Induction of ovulatory oestrus in true anoestrous buffaloes during low breeding season

A fertility treatment trial of anoestrous buffaloes was undertaken on a well managed dairy farm in the low breeding season. Forty lactating buffaloes, 12 each from first and second parity and 16 from third or higher parity, not seen in oestrus for at least 3 to 5 months were diagnosed anoestrous by rectal examination. A subcutaneous ear implant containing 3 mg of norgestomet was inserted, accompanied by an intramuscular injection of 3 mg norgestomet and 5 mg of oestradiol valerate (Syncro-mate B, Intervet). After 9 days the implant was removed and 600 IU of PMSG (Intervet) were given intramuscularly. Irrespective of oestrous behaviour, the animals were inseminated with frozen semen at two fixed times: 48 and 72 h after removal of the implant. Thirty animals having calved in the same period as the experimental animals and not seen in oestrus since then served as controls. Milk samples for progesterone analysis were taken on the day of insertion of the implant, the day of removal and on days 10 and 22 after the second A.I. Progesterone determination by means of an enzyme immunoassay (EIA) revealed that 33 buffaloes out of 40 (82.5%) were in true anoestrus. Ovulation occurred in 21 buffaloes out of 30 (70%). Three buffaloes could not be followed up further. The overall conception rate was 53.3%. The parity-wise conception rate was 40%, 44.4% and 72.2% in first, second and third or higher parity, respectively. None of the control animals displayed oestrus during the course of the study.     

Synchronization of estrus and fertility in goats with norgestomet ear implants

Estrus was synchronized in 64 dairy goats in July with norgestomet ear implants. Half the does received ear implants that contained 6 mg norgestomet and the remaining does received implants that contained 3 mg. Implants were left in place for 11 days. Each doe received i.m. injections of 400 IU PMSG and 50 mug cloprostenol 24 hours prior to implant removal. Twenty-eight of 32 does (87.5%) that received 6 mg or 3 mg norgestomet exhibited onset of estrus within 24 hours of implant removal. All does had exhibited onset of standing estrus by 43 hours after implant removal. Does were hand-mated to fertile bucks twice daily while in standing estrus. There were no differences between does implanted with 6 mg or 3 mg in fertility to the induced estrus (74.2% vs 75% kidding), mean length of gestation (151.0 +/- 3.2 vs 151.6 +/- 2.0 days), mean number of kids per doe (2.1 +/- 0.8 vs 2.3 +/- 0.7) or in mean kid weights (3.10 +/- 0.80 vs 3.06 +/- 0.86 kg) (6 mg vs 3 mg, respectively). It was concluded that ear implants that contained 3 mg of norgestomet were equally as effective as implants that contained 6 mg for synchronization of estrus in dairy goats.     

Induction of multiple ovulations during the ovulatory season in mares

The efficacy of an equine pituitary extract for induction of multiple ovulations during the ovulatory season was studied in 112 horse mares in four experiments. Combined for all experiments, 70% of the mares (78 112 ) had multiple ovulations for an average of 3.0 ovulations per mare. The interval between first and last ovulation was decreased (P<0.01) when human chorionic gonadotropin (hCG) was included in the treatment regimen (0.0 +/- 0.0 versus 1.6 +/- 0.4 days). Ovulation rate was lower (P<0.01) when extract treatment was initiated at day 19 (1.3 +/- 0.2) than when initiated at day 15 post-ovulation (2.9 +/- 0.5). Initiation of extract treatment at day 11 was as effective as initiation at day 15, with or without an injection of prostaglandin F(2alpha) on the first day of extract treatment. Increasing the dose of extract from 750 to 1500 or 2250 units per day did not significantly increase the ovulatory response.     

Effect of ram exposure at the end of progestagen treatment on estrus synchronisation and fertility during the breeding season in ewes

Two experiments were conducted to examine the effects of ram exposure during the breeding season, in combination with progestagen treatment on estrus synchronization, fertility the LH surge and ovulation in ewes. Experiment 1 was subdivided into experiments 1a and 1b. In all experiments cross-bred ewes were treated with an intravaginal sponge for 12-14 days and three days before sponge withdrawal ewes were divided into control (no further treatment; n=191, 103 and 50 for experiments 1a, 1b and 2, respectively) or ram exposed (three mature rams per 50 ewes were introduced; +Ram; n=187, 99 and 49 for experiments 1a, 1b and 2, respectively). At sponge withdrawal ewes in Experiments 1a and 2 received 500 IU eCG and rams were removed from all the +Ram groups. In Experiments 1a and 1b, raddled, entire rams were introduced to ewes 48 h after sponge withdrawal. The timing of mating was recorded and ewes were maintained until lambing. In Experiment 2, estrus behavior was determined every 4 h and the time of the LH surge and ovulation were determined from a subset of 10 ewes per group. In Experiment 1a, less +Ram ewes were bred by 48 h after ram introduction (control 98% versus +Ram 89%, P<0.001) and in Experiments 1a and 1b 14% fewer (P<0.05) of the ewes bred in the first 3 h after ram introduction lambed to that service. In Experiment 1a, ram exposed ewes had a lower litter size than control ewes (1.93+/-0.06 versus 1.70+/-0.06 lambs per ewe; P<0.05). In Experiment 2, rams advanced (P<0.05) estrus, the LH surge and ovulation by 2-6 h compared with control ewes. We speculate that exposure of ewes to rams increased LH secretion and that this in turn increased follicle development and the production of oestradiol that led to a more rapid onset of estrus, the LH surge and ovulation compared to control ewes. Unexpectedly, ewes that were bred had lower fertility in the +Ram groups than control groups.     

Induction of synchronized estrus and fertility in anestrous ZebuxTaurus crossbred cows

A major cause for reproductive failures in Zebu x Taurine crossbred cows is postpartum anestrus. Crossbred cows were diagnosed to be in postpartum anestrus by palpation per rectum of nonfunctional ovaries. To induce synchronized estrus, the cows were treated by placement of a progesterone releasing intravaginal device (PRID) for various number of days, together with a single administration of prostaglandin F(2) alpha (PGF, 5 mg intravulvosubmucos), estradiol-17beta (E2, 1 mg i.m.) or pregnant mare serum gonadotrophin (PMSG, 500 IU i.m.). Administration of PRID for 7 d, and of E2 and PMSG on Day 6, significantly improved the degree of behavioral estrus manifestation compared to single PRID for 12 d or PRID for 7 d, and of PGF on Day 6. However, the treatment combination of PRID and PMSG alone was associated with higher (P < 0.01) conception rate to 2 fixed time A.I. at induced estrus. The mean interval from treatment to conception was also shortest (P < 0.01) for this group. These results suggest that administration of PRID for 7 d, and of PMSG on Day 6 is highly effective in achieving synchronized behavioural estrus, a near normal CR to fixed time A.I. and a shorter interval from treatment to conception in anestrus Zebu x Taurine crossbred cows under Indian field conditions.     

Follicular dynamics during the ovulatory season in goats

Growth and regression of ovarian follicles>or=3 mm were studied by transrectal ultrasonography for 4 interovulatory intervals in each of 5 Saanen goats. The observed number of growing identified 4-mm follicles per day differed (P<0.05) from randomness, indicating that follicles, on the average, emerged in groups (waves). Averaged over all interovulatory intervals, the number of 3-mm follicles on each day that later reached >or=6 mm followed a pattern of significant peaks on Days 0 (ovulation), 4,8 and 14. A follicular wave was defined by consecutive days of entry of follicles>or=6 mm into the wave, and the day of emergence was defined as the first day that the >or=6 mm follicles were 3 mm. In 15 of 20 (75%) interovulatory intervals, 1 wave emerged during each of Day -2 to Day 1 (Wave 1); Days 2 to 5 (Wave 2); Days 6 to 9 (Wave 3); and Days 10 to 15 (Wave 4). Ovulation occurred during Wave 4. The mean days of emergence of Waves 1 to 4 were Days -1, 4, 8 and 13, respectively. However, in 5 of these 15 interovulatory intervals, 50% of the apparent waves merged or were continuous so that a distinction could not be made between 2 waves. The largest follicle grew to a larger (P<0.05) maximum diameter for Waves 1 (8.7+/-0.3 mm) and 4 (9.7+/-0.3 mm) than for Waves 2 (7.2+/-0.2 mm) and 3 (7.3+/-0.2 mm). The following observations suggested that the phenomenon of follicular dominance was more common during Waves 1 and 4 than during Waves 2 and 3: 1) the interwave intervals (days) were longer (P<0.05) for Waves 1 (3.4+/-0.2) and 4 (4.3+/-0.6) than for Waves 2 and 3 (2.5+/-0.2 for each wave) and 2) the correlation between maximum diameter of largest follicle and the subsequent interwave interval was significant for Waves 1 and 4 but not for Waves 2 and 3. The 5 remaining interovulatory intervals were irregular and involved more than 4 waves, including 2 interovulatory intervals with prolonged follicular phases (14 and 21) and failures of ovulation. In conclusion, the predominant follicular-wave pattern was 4 waves with ovulation from Wave 4, and apparent follicular dominance was expressed during some follicular waves, especially during Waves 1 and 4.     

Cervical patency during non-ovulatory and ovulatory estrus cycles in domestic cats

The cervix functions as a barrier to spermatozoa. Vaginal artificial insemination in cats is, therefore, likely to be successful only at the period of estrus when the cervix is open. This study aimed to define the period of cervical patency in cats in both non-ovulatory and ovulatory estrus cycles. A total of 15 reproductive cycles were studied in six cats during the estrous stage. Cervical patency was monitored with the cats under sedation, by infusing 2 mL of Iohexol contrast medium via a 3.5 French tomcat catheter into the cranial vagina during estrus. Day one of estrus was defined as the first day the cats showed estrous behavior. Non-ovulatory cycles were characterized by a serum progesterone concentration on days 11-15 that was below 5 nmol/L and a normal interestrus interval of 7-14 days. Ovulatory cycles were characterized by a serum progesterone concentration on days 11-15 that was above 5 nmol/L and an interestrus interval that exceeded 30 days. The cervix was considered to be open when the contrast medium was seen to enter the uterus, and to be closed when the contrast medium remained in the vagina. Blood samples were collected at each examination and were assayed for estradiol-17beta and progesterone concentrations. The cervix was open on the first day of standing estrus at a mean estradiol-17beta serum concentration of 87.4+/-21.8 pmol/L (range 14 to >or=180 pmol/L) and closed at an estradiol concentration of 47.1+/-12.4 pmol/L (range 4 to >or=180 pmol/L). In the ovulatory cycles the cervix was closed at a progesterone concentration of 9.8+/-4.4 nmol/L (range 0.6-28.4 nmol/L). There was no difference in the duration of cervical patency in non-ovulatory and ovulatory cycles (5.5+/-1.2 days and 5.2+/-0.5 days, respectively) (p>0.05). The higher overall mean concentrations of estradiol-17beta seen in the ovulatory cycles than in the non-ovulatory cycles, indicate that a high level of estradiol is necessary for induction of ovulation. Ovulation in 60% of unmated females in this study indicates that the techniques used for evaluation of cyclus stage and cervical opening have the potential to induce ovulation in the cat. This study demonstrates that cervical patency is not influenced by the occurrence of ovulation, but is due to individual variations between cats.     

The influence of ovarian status on response to estrus synchronization treatment in dairy goats during the breeding season

The influence of ovarian status (presence of a corpora lutea and follicles) on the times of the onset of estrus, LH peak and ovulation rate at a synchronized estrus was evaluated in 73 Alpine and Saanen cyclic goats. Does were treated for 11 d with 3 mg norgestomet implants or 45mg fluorogestone acetate (FGA) sponges. They also received 400 IU of PMSG and 50 μg of a PGF_2α analog on Day 9 of progestagen priming. Follicles (1 to 7 mm) and corpora lutea (CL) were counted by laparoscopy on Days 0 and 9 of progestagen treatment and 5 or 6 d after the synchronized estrus. Estrus was detected every 4 h from 16 to 60 h after the end of progestagen treatment using a vasectomized buck. The LH concentration was determined by radioimmunoassay (RIA) in blood samples collected every 4 h for 24 h beginning at the time of the onset of estrus. The number of follicles on Days 0 and 9 of progestagen treatment was not related to the time of the onset of estrus and occurrence of the LH peak or to ovulation rate. The number of CL on Day 9 influenced the time of occurrence of the LH peak but not the time of the onset of estrus. Thus, in does with 2 or 3 CL on Day 9, the LH peak occurred at 46.9 h after the end of progestagen treatment, and in does with 1 or 0 CL at 42.2 and 42.5 h, respectively, after treatment, suggesting that the number of CL at luteolysis is a factor in the variability of response after the synchronization of estrus.     

Folliculogenesis during the transitional period and early ovulatory season in mares

Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequent wave, the previous dominant follicle regressed. The mean (+/- s.d.) length of the interval between successive waves was 10.8 +/- 2.2 days. Before the emergence of waves (identified by a dominant follicle), follicular activity seemed erratic and follicles did not reach greater than 35 mm. During the interovulatory interval, 6 mares developed 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares developed only 1 detected wave (the ovulatory wave). The ovulatory follicle at the end of the transitional period reached 20 mm earlier (Day - 15), grew slower (2.6 +/- 0.1 mm/day; mean +/- s.e.m.) but reached a larger diameter on Day - 1 (50.5 +/- 1.1 mm) than for the ovulatory follicle at the end of the interovulatory interval (Day - 10, 3.6 +/- 0.2 mm/day, 44.4 +/- 1.0 mm, respectively; P less than 0.05 for each end point). The interval from cessation of growth of the largest subordinate follicle to the occurrence of ovulation was longer (P less than 0.05) for end of the transitional period (9.5 +/- 0.7 days) than for the end of the interovulatory interval (6.8 +/- 0.6 days). Results demonstrated the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of 2 waves during some of the first oestrous cycles of the year.     

Synchronization of estrus in beef heifers with a norgestomet implant and prostaglandin F2alpha

In a 5-year study (1973-1977), 281 cycling beef heifers were treated with a 7-day norgestomet (SC21009) ear implant and an intramuscular injection of prostaglandin F(2alpha) (PGF(2alpha)) at the time of implant removal or 24 hr before implant removal. Percentages of heifers in estrus by 36, 48, 60, 72, and 120 hr after implant removal were 32.4, 52.7, 71.6, 80.1, and 93.2, respectively. Onset of estrus occurred an average of 49.8 +/- 4.7 hr after treatment. Percentages of heifers in estrus 36 hr after treatment were 5.7 and 51.7 for those with a corpus luteum and those without a corpus luteum (or determined regressing by palpation) at implant removal, respectively. When PGF(2alpha) was injected 24 hr before implant removal, 55% of the heifers were in estrus by 36 hr after implant removal compared to 30% when PGF(2alpha) was injected at the time of implant removal; however, by 60 hr after implant removal the difference was 76% vs. 71%. First-service conception rates for synchronized and nonsynchronized heifers were 62.2% and 59.6%, respectively. During 1976 and 1977 heifers were checked for estrus every 4 hr and inseminated 2, 6, 10, 14, 18, 22, 26, or 30 hr after first detected to be in standing estrus. Conception rate was not significantly affected by time of insemination but tended to be higher for heifers bred 26 and 30 hr after first being detected in standing estrus (78.9% and 70.0% vs. average 59.2%). Treatment with a 7-day norgestomet implant plus a single injection of PGF(2alpha) 24 hr before or at implant removal appears to be a practical technique for synchronizing estrus in cycling heifers without affecting conception.     

Copy number variations in high and low fertility breeding boars

Background

In this study we applied the extreme groups/selective genotyping approach for identifying copy number variations in high and low fertility breeding boars. The fertility indicator was the calculated Direct Boar Effect on litter size (DBE) that was obtained as a by-product of the national genetic evaluation for litter size (BLUP). The two groups of animals had DBE values at the upper (high fertility) and lower (low fertility) end of the distribution from a population of more than 38,000 boars. Animals from these two diverse phenotypes were genotyped with the Porcine SNP60K chip and compared by several approaches in order to prove the feasibility of our CNV analysis and to identify putative markers of fertility.

Results

We have identified 35 CNVRs covering 36.5 Mb or ~1.3% of the porcine genome. Among these 35 CNVRs, 14 were specific to the high fertility group, while 19 CNVRs were specific to the low fertility group which overlap with 137 QTLs of various reproductive traits. The identified 35 CNVRs encompassed 50 genes, among them 40 were specific to the low fertility group, seven to the high fertility group, while three were found in regions that were present in both groups but with opposite gain/loss status. A functional analysis of several databases revealed that the genes found in CNVRs from the low fertility group have been significantly enriched in members of the innate immune system, Toll-like receptor and RIG-I-like receptor signaling and fatty acid oxidation pathways.

Conclusions

We have demonstrated that our analysis pipeline could identify putative CNV markers of fertility, especially in case of low fertility boars.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1473-9) contains supplementary material, which is available to authorized users.     

Effect of oestrus synchronization methods on oestrus behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes

The objective of this study was to determine the effect of oestrous synchronization methods on oestrous behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes. In Experiment 1, oestrous behaviour and timing of ovulation were determined from (n=34) oestruses. The mean (+/- S.E.M.) time of ovulation after the onset of standing oestrus was greater (P<0.05) in PGF(2alpha)-induced luteolysis (30.6+/-1.5h) compared to Ovsynch buffaloes (15.0+/-0.8h). In Experiment 2, pregnancy rates were compared between two methods of synchronization (detected oestrus and Ovsynch protocol) during the breeding and low breeding seasons. Pregnancy rates of buffaloes bred at detected oestrus (62.5%) or by the Ovsynch protocol (36.3%) during the breeding season did not differ significantly (P>0.05) from those which were inseminated during the low breeding season (55.5%) and (30.4%), respectively. This study demonstrates clearly that (1) timing of ovulation in Nili-Ravi buffalo is about 30h after the onset of standing oestrus and (2) buffaloes can be successfully synchronized with optimum fertility using either PGF(2alpha) alone (detected oestrus) or using (Ovsynch protocol) during low breeding season, to calve during the period when milk availability is short.     

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.     

Effects of time of PMSG and fixed-time GnRH injections on estrus incidence and fertility in physiologically different ewes pre-treated with progestogen-impregnated vaginal sponge during the nonbreeding season

A 2 × 2 factorial study for hormonal treatment was designed in 85 seasonally anestrous ewes with physiologically different status (nonparous, dry, and postpartum). All ewes were pre-treated with 60 mg of 6-methyl-17-acetoxy-progesterone (MAP) vaginal sponge for nine days and divided into four groups: Group I (22 ewes) — an i. m. injection of 600 i.u. pregnant mare's serum gonadotropin (PMSG) at the sponge removal (Day 0) and a single i.m. injection of 100 ug synthetic gonadotropin releasing hormone (GnRH) at 36 h after the sponge removal; Group II (21 ewes) — a PMSG injection at Day 0 and a saline injection at 36 h after the sponge removal; Group III (21 ewes) — a PMSG injection two days before the sponge removal and the GnRH injection at 24 h after the sponge removal; and Group IV (21 ewes) — a PMSG injection at Day -2 and a saline injection at 24 h after the sponge removal. The treated ewes were allowed to mate once with rams for five days after treatment. Estrus incidence and lambing rates were low (69.4% and 27.1%, respectively), probably due to the mating system and poor body condition of ewes used in the study. No effect of PMSG injection two days before with-drawal of MAP sponge and the fixed-time GnRH injection were observed in estrus incidence, fertility, and prolificacy. The present study indicates that the physiological status of ewes combined with management systems including feeding and mating would be important for out-of-season breeding with hormonal treatment.     

Climate factors affecting fertility after cervical insemination during the first months of the breeding season in Rasa Aragonesa ewes

This study was carried out to examine the impact of several climate variables on the pregnancy rate after cervical artificial insemination (AI) of Rasa Aragonesa ewes. Data were derived from 8,977 inseminations in 76 well-managed flocks performed during the first month of the breeding season (July to October). The following data were recorded for each animal: farm, year, month of AI, parity, lambing–treatment interval, inseminating ram, AI technician, and climatic variables such as mean, maximum and minimum temperature, mean and maximum relative humidity, rainfall, and mean and maximum temperature–humidity index (THI) for each day from day 12 before AI to day 14 post-AI. Means were furthermore calculated for the following periods around AI (day 0): ?12 to 0, ?2 to 0, AI day, 0 to 2, and 0 to 14. Logistic regression analysis indicated that the likelihood of pregnancy decreased when maximum temperature in the 2 days prior to AI was higher than 30 °C (by a factor of 0.81). Fertility was also lower for primiparous ewes and in multiparous ewes with more than five previous parturitions. Other factors with significant impact on fertility were flock, technician, inseminating ram, and a lambing–AI interval longer than 240 days. It was concluded that the 2 days prior to AI seems to be the period when heat stress had the greatest impact on pregnancy rate in Rasa Aragonesa ewes.     

Methods of identifying and inseminating nonpregnant beef females after synchronization of second estrus with norgestomet implants

Beef females (547) were included in three experiments to evaluate methods of identifying and inseminating nonpregnant beef females after synchronization of second estrus with norgestomet implants. In the first experiment, heifers not pregnant to the first insemination were identified for insemination via estrus (inseminated via the a.m./p.m. rule or 48 h after implant removal). In the second experiment, females not pregnant to the first insemination were identified for insemination via estrus (inseminated via the a.m./p.m. rule) or progesterone concentrations < 1.5 ng/mL at implant removal (inseminated 48 h after implant removal). In the third experiment, heifers not pregnant to the first insemination were identified for insemination via progesterone concentrations (as in experiment 2) or anterior vagina electrical resistance values < 81 ohm resistance 48 h after implant removal (inseminated after resistance measured). All methods of identifying and inseminating nonpregnant females were equally effective (P > 0.10) and did not effect (P > 0.10) calving rates from the first and second AI.     

Induction of a new follicular wave in holstein heifers synchronized with norgestomet

Treatments with progestin to synchronize the bovine estrous cycle in the absence of the corpus luteum, induces persistence of a dominant follicle and a reduction of fertility at doses commonly utilized. The objective of the present research was to induce a new wave of ovarian follicular development in heifers in which stage of the estrous cycle was synchronized with norgestomet. Holstein heifers (n=30) were used, in which estrus was synchronized using two doses of PGF2alpha i.m. (25 mg each) 11 days apart. Six days after estrus (day 0=day of estrus) heifers received a norgestomet implant (6 mg of norgestomet). On day 12, heifers were injected with 25 mg of PGF2alpha i.m. and assigned to treatments (T1 to T4) as follows: treatment 1, heifers received a second norgestomet implant (T1: N+N, n=6), treatment 2, received 100 microg of GnRH i.m. (T2: N+GnRH, n=6), treatment 3, 200 mg of progesterone i.m. (T3: N+P4, n=6), treatment 4, control treatment with saline solution i.m. (T4: N+SS); in the four treatments (T1 to T4) implants were removed on day 14. For treatment 5, heifers received 100 microg of GnRH i.m. on day 9 and 25 mg of PGF2alpha i.m. (T5: N+GnRH+PGF2alpha) at the time of implant removal (day 16). Ovarian evaluations using ultrasonographic techniques were performed every 48 h from days 3 to 11 and every 24 h from days 11 to 21. Blood samples were collected every 48 h to analyze for progesterone concentration. A new wave of ovarian follicular development was induced in 3/6, 6/6, 3/6, 1/6 and 6/6, and onset of estrus in 6/6, 0/6, 6/6, 6/6 and 6/6 for T1, T2, T3, T4 and T5, respectively. Heifers from T1, T3 and T4 that ovulated from a persistent follicle, showed estrus 37.5 +/- 12.10 h after implant removal and heifers that developed a new wave of ovarian follicular development showed it at 120.28 +/- 22.81 h (P<0.01). Ovulation occurred at 5.92 +/- 1.72 and 2.22 +/- 1.00 days (P<0.01), respectively. Progesterone concentration was <1 ng/ml from days 7 to 15 in T1, T2 and T4; for T3 progesterone concentration was 2.25 +/- 0.50 ng/ml on day 13 and decreased on day 15 to 0.34 +/- 0.12 ng/ml (P<0.01). For T5, progesterone concentration was 1.66 +/- 0.58 ng/ml on day 15. The more desirable results were obtained with T5, in which 100% of heifers had a new wave of ovarian follicular development induced, with onset of estrus and ovulation synchronized in a short time period.     

An increase in parental investment during the breeding season

The intensity of nest-defence aggression by female redwinged black birds (Agelaius phoeniceus) with eggs decreased late in the breeding season, while aggression at this time increased amongst females defending broods. High predation pressure late in the breeding season decreased the probability of survival of the late nesting attempts, so that females with young had a much greater chance of success than females with eggs at this time. The observed changes in aggressive responses are predicted by the theory of parental investment.     

Responses of different doses of prostaglandin F(2) alpha on estrus induction, fertility and progesterone levels in subestrous buffaloes

Responses of different doses of PGF(2) alpha (Lutalyse) on estrus induction, fertility, and progesterone levels were studied in buffaloes. Of the total 70 subestrous buffaloes, 71.0 percent (50) exhibited estrus and 44.0 percent (22) conceived to induced estrus with different doses of PGF(2) alpha. Serum progesterone levels were variable before treatment of PGF(2) alpha in subestrous buffaloes and ranged from 0.60 to 4.90 ng/ml. An abrupt decrease in progesterone levels was observed within 24 hours of treatment with 30 mg or 5.0 mg PGF(2) alpha given intramuscularly or by intrauterine fusion, respectively. Serum progesterone levels further decreased and were minimum or similar to those seen in spontaneous estrus (/ 0.5ng/ml) on day 2 to 5 or 6 after PGF(2) alpha treatment. Progesterone patterns further revealed that, in most of the buffaloes, corpora lutea were formed and were functional after the treatment. With 2.5 mg of PGF(2) alpha administered into the uterus, morphological regression of corpus luteum and progesterone were not adequate to induce estrus and ovulation.