Factors Affecting Pregnancy Rate in Artificial Insemination with Frozen Semen During Non-Breeding Season in Murciano–Granadina Goats: a Field Assay

An artificial insemination programme was carried out to study the effect of factors such as depth of semen deposition, inseminator skill, farm, sire and expression of oestrus on pregnancy rate in Murciano-Granadina (MG) goats during non-breeding season and using frozen semen. Frozen-thawed semen from six males was applied by three technicians to inseminate a total of 551 goats in 17 farms distributed throughout the Mediterranean area of Spain. Pregnancy rate was determined at 6 weeks after insemination by transabdominal ecography. Overall pregnancy rate was 57%. Farm and depth of semen deposition affected pregnancy rate, whereas the sire and the technician had no effect. The deeper the semen was deposited in the genital tract, the higher was the rate of pregnancy obtained, being greater when the catheter reached the uterus. In spite of the relevant difference observed (48.2% vs 59.0%), pregnancy rate of females not coming into oestrus until 30 h after sponge removal was not significantly different, compared with those showing oestrus during the OD procedure. In conclusion, our field assay data on AI in MG goat with frozen-thawed semen showed that post-cervical insemination presented significantly greater pregnancy rate in comparison to when semen is deposited in the vagina or in the caudal part of the cervix.     

Timing of artificial insemination in postpartum beef cows following administration of the CO-Synch + controlled internal drug-release protocol

This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) at 54 or 66 h after administration of the CO-Synch + controlled internal drug-release (CIDR) protocol. Cows (n = 851) at 2 locations over 2 yr (yr 1, n = 218 and 206; and yr 2, n = 199 and 228 at the 2 locations, respectively) were stratified by age, BCS, and days postpartum to 1 of 2 FTAI intervals. Cows were administered GnRH (100 mug, i.m.) and were equipped with a CIDR insert (1.38 g of progesterone) on d 0. Controlled internal drug-release inserts were removed 7 d later at the time PGF(2alpha) (25 mg, i.m.) was administered (d 7). Continuous estrus detection was performed at location 2 by using the HeatWatch Estrus Detection System; the transmitters were fitted at the time of PGF(2alpha) and removed at the time of AI. Artificial insemination was performed at predetermined fixed times [54 h (FTAI 54; n = 424) or 66 h (FTAI 66; n = 427) after PGF(2alpha)] and all cows were administered GnRH (100 mug, i.m.) at AI. Two blood samples were collected on d -10 or -8 and immediately before treatment initiation to determine the pretreatment estrous cyclicity status of cows [progesterone >/=0.5 ng/mL (FTAI 54, 288/424 = 68%; FTAI 66, 312/427 = 73%; P = 0.07)]. Pregnancy rates were greater (P < 0.01) among cows that exhibited estrus than among those that did not (123/163 = 76% and 150/270 = 56%, respectively). There were no treatment x location interactions within year (P > 0.10) for age, days postpartum, or BCS; thus, the results were pooled for the respective treatments. Pregnancy rates were greater for FTAI 66 than FTAI 54 (P = 0.05; 286/426 = 67% vs. 257/424 = 61%, respectively). Pregnancy rates resulting from FTAI did not differ between year (P = 0.09), farm (P = 0.80), AI sire (P = 0.11), or technician (P = 0.64). There was no difference between pregnancy rates resulting from FTAI based on pretreatment cyclicity status (P = 0.30), and there was no difference between treatments in final pregnancy rates (P = 0.77). In summary, pregnancy rates resulting from FTAI following CO-Synch + CIDR at 66 h were greater than those resulting from FTAI at 54 h.     

Effect of delaying the time of insemination with sex-sorted semen on pregnancy rate in Holstein heifers

The objective of the study was to evaluate the interval from onset of oestrus to time of artificial insemination (AI) to obtain the optimum pregnancy rate with sex-sorted semen in Holstein heifers. Heifers in oestrus were detected and inseminated only by using heat–rumination neck collar comprised electronic identification tag at the age of 13–14 months. Heifers (n = 283) were randomly assigned to one of three groups according to the timing of insemination at 12–16 hr (G1, n = 97), at 16.1–20 hr (G2, n = 94) and at 20.1–24 hr (G3, n = 92) after reaching the activity threshold. The mean duration of oestrus was 18.6 ± 0.1 hr, and mean peak activity was found at 7.5 ± 0.1 hr after activity threshold. The mean interval from activity threshold to ovulation was 29.4 ± 0.4 hr. The overall pregnancy per AI (P/AI) was 53.0% at 29–35 days and 50.9% at 60–66 days after AI. There was a significant reduction between G1 (13.8 ± 1.4 hr) and G3 (7.9 ± 1.4 hr) related to the intervals from AI to ovulation time. Sex-sorted semen resulted in significantly higher P/AI at 29–35 days when heifers inseminated in G3 (60.9%) after oestrus than those inseminated in G1 (49.5%) and G2 (48.9%). In terms of fertility, when the temperature–humidity index (THI) was below the threshold value (THI ≤65) at the time of AI, there was a tendency (≤65; 57.2% vs. > 65; 47.1%) for high pregnancy rate. There was no effect of sire on P/AI. In addition, the interaction of the technician with the time of AI was found significant, and three-way interaction of technician, sire and time of AI was tended to be significant on pregnancy rate. Thus, in addition to delaying the time of insemination (between 20.1 and 24 hr) after oestrous detection, THI and experienced technician were also found to be critical factors in increasing fertility with the use of sex-sorted semen in Holstein heifers.     

Role of the sensitivity of detection of oestrus in the submission rate of cows treated to resynchronise oestrus

OBJECTIVE: To determine if failure to detect oestrus in cows treated to resynchronise oestrus leads to fewer cows being inseminated than are truly in oestrus. PROCEDURE: Cows in three herds were enrolled in a controlled breeding program that involved synchronisation of oestrus for a first round of artificial insemination (AI) followed by resynchronisation for a second round of AI. Just before oestrus was expected at the second round of AI, aids for the detection of oestrus were fitted, which included pedometers, radiotelemetric transmitters (HeatWatch), tail-paint and heatmount detectors. Milk samples were collected at the second round of AI (day 33, herds A and B; day 35, herd C of the treatment program) and were used in combination with pregnancy testing to determine the number of cows that were in oestrus (milk progesterone < 2.0 ng/mL) and cows that were not in oestrus (milk progesterone > 2.0 ng/mL or pregnant at second round of AI) at the time samples were collected. RESULTS: The mean sensitivity of detection of oestrus at the resynchronised oestrus was 92.5% and did not differ significantly between herds (P = 0.19). A total of 75% (60/80) of cows that were retrospectively determined to be not pregnant at the time of the second round of AI were classified as having high (> or = 2.0 ng/mL) concentrations of progesterone in milk at that time. Pregnancy testing of cows about 35 days after AI suggested that early pregnancy loss also contributed to a reduction in submission rates at the resynchronised oestrus. CONCLUSION: Failure to submit cows for insemination at a resynchronised oestrus was mainly due to cows not being in oestrus rather than due to a failure to detect oestrus.     

Effects of different five-day progesterone-based fixed-time AI protocols on follicular/luteal dynamics and fertility in dairy cows

This study compares in two experiments the responses of lactating dairy cows to four different progesterone-based protocols for fixed-time artificial insemination (FTAI) in terms of their effects on follicular/luteal dynamics and fertility. The protocols consisted of a progesterone intravaginal device fitted for five days, along with the administration of different combinations of gonadotropin releasing hormone, equine chorionic gonadotropin and a single or double dose (24 h apart) of prostaglandin F_2α. In Experiment I, the data were derived from 232 lactating cows. Binary logistic regression identified no effects of treatment on ovulation failure or multiple ovulation 10 days post artificial insemination (AI). Based on the odds ratio, the likelihood of ovulation failure was lower (by a factor of 0.1) in cows showing at least one corpus luteum (CL) upon treatment than in cows lacking a CL; repeat breeders (> 3 AI) and cows with multiple CLs at treatment showed lower (by a factor of 0.44) and higher (by a factor of 9.0) risks of multiple ovulation, respectively, than the remaining animals. In Experiment II, the data were derived from 5173 AIs. The independent variable treatment failed to affect the conception rate 28–34 days post AI, twin pregnancy or early fetal loss 58–64 days post AI. The results of this study demonstrate the efficacy of 5-day progesterone-based protocols for FTAI. All four protocols examined were able to induce ovulation in both cyclic and non-cyclic animals so that FTAI returned a similar pregnancy rate to spontaneous estrus. Our results suggest that the ovarian response and fertility resulting from each treatment are due more to the effect of ovarian structures at treatment than to the different combinations of hormones investigated.     

Influence of category-heifers,primiparous and multiparous lactating cows-in a large-scale resynchronization fixed-time artificial insemination program

This study was conducted to evaluate the influence of category (heifers, primiparous or multiparous cows) on pregnancy rates in a large scale resynchronization ovulation program. Nelore heifers (n = 903), primiparous lactating cows (n = 338) and multiparous lactating cows (n = 1,223) were synchronized using a conventional protocol of estradiol/P4-based fixed-time artificial insemination (FTAI). Thirty days after ultrasonography, females who failed the first FTAI were resynchronized with the same hormonal protocol prior to a second FTAI. The pregnancy status of each cohort was evaluated by ultrasonography 30 days after each FTAI. The average conception rate after the first FTAI and resynchronization was 80.5%. Heifers had a higher conception rate (85%) than primiparous (76%) or multiparous cows (78%; p = 0.0001). The conception rate after the first FTAI was similar among heifers (57%), primiparous cows (51%) and multiparous cows (56%; p = 0.193). After the second FTAI, heifers exhibited a higher conception rate (66%) than primiparous or multiparous cows (51%; p = 0.0001). These results demonstrate the feasibility of resynchronization in large beef herds for providing consistent pregnancy rates in a short period of time. We also demonstrated that ovulation resynchronization 30 days after FTAI is particularly effective for heifers, providing a conception rate of up to 66%.     

Pregnancy Rates in Lactating Holstein–Friesian Cows after Artificial Insemination with Sexed Sperm

The effects of artificial insemination (AI) using sexed sperm on pregnancy rates have seldom been studied in lactating dairy cows on commercial dairy farms. We evaluated pregnancy results after AI of 306 lactating dairy cows, of which 157 were inseminated with 2x10(6) frozen/thawed sexed sperm and 149 with 15x10(6) frozen/thawed unsexed sperm. The average pregnancy and calving rates were 21.0% and 20% for the sexed-sperm AIs and 46% and 45% for the unseparated control-sperm AIs respectively (p<0.001). The proportion of female calves derived from sexed-sperm AI was 82% compared with 49% for control AI (p<0.01). The proportion of live and healthy calves in single births was 100% for sexed-sperm AI and 97% for control AI (p>0.05). Our results indicate that AI with low-dose sexed sperm under field conditions in commercial dairy herds without oestrus synchronization results in significantly reduced pregnancy rates compared with normal-dose AI. Improved insemination strategies combined with increased sperm doses are needed before the use of sexed sperm can be of any significant benefit for the dairy and beef industry.     

Does the Amount of Progesterone in Intravaginal Implants Used to Synchronise Oestrus Affect the Reproductive Performance of Brahman Heifers Artificially Inseminated at a Fixed Time

The study tested the hypothesis that reduced intravaginal implant progesterone (P₄) concentration to synchronise oestrus would increase pregnancy rates to fixed‐time artificial insemination (FTAI) in Bos indicus heifers. Brahman heifers (n = 294; 2 year) were body condition scored (BCS), weighed and scanned for presence of a corpus luteum (CL). Only cyclic heifers were selected and allocated randomly within BCS and 25 kg bodyweight category to one of three P₄ treatment groups. On day 10, heifers received a P₄ implant (CueMate‐1‐pod, 0.78g P₄; CueMate‐2‐pod, 1.56g P₄; or CIDR‐B, 1.9g P₄), 2 mg oestradiol benzoate (ODB) intramuscularly (IM) and 250 ug cloprostenol IM. At day 2, the implant was removed, 250 ug cloprostenol was injected IM and tail paint applied. The heifers received 1 mg ODB 24 h later and were FTAI 48–54 h after implant removal (day 0). Ten randomly selected heifers per group were blood sampled and scanned at days 10, 2, 0 and 6 to define the P₄ profiles pre‐ and post‐FTAI. Heifers were heat‐detected 18–20 days post‐FTAI and oestrous heifers AI’d by the AM/PM rule. Bulls joined the heifers on day 27 post‐FTAI. Transrectal ultrasonography estimated conception date on day 72. Statistical analysis examined the effects of treatment, technician, semen, ovarian status, BCS and liveweight, on pregnancy rate (PR) to FTAI. There was no significant difference (p = 0.362) in PR between treatment groups (CueMate 1‐pod, 36.4%; CueMate 2‐pod, 39.6%: CIDR‐B, 28.3%), but PR was higher in those heifers with increased BCS between FTAI and pregnancy diagnosis (p = 0.005). Thirty‐three per cent of monitor heifers had plasma P₄ concentrations of <1 ng/ml on day 6 after FTAI; only 20% of these conceived vs 60% of heifers with P₄ ≥ 1 ng/ml. In summary, no significant difference in PR was identified between treatments but good BCS and a rising plane of nutrition were critical to PR of these pure grade Brahman heifers in northern Australia.     

Progesterone concentration in defatted milk of dairy cows in early pregnancy.

Progesterone concentrations have been measured in defatted milk of British Friesian cows of four herds during the oestrus cycles (other than short cycles) immediately before artificial insemination (AI) at oestrus and immediately after AI (in non-pregnant cows), and during early pregnancy. Differences in mean progesterone concentrations between herds were significant (P less than 0.05) on all days within the day 10-18 period after AI, both in pregnant and in non-pregnant, inseminated cows but were not significant between pregnant and non-pregnant cows within herds until day 17 or 18. It is concluded that up to this time (that of luteolysis in non-pregnant cows) undefined factors, variable among herds, can have a much greater influence on the rate of progesterone secretion by corpora lutea and consequent progesterone concentration in plasma and milk than does the presence of conceptuses. Maximum mean progesterone concentration reached during early pregnancy in two herds did not differ significantly; it was reached in the 11-15-day period in one herd but not until 46-50 days in the second. Mean progesterone concentration declined after day 90.     

Repeated oestrus synchronisation of beef cows with progesterone implants and the effects of a gonadotrophin-releasing hormone agonist at implant insertion

A group of 97 spring-calving beef cows were initially oestrus synchronised with controlled internal drug release (CIDR) intravaginal progesterone implants inserted for nine days and a prostaglandin injection on day 7. Approximately half the cows were given 10 microg buserelin when the implants were inserted, and they all received a single fixed-time artificial insemination (AI) 56 hours after the withdrawal of the implants. The overall pregnancy rate to the first synchronised AI was 55 per cent, the buserelin-treated cows having a pregnancy rate of 63 per cent compared with 47 per cent in the untreated cows (P>0.05). Sixteen days after the first synchronised AI all the cows were re-implanted with used CIDR implants which were removed five days later, and the cows received a second synchronised AI on days 23 to 24. Cows which received the second AI were implanted with new CIDR devices 16 days later and these were removed after five days and the non-pregnant cows received a third synchronised AI. The pregnancy rates to the second and third synchronised services were 74 per cent and 75 per cent, respectively.     

Improving the Reproductive Efficiency by Zoo-Technical Methods at a Dairy Farm

This trial was conducted on a Hungarian dairy farm between July 2001 and December 2004. The objective of this work was to improve the reproductive efficiency with relatively high milk production. At the beginning of this trial blood and fodder samples were taken for checking the metabolic status of the animals in order to determine their health condition. The nutritive value of the daily ration for all groups met with the requirements of the Hungarian National Standard and almost all serum metabolic parameters differed between the milking and pregnant animals. Early pregnancy detection (by ultrasound) and ovulation synchronizing methods were introduced to optimize reproductive performance. The oestrus cycle was also checked by ultrasound and open cows were treated by the appropriate method in order to inseminate them as soon as possible. Efficiency of artificial insemination (AI) followed by a single prostaglandin F2alpha (PGF2alpha) and Ovsynch treatment was similar (30.8% and 29%) and less effective than AI after natural heat detection (37.1%). Provsynch (Pre-synch followed by Ovsynch) was the most effective ovulation synchronization method (conception rate=42.6%; p<0.01). Although milk production increased between 2002 and 2004 by approximately 600 kg per cow, the calving period decreased by 20 days and the number of AIs per pregnancy was also improved (0.8 AI per conception). These findings are really beneficial economically because the decrease in the calving interval returns profit for the dairy farms; one open day costs euro2.5/cow. Economical analysis showed a high profit ratio from the reproductive 'investment' on this farm. Every invested euro yielded approximately euro10.     

Re-insertion of a progesterone-containing intravaginal device to synchronise returns to oestrus in dairy heifers

Recommendations for oestrus synchronisation of dairy heifers using progesterone-containing intravaginal devices suggest re-insertion of used devices 16 days after first insemination for a period of 5 days to allow a second opportunity for artificial insemination. Controlled studies on the effectiveness of re-using intravaginal devices to synchronise returns to oestrus in non-pregnant dairy heifers are lacking. A clinical trial was conducted involving 750 Friesian heifers in 13 herds. After an initial synchronisation programme, the used intravaginal devices were re-inserted 14 or 16 days after first insemination into half of the heifers in each herd for a period of 5 days. After the first synchronisation programme, 47.5% of heifers remained non-pregnant. Re-insertion of used intravaginal devices for 5 days significantly increased the number of non-pregnant heifers detected in oestrus and inseminated by 48 hours after device removal compared to heifers in which devices were not re-inserted (45.2% v. 27.3%, p < 0.05, in herds where intravaginal devices were re-inserted on day 14; 48.8% v. 13.6%, p < 0.05, in herds where intravaginal devices were re-inserted on day 16). Re-insertion at 14 or 16 days after first insemination was equally effective in increasing visible returns to service. However, the number of non-pregnant heifers synchronised for a second round of artificial insemination was less than expected. Conception rate to the re-synchronised oestrus was unaffected by the treatment. It is concluded that the additional procedures of CIDR re-insertion, removal, tailpainting and insemination involved in there-synchrony programme, and the relatively low in-calf rate to the re-synchronised round of insemination, reduced the potential benefits of re-synchronisation.     

Use of Vaginal Electrical Resistance to Diagnose Oestrus,Dioestrus and Early Pregnancy in Synchronized Tropically Adapted Beef Heifers

The primary objective of this study was to determine whether a single measurement of intravaginal electrical resistance (VER), using the commercially available Ovatec^® probe, can discriminate between dioestrus and oestrus in Bos indicus females, which had been treated to synchronize oestrus. Santa Gertrudis heifers (n = 226) received one of three oestrous synchronization treatments: double PGF_2α 10 days apart, 8‐day controlled internal drug release (CIDR) treatment or CIDR pre‐synchronization + PGF_2α 10 days after CIDR removal. The heifers were inseminated within 12 h following observed oestrus, or, if not observed, at a fixed time approximately 80 h, following the last synchronization treatment. They were palpated per rectum for signs of pregnancy 9 weeks after artificial insemination (AI). Vaginal electrical resistance measurements were taken at the completion of synchronization treatments (presumed dioestrus), immediately prior to AI (oestrus), and then at 3 and 9 weeks post‐AI. Mean VER differed between presumed dioestrus and oestrus (113.7 vs 87.4, p < 0.001). The area under the receiver operating characteristics (ROC) curve was 0.925, indicating that VER was highly discriminatory between dioestrus and oestrus. Vaginal electrical resistance at time of AI was negatively associated with odds of conception when all inseminations were included in the analyses [odds ratio (OR) = 0.97; 95% CI 0.95–1.00; p = 0.018], but not when fixed time AIs were excluded (OR = 1.00; 95% CI 0.97–1.03; p = 0.982). Mean VER readings differed between pregnant and non‐pregnant animals at both 3 weeks (120.5 vs 96.7, p < 0.001) and 9 weeks (124.0 vs 100.3, p < 0.001) post‐AI. However, 3‐ and 9‐week VER measurements were not highly discriminatory between pregnancy and non‐pregnancy (area under ROC curve = 0.791 and 0.736, respectively). Mean VER at time of AI for animals diagnosed in oestrus differed between each of the oestrous synchronization treatments (84.7, 73.6 and 78.9, groups 1–3 respectively, p < 0.001). These findings suggest that measurement of VER may improve accuracy of oestrus diagnoses when selecting cattle for AI following oestrous synchronization programmes involving tropically adapted cattle.     

Radioimmunoassay of milk progesterone as a tool for fertility control in smallholder dairy farms

This study focused on the use of radioimmunoassay of progesterone in milk for the diagnosis of post-partum ovarian cyclicity and accurate detection of oestrus and non-pregnancy in cows in the artificial insemination (AI) programme in Bangladesh. In Investigation 1, milk samples were collected on day 0 (day of AI), day 9–13 and day 21–24 from 444 milking cows of various breeds presented for the first post-partum insemination by 413 farmers living at 182 villages/regions in Mymensingh District from 6 AI centres and sub-centres. Each cow was then examined three times after each AI until it stopped returning to oestrus. Sixty to 90 days after the last AI, the cows were examined per rectum to confirm the pregnancy. Milk progesterone data on day 21–24 contributed to a clear diagnosis with respect to non-pregnancy in 100% cows, indicating a possible use of this progesterone assay for identifying non-pregnant cows in AI programmes. In Investigation 2, milk progesterone was monitored two times in a month with a 10-day interval in 88 cows. The samples were taken between 10 days after calving and the first detected oestrus, followed by two more samples 10 days apart. The proportion of cows accurately detected in oestrus was 30%. Another 30% were stated to be in oestrus when they were not (false positive) and 40% were not detected when they were in oestrus (false negative). The mean intervals between calving and oestrus and between calving luteal activity were 40 to 362 days (median = 120, n = 82) and 34 to 398 (median = 111, n = 64) days, respectively. The body condition scores at calving and at the initiation of luteal activity influenced the interval between calving and luteal activity (p < 0.05). Cows suckled twice daily initiated luteal activity earlier than their counterparts suckled several times daily (p < 0.05). Determination of progesterone in milk on day 21–24 is a good means for detecting non-pregnant cows.     

Calving rates in a tropical beef herd after treatment with a synthetic progestagen, norgestomet, or a prostaglandin analogue, cloprostenol

Maiden heifers and lactating cows of known ovarian status and of several breeds were treated with a synthetic prostaglandin, cloprostenol, or a synthetic progestagen, norgestomet, at the start of an artificial insemination (AI) program. Animals in the cloprostenol treatment received 2 injections 10 days apart. Over the next 26 days those animals that showed oestrous behaviour were inseminated. Synchronisation rates and calving rates to insemination over the first 7 days were calculated. Those in the norgestomet treatment received an implant of norgestomet plus an injection of norgestomet and oestradiol valerate. The implant was removed 10 days later and the animals were given an injection of pregnant mare serum gonadotrophin (PMSG). They were inseminated at 48 h (maiden heifers) or 56 h (lactating cows) after implant removal. Calving rates to fixed-time insemination were recorded. After completion of the AI program the animals in both treatments were joined with bulls. Overall calving rates (AI plus bulls) were calculated. By day 7 of the program, 82% of the maiden heifers and 76% of the lactating cows in the cloprostenol treatment had been detected in oestrus. By day 21 the respective figures were 99% and 81% Norgestomet treatment had an immediate and a prolonged effect on ovarian activity in those females classified as having inactive ovaries at the start of the AI program. Calving rates of those females to fixed-time AI and overall were similar to those of the females with active ovaries in both treatments. Their calving rates to fixed-time insemination, and overall calving rates for the lactating females, were significantly higher than the corresponding values of their contemporaries treated with cloprostenol and inseminated on observed oestrus over 7 days. For those females classified as having active ovaries at the start of the AI program, calving rates to first insemination and overall were similar for both treatments. Overall calving rates of lactating cows of each breed were, with one exception, higher in the norgestomet treatment than in the cloprostenol treatment. Although norgestomet treatment was more expensive than cloprostenol treatment, the advantage in calf crop resulted in an overall monetary advantage to the norgestomet treatment.     

Comparison of four methods for detection of oestrus in dairy cows with resynchronised oestrous cycles

OBJECTIVE: To compare the sensitivity and positive predictive value of four methods for detection of oestrus in dairy cows with resynchronised oestrous cycles. PROCEDURE: Oestrous cycles in cows in three herds were synchronised for a first round of artificial insemination (AI) and then resynchronised for a second round of AI. Sensitivity and positive predictive value of four aids (pedometers, radiotelemetric transmitters [HeatWatch; HW], tail-paint and heatmount detectors) that were used to detect the resynchronised oestrus were compared. Milk progesterone concentration and pregnancy testing at 12 weeks were used as the reference standard for cows being in oestrus. RESULTS: The mean sensitivity and positive predictive value for detecting the resynchronised oestrus, for each aid that was used, was > 80%. Tail-paint was significantly more sensitive at detecting oestrus compared to heatmount detectors (P = 0.002), but not significantly more sensitive than pedometers (P = 0.07) or HW (P = 0.55) for detecting oestrus (91.3, 85.7; 81.4 and 88.4%, respectively). Positive predictive value of HW for detecting oestrus was greater than tail-paint (P = 0.014) and heatmount detectors (P = 0.024) but not pedometers (P = 0.25; 100, 91.7, 92.9 and 87.5%, respectively). Positive predictive value of heatmount detectors was greater than pedometers in herd C (93.4% vs 73.3%; P = 0.035) but not in herds A (95.0% vs 90.0%; P = 0.56) or B (90.8% vs 100%; P = 0.10). No other significant differences in sensitivity or positive predictive value of detection of oestrus were found between aids. CONCLUSION: Tail-paint, heatmount detectors, pedometers and HW provide a high sensitivity (> 80%) and positive predictive value (> 85%) of detecting oestrus in dairy cows with resynchronized oestrous cycles.     

Comparison of two doses of oestradiol benzoate administered at a resynchronised oestrus on reproductive performance of dairy cows

OBJECTIVE: To compare the effects of two doses of oestradiol benzoate (ODB) administered as part of a treatment designed to resynchronise returns to oestrus on the reproductive performance of cows in a controlled breeding program. DESIGN: Cohort study. PROCEDURE: Lactating dairy cows on two farms were treated to synchronise three successive oestrous cycles. An intravaginal progesterone releasing insert (IVP4) was used to synchronise the first oestrous cycle. The cows were then treated 15 days after the first treatment by reinsertion of an IVP4 that had been used to synchronise the first oestrus and administration of 1.0 mg of oestradiol benzoate (ODB) i.m. at device insertion. The IVP4 device was removed 8 days later and either 0.5 (n = 421) or 1.0 mg of ODB (n = 446) was administered 24 h later. Injections of (ODB) with or without the use of an IVP4 were used to synchronise the third oestrous cycle. Different synchronisation treatments were used to synchronise first and third oestrous cycles but differences were included in statistical models to account for variation in the data. This enabled examination of effects due to differences in the dose of ODB used to synchronise the second synchronised oestrus. RESULTS: The dose of ODB (0.5 or 1.0 mg) administered just before the second synchronised oestrus did not significantly (P > 0.10) affect the cumulative pregnancy rates over three successive rounds of artificial insemination, the mating start date to the conception intervals, the conception rates to the first or second insemination, the proportion of cows submitted for insemination at the second synchronised oestrus or the proportion of cows that were not pregnant yet failed to show signs of oestrous (phantom cows) identified within each herd. CONCLUSION: There was no difference in reproductive performance between cows receiving either 0.5 mg or 1.0 mg ODB after removal of used IVP4 devices that had been inserted to resynchronise them for a second insemination.     

Pregnancy and offspring sex ratio following insemination with SexedULTRA and conventional semen in cows in a commercial beef operation

Pregnancy rate per AI (PR/AI) and breeding season pregnancy rates between insemination with sexed semen (SS; at 18 hr after the onset of oestrus) and conventional semen (CS; at 12 hr after the onset of oestrus,) and offspring gender ratio between two groups were compared. Angus cross cows (n = 686, during 2019 and 2020 breeding seasons) were oestrus-synchronized using Select-Synch + CIDR protocol and were observed thrice daily for oestrus until 72 hr after PGF2α administration. Cows expressed oestrus (n = 513) were inseminated with either SS (n = 246; SexedULTRA 4M™; y chromosome-bearing sperm) or CS (n = 267). Cows (n = 173) that failed to express oestrus at 72 hr after PGF2α received 100 μg of GnRH and CS insemination concomitantly. Two weeks later, cows were penned with natural service sires (bull:cow ratio 1:25) for 45 days. Pregnancy was diagnosed 30 days after bull removal. Calves' gender was determined at birth. For cows that expressed oestrus, PR/AI did not differ (p > .1) between SS (65.0%) and CS (66.7%) groups. The overall PR/AI differed (p < .05) between SS (65.0%) and CS (56.4%) groups. The natural service PR differed (p < .001) but breeding season PR (p > .05) did not differ between SS vs. CS groups. Bull:heifer gender ratio following AI was 88:12 and 52:48 for SS and CS groups, respectively, with an overall 66:34 ratio. Bull:heifer gender ratio for the two breeding seasons was 79:21 and 52:48 for SS and CS groups, respectively, with an overall 62:38 ratio. In conclusion, the fertility of SS insemination at 18 hr after onset of oestrus was 97% of CS insemination at 12 hr after onset of oestrus. Though breeding season pregnancy did not differ between SS and groups, preferred calf gender was 25 percentage points greater for SS over CS application. The gender accuracy was 88%.     

Synchronisation of oestrus and reproductive performance of dairy cows following administration of oestradiol benzoate or gonadotrophin releasing hormone during a synchronised pro-oestrus

OBJECTIVE: To compare the use of gonadotrophin releasing hormone (GnRH) and oestradiol benzoate (ODB) administered following a synchronised pro-oestrus on reproductive performance of lactating dairy cows and the submission rates of non-pregnant cows following resynchronisation. DESIGN: Cohort study. PROCEDURE: Lactating Holstein cows enrolled in a controlled breeding program were first treated with an intravaginal progesterone releasing insert (IVP4) for 8 days, 2.0 mg of ODB intramuscular (i.m.) at device insertion (Day 0), an analogue of PGF2alpha at device removal and either 1.0 mg of ODB i.m., 24 h after device removal (ODB group, n = 242), or 0.25 mg of a GnRH agonist (GnRH group, n = 152) injected i.m. approximately 34 h after device removal. Every cow was artificially inseminated between 49 and 56 h after removal of its insert (Day 10). Cows detected in oestrus 1 day after artificial insemination (AI) that were not detected in oestrus on the previous day were re-inseminated on that day. All cows treated on Day 0 were resynchronised for reinsemination by insertion of a used IVP4 device on Day 23. Oestradiol benzoate at a dose of 1.0 mg was administered i.m. at the time of device insertion. Inserts were removed 8 days later (Day 31) and 1.0 mg of ODB was injected i.m. 24 h later. Those cows detected in oestrus between Days 31 and 35 were artificially inseminated. On Day 46 these cows were resynchronised for a third round of AI by insertion of an IVP4 device, used previously to synchronise cows for the first and second rounds of AI, and administration of 1.0 mg of ODB i.m.. Eight days later inserts were removed. Cows detected in oestrus between Days 54 and 58 were artificially inseminated. Bulls were run with the herd between rounds of AI and removed after 21 weeks of mating. RESULTS: Treatment with ODB or GnRH at the first synchronised pro-oestrus did not significantly alter the reproductive performance over three rounds of AI or over a 21-week breeding period. Treatment also did not alter submission rates at the second round of AI or the proportion of non-pregnant and non-return cows ('phantom' cows) detected and did not result in significant differences in concentrations of progesterone in plasma 10 and 18 days after removal of inserts at the first round of AI. Treatment with GnRH reduced the proportion of cows detected in oestrus at the first round of AI (36.2 vs 97.5%; P < 0.001). CONCLUSION: Administration of GnRH compared to ODB at a synchronised pro-oestrus results in similar reproductive performance. Treatment with GnRH reduced the proportion of cows detected in oestrus following treatment. This may offer advantages to the way AI is managed by enabling insemination at a fixed-time and removing the need for the detection of oestrus.     

Genetic and Environmental Correlations Among Female Fertility Traits,and Between the Ability to Show Oestrus and Milk Production in Dairy Cattle

Genetic and environmental correlations were estimated both between the ability to show oestrus and milk production, and among different fertility traits (heat-intensity score, number of days between consecutive inseminations, number of inseminations per service period, interval between calving and first or last insemination, and interval between first and last insemination). Milk production was measured as the average of the energy-corrected milk yield on second and third monthly test days. The number of records were approximately 450000, 350000, 180000 and 75000 in the heifer period, first, second and third lactations, respectively. A linear, trivariate model that included the effects of herd-year, year, month, age and cow's sire was applied. The results indicated that further selection for increased milk production is not expected to deteriorate heat intensity. The number of days between calving and first insemination, the number of inseminations and the heat intensity were complementary, and can be recommended for a selection index for fertility.