- 3 days postpartum and the cows were inseminated at observed oestrus following the third dose of PGF(2alpha). Cows in treatment 3 (PG) had a single administration of 15 mg PGF(2alpha) i.m. at 57+/-3days postpartum and were inseminated as in treatment 2. Mean daily ambient temperature was 10.9 degrees C in winter (November-March) and 20.2 degrees C in summer (June-October). The cows were confined in an open-fronted shed and had ad libitum access to a complete diet with a 37:63 forage to concentrate ratio. Body condition score was assessed at 57 +/- 3 days postpartum. Cow rectal temperature at insemination, milk yield, reproductive data and climatic variables were recorded. Blood samples were collected for progesterone assay on days 4, 11, 18, 25, 32, 39 and 46 post-AI from 54 of the cows (19 GPG; 17 PG-PG; 18 PG). Pregnancy rate to first AI was 36.7% (11/30) for GPG and 16.7% (5/30) for both PG-PG and PG treatments. The difference was not significant. The cumulative pregnancy rate after third AI were GPG 83.3% (25/30), PG-PG 60.0% (18/30) and PG 60.0% (18/30; P<0.057). The cumulative pregnancy rate for cows inseminated in the winter (81.0%; 34/42) was higher (P<0.01) than for those inseminated in the summer (56.3%; 27/48). The interval from calving to first service was shorter (P<0.05) in treatment PG-PG (65.4+/-1.3 days) than in PG (69.2+/-1.3 days). Mean plasma progesterone concentrations post-AI of pregnant cows were higher (P<0.001) for GPG cows than those for PG-PG and PG cows. Plasma progesterone levels of pregnant cows tended to be higher (P=0.087) in winter than in summer. In conclusion, although the cumulative pregnancy rate was higher for GPG cows, it may be appropriate to correct the nutrition and management of the herd before resorting to synchronisation techniques to improve animal reproductive performances.