A Five-Day Progesterone Plus eCG-Based Fixed-Time AI Protocol Improves Fertility Over Spontaneous Estrus in High-Producing Dairy Cows Under Heat Stress

This study compared the efficiency of a five-day or standard (nine-day) progesterone-based regimen combined with equine chorionic gonadotrophin (eCG) in a fixed-time AI (FTAI) protocol for dairy cows. The data examined were derived from 3577 inseminations conducted in three dairy herds. Animals with no estrus signs detected over 21 days were randomly assigned to a PRID-9 or PRID-5 group. Cows in each group received a progesterone intravaginal device (PRID) for 9 or 5 days, respectively, PGF_2α and eCG on PRID removal, and GnRH 48 h later. Fixed-time AI was performed 12 h after the GnRH dose. Cows artificially inseminated following spontaneous estrus during the study period were considered as controls. Based on the odds ratio, the likelihoods of animals in PRID-9 in the warm (conception rate [CR] of 22.3%) and cool (32% CR) periods, and control animals in the warm period (26.6% CR) becoming pregnant were reduced (by factors of 0.6, 0.3 and 0.4, respectively) compared with the control animals in the cool period (CR of 43.7%). The risk of a twin pregnancy was higher (51.4%) for cystic PRID-9 cows (by a factor of 3.6) and lower (9.9%) for cyclic PRID-5 animals (by a factor of 0.4) compared with the PRID-9 cyclic cows. These findings indicate that the proposed protocol achieves similar results during the cool or warm season to those obtained when AI is conducted at spontaneous estrus during the cool season. In addition, PRID-5 reduced twin pregnancy compared with PRID-9.     

Calving rates of Brahman and Brahman-cross cows to fixed-time insemination after treatment with pregnant mare serum gonadotrophin and intravaginal progesterone

In 2 experiments involving 151 non-lactating and 107 lactating Brahman or Brahman-cross cows, the effects of progesterone treatments (PRID) of 2 durations (7 v 14 days) and injections of pregnant mare serum gonadotrophin (PMSG) at 3 doses (O v 375 v 750 IU) were examined. All cows were inseminated with frozen/thawed semen 54 to 58 and 70 to 74 hours after PRID removal. Calving rates of non-lactating cows (38%) were unaffected by breed or treatment but were higher in previously cyclic than acyclic cows (44% v 19%, P less than 0.025) and in cows which exhibited oestrus after treatment (52% v 23%, P less than 0.001). Calving rates of lactating cows were not affected by these factors but were affected by treatment; PMSG produced no significant effect after a 7-day PRID treatment (33% overall) but increased calving rates after 14-day PRID treatments (22% v 46% v 37% for 0, 375 and 750 IU respectively, P less than 0.10). Comparisons of calving rates of lactating cows treated with 14-day PRID and PMSG and artificially inseminated, and untreated naturally mated cows, showed that treatment significantly increased the proportion of cows conceiving in the first 35 days of the mating period (50% v 23%, P less than 0.025). The results show that treatment with PRID for 14 days and PMSG can overcome post-partum anoestrus in lactating Brahman and Brahman-cross cows leading to significant reductions in the calving to conception interval.     

Induction of oestrus by administering Inhibin antiserum along with equine chorionic gonadotropin in anoestrous bitches

As dogs experience oestrus only once or twice a year, it is necessary to establish an effective method of oestrous induction for efficient breeding. In the present study, we evaluated inhibin antiserum (IAS) on oestrous induction in anoestrous females. Bitches were administered 0.5 ml/kg IAS or a mixture of 50 IU/kg equine chorionic gonadotropin (eCG) and 0.5 ml/kg IAS and 500 IU human chorionic gonadotropin (hCG) administered 7 days after the mixture injection. As a control, bitches received 50 IU/kg eCG, with 500 IU hCG administered 7 days after eCG injection. Blood-tinged vaginal discharge, vulvar swelling, plasma progesterone concentrations and ovarian follicular development were assessed from day 0 to day 14. IAS alone injection did not induce oestrus in bitches at the anoestrous stage. Conversely, vulvar swelling, blood-tinged vaginal discharge and an estimated luteinizing hormone (LH) surge appeared on days 3–7, days 3–6 and days 7–9 after the IAS+eCG mixture injection, respectively, in all five bitches at the anoestrous stage. The average number of developing and ovulated follicles in bitches administered IAS+eCG was 8.8 and 9.6 respectively. A single eCG injection followed by hCG induced oestrous signs, with an average of 8.3 developing follicles and 4.5 ovulated follicles. This study revealed that IAS alone did not induce oestrus, but when IAS was used in combination with eCG, it induced oestrus and promoted a considerable number of ovulations in anoestrous dogs.     

Fertility of Bunaji (Zebu) Cows after Treatment with PRID with or without PGF2α

A study was undertaken to determine the oestrus response and fertility rates of zebu cows treated with PRID alone or in combination with PGF2alpha. A total of 184 non-suckled cycling Bunaji cows were allotted randomly to four treatment groups of 46 animals per group as follows: group 1 (PRID-12), PRID was inserted for 12 days; group 2 (PRID+7+PGF2alpha-6, PRID was inserted for 7 days and PGF2alpha was administered intramuscularly 1 day prior to PRID withdrawal; group 3 (PRID-7+PGF2alpha-7, PRID was inserted for 7 days and PGF2alpha was administered intramuscularly on the day of PRID withdrawal; group 4 (2 x PGF2alpha-13, two intramuscular injections of PGF2alpha 13 days apart. At the end of each treatment period, the cows were observed for 7 days for behavioural oestrus and were inseminated 12 h following detection of oestrus. Pregnancy was diagnosed by rectal palpation 30-40 days post-insemination. The respective oestrus response rates were 78.3%, 76.1%, 87.0% and 89.1% for groups 1-4. While the corresponding pregnancy rates were 39.1%, 41.3%, 52.2% and 52.2%, the conception rates were 50.0%, 54.3%, 60.3% and 58.6% for groups 1-4. Although individual variations in progesterone levels were observed, the progesterone profiles were generally typical and normal. The results of the study have confirmed the effectiveness of the four regimes in synchronizing and controlling oestrus and ovulation in Bunaji cows. However, groups 3 and 4 showed some superiority over the other treatments. The results of this study provide feasible options from which clinicians involved in intensive breeding programmes and herd health fertility programmes can choose.     

Conception rates in cows after various synchronisation techniques using progesterone releasing intravaginal devices

The effects of different treatments for oestrus synchronisation on the incidence of oestrus and fertility levels in dairy cows were studied in 2 experiments. In Experiment 1, 200 lactating cows were allotted to 5 groups and the treatments imposed were either; 1: Untreated controls, 2: An injection of 0.5 mg of cloprostenol followed 13 days later by a progesterone releasing intravaginal device (PRID) inserted for 12 days, 3: A PRID, with a capsule containing 10 mg of oestradiol benzoate (ODB) attached, inserted for 12 days, 4: A PRID inserted for 12 days with 0.5 mg of cloprostenol administered 24 h before PRID removal or, 5: As for 4 but 14 days after fixed-time insemination a second PRID was inserted for 12 days. Treated cows were inseminated 56 h after PRID removal and at an observed oestrus during the subsequent 30 days. The control group was inseminated at an observed oestrus during this 30-day period. For treatments 2, 3, 4 and 5, respectively, the percentage of cows showing oestrus by 60 h after PRID removal was 70, 40, 67 and 43 and conception rates to the fixed time insemination were 34, 33, 49 and 29%. Calving rates of cows inseminated at an observed oestrus during a 30-day period were 70, 75, 70, 83 and 82% for treatments 1, 2, 3, 4 and 5, respectively. In Experiment 2, 60 lactating cows were divided into 2 groups and the treatments imposed were either 1: An injection of 0.5 mg of cloprostenol followed 13 days later by a PRID inserted for 12 days or 2: As for 1 but 14 days after fixed-time insemination a second PRID was inserted for 12 days. Treated cows were inseminated 56 h after PRID removal and at an observed oestrus over a period from the first insemination to 6 days after removal of the second PRID. For treatments 1 and 2, respectively, 73 and 71% of cows showed oestrus by 60 h after removal of the first PRID and 40% and 46% conceived to the fixed time insemination. The conception rates to inseminations over the treatment period were 73 and 70% for treatments 1 and 2, respectively. None of the treatments resulted in conception rates which were lower than those of control cows provided that treated cows were reinseminated at observed oestrus. Treatment 4 provided the most practicable technique for oestrus synchronisation.     

The use of progesterone administered intravaginally and pregnant mare serum gonadotrophin given by injection in controlled breeding programs in beef and dairy cattle

Five experiments involving 1,244 cows and heifers were carried out to investigate the factors which might influence the calving performance to fixed-time artificial insemination following intravaginal administration of progesterone (PRID) and intramuscular injection of pregnant mare serum gonadotrophin (PMSG). Factors examined were duration of PRID treatment, time of treatment after calving, time and dose PMSG and lactational status. Experiments 1, 2 and 3 were carried out on milked Friesian cows, experiment 4 on Friesian heifers and experiment 5 on suckled and dry Herefords. All cows were inseminated once with frozen/thawed semen 54 to 58 h or 46 to 50 h after completion of PRID treatment. Overall there was a progressive increase in calving rates with an increase in the duration of treatment from 12 to 14 to 16 days but there was little or no effect of time after calving (4 v 7 weeks) at which treatment was commenced. The poorer calving performance of cows treated for 12 to 14 days was associated with relatively high peripheral levels of plasma progesterone at the time of the PRID removal, suggesting the presence at the end of treatment of residual secretory luteal tissue. There was an effect on calving performance of PMSG given at the time of PRID removal but its effect varied according to the duration of PRID treatment. After 12 days treatments (experiments 1 and 5) PMSG had little effect, whereas after 14 days treatments, 0, 500 and 750 IU PMSG gave calving rates of 27%, 40% and 46% in experiment 2 and 5%, 24% and 38% in experiment 5.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a Progesterone‐Based Oestrous Synchronization Protocol in 51‐ to 57‐Day Postpartum High‐Producing Dairy Cows

The aim of this study was to investigate the effect of applying a progesterone‐based oestrous synchronization protocol at 51–57 days postpartum in high‐producing dairy cows. The data analysed were derived from 1345 lactating cows. Cows between 51 and 57 days postpartum were assigned to the groups: control, PRID (receiving a progesterone‐releasing intravaginal device for 9 days, and prostaglandin F_2α 24 h before PRID removal) or GnRH–PRID (the same as the PRID group plus GnRH at PRID insertion). Oestrus was detected by using pedometers and confirmed by examination of the genital tract at AI. Oestrous and conception rates before days 71–77 postpartum, pregnancy loss in early pregnant cows or the cumulative conception rate registered on day 120 postpartum were considered as the dependent variables in four consecutive logistic regression analyses. Based on the odds ratios, the oestrous rate increased by a factor of 1.73 in cows showing oestrus before treatment for each unit increase in the number of previous oestruses; decreased by a factor of 0.44 in the control group with respect to the treatment groups; and by a factor of 0.61 in cows without luteal structures at treatment with respect to cows with corpora lutea. The conception rates of cows inseminated before days 71–77 postpartum remained similar across the groups, whereas the likelihood of pregnancy loss for cows becoming pregnant during this period was 0.11 times lower in the PRID group than in the control. Based on the odds ratio, the likelihood of a higher cumulative conception rate on day 120 postpartum: increased in cows showing oestrus before treatment by a factor of 1.41 for each unit increase in the number of previous oestruses, was reduced 0.56‐fold in control cows compared with treated cows, and was also reduced by a factor of 0.98 for each kilogram of milk production increase recorded at treatment. In conclusion, although oestrous synchronization programmes performed in this study did not improve fertility, cows treated with progesterone could be inseminated earlier than untreated cows, such that the treatments increased the cumulative pregnancy rates determined on day 120 postpartum. In addition, fewer pregnancy losses were observed in early pregnant cows in the PRID group than the GnRH–PRID group.     

Improving reproductive performance in lactating dairy cows by synchronizing ovulation or inducing oestrus

Lactating crossbred Holstein-Friesian dairy cows (n = 331) were started on an Ovsynch regimen 68 +/- 8.2 days after calving; 200 micrograms GnRH intramuscularly (i.m.) on Days 0 and 9, and 35 mg prostaglandin F2 alpha i.m. on Day 7. Thirty-eight and 31 cows (11.5 and 9.4%, respectively) were in oestrus on Days 0 to 6 and 7 to 8, respectively, and inseminated, and the remainder were fixed-time inseminated (on Day 10). For these three groups, pregnancy rates (60-65 days after breeding) were 31.6, 38.7 and 34.0%, respectively (P = 0.82) and calving rates were 100, 100 and 89.9% (P = 0.23). In a preliminary trial, twelve lactating cows (45 to 60 days postpartum) with inactive ovaries were given 1500 IU eCG i.m.; 10 were in oestrus within 10 days after treatment (and inseminated) and eight of these were pregnant (30 days after breeding). The Ovsynch program resulted in acceptable reproductive performance in cyclic cows and eCG treatment has considerable promise for inducing oestrus in anoestrous cows.     

Multiple use of progesterone releasing intravaginal devices for synchronisation of oestrus and ovulation in cattle

Experiments were conducted to investigate the possibility of using progesterone releasing intravaginal devices (PRIDs) more than once, for the purpose of synchronising oestrus and ovulation in dairy cows. In an initial study, PRIDs were inserted into 6 ovariectomised cows for 12 days on 3 separate occasions and blood samples were collected for progresterone assay. After removal, 3 PRIDs were sterilised by autoclaving and the other 3 by gassing with ethylene oxide. After PRID insertion progesterone concentration in plasma rose rapidly. Autoclaved PRIDs which were reused once and then twice, maintained blood progesterone profiles which were comparable to the release of progesterone from a new PRID. This was not the case when PRIDs were re-used after gas sterilisation. In a second study, PRIDs were inserted into 41 dairy cows for 9 days and an injection of prostaglandin F2o was given one day before PRID removal. Onset of oestrus was determined by observation at intervals of 3 h for 30 min and time of ovulation was determined by endoscopy approximately 30 h after onset of oestrus. PRIDs were autoclaved after removal and re-used twice. In cows which received new PRIDs, 85% came into oestrus between 30 and 60 h after removal. When PRIDs were used for the second time, 100% of cows showed oestrus within 30 to 60 h. When PRIDs were used for the third time the interval between PRID removal and onset of oestrus was highly variable. Only 29% of cows showed oestrus within 30 to 60 h whereas 59% showed oestrus between 12 and 42 h after PRID removal. The distribution in estimated time between PRID removal and ovulation followed closely the distribution of onset of oestrus for each insertion of PRIDs. The synchrony of ovulation was most concentrated for the second use of PRIDs and least for the third use. A few cows did not follow the general pattern of response. Indications that the PRID may be used more than once for synchronising oestrus and ovulation in the dairy cow, and the adoption of a 9-day PRID insertion interval in any synchronisation schedule should result in a significant reduction in the cost of this technology.     

Fertility of N'dama and Bunaji Cattle to Artificial Insemination Following Oestrus Synchronization with PRID and PGF2α in the Hot Humid Zone of Nigeria

A study was undertaken to determine the effectiveness of a progesterone-releasing intravaginal device (PRID) and prostaglandin F2 alpha (PGF2alpha) in synchronizing oestrus in N'dama and Bunaji cows and heifers and the fertility following artificial insemination at the synchronized oestrus. A total of 116 cows and heifers (58 N'dama and 58 Bunaji) were used in two separate trials. In the first trial, oestrus was synchronized using a PRID, which was inserted for 12 days; in the second trial, oestrus was synchronized by giving two injections of PGF2alpha 13 days apart. Only animals that did not respond to the first injection were given the second injection. At the end of each treatment period, the animals were observed for oestrus for 7 days and inseminated approximately 12 h following detection of oestrus. Standing to be mounted was the single criterion used to judge an animal to have been in oestrus. PGF2alpha and PRID were both effective in synchronizing oestrus in N'dama and Bunaji cows and heifers. The respective oestrus response rates, pregnancy rate and conception rates for PRID and PGF2alpha were 85.7%, 53.6% and 62.5% for PRID, and 91.7%, 68.3% and 74.6% for PGF2alpha. N'dama cattle showed significantly (p<0.05) better oestrus response rate, pregnancy rate and conception rate than Bunaji cattle following both PRID and PGF2alpha treatments. The pregnancy rate and conception rate following PGF2alpha treatment were better (p < 0.05) than for PRID, although the oestrus response rate did not differ. It is concluded that both PRID and PGF2alpha are effective in synchronizing oestrus in N'dama and Bunaji cattle in the hot humid zone of Nigeria and the fertility to artificial insemination at the synchronized oestrus was normal and acceptable. Thus, PRID and PGF2alpha can effectively be used in intensive breeding programmes for the rapid multiplication and distribution of both cattle breeds, especially the N'dama, which is a unique and beneficial animal genetic resource for the tsetse infested hot humid zone of Nigeria.     

The reproductive performance of anoestrous dairy cows following treatment with progesterone and oestradiol prior to the start of mating

AIMS: To determine the reproductive performance of cows diagnosed as anoestrus prior to the planned start of mating (PSM) when they were either treated when first diagnosed, or left untreated until 16 days after the PSM. METHODS: A clinical trial was conducted during the 1996/97 and 1997/98 breeding seasons involving 823 anoestrous dairy cows in 14 herds. On Day -8 (PSM = Day 0), cows in one group (Treated) were each treated with an intravaginal device containing 1.9 g of progesterone (CIDR). The CIDR device was removed on Day -2, and on Day -1 each cow was injected intramuscularly with 1 mg oestradiol benzoate. Cows in the second group (Control) remained untreated at the time of first examination. All cows detected in oestrus after the PSM were mated by artificial insemination (AI) or a bull. Sixteen days after the PSM, all cows that had not been mated were presented for veterinary examination, and those which were still classified as anoestrus were treated with the previously described CIDR regimen. Pregnancy status and approximate date of conception were determined by palpation per rectum 10 -13 weeks after the PSM or 6 weeks after the end of the mating period. RESULTS: Treatment of anoestrous cows 8 days before the PSM significantly increased the number of cows detected in oestrus (95.0% vs 63.1%; p<0.001) and conceiving (59.5% vs 38.8%; p<0.001) during the first 21 days of mating, and reduced the interval from PSM to conception by 7.5 days (p<0.001). There was no significant difference between the conception rate of cows mated following the CIDR treatment regimen compared to cows mated at their first spontaneous oestrus after calving (52.4% vs 58.3%; p = 0.143). CONCLUSION: Diagnosis and treatment of anoestrous dairy cows prior to the start of mating significantly improves their reproductive performance under the seasonal mating conditions typical of spring-calving New Zealand dairy herds.     

Clinical response of ovarian cysts in dairy cows after PRID treatment

We investigated the therapeutic effects of a progesterone releasing intravaginal device (PRID) on cystic ovarian disease (COD) and reproduction performance of cows. The possible influence of PRID on metabolic and/or health status was also examined. A total of 40 Holstein-Friesian cattle, with ovarian cystic structures, > or =2.5 cm in diameter, persisting for more than 7-14 days, without a corpus luteum (CL) were used for the study. PRID or placebos were inserted into the vagina for 12 days. Five animals lost the intravaginal device before removal and one was culled. Based on plasma progesterone concentration on the day of treatment, 20 (17 PRID and 3 placebos) of the remaining 34 cows had follicular cysts (progesterone < or =1 ng/ml) and 14 (10 PRID and 4 placebos) had luteal cysts (progesterone >1 ng/m l). Fourteen (82%) of the PRID-treated follicular cystic cows responded with formation of a CL within 14 days after treatment, and an overall conception rate of 53.8%. Likewise, 70% of the treated luteal cystic cows responded with CL formation and 71.4% conception rate. No significant differences were observed in hematocrit (Ht), white blood cell count and serum levels of glucose, blood urea nitrogen, aspartate aminotransferase, and alanine aminotransferase, between the day of PRID insertion and removal, in animals with follicular and luteal cysts. PRID treatment resulted in ovulation 2-4 days later and formation of a CL in cows that recovered.     

Effects of different five-day progesterone-based synchronization protocols on the estrous response and follicular/luteal dynamics in dairy cows

This study compared the responses shown by lactating dairy cows to four different P4-based protocols for AI at estrus. Cows with no estrous signs 96 h after progesterone intravaginal device (PRID) removal were subjected to fixed-time AI (FTAI), and their data were also included in the study. In Experiment I, follicular/luteal and endometrial dynamics were assessed every 12 h from the beginning of treatment until AI. The estrous response was examined in Experiment II, and fertility was assessed in both experiments. The protocols consisted of a PRID fitted for five days, along with the administration of different combinations of gonadotropin releasing hormone (GnRH), equine chorionic gonadotropin and a single or double dose (24 h apart) of prostaglandin F_2α. In Experiment I (40 cows), animals receiving GnRH at the start of treatment showed a significantly higher ovulation rate during the PRID insertion period while estrus was delayed. In Experiment II (351 cows), according to the odds ratios, cows showing luteal activity at the time of treatment were less likely to show estrus than cows with no signs of luteal activity. Treatment affected the estrous response and the interval from PRID removal to estrus but did not affect conception rates 28–34 days post AI. Primiparous cows displayed a better estrous response than multiparous cows. Our findings reveal acceptable results of 5-day P4-based protocols for AI at estrus in high-producing dairy cows. Time from treatment to estrus emerged as a good guide for FTAI after a 5-day P4-based synchronization protocol.     

The time of oestrus and ovulation following various synchronisation techniques using progesterone impregnated intravaginal devices

SUMMARY Progesterone releasing intravaginal devices (PRIDs) were used in 4 experiments involving 67 cattle to study the effect of the stage of the oestrous cycle and of oestradiol benzoate (ODB) administration on the time interval from PRID removal to oestrus and/or ovulation. Cows in which PRIDs were inserted on days 2 to 4 of the oestrous cycle for 14 days were subsequently observed by endoscopy to ovulate significantly later than cows given identical treatments on days 13 and 14 of the cycle. The concentration of progesterone was higher in the former group at the time PRIDs were removed and remained at a higher level for 3 days thereafter. The length of the oestrous cycle of untreated heifers was significantly longer than in heifers treated for 12 days with PRIDs only inserted on day 3 of cycle (19.7 v 18.2; p <0.01). Treatment with PRIDs inserted for 12 days together with ODB further shortened the cycle length from 18.2 days to 16.9 days (p <0.01). The intervals from PRID removal to onset of standing oestrus in heifers treated with PRID only and those treated with PRID and ODB were 80h and 45h, respectively (p <0.01); the respective variances were 280 and 4; p <0.01). Plasma progesterone concentration, at PRID removal, was 3 times higher in heifers treated with PRID only than in heifers treated with PRID and ODB (p <0.01) and the interval from PRID removal to the lowest progesterone value following it was 3.8 and 1.2 days for the 2 groups, respectively (p <0.05). The study indicated that the stage of oestrous cycle at PRID insertion is an important factor which influences the interval from withdrawal of PRIDs to ovulation. The results suggest closer synchronisation would follow insertion in the mid-luteal phase (Day 13 to 14) or use of ODB treatment at the time of insertion of PRIDs.     

Insemination at the second of two induced oestrous periods in anoestrous dairy cows increases conception rates to first service

AIM: To determine whether mating previously anoestrous cows on their second, rather than first, oestrus post pm-turn could increase conception rates to that service. METHODS: Cows diagnosed as anovulatory anoestrus were allocated to two groups, starting treatment on Day -17 (OES2) or on Day -7 (OESI) where the date of the planned start of mating = Day 0. All cows were treated with intravaginal progesterone (CIDR device) for 6 days and an injection of 1 mg oestradiol benzoate 24 h after removal of the device. Cows in the OES2 group were also injected with prostaglandin F2alpha on Day 0. RESULTS: During the first 7 days of mating, 61.8% (207/335) and 88.2% (328/372) of cows in the OES2 and OESl groups, respectively, were inseminated on detection of oestrus (p <0.001). Oestrus without ovulation occurred in 1.5% of cows in the OES2 group and 6.2% of cows in the OESl group during this period (p <0.01). Of those cows inseminated in the first week of mating, conception rates were 54.0% in the OES2 group and 45.5% in the OESl group (p = 0.05). There was no significant difference in median interval from start of mating to conception between the two groups (24 and 22 days for OES2 and OESl, respectively, p >0.05). CONCLUSION: Mating previously anoestrous cows on their second, rather than first oestrus post partum increased conception rates to that service. However, median intervals from start of mating to conception were not altered.     

Effect of hCG Treatment on the Oestrous and Ovulation Responses to FSH in Prepubertal Gilts

To ensure sufficient numbers of pregnant females, particularly at hotter times of the year, hormonal induction of gilt oestrus may be necessary. However, the gilt oestrus and ovulation responses to gonadotrophin treatment have often proven unpredictable. The objective of this study was to examine possible reasons for this unpredictability. Prepubertal gilts (approximately 150 days of age, n = 63) were assigned to one of three treatments: injection of 300 IU hCG (n = 15); pre-treatment with 100 mg FSH in polyvinylpyrrolidinone administered as 2 × 50 mg injections 24 h apart, followed by 600 IU eCG at 24 h after the second FSH injection (n = 23); or FSH pre-treatment as above followed by 300 IU hCG at 24 h after the second FSH injection (n = 25). To facilitate oestrus detection, gilts were exposed to a mature boar for 15 min daily for 7 days. Blood samples were obtained on the day of eCG or hCG injection and again 10 days later and gilt ovulation responses determined based on elevated progesterone concentrations. The oestrus responses by 7 days were 6.7%, 17.5% and 64.0% for gilts treated with hCG, FSH + eCG and FSH + hCG, respectively (p < 0.001). The oestrous gilt receiving hCG alone and one oestrous FSH + hCG gilt did not ovulate, all other oestrous gilts ovulated. A further two anoestrous FSH + eCG-treated gilts ovulated. These data suggest that FSH pre-treatment facilitated the development of ovarian follicles to the point where they became responsive to hCG, but had little effect on the response to eCG.     

The effect of the seasons on the ovarian response in sheep after the administration of the serum gonadotropin, PMSG

In the autumn oestrus season, 20 Slovak Merino ewes were exposed to synchronization of oestrus, treated with the PGF2alfa at doses 125 micrograms (Oestrophan, inj. Spofa). followed by an injection of PMSG at doses 1000 IU (Antex Leo Denmark) and 50,000 IU of Vitamin A (Axerophtol Spofa). 23 anoestrus ewes were synchronized with an intravaginal sponges containing 20 mg of chlorsuperlutine (Agelin, Spofa) for 12 days and after sponge withdrawal, the ewes were injected with 750 and 1000 IU of PMSG (Antex Leo Denmark). Ovulatory response was observed and the possibility of ova recovered from the genital organs in ewes after synchronization of oestrus and superovulation in oestrus season. Higher values of the total follicular response (CFO), and the average number of ovulation (PO) after administering equal doses of PMSG were found out both in anoestrus ewes (CFO 6.62 +/- 4.24; PO 4.25 +/- 4.52) and in oestrus ewes (CFO 2.70 +/- 2.10; PO 2.60 +/- 1.74; resp. CFO 2.80 +/- 1.83; PO 3.4 +/- 3.0), if the ewes were treated with PMSG together with vitamin A. The average number of ova flushed was higher in anoestrus ewes (3.0-0.5) than in oestrus ewes (1.67-3.75). In both trials the equal ratio in the number of released ova was gained from ewes of experimental groups (83-88% of the total number). After ova flushing from the genital organs in ewes of the experimental groups most ovas were found in the isthmatal part of the uterine tube (36-60%). On the basis of gained results it was concluded, that synchronized oestrus ewes on receiving PMSG in anoestrus season the ovarial response was more significant than in autumn breeding season.     

The reproductive performance of anoestrous dairy cows following treatment with progesterone and oestradiol prior to the start of mating

Aims: To determine the reproductive performance of cows diagnosed as anoestrus prior to the planned start of mating (PSM) when they were either treated when first diagnosed, or left untreated until 16 days after the PSM.

Methods: A clinical trial was conducted during the 1996/97 and 1997/98 breeding seasons involving 823 anoestrous dairy cows in 14 herds. On Day-8 (PSM = Day 0), cows in one group (Treated) were each treated with an intravaginal device containing 1.9 g of progesterone (CIDR).The CIDR device was removed on Day-2, and on Day-1 each cow was injected intramuscularly with 1 mg oestradiol benzoate. Cows in the second group (Control) remained untreated at the time of first examination. All cows detected in oestrus after the PSM were mated by artificial insemination (AI) or a bull. Sixteen days after the PSM, all cows that had not been mated were presented for veterinary examination, and those which were still classified as anoestrus were treated with the previously described CIDR regimen. Pregnancy status and approximate date of conception were determined by palpation per rectum 10-13 weeks after the PSM or 6 weeks after the end of the mating period.

Results: Treatment of anoestrous cows 8 days before the PSM significantly increased the number of cows detected in oestrus (95.0% vs 63.1%;p < 0.001) and conceiving (59.5% vs 38.8%;p < 0.001) during the first 21 days of mating, and reduced the interval from PSM to conception by 7.5 days (p < 0.001). There was no significant difference between the conception rate of cows mated following the CIDR treatment regimen compared to cows mated at their first spontaneous oestrus after calving (52.4% vs 58.3%; p = 0.143).

Conclusion: Diagnosis and treatment of anoestrous dairy cows prior to the start of mating significantly improves their reproductive performance under the seasonal mating conditions typical of spring-calving New Zealand dairy herds.     

Treatment of post-partum anoestrous dairy cows with progesterone, oestradiol and equine chorionic gonadotropin

Anoestrus in lactating dairy cows at the start of the breeding season is a major form of reproductive wastage for seasonal dairy production based on pasture. The objective of this study was to compare the reproductive performance of anoestrous cows that were treated with a combination of progesterone, oestradiol and equine chorionic gonadotrophin either 10 days before (T-10, n = 2 19) or 16 days after (T+16, n = 229) the start of the breeding season. A higher percentage of cows in the T-10 group were detected in oestrus and inseminated during the first 6 days of breeding than those in the T+16 group (69.4% v. 26.2%. p <0.001). However, the percentage of cows detected in oestrus by Day 16 was similar between the two treatment groups (T10 v. T+ 16; 77.7% v. 76.7%). There was no difference between treatment groups in conception rate to the first (51.2% v. 59.0%) or the second insemination (50.8% v. 57.6%), in pregnancy rate over the first 49 days (74.0% v. 75.1%), in empty rate (10.0% v. 10.5%) or in the mean day of conception from the start of the breeding season (24.0 v. 25.7 days). These results suggest that, under favourable environmental conditions, treatment of anoestrous cows with the programme used in this trial can be performed 16 days after the start of the breeding season with similar results to that performed 10 days before the start of the breeding season. Further studies are needed to determine if this is the case under different environmental conditions or for other treatment programmes.     

Synchronization of estrus in beef cattle with norgestomet and estradiol valerate

Fifty-six cows received a norgestomet implant and an injection of norgestomet and estradiol valerate; half (n = 28) received 500 IU equine chorionic gonadotrophin (eCG) at implant removal, 9 d later. A third group (n = 25) received 2 doses of cloprostenol (500 micrograms) 11 d apart. Estrous rate was higher (P < 0.05) for cows given norgestomet and estradiol plus 500 IU eCG (75.0%) than for those receiving cloprostenol (44.0%); for those receiving norgestomet and estradiol alone, it was intermediate (67.8%). Pregnancy rates to artificial insemination (after estrus or timed) were higher (P < 0.05) for cows given norgestomet and estradiol than for those given cloprostenol (23 of 28, 82.1% vs 13 of 25, 52.0%), and intermediate (67.8%) for those given norgestomet and estradiol plus eCG. In a second experiment, for heifers treated with norgestomet and estradiol plus eCG (n = 15) or with 2 doses of cloprostenol (n = 16), estrous rates were 66.7% vs 56.2% (P > 0.5), ovulation rates were 100.0% vs 81.2% (P = 0.08), intervals from implant removal or cloprostenol treatment to estrus were 48.0 +/- 4.4 hours vs 61.3 +/- 7.0 hours (P = 0.12) and to ovulation were 70.4 +/- 4.4 hours vs 93.2 +/- 7.5 hours (P < 0.01), respectively; pregnancy rates were 41.7 and 35.7%, respectively (P > 0.5). Norgestomet and estradiol were as good as (heifers) or superior to (cows) a 2-dose cloprostenol regimen. In cows given norgestomet and estradiol, injecting eCG at implant removal did not significantly improve estrous or pregnancy rates.