Effect of gonadotrophin releasing hormone on conception rate in repeat-breeder dairy cows

The effect of gonadotrophin releasing hormone (GnRH) on conception rate was studied in 961 repeat-breeder cows in five California dairy farms. Cows were injected with GnRH or saline at the time of the fourth insemination. All breeding was by artificial insemination (AI) using frozen semen from two bulls. Conception rate for GnRH-treated cows was higher than for controls (47.0 vs 37.7%, P < 0.01). There was no significant difference in conception rate between the two bulls or among five AI technicians. How GnRH acts upon fertility in repeat-breeder cattle has not been determined.     

Repeated insemination in Michigan Holstein-Friesian cattle: Incidence, descriptive epidemiology and estimated economic impact

Twenty-two Michigan dairy herds participating in a computerized herd-health program were studied to determine the incidence and epidemiologic characteristics of repeat-breeder syndrome. A cow with repeat-breeder syndrome was defined as having been inseminated three or more times within the same lactation. Repeat-breeder syndrome was observed in 24% of 3,309 lactations. Cost components associated with unsuccessful inseminations included costs of delayed conception, extra inseminations, extra veterinary service and losses due to culling. Lactations with repeat-breeder syndrome were associated with a loss of approximately $385. An estimated extra cost of $140 was associated with a second insemination, $279 with three inseminations, $429 with four inseminations and $612 with five inseminations.     

Conception rates of dairy cows following early not-pregnant diagnosis by ultrasonography and subsequent treatments with shortened Ovsynch protocol

Our objective was to determine the feasibility of prompt reinsemination of dairy cows when diagnosed not pregnant 27-29 days after first-service timed AI (TAI). We assumed that a first-wave dominant follicle was present at that time that would ovulate in response to GnRH once precocious luteal regression was induced after administration of PGF(2alpha). Cows that had not been detected in estrus and reinseminated by Days 27-29 after a first-service TAI were diagnosed not pregnant by ultrasonography. Nonpregnant cows from three herds were assigned randomly to receive either no further treatment until reinsemination (controls; n=189); 25mg i.m. of PGF(2alpha) and then reinsemination according to detected estrus (81 of 108) or at 72-80h after PGF(2alpha) treatment (PGF) in the absence of estrus (27 of 108); or 25mg i.m. of PGF(2alpha) followed by 100 microg i.m. of GnRH 48h later (PGF+GnRH) and then reinsemination after detection of estrus (9 of 160) or at 16-20h after GnRH (151 of 160). Blood samples were collected at the time of the not-pregnant diagnosis and again 48h later. Concentrations of progesterone before treatment with PGF(2alpha) were elevated (<1ng/ml) in 61% of the cows when PGF(2alpha) was administered and 81% of the cows given PGF(2alpha) had low (<1ng/ml) concentrations of progesterone 48h after PGF(2alpha). Treated cows were re-inseminated earlier (P<0.01; 31+/-1days) after first-service TAI than controls (55+/-1days). Conception rates after treatment were not different among treatments: PGF (22%), PGF+GnRH (23%), and control (23%). Average intervals from calving to conception were 22-23 days less (P<0.001) in treated cows than in controls. We concluded that treating nonpregnant cows with PGF(2alpha) on Days 27-29 after insemination produced acceptable conception rates when inseminations were made after detected estrus or when TAI was used after GnRH treatment. Further, both treatments reduced days between first-service TAI and second inseminations, and days from calving to conception.     

Intraperitoneal insemination in repeat-breeder cows: a preliminary report

Intraperitoneal insemination of 62 repeat-breeder dairy cows resulted in 9 pregnancies. The pregnancy rate was not different for intraperitoneal or uterine inseminations. In nonpregnant cows, reproductive variables such as the percentage of cows returning to estrus, the average interval from insemination to the next estrus, and the pregnancy rate following subsequent uterine insemination were not influenced by intraperitoneal insemination. Our results suggest that intraperitoneal insemination could be an alternative procedure to the usual deposition of semen into the uterus in repeat breeder cows.     

Incidence of delayed ovulation in Holstein heifers and its effects on fertility and early luteal function

In the first of 3 experiments 134 first-service and 108 repeat-breeder Holstein heifers were palpated at 12-hour intervals starting 24 hours after insemination to compare the incidence of delayed ovulation in the 2 groups. Delayed ovulation was defined as failure to ovulate within the first 24 hours after insemination. Ovulation occurred within 24 hours post insemination in 92.1% of the animals and was delayed in 7.9% of the cases, with no differences between first-service and repeat-breeder heifers, indicating that the subfertility of the repeat-breeder animals was not due to delayed ovulation. The duration of the delay was at most 12 hours since all the animals had ovulated by 36 hours post insemination. Conception rate of the 19 animals with delayed ovulation (42.1%) was not different (P>0.05) from that of the 223 heifers that ovulated on time (44.8%). In a second experiment, no differences were detected between 15 heifers with delayed ovulation and 15 animals that ovulated on time with respect to their progesterone concentrations during the first 8 days post insemination, indicating that delayed ovulation is not associated with delayed luteinization or subnormal early luteal function. In the third experiment, the conception rate of 126 repeat-breeder heifers that were treated with hCG at the time of insemination was 26.7%; the conception rate of 101 repeat-breeder heifers that were inseminated twice, at 12 and 24 hours after the onset of estrus, was 34.6%; and the conception rate of 105 repeat-breeder heifers which were not treated with hCG and which were inseminated only once was 30.5% (P>0.05) It is concluded that delayed ovulation is not an important cause of infertility and does not constitute an important component of the repeat-breeding syndrome in Holstein heifers.     

Comparison of treatment of pyometra with estradiol cypionate or cloprostenol followed by infusion or non-infusion with nitrofurazone

One hundred-fifty-two dairy cows affected with pyometra were treated either with cloprostenol (CLP) or with estradiol cypionate (ECP). The cows which failed to respond within 7-10 days were re-treated with the same drug used in the first treatment. Half of the cows which responded to these treatments received intrauterine infusions with 50 cc nitrofurazone solution. After two treatments, 72 (94.9%) of 79 cows in the CLP group had evacuated the purulent exudate from their uteri whereas only 57 (78.1%) of 73 cows in the ECP group had responded (P<0.005). Treatment-to-breeding and treatment-to-conception intervals were not different between the ECP and CLP groups. The number of services/conception was not different up to the 4th service (3.16 vs 3.57, respectively, P>0.1). Eight (9.3%) of 86 CLP treated and 3 (5.1%) of 59 ECP treated cows had recurrence of pyometra (P>0.1). Incidence of follicular cysts within 30 days after treatment was 16.4% (13 79 ) and 7.0% (4 57 ) among CLP and ECP groups, respectively (P>0.1). Two of 106 CLP (1.9%) and 5 of 107 ECP treatments (4.7%) were associated with subsequent perimetritis and adhesions. Intrauterine infusion of nitrofurazone increased the number of services/ conception (3.57 vs 2.21, P<0.01). Cloprostenol was superior to ECP as an initial treatment of bovine pyometra. Intrauterine infusion of nitrofurazone following evacuation of the uterus appeared not to be effective in prevention of relapses and had a negative effect on conception rates.     

A Survey of the Postpartum Reproductive Performance of Dairy Cows with Fertility Problems in Southern Iceland

The purpose of this survey was to evaluate the reproductive performance of dairy cows on problem farms in southern Iceland. In all 229 cows on 6 farms were studied. The animals were examined clinically by rectal palpation, once a month. Blood samples were taken 2–5 and 7–10 weeks after calving. The blood samples were analysed for the contents of glucose, urea, inorganic phosphate, calcium and magnesium. Milk samples for progesterone profiles were taken, by the farmer, every 4th day from day 10 postpartum until first oestrus. Because of this sampling method, 128 cows had no rise in progesterone levels, when milk sampling was stopped. These 128 animals were excluded from the study. The results are based on 101 animals. There was a large variation between cows in postpartum reproductive performance. In the total material 1st ovulation occurred later than reported in many other countries. Fifty percent of the cows had ovulated 35 days after calving and 90 percent 70 days after calving. The first luteal phase was short in about 60 % of the cows. The progesterone values assayed from those short cycles were lower than the values assayed from the following cycle. First artificial insemination (ai) was on the average 77 days postpartum (pp). The conception rate to first service was 49 %. Of 100 milk samples taken at the time of ai, 20 had high progesterone value. This indicates a high frequency of luteal phase inseminations. Clinical ketosis was diagnosed in 35 cows. Of these, 31 had a low glucose value. Cows with clinical ketosis ovulated, on the average, later than other animals and 24 ovulated later than 40 days pp. The results indicated that the fertility problems of these cows studied were late ovulations, low conception rate, probably in part, due to luteal phase inseminations, and a high frequency of ketosis which could be caused by low quality feedstuff.     

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.     

Associations between the manipulation of patterns of follicular development and fertility in cattle

The wave-like patterns of ovarian follicular development in cattle can be manipulated by shortening the luteal phase with prostaglandin F2alpha (PGF), lengthening the period of follicle dominance with progesterone or curtailing follicle development with GnRH or oestradiol as 17beta, benzoate or cypionate. These hormones can also be used to synchronise ovulation allowing timed inseminations without detected oestrus. Progesterone, PGF, GnRH and oestradiol benzoate have each been used to increase conception rates in some situations, but their use has reduced them in others. For example, inseminations made within 96 h of a single injection of PGF administered during the luteal phase were associated with increased conception rates in dairy cows whereas double injection protocols reduced conception rates. The three forms of oestradiol and GnRH have greater effects on follicular development following divergence and dominance than following wave emergence. This can mean that follicles of differing maturity will be present about 7 days later and can result in varied intervals to the onset of oestrus following a PGF injection. The consequent variation in ovulation time can be reduced by injecting GnRH or an oestradiol during pro-oestrus. This means that some less mature follicles will ovulate, forming corpus luteum (CL) associated with a slower rise in plasma progesterone and lower mid-luteal concentrations. The lower conception rates recorded with single timed inseminations with synchronised ovulations have been associated with increased prevalences of short cycles in lactating dairy cows (with GnRH), with long luteal phases in cows and heifers (with oestradiol benzoate) and with embryo loss following positive pregnancy diagnosis (as with Ovsynch in lactating Holstein cows). Extensive Canadian studies have demonstrated that these same hormones can be successfully used without these limitations and reliably obtaining conception rates over 50% and up to 70% in beef cattle that have been supplemented with a progestin during the period of ovarian follicle synchronisation. The inherently lower fertility of Holstein cows during early lactation may be contributing to the reduced effectiveness of hormonal treatments for synchronised follicle development and ovulation. The role of reduced dose rates of GnRH in compromising this effectiveness needs to be determined if the potential of these treatments realised with beef cattle is to be achieved with lactating Holstein cows.     

Induction of estrus in suckled female yaks (Bos grunniens) and synchronization of ovulation in the non-sucklers for timed artificial insemination using progesterone treatments and Co-Synch regimens

The objectives of the present study were to evaluate the induction of estrus and fertility in yak cows treated with Co-Synch regimens or progesterone (P(4)). In Experiment 1, postpartum suckled yaks were assigned to three treatments: (1) A (n=28), insertion of an intravaginal device containing P(4) (CIDR) on Day 0, PGF(2alpha) (i.m.) on Day 6 and PMSG (i.m.) at the time of CIDR removal on Day 7 (P(4)-PGF(2alpha)-PMSG); (2) B (n=21), PGF(2alpha) (i.m.) on Day 6 and PMSG on Day 7; (3) C (n=26), control group. Seven yak bulls were grazed with the cows for natural breeding. Rate of estrus within 96h of the end of treatment was greater (P<0.05) in A (100.0%) than in B (28.6%) or C (0.0%). First service conception rate (CR) determined by serum P(4) on Day 21 after breeding was greater (P<0.05) in A (78.6%) than in B (22.2%). Also, pregnancy rate (PR) during the breeding season was greater (P<0.05) in A (82.1%) than in B (19.0%) and C (7.7%). In Experiment 2, non-suckled yaks that calved in previous years but not in the current year were assigned to three treatments: (1) A (n=31), GnRH (i.m.) on Day 0, followed by PGF(2alpha) on Day 7 and timed artificial insemination (TAI) concurrently with GnRH treatment on Day 9 (Co-Synch regimen); (2) B (n=50), a CIDR device for 7 days plus PGF(2alpha) and PMSG at the time of CIDR withdrawal on Day 7 and TAI on Day 9 (P(4)-PGF(2alpha)-PMSG); (3) C (n=50), yak cows were artificially inseminated at spontaneous estrus. Frozen semen of Holstein and Jersey were used for insemination in Experiment 2. The CR assessed by rectal palpation 35 days after TAI was not different in A (22.6%), B (30.0%) and C (33.3%), but PR was greater in A and B than in C, when based on those cows presented for estrous synchronization programs. It is concluded that P(4)-PGF(2alpha)-PMSG protocol could efficiently induce estrus and result in an acceptable pregnancy rate in postpartum suckled yak cows. This technique and Co-Synch regimen can be applied successfully for TAI of non-suckled yak cows.     

Fertility following fixed-time AI or insemination at observed estrus in Ovsynch and Heatsynch programs in lactating dairy cows

The objective of this study was to compare the conception rate for fixed-timed artificial insemination (FTAI) and observed heat artificial insemination (HAI) prior to the scheduled FTAI in Ovsynch and Heatsynch synchronization protocols. In Experiment 1, lactating dairy cows (n=535) received two set-up injections of 25mg prostaglandin F(2alpha) (PGF(2alpha)) i.m., 14 days apart starting at 36+/-3 days in milk (DIM). Cows were blocked by parity and were randomly allocated to either Ovsynch or Heatsynch groups. All cows received 100 microg of GnRH i.m. 14 days after the second set-up injection of PGF(2alpha), followed by a third injection of 25mg PGF(2alpha) i.m., 7 days later. In the Ovsynch group, HAI cows (n=29) were bred on standing estrus after the third PGF(2alpha) before the scheduled second GnRH, whereas FTAI cows (n=218) that were not observed in estrus, received a second injection of 100 microg of GnRH i.m., 48 h after the third PGF(2alpha) and received TAI 8 h after the second GnRH. In the Heatsynch group, all cows (n=288) received 0.5 mg of estradiol cypionate (ECP) 24 h after third PGF(2alpha) and HAI cows (n=172) were bred on standing estrus and FTAI cows (n=116) that were not observed in estrus, received TAI 72 h after the third PGF(2alpha). In Experiment 2, repeat breeder cows (n=186) were randomly assigned to either Ovsynch or Heatsynch groups. The FTAI and HAI cows were inseminated similar to Experiment 1. All cows were observed for estrus three times daily. The associations with the conception rate were modeled with logistic regression separately for Experiments 1 and 2. Of all the variables included in the model in Experiment 1, type of AI (HAI versus FTAI, P=0.0003) and parity (primiparous versus multiparous, P=0.05) influenced the first service conception rate. Over-all conception rate and first service conception rate for HAI cows were higher compared to FTAI cows (33.8% versus 21.3%, and 35.3% versus 21.0%; P=0.001). In the Heatsynch group, cows that received HAI had significantly higher over-all conception rate and first service conception rate compared to FTAI (35.2% versus 17.3% and 36.0% versus 15.5%; P=0.0001). The conception rates in repeat breeder cows for HAI and FTAI (30.1% versus 22.3%) were not different (P>0.1). In conclusion, it was recommended to include AI at observed estrus and fixed-time AI for cows not observed in estrus in order to improve the conception rate in synchronization protocols.     

Comparative fertility of normal and repeat-breeding cows as embryo recipients

Morphologically normal embryos were transferred surgically into uteri of normal and repeat-breeder cows at seven days post-estrus to compare embryo survival rates in the two kinds of cows. All cows were less than ten years of age and had no abnormal genital discharges, cystic ovarian follicles, or anatomical abnormalities of the reproductive tract. Normal cows had not been inseminated after last calving. Repeat-breeders had at least four infertile services within the past six months (average of 6.2 services after calving). To test fertility of repeat-breeders at synchronized estrus, 22 anatomically-normal repeat-breeders were treated by intramuscular (i.m.) injection with prostaglandin F(2)alpha (PGF(2)alpha) on day 11 of an estrous cycle (estrus = day 0) and inseminated at induced estrus; 11 cows (50%) had a normal fetus at necropsy on day 60. Twenty-three repeat-breeders and 23 normal cows were assigned as embryo recipients and treated i.m. with PGF(2)alpha to synchronize estrus. All embryo donors were normal cows. Donors were treated with FSH and PGF(2)alpha and inseminated at estrus. On day 7 after estrus, embryos were recovered nonsurgically from donors and one embryo was transferred through a flank incision to the anterior end of the uterine horn adjacent to the corpus luteum of each recipient. Recipients that did not return to estrus were necropsied at day 60. Of 28 normal and 23 repeat-breeder recipients, 23 normal cows (82%) and 16 repeat breeders (70%) were pregnant at day 60 (P=0.235). Thus, at seven days post-estrus, the maternal environment of most of these repeat-breeders was satisfactory for maintaining pregnancy.     

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

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

Combined administration of gonadotropin-releasing hormone, progesterone, and meloxicam is an effective treatment for the repeat-breeder cow

In practice, the etiologic treatment of the repeat-breeder cow is nearly infeasible. In this study, we tested the hypothesis that a combined treatment would benefit the conception rate of repeat-breeder cows. The components of this regimen target ovulation defects, late progesterone (P4) rise, and premature luteolysis. In a 5-year period, 402 repeat-breeder cows were divided in five groups, and treatment regimens consisted of the following: gonadotropin-releasing hormone (GnRH; Group 1, n = 115, 0.012 mg buserelin im 4 to 6 h before artificial insemination); P4 (Group 2, n = 51, 100 mg P4 intravaginally, on Days 5 to 7); meloxicam (Group 3, n = 31, 0.5 mg kg⁻¹, 24 h⁻¹ melοxicam sc, on Days 16 to 18); GnRH + P4 + meloxicam (Group 4, n = 98); and no treatment (Group 5, control, n = 107). Artificial insemination was conducted only after overt estrus; thereafter, the duration of the estrous cycle was assessed in all cows that were detected to return to heat. The conception and pregnancy rate was compared among groups. The proportion of cows that returned to estrus after artificial insemination did not differ among groups; the duration of estrous cycle was the shortest in Group 1 and the longest in Group 4. In Group 4, pregnancy rate was higher (P < 0.05) than that of Groups 1 and 5 (35.71% vs. 20.00% and 17.76% for Groups 4, 1, and 5, respectively), but though numerically higher, it did not differ statistically from that of Groups 2 (27.45%) and 3 (22.58%). Our results imply that a multifaceted protocol has to be applied for the successful treatment of the repeat-breeder cow.     

Prostaglandin F(2)alpha usage in a dairy reproduction program for treatment of unobserved estrus, pyometra and ovarian luteal cysts

A retrospective study was conducted to evaluate the outcome of 223 prostaglandin F(2)alpha (PGF) treatments given to lactating Holstein and Jersey cows over a 44-mo period. The cows were part of a commercial dairy herd. Treated cows were given PGF (25 mg i.m.) because they had not been observed in estrus or because they had been diagnosed as having a luteal cyst or pyometra. Outcome of treatments was assessed for frequency of response to treatment (the detection of estrus), time interval to detection and pregnancy outcome of breedings at PGF induced estrus. Of the 223 administrations of PGF, 70% (156 223 ) were given for unobserved estrus, 12.1% (27 223 ) were given for cystic ovarian disease and 15.2% (34 223 ) were given for pyometra. Estrus was detected in 55.3% (120 217 ) of cows over a period of 36 to 130 hours after PGF administration. Interval to estrus and response rates were not influenced by the reason for treatment. Mean time interval to response was 79.1 h. Time interval for response was affected by season (P < 0.01) housing location (P < 0.01) and lactation number (P < 0.05). Insemination was performed following 157 of the treatments. For cows treated for unobserved estrus, insemination was performed in response to estrus or at 80 h if no estrus had been previously seen. Of this group, 39.7% (58 146 ) failed to show estrus and were inseminated at 80 h. Reinsemination was required for 22.7% (20 88 ) of the cows that manifested estrus following insemination at 80 h. Overall conception rate was 41.4% (65 157 ). Cows inseminated in response to estrus had a 53.4% (47 88 ) conception rate, and appointment bred (80 h) cows had a 20.7% (12 58 ) conception rate. Factors significantly influencing conception were response to PGF administration (P < 0.05), season (P < 0.01) and lactation number (P < 0.01). It was concluded that estrus detection efficiency affects the outcome of PGF administration and that conception rates resulting from 80 h breeding when no estrus is observed may be unacceptably low.     

Effects of benzyl alcohol on the bovine oestrous cycle and subsequent fertility

A uterine infusion varying in volume from 5 to 40 ml and containing from 0.5 to 2.0 ml of benzyl alcohol shortened the length of the oestrous cycle in cows treated in the early luteal phase and prolonged the oestrous cycle in some cows in the late luteal phase. Results with 399 infusions produced a concentration of cows in oestrus from 8 to 13 days after treatment. The conception rate for 198 inseminations at the first post-treatment oestrus was 59.6% compared to 59.2% obtained in 471 untreated cows.     

Treating cattle with progesterone as well as a GnRH analogue affects oestrous cycle length and fertility.

Initiating the chronic administration of progesterone to cattle during metoestrus will produce shortened oestrous cycles containing one or two wave-like sequences of ovarian follicle development. Conception rates are reduced to inseminations at the oestrus preceding these shortened cycles. In contrast, a single injection of the GnRH analogue, buserelin, around mid-dioestrus can lengthen the oestrous cycle by increasing the proportion of cycles with three waves of follicular development and may also increase conception rates. A series of trials was conducted to test the hypothesis that the adverse effects of progesterone on oestrous cycle length and conception rate could be prevented with a strategic injection of GnRH. In Trial 1, progesterone was administered per vaginum to heifers for 10 days from Day 2 or 3 (Oestrus = Day 0) and with (n = 42) or without (n = 46) an injection of a GnRH analogue (10 microg buserelin) on Day 12 or 13. Other heifers (n = 44) served as an untreated control group. The average inter-oestrous interval (IOI) for those heifers treated only with progesterone was 17.0 days and was less (p<0.05) than the average intervals for those also receiving GnRH (20.2 days) or in the control group (20.0 days). In Trial 2, 45 heifers were inseminated following a synchronised oestrus. Progesterone was administered as in Trial 1 to 22 of the heifers. Their conception rate was 45.4% and this was less (p<0.05) than the 73.9% obtained with their 23 untreated contemporaries. Trial 3 was completed using 530 cows in commercial dairyherds. The 259 cows receiving progesterone and GnRH (buserelin) after their first inseminations had a conception rate of 68.3% compared to 56.1% for their 271 untreated herdmates (p<0.05%). Heifer calves born to treated cows had heavier birthweights (33.4 vs. 31.1 kg; p<0.05), but birthweights of bull calves were unaffected (35.5 vs. 35.8 kg). Gestation lengths for cows conceiving to first inseminations were similar for treated and control groups (280.9 vs. 280.5 days). The results of these trials confirmed the hypothesis that a strategic injection of the GnRH analogue, buserelin, could prevent the reductions in oestrous cycle length and conception rate associated with the chronic metoestrous administration of progesterone.     

Analysis of fertility indices of cows with extended postpartum anestrus and other reproductive disorders compared to normal cows

An analysis of computerized data on the incidence and consequences of reproductive disorders was performed on 84,818 lactations in more than 100 high producing Kibbutz dairy herds during six semiannual recording periods. The average incidence of primary reproductive disorders, which included retained placenta, abnormal lochia, endometritis, postpartum anestrus, cystic ovaries, negative pregnancy examinations and repeat breeders, was 50.4%. During all recording periods we were able to observe recurrence and repeatability of these reproductive disorders and of the fertility indices consequently seen. Cows with uterine infections diagnosed and treated before Day 20 post partum had better fertility indices than those diagnosed and treated later. The conception rate to first inseminations and the overall conception rate to all inseminations of cows with postpartum anestrus was significantly lower, while the percentage of "problem cows" (not pregnant by Day 150 post partum) was significantly higher, than in normal cows. The incidence of cystic ovaries in cows with a previous diagnosis of reproductive disorders was 2 to 3 times higher when compared to cows without such a diagnosis.     

Reproductive performance of repeat breeders in dairy herds

The objectives were to characterize repeat breeding in dairy cows, including reproductive performance and risk factors. Data from 613 Holstein Friesian cows in nine dairy herds across Japan were enrolled. A repeat breeder was defined as a cow that did not become pregnant after three inseminations, despite no clinically detectable reproductive disorders. In contrast, cows that became pregnant within three inseminations were considered to have normal fertility. Of the 613 cows, 87.3% eventually became pregnant after repeated AI (maximum calving to conception interval was 435 d). Mean (±SEM) first AI conception rate, days in milk at first AI, calving to conception interval and service per conception were 38.3%, 82 ± 2 d, 125 ± 3 d, and 2.0 ± 0.1 times, respectively. Normal fertility cows (n = 479) required only 114 ± 3 d to conceive and 1.7 ± 0.1 inseminations per pregnancy, whereas repeat breeders (n = 86) required significantly more days to conceive (211 ± 10) and more inseminations per pregnancy (4.7 ± 0.2). Based on survival analysis, it took 94 d after calving for 50% of normal fertility cows to become pregnant, compared to 155 d for repeat breeders. For repeat breeders, 31.4, 50.0, and 58.1% became pregnant within 210, 300, and 435 d after calving, respectively. The risk factors for repeat breeding were parity (relative risk [RR] = 0.809; P = 0.058), resumption of postpartum ovarian cycles (RR = 1.928; P = 0.009), and days in milk at first AI (RR = 0.991; P = 0.039). In conclusion, repeat breeder dairy cows had very poor reproductive performance. Lower parity, abnormal resumption of postpartum ovarian cycles, and shorter days in milk at first AI were risk factors for repeat breeding.     

Comparison of pregnancy rates of repeat-breeder dairy cows given gonadotropin releasing hormone at or prior to the time of insemination

A total of 585 repeat-breeder dairy cows was used to study the effect of GnRH treatment, either at or prior to insemination, on the pregnancy rate. The cows were divided into 6 treatment groups. Cows in Group 1 (n = 142) were observed in estrus, and 11 +/- 0.42 hours (mean +/- SEM) later they were given 100 ug, i.m. gonadotropin releasing hormone (GnRH) and were inseminated. Cows in Group 2 (n = 139) were observed in estrus and were inseminated 11.4 +/- 0.43 hours later. Cows in Group 3 (n = 33) were monitored for estrus with an activated heatmount detector but were not observed in estrus; they were inseminated 1.5 +/- 0.87 hours later and were given 100 ug, i.m. GnRH. Cows in Group 4 (n = 35) were not observed in estrus, but they did activate the heatmount detector and were inseminated 2.2 +/- 0.87 hours later. Cows in Group 5 (n = 107) were observed in estrus, given 100 ug, i.m. GnRH 2.0 +/- 0.40 hours later, and were inseminated 9 +/- 0.60 hours after GnRH treatment. Cows in Group 6 (n = 129) were observed in estrus and were inseminated 10 +/- 0.50 hours later. Pregnancy rates were analyzed by Chi-square. Interactions between pregnancy rate, treatment and time of insemination were evaluated using ANOVA and LSM (P < 0.05). There was no effect on pregnancy rate when GnRH was given at or prior to insemination. Cows inseminated on the basis of observed estrus had a higher pregnancy rate (P < 0.05) than cows inseminated on the observation of an activated heatmount detector. From the results of this study, it is concluded that treatment with GnRH at or prior to insemination did not improve the pregnancy rate of repeat-breeder dairy cows.