Fertility of swamp buffalo following the synchronization of ovulation by the sequential administration of GnRH and PGF2alpha combined with fixed-timed artificial insemination

This study evaluated fertility in swamp buffalo after synchronization of ovulation combined with fixed time artificial insemination. At the start of the study, designated day 0, from a group of 98 female Thai swamp buffalo, 55 buffalo (heifers n° = 20 and cows n° = 35) were selected to be synchronized with GnRH (Day 0) followed by PGF₂alpha (Day 7) and a second treatment with GnRH (Day 9). All buffalo were inseminated at two fixed times 12 h and 24 h after the second injection of GnRH (Ovsynch+TAI group); a second group of 43 buffalo (heifers n° = 19 and cows n° = 24) were not treated and were artificially inseminated (AI) at natural estrus (AI group). Blood samples were taken 22 days after insemination to evaluate progesterone plasma levels. In the Ovsynch+TAI group, overall conception rate (CR; i.e. the number of cows with progesterone >4.0 ng/ml on day 22 after AI divided by the number of animals inseminated), was 38.1% and overall pregnancy rate (PR; i.e. the number of cows that were pregnant at day 50-60 after insemination divided by the number of animals inseminated), was 32.7%. In the AI group overall CR and PR was 34.9%.Within the Ovsynch+TAI group, CR and PR were reduced (P < 0.05) in heifers compared with cows (CR 15.0% vs. 51.4% for heifers and cows, respectively; PR 15.0% vs. 42.9% for heifers and cows, respectively). Within the AI group the efficacy of treatment was similar between heifers and cows (CR and PR 31.6% for heifers and 37.5% for cows).In conclusion, this study indicates that in swamp buffalo it is possible to synchronize ovulation and use timed artificial insemination with the Ovsynch+TAI protocol.     

Pregnancy rates following AI with sexed semen in Mediterranean Italian buffalo heifers (Bubalus bubalis)

The use of sexed semen in farm animal production and genetic improvement has been shown to be feasible with variable degree of efficiency in a number of species, and proved to be economically viable in cattle. In the last two decades, various newly developed reproductive technologies applicable in buffaloes have mushroomed. Recently, following the birth of the first buffalo calves using AI with sexed semen, commercial interest to exploit sexing of semen in this species too is aroused. In order to verify the successful adoption of this technology in the buffalo, the present study on the use of sexed semen for AI was carried out and compared with conventional artificial insemination using nonsexed semen. A total of 379 buffalo heifers were used for synchronization of ovulation using the Presynch protocol in the South of Italy. Selected animals at the time of AI were randomly allocated to three different experiment groups: (1) 102 animals subjected to AI in the body of the uterus with sexed semen (SS body); (2) 104 animals subjected to AI in the horn of the uterus with sexed semen (SS horn); and (3) 106 animals subjected to AI in the body of the uterus with conventional nonsexed semen (NSS body). Semen of three buffalo bulls was sexed by a collaborating company and commercially distributed in 0.25 mL straws with a total of 2 million sexed spermatozoa. Pregnancy rates were first assessed at Day 28 following AI, and rechecked at Day 45 by ultrasound. Pregnancy rates were nonsignificantly different between animals inseminated with sexed or nonsexed semen: 80/206 (38.8%) and 40/106 (37.7%), respectively (P = 0.85). However, site of insemination of sexed semen affected pregnancy rate significantly as higher pregnancy rates were obtained when sexed semen was deposited into the body rather than the horn of the uterus: 46/101 (45.5%) and 34/105 (32.3%), respectively (P = 0.05). In conclusion, the use of sexed semen in buffalo heifers gave satisfactory and similar pregnancy rates when compared with conventional nonsexed semen. Deposition of sexed semen into the body of the uterus, however, increased pregnancy rates significantly.     

The effects of GnRH treatment at the time of AI and 12 days later on reproductive performance of high producing dairy cows during the warm season in northeastern Spain

It was hypothesized that gonadotropin-releasing hormone (GnRH) treatment at the time of insemination and 12 days later increases conception rates. The aim of the present study was to evaluate the effects of GnRH treatment at the time of insemination or at the time of insemination and 12 days later on reproductive performance during the warm season in high producing dairy cows. The effect of GnRH treatment on the incidence of subsequent twin pregnancies and pregnancy losses was also evaluated. Data were analyzed using logistic regression methods. Of the entire series of 1289 AI, 373 (29%) resulted in pregnancy. Three study groups were established to evaluate the effects of treatment on the conception rate: control (untreated cows, n=431), GnRH-0 (cows receiving GnRH at AI, n=429) or GnRH-0+12 (cows receiving GnRH at AI and at AI+12 days, n=429). Conception rates were 20.6% (89/431), 30.8% (132/429) and 35.4% (152/429) for animals receiving no treatment, GnRH at AI, and GnRH at AI and 12 days later, respectively. Based on the odds ratio, the probability of pregnancy was 0.80 and 0.46 times less likely for cows receiving treatment GnRH-0 and no treatment, respectively, than for cows receiving treatment GnRH-0+12 (reference). Of the 373 pregnant animals, 326 (87.4%) bore singletons and 47 (12.6%) carried twins. The effects of treatment on the dependent variables: twin pregnancy, additional corpus luteum and pregnancy loss were analyzed. Pregnancy loss between 38 and 90 days after insemination was registered in 30 (8%) cows: 17 (5.2%) in single and 13 (27.7%) in twin pregnancies. Fifty-six (15%) cows had an additional corpus luteum. No pregnancy losses were recorded in these cows. Treatment had no effect on the twin pregnancy rate. The treatment GnRH at AI and 12 days later increased the chances of an additional corpus luteum by a factor 3.7 (using the control group as reference). In conclusion, our results support the hypothesis that GnRH treatment at the time of insemination and 12 days later increases the conception rate in high producing dairy cows during the warm season. Although lower than double treatment, strong benefits were also registered following a single GnRH treatment at insemination. Under these conditions, treatment fails to affect the twin pregnancy rate yet increases the incidence of an additional corpus luteum in pregnant cows.     

Effect of insemination time of frozen semen on incidence of uterine fluid in mares

Ninety five mares were inseminated with frozen semen either within 12 h before ovulation or within 8 h after ovulation. The effect of preovulatory versus postovulatory insemination (AI) on the subsequent detection of uterine fluid was studied. The overall pregnancy rate was 43% and this was not significantly influenced by preovulatory or postovulatory insemination. When mares were first examined 12 h after AI, 18 of 52 mares (35%) had accumulated uterine fluid. However, when mares were first examined 18 to 24 h after AI, only 6 of 43 mares (14%) had uterine fluid. Presence of intrauterine fluid significantly lowered pregnancy rates. Timing of insemination did not affect incidence of uterine fluid. Serum concentrations of estrogen and progesterone at time of insemination did not influence uterine clearance or pregnancy rates, but both hormones were higher at preovulatory than at postovulatory inseminations. We concluded that there was no evidence that postovulatory inseminations would predispose mares to persistence of uterine fluid after AI.     

Serum progesterone and 17 beta-estradiol concentrations during pregnancy of Bactrian camel (Camelus bactrianus)

Serum progesterone and 17 beta-estradiol during pregnancy in the Bactrian camel were measured by radioimmunoassay. Serum progesterone concentrations increased by 15 d after artificial insemination (AI) and remained elevated throughout most of gestation, the mean concentrations (3.06 +/- 0.49 to 8.51 +/- 4.80 ng/mL) were similar to those reported for many species during the same stage of pregnancy. Serum 17 beta-estradiol increased significantly from 11 m.o. of pregnancy with peak mean concentrations of 617.47 +/- 32.56 pg/mL at the 11.5 m.o.     

Comparison of pregnancy rates with two estrus synchronization protocols in Italian Mediterranean Buffalo cows

The aim in this study was to compare two estrus synchronization protocols in buffaloes. Animals were divided into two groups: Group A (n=111) received 100 microg GnRH on Day 0, 375 microg PGF(2alpha) on Day 7 and 100 microg GnRH on Day 9 (Ovsynch); Group B (n=117) received an intravaginal drug release device (PRID) containing 1.55 g progesterone and a capsule with 10mg estradiol benzoate for 10 days and were treated with a luteolytic dose of PGF(2alpha) and 1000 IU PMSG at the time of PRID withdrawal. Animals were inseminated twice 18 and 42 h after the second injection of GnRH (Group A) and 60 and 84 h after PGF(2alpha) and PMSG injections (Group B). Progesterone (P(4)) concentrations in milk samples collected 12 and 2 days before treatments were used to determine cyclic and non-cyclic buffaloes, and milk P(4) concentrations 10 days after Artificial insemination (AI) were used as an index of a functional corpus luteum. Cows were palpated per rectum at 40 and 90 days after AI to determine pregnancies. All previously non-cyclic animals in Group B had elevated P(4) (>120 pg/ml milk whey) on Day 10 after AI. Accordingly, a greater (P<0.01) relative percentage of animals with elevated P(4) 10 days after AI were observed in Group B (93.2%) than in Group A (81.1%). However, there was no difference in overall pregnancy rates between the two estrus synchronization protocols (Group A, 36.0%; Group B 28.2%). When only animals with elevated P(4) on Day 10 after AI were considered, pregnancy rate was higher (P<0.05) for animals in Group A (44.4%) than Group B (30.3%). The findings indicated that treatment with PRID can induce ovulation in non-cyclic buffalo cows. However, synchronization of estrus with Ovsynch resulted in a higher pregnancy rate compared with synchronization with PRID, particularly in cyclic buffalo.     

Effect of site of deposition on the fertility of sheep inseminated with frozen-thawed semen

The widespread use of artificial insemination (AI) in sheep is currently prevented due to the lack of a cost effective insemination technique utilising frozen-thawed semen. The objective of the present study was to determine if the deposition of frozen-thawed semen in the vaginal fornix would result in a pregnancy rate comparable to that achieved following cervical insemination. Multiparous ewes of various breeds were synchronised and inseminated into either the vaginal fornix (n=78) or the cervix (n=79), at 57 h post sponge removal, with frozen-thawed semen. Information on mucus secretion and the depth to which it was possible to penetrate the cervix at insemination (cervically inseminated ewes only) was recorded at the time of AI. Pregnancy rate was subsequently determined either by return to service (oestrus) or after slaughter 30 days post insemination. Insemination site did not significantly influence pregnancy rate using frozen-thawed semen (36.2% compared to 27.6% for cervical and vaginal fornix insemination, respectively; P=0.26). Whilst depth of cervical penetration was positively associated with pregnancy rate (P<0.05), this association needs to be interpreted with caution as none of the ewes where the cervix could not be penetrated (score=0) was pregnant. In conclusion, pregnancy rate following insemination of frozen-thawed semen into the vaginal fornix was within 10% points of that obtained following cervical AI of frozen-thawed semen. As insemination into the vaginal fornix is technically easier than cervical insemination, it may be more practical for use in large scale applications.     

Synchronization of estrus in yearling beef heifers with the melengestrol acetate/prostaglandin F(2alpha) system: efficiency of timed insemination 72 hours after prostaglandin treatment

Two experiments were conducted to determine the conception rates of heifers time-inseminated following melengestrol acetate/prostaglandin F(2alpha) (MGA/PG) estrous synchronization treatment. In Experiment 1, timed insemination of heifers at 72 h after the PG injection, without regard for behavioral estrus, tended to improve (P < 0.15) the percentage of heifers pregnant to artificial insemination (AI) compared with that of synchronized heifers bred 12 h after they were first detected in estrus. In the timed-insemination treatment, heifers exhibiting behavioral estrus 48 to 72 h after PG tended to have an increased (P < 0.15) conception rate to AI compared with heifers exhibiting estrus within 48 h of PG administration. In Experiment 2, the number of heifers conceiving to AI following the MGA/PG estrous synchronization regimen was increased by mass insemination of all heifers not exhibiting estrus by 72 h after PG. The pregnancy rate to AI was higher in heifers with serum progesterone (P(4)) concentrations higher than 1 ng/ml compared with that of heifers with concentrations lower than 1 ng/ml. Of heifers with serum P(4) greater than 1 ng/ml, the pregnancy rate to AI tended to be higher when concentrations exceeded 2 ng/ml than when concentrations were 1 to 2 ng/ml. In cyclic heifers, timed insemination can increase the percentage of heifers pregnant after being synchronized with MGA/PG.     

Storage of buffalo (Bubalus bubalis) semen

Characteristics of buffalo semen, diluents used for liquid storage, aspects involved in freezing and thawing of semen are reviewed, and fertility results after artificial insemination (AI) with frozen-thawed semen are given.     

Short-term dietary effects on reproductive wastage after induced ovulation and artificial insemination in primiparous lactating Sarda ewes

Short-term effects of nutrition on conception rate (CR), ovulation rate (OR), ova and embryo losses (OEL) during the first 50 days following insemination and total reproductive wastage after ovulation (TRW), were investigated in primiparous lactating Sarda ewes after oestrous synchronisation and cervical [corrected] artificial insemination (AI). Eighty ewes grazing a green high-quality pasture were offered one of three iso-energetic supplements from day 14 before to day 2 after AI: whole maize grain (M); soyabean meal (S); maize gluten meal (G); or served as controls (C). Supplements G and S were iso-nitrogenous but provided different amounts of rumen undegradable digestible protein. The intake of herbage and digestible dry matter, measured by the n560 mg/l was associated with lower CR. Ranking by ovulation groups of CR was single相似文献   

Exogenous prostaglandin F(2)alpha at time of ovulation improves reproductive efficiency in repeat breeder sows

In order to determine if PGF(2)alpha could improve fertility in repeat breeder females when added to semen used for artificial insemination (AI) the following trial was performed. In a large indoor Hungarian production unit of 2000 sows, 667 repeat breeding females were assigned to two groups and were treated as follows: Group 1 (n=322), received PGF(2)alpha, added to the semen immediately before AI; Group 2 (n=345), received AI with untreated semen. Conception rate, farrowing rate, subsequent total and live born litter size and subsequent weaning to estrus intervals were evaluated. Conception and farrowing rates revealed highly significant differences between the PGF(2)alpha-treated and nontreated animals (P<0.001). Subsequent total born (P<0.07), and live born litter size (P<0.13), and subsequent weaning to estrus intervals (P<0.23) showed no significant differences. It is reasonable to suggest that exogenous PGF(2)alpha added to AI semen improves conception and farrowing rates.     

Effects of administration of gonadotropin-releasing hormone at artificial insemination on conception rates in dairy cows

A controlled trial investigating the effect on conception of administration of 250 μg of gonadotropin-releasing hormone (GnRH) at artificial insemination (AI) in dairy cows in seasonal or split calving herds was conducted. Time of detection of estrus, body condition, extent of estrous expression, treatment, breed, age and milk production from the most recent herd test of the current lactation was recorded. Cows were tested for pregnancy with fetal aging between 35 and 135 days after AI. Sixteen herds provided 2344 spring-calved cows and 3007 inseminations. Logistic regression adjusting for clustering at herd level was used to examine the effect of treatment for first (2344) and second (579) inseminations separately. For first AI, treatment significantly improved conception rate in cows with milk protein concentrations of 3.75% or greater and for cows with milk protein concentrations between 3.00% and 3.50% and less than 40 days calved; increased conception rate from 41.2% to 53.4%. Treatment reduced conception rates in cows with milk protein concentrations of 2.75% or less. Treating only cows identified as responding positively to treatment (11% of all study cows) was estimated to increase first service conception rate in herds from 48.1% to 49.4%. There was no significant effect of treatment on conception to second AI, nor any significant interactions. These findings indicate that GnRH at AI should be limited to the sub-group cows most likely to respond. The positive effect of GnRH at AI may be mediated through improved oocyte maturation and/or improved luteal function, rather than by reducing AI-to-ovulation intervals.     

Fertility of high-yielding dairy cows following superovulation and non-surgical recovery of embryos

It was the aim of this investigation to study the combined effect of superovulation and non-surgical recovery on the fertility of the donor animals. Injection of a prostaglandin analogue at the day of collection (days 6–8 after standing heat), significantly shortened the super-ovulatory estrus cycle (21.3 ± 10.0 days), when compared with untreated donor animals (38.7 ± 15.1 days). The prostaglandin treatment, however, also led to more irregular estrous cycles, resulting in a lower pregnancy rate after first insemination (47%) and a need for more inseminations per conception (2.00 ± 1.00), than in animals not treated with prostaglandin analogue (92.3% and 1.06 ± 0.29 AI/conception). For all animals these parameters were 66.6% and 1.60 ± 0.99 AI/conception). The average time from calving to pregnancy was 143.1 ± 34.3 days, slightly longer for prostaglandin treated (148.2 ± 39.4 days) than for untreated animals (137.3 ± 22.8 days). One animal developed endometritis and one had adhesions in the $\text{bursa ovarii}$. It was found that most donors attained normal fertility, and that superovulation was more likely to affect the fertility (abnormal cyclicity, early embryonic mortality e.g.) than the flushing of the uterus. Treatment with a prostaglandin analogue at the day of collection did not improve the subsequent fertility.     

Luteal function and conception in lactating cows and some factors influencing luteal function after first insemination

The objective of this study was to investigate the types and incidence of luteal sub-function in lactating cows after artificial insemination (AI) and their relationship with pregnancy, and to clarify the relationship between luteal function and parity, body condition score (BCS), milk yield, and dietary intake. In 19 cows, milk samples were collected daily from AI to confirmation of pregnancy. Milk progesterone concentrations were determined by EIA. Based on peak progesterone concentration and the day of onset of luteal phase, 15 of 30 progesterone profiles (50%) were normal, with progesterone concentration reaching 1.0 ng/ml within 5 days after insemination and > or =2.0 ng/ml thereafter. In addition, 6 (20%) were insufficient, (progesterone concentration remained < 2.0 ng/ml), 5 (17%) were delayed (progesterone reached 1.0 ng/ml after 5 days), 2 (7%) were both delayed and insufficient, one (3%) was short (progesterone >1.0 ng/ml for only 7 days), and one (3%) remained basal. Cows with a normal profile had a higher (P < 0.05) pregnancy rate than those with an abnormal profile (87% versus 33%, respectively). The amount of progesterone secreted in milk after first AI, as indicated by progesterone area under curve (AUC), was negatively correlated with milk yield (r = -0.83, P < 0.01), dry matter intake (r = -0.81, P < 0.05), total digestible nutrients (r = -0.82, P< 0.05), and digestible crude protein (r = -0.79, P <0.05). Cows that produced more milk and consumed more dry matter had less progesterone during the luteal phase. In conclusion, abnormal luteal function was associated with reduced pregnancy rates and high milk production and increased dietary intake during breeding were associated with reduced progesterone concentrations.     

Delaying childbearing: effect of age on fecundity and outcome of pregnancy.

OBJECTIVES--To study the age of the start of the fall (critical age) in fecundity; the probability of a pregnancy leading to a healthy baby taking into account the age of the woman; and, combining these results, to determine the age dependent probability of getting a healthy baby. DESIGN--Cohort study of all women who had entered a donor insemination programme. SETTING--Two fertility clinics serving a large part of The Netherlands. SUBJECTS--Of 1637 women attending for artificial insemination 751 fulfilled the selection criteria, being married to an azoospermic husband and nulliparous and never having received donor insemination before. MAIN OUTCOME MEASURES--The number of cycles before pregnancy (a positive pregnancy test result) or stopping treatment; and result of the pregnancy (successful outcome). RESULTS--Of the 751 women, 555 became pregnant and 461 had healthy babies. The fall in fecundity was estimated to start at around 31 years (critical age); after 12 cycles the probability of pregnancy in a woman aged greater than 31 was 0.54 compared with 0.74 in a woman aged 20.31. After 24 cycles this difference had decreased (probability of conception 0.75 in women greater than 31 and 0.85 in women 20.31). The probability of having a healthy baby also decreased--by 3.5% a year after the age of 30. Combining both these age effects, the chance of a woman aged 35 having a healthy baby was about half that of a woman aged 25. CONCLUSION--After the age of 31 the probability of conception falls rapidly, but this can be partly compensated for by continuing insemination for more cycles. In addition, the probability of an adverse pregnancy outcome starts to increase at about the same age.     

Influence of rumen protein degradability on productive and reproductive performance in buffalo cows

The present study aimed to ascertain the influence of crude protein (CP) digestibility in the rumen on the quantity and quality of milk production and reproductive performance, blood (BU) and milk (MU) urea, haematological profile and vaginal mucus urea, ammonia and potassium of buffalo cows. Lactating buffaloes (n = 84), 60 days in milk, were randomly subdivided into Group C (control, n = 42) and Group T (fed a diet supplemented with Aspergillus oryzae, n = 42). In three fistulated buffalo, the diet supplemented with Aspergillus oryzae showed a decrease (P < 0.01) in protein digestibility in the rumen (79.3 vs. 45.9%). No differences were registered in productive performance. Nine buffaloes not in oestrus during the dietary treatment (Groups T1 and C1), 30 days in milk, were used to study the haematological profile and to determine milk urea and ammonia in the vaginal mucus. The animals in Group T1 had higher ammonia values in the blood (P < 0.01) but not in the vaginal mucus than Group C1. A relationship was found between MU and BU. MU was influenced by CP intake and dry matter intake. No differences between the treatments were observed in reproductive performance and the conception rate and calving interval were 37.9% and 41.4% (90 trial-day) and 449 and 419 days respectively in Groups T and C. Reproductive performance was not influenced by high levels of BU nor by blood ammonia levels, although the latter were higher in the group fed the diet supplemented with Aspergillus oryzae.     

The effect of a progesterone releasing intravaginal device (PRID) on pregnancy risk to fixed-time insemination following diagnosis of non-pregnancy in dairy cows

The objective was to compare the probability of pregnancy after fixed-time insemination in cows diagnosed as non-pregnant and re-inseminated following the Ovsynch protocol, with or without exogenous progesterone. Cows (n=415) used in this study originated from 25 farms. Upon diagnosis of non-pregnancy between 30 and 60 days after AI, cows were randomly assigned to receive either a progesterone releasing intravaginal device (PRID; n=208) or a placebo intravaginal device (PID; n=207). All cows received GnRH at enrollment (Day 0), PGF(2alpha) concurrent with intravaginal device removal 7 days later, GnRH on Day 9 and fixed-time insemination 16h later (Day 10). Cows observed in estrus prior to Day 7, had the device removed and were inseminated. Ovaries were examined by transrectal palpation at the time of enrollment and the prominent structures were assessed and recorded. Body condition score, lameness status, interval from previous insemination, and times bred at enrollment were recorded. At intravaginal device removal, the occurrence and intensity of vaginitis was determined according to the amount of debris on the device. Overall, the intravaginal device retention rate was 91%. A total of 5.2% of PID-treated cows and 2.9% of PRID-treated cows were detected in estrus within the 7 days treatment period. Pregnancy status was diagnosed between 30 and 56 days after insemination and all cows were followed for a minimum of 150 days after enrollment. Approximately 28% of cows had evidence of mild vaginitis in response to the intravaginal device, whereas 6% of cows had copious debris associated with the intravaginal device at removal. The probability of pregnancy after fixed-time insemination was 43.8% versus 34.9% in PRID-treated versus PID-treated animals. Exogenous progesterone provided through an intravaginal device to non-pregnant cows that had not displayed estrus improved the probability of pregnancy after fixed-time AI.     

Artificial insemination in domestic cats (Felis catus)

Artificial insemination (AI) in cats represents an important technique for increasing the contribution of genetically valuable individuals in specific populations, whether they be highly pedigreed purebred cats, medically important laboratory cats or endangered non-domestic cats. Semen is collected using electrical stimulation, with an artificial vagina or from intact or excised cauda epididymis. Sperm samples can be used for AI immediately after collection, after temporary storage above 0 degrees C or after cryopreservation. There have been three and five reports on intravaginal and intrauterine insemination, respectively, and one report on tubal insemination with fresh semen. In studies using fresh semen, it was reported that conception rates of 50% or higher were obtained by intravaginal insemination with 10-50x10(6) spermatozoa, while, in another report, the conception rate was 78% after AI with 80x10(6) spermatozoa. After intrauterine insemination, conception rates following deposition of 6.2x10(6) and 8x10(6) spermatozoa were reported to be 50 and 80%, respectively. With tubal insemination, the conception rate was 43% when 4x10(6) spermatozoa were used, showing that the number of spermatozoa required to obtain a satisfactory conception rate was similar to that of cats inseminated directly into the uterus. When frozen semen was used for intravaginal insemination the conception rate was rather low, but intrauterine insemination with 50x10(6) frozen/thawed spermatozoa resulted in a conception rate of 57%. Furthermore, in one report, conception was obtained by intrauterine insemination of frozen epididymal spermatozoa. Overall, there have been few reports on artificial insemination in cats. The results obtained to date show considerable variation, both within and among laboratories depending upon the type and number of spermatozoa used and the site of sperm deposition. Undoubtedly, future studies will identify the major factors required to consistently obtain reliable conception rates, so that AI can become a practical technique for enhancing the production of desirable genotypes, both for laboratory and conservation purposes.     

Artificial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (ICI 80996): I. Fertility

Two trials were conducted over a two-year period with 519 cycling Bos taurus x Bos indicus heifers and cows. The objectives of these trials were: 1) To compare fertility of artificial insemination at the cloprostenol-induced estrus and the naturally occurring estrus, 2) To evaluate the fertility of artificial insemination at a predetermined time (Timed AI) following an estrous synchronization regime with cloprostenol (CLP) and 3) To define the optimum interval from a second CLP treatment for Timed AI. In Trial I, 128 animals were assigned to four treatments: 1) Controls, which were inseminated at the natural occurring estrus; 2) timed AI at 72 hr and again at 96 hr post-second CLP; 3) Timed AI at 72 hr post-second CLP and 4) AI at the CLP-induced estrus. Trial II included 391 heifers distributed among six treatments; 1) Timed AI between 70 and 90 hr post-second CLP; 2) Sham AI between 70 and 90 hr post-second CLP, 3) Chute Stress between 70 and 90 hr post-second CLP; 4) AI at the CLP-induced estrus; 5) Control-AI at the naturally occurring estrus and 6) Non-treated and exposed to fertile bulls. The fertility of the animals artificially inseminated at the CLP-induced estrus was similar to that of insemination at the naturally occurring estrus in Trial I and Trial II (30 vs 46%; 37 vs 38%, respectively). The first service pregnancy rates of the animals bred at a predetermined time were similar to those bred at the CLP-induced estrus in Trial I, but lower in Trial II (P < .01).     

Risk factors for resumption of postpartum estrous cycles and embryonic survival in lactating dairy cows

The objectives of this study were to evaluate factors associated with resumption of postpartum estrous cycles and embryonic survival in lactating dairy cows. Holstein cows, 6396 from four dairy farms were evaluated to determine the relationships among parity, body condition score (BCS) at calving and at AI, season of year when cows calved, and milk yield on resumption of postpartum estrous cycles by 65 days postpartum, and all the previous variables, estrual or anestrus and AI protocol on conception rates and embryonic survival at the first postpartum insemination. Cows had their estrous cycle pre-synchronized with two PGF_2α injections given 14 days apart and were inseminated between 69 and 82 days postpartum following either an estrous or ovulation synchronization protocol initiated 12–14 days after the presynchronization. Blood was sampled and analyzed for progesterone twice, 12–14 days apart, to determine whether cows had initiated onset of estrous cycles after calving. Cows were scored for body condition in the week after calving, and again at AI, between 69 and 82 days postpartum. Pregnancy was diagnosed at 30 ± 3 and 58 ± 3 days after AI. Farm influenced all reproductive outcomes evaluated. More (P < 0.0001) multiparous than primiparous cows had initiated estrous cycles. Onset of estrous cycles was also influenced (P < 0.01) by BCS at calving and at AI, BCS change, season, and milk yield. More (P < 0.001) cows that had initiated estrous cycles than anestrous cows were pregnant at 30 and 58 days after AI, but anestrus did not affect pregnancy loss. Conception rates were also influenced (P < 0.01) by parity, BCS at calving and AI, BCS change, and season; however, milk yield and insemination protocol were not associated with conception rates at 30 and 58 days after AI. Factors that reduced conception rate on day 30 after AI also increased pregnancy loss between 30 and 58 days of gestation. Improving BCS at calving and AI, minimizing losses of BCS after calving, and hastening onset of estrous cycles early postpartum are all expected to increase conception because of enhanced embryonic survival.