Comparison of fertility,regular returns-to-estrus,and calving interval between Ovsynch and CO-synch + CIDR protocols in dairy cows

The main aims of the present study were to compare the pregnancy rate (PR), regular returns-to-estrus, and calving interval of a CO-Synch + controlled internal drug release (CIDR) device, commonly used to synchronize ovulations in beef cows, with the classical Ovsynch protocol in high-producing dairy cows. Holstein-Friesian cows (n = 128) from six commercial dairy herds, ≥40 days postpartum and not previously inseminated, were randomly assigned to one of two treatments. Cows submitted to Ovsynch protocol (group OS as control group; n = 66) received 10 μg of a GnRH analogue 7 days before and 48 hours after 25 mg PGF_2α, followed by artificial insemination (AI) 16 hours after the second GnRH administration. Cows submitted to CO-Synch + CIDR (1.38 g of progesterone) inserted for 7 days beginning at the first GnRH administration (group CoS + CD; n = 62) had the second administration of GnRH concurrent with AI, 64 hours after CIDR removal/PGF_2α administration. Nonpregnant cows with return-to-estrus between 18 and 24 days after first AI were reinseminated (second AI). Logistic regressions were used to analyze PR and returns-to-estrus. No effect of group or herd was observed in PR at first timed AI. However, the sum of cows pregnant at first AI and nonpregnant cows with regular returns-to-estrus and the total PR (first + second AI) were influenced by group treatment. Overall, cows of group CoS + CD (total PR = 56.5%) were 2.1 times more likely to became pregnant after AI and until first regular returns-to-estrus than cows of group OS. The calving interval was lower in group CoS + CD (425.9 ± 78.8 days; ±SD) than in group OS (475.3 ± 83.7 days). The CO-Synch + CIDR protocol was reliable to use in dairy herds and provided reproductive advantages when compared with Ovsynch protocol.     

The use of embryo transfer in the field for increased calf crops in beef and dairy cattle

Non-surgical transfer of one embryo to 63 previously synchronized inseminated recipients was performed on farms to induce twinning in beef and dairy cattle. All the transfers were done by technicians of A.I. centers. After calving, a twinning rate of 44.4% was achieved with no differences between beef Charolais heifers (45.4%), lactating Normande cows (42.8%) and dairy Friesian cows (45.4%). Compared with controls, the calving crop after a three-breeding-cycle period was significantly higher with recipients: 1.16 calf per treated recipient vs. 0.83 calf per control animal. It would seem that the possibility of obtaining about one-third more calves with embryo transfer could be of economical interest to increase meat production from cattle herds.     

Pregnancy outcome in dairy and beef cattle after artificial insemination and treatment with seminal plasma or transforming growth factor beta-1

Reduced capability of the uterus to support pregnancy in the absence of its interaction with secretions from male accessory glands has been demonstrated in rodents and to some extent in pigs. However, in cattle, the role of postmating inflammatory response on pregnancy success has not been studied. The current study examined the influence of uterine presensitization with seminal antigens at breeding on pregnancy outcome in cows. Lactating beef (n = 1090) and dairy (n = 800) cows received 0.5 mL seminal plasma (SP), 40 ng recombinant human transforming growth factor-β1 (rhTGF-β1), or 0.5 mL bovine serum albumin (BSA), or were left untreated before or at insemination. Semen was deposited into the anterior cervix using a second insemination gun. Pregnancy was diagnosed at 35 to 40 d postinsemination by transrectal ultrasonography or from records of calves born the subsequent calving season. Pregnancy rates in beef cows did not differ among treatments but differed among trials (69.8%, 52.5% vs. 40.3%; P < 0.05). In trials where average pregnancy rates were below 50%, treatments with TGF-β1 but not SP tended (P < 0.07) to increase pregnancy rates in beef cows. In dairy cows, SP and TGF-β1 improved pregnancy outcome by 10 percentage points, but these increments did not achieve statistical significance. In conclusion, this study did not find any conclusive evidence for the effect of TGF-β1 or seminal plasma on pregnancy outcome in lactating dairy or beef cows but realized marginal improvements when pregnancy rates were below 50% (compromised fertility).     

Luteal function,largest follicle,and fertility in postpartum dairy cows treated with 14dCIDR-PGF2α versus 2xPGF2α-Ovsynch for timed AI

A method for timed artificial insemination (AI) that is used for beef cows, beef heifers, and dairy heifers employs progesterone-releasing inserts, such as the controlled internal drug release (CIDR; Zoetis, New York, NY, USA) that are left in place for 14 days. The 14-day CIDR treatment is a method of presynchronization that ensures that cattle are in the late luteal phase of the estrous cycle when PGF_2α is administered before timed AI. The objective of this study was to test the effectiveness of the 14dCIDR-PGF_2α program in postpartum dairy cows by comparing it with the traditional “Presynch-Ovsynch” (2xPGF_2α-Ovsynch) program. The 14dCIDR-PGF_2α cows (n = 132) were treated with a CIDR insert on Day 0 for 14 days. At 19 days after CIDR removal (Day 33), the cows were treated with a luteolytic dose of PGF_2α, 56 hours later were treated with an ovulatory dose of GnRH (Day 35), and 16 hours later were inseminated. The 2xPGF_2α-Ovsynch cows were treated with a luteolytic dose of PGF_2α on Day 0 and again on Day 14. At 12 days after the second PGF_2α treatment (Day 26), the cows were treated with GnRH. At 7 days after GnRH, the cows were treated with PGF_2α (Day 33), then 56 hours later treated with GnRH (Day 35), and then 16 hours later were inseminated. There was no effect of treatment or treatment by parity interaction on pregnancies per AI (P/AI) when pregnancy diagnosis was performed on Day 32 (115/263; 43.7%) or Days 60 to 90 (99/263; 37.6%) after insemination. There was an effect of parity (P < 0.05) on P/AI because primiparous cows had lesser P/AI (35/98; 35.7%) than multiparous cows (80/165; 48.5%) on Day 32. Cows observed in estrus after the presynchronization step (within 5 days after CIDR removal or within 5 days after the second PGF_2α treatment) had greater P/AI than those not observed in estrus (55/103; 53.4% vs. 60/160; 37.5%; observed vs. not observed; P < 0.01; d 32 pregnancy diagnosis). When progesterone data were examined in a subset of cows (n = 208), 55.3% of cows had a “prototypical” response to treatment (i.e., the cow had an estrous cycle that was synchronized by the presynchronization treatment and then the cow responded appropriately to the subsequent PGF_2α and GnRH treatments before timed AI). Collectively, cows with a prototypical response to either treatment had 52.2% P/AI that was greater (P < 0.001) than the P/AI for cows that had a nonprototypical response (19%) (P/AI determined at 60–90 days of pregnancy). In conclusion, we did not detect a difference in P/AI when postpartum dairy cows were treated with 14dCIDR-PGF_2α or 2xPGF2α-Ovsynch before timed AI. The primary limitation to the success of either program was the failure of the cow to respond appropriately to the sequence of treatments.     

Risk factors associated with detailed reproductive phenotypes in dairy and beef cows

The objective of this study was to identify detailed fertility traits in dairy and beef cattle from transrectal ultrasonography records and quantify the associated risk factors. Data were available on 148 947 ultrasound observations of the reproductive tract from 75 949 cows in 843 Irish dairy and beef herds between March 2008 and October 2012. Traits generated included (1) cycling at time of examination, (2) cystic structures, (3) early ovulation, (4) embryo death and (5) uterine score; the latter was measured on a scale of 1 (good) to 4 (poor) characterising the tone of the uterine wall and fluid present in the uterus. After editing, 72 773 records from 44 415 dairy and beef cows in 643 herds remained. Factors associated with the logit of the probability of a positive outcome for each of the binary fertility traits were determined using generalised estimating equations; linear mixed model analysis was used for the analysis of uterine score. The prevalence of cycling, cystic structures, early ovulation and embryo death was 84.75%, 3.87%, 7.47% and 3.84%, respectively. The occurrence of the uterine heath score of 1, 2, 3 and 4 was 70.63%, 19.75%, 8.36% and 1.26%, respectively. Cows in beef herds had a 0.51 odds (95% CI=0.41 to 0.63, P<0.001) of cycling at the time of examination compared with cows in dairy herds; stage of lactation at the time of examination was the same in both herd types. Furthermore, cows in dairy herds had an inferior uterine score (indicating poorer tone and a greater quantity of uterine fluid present) compared with cows in beef herds. The likelihood of cycling at the time of examination increased with parity and stage of lactation, but was reduced in cows that had experienced dystocia in the previous calving. The presence of cystic structures on the ovaries increased with parity and stage of lactation. The likelihood of embryo/foetal death increased with parity and stage of lactation. Dystocia was not associated with the presence of cystic structures or embryo death. Uterine score improved with parity and stage of lactation, while cows that experienced dystocia in the previous calving had an inferior uterine score. Heterosis was the only factor associated with increased likelihood of early ovulation. The fertility traits identified, and the associated risk factors, provide useful information on the reproductive status of dairy and beef cows.     

Comparison of artificial insemination and natural service cost effectiveness in dairy cattle

Reproductive efficiency in the dairy herd is the most important factor for its economic success and a major concern for dairy farmers when using artificial insemination (AI) or natural service (NS). Our objectives were to estimate, compare and analyse the costs associated with breeding cattle by do-it-yourself (DIY) AI and NS and identify the factors that influence them, under typical dairy farming conditions in Greece. A simulation study was designed based on data from 120 dairy cattle farms that differed in size (range 40 to 285 cows) and milk production level (4000 to 9300 kg per cow per year). Different scenarios were employed to estimate costs associated directly with AI and NS as well as potentially extended calving intervals (ECI) due to AI. Results showed that bull maintenance costs for NS were €1440 to €1670 per year ($1,820 to $2,111). Direct AI costs were higher than those for NS for farms with more than 30 cows and ECI constituted a considerable additional burden. In fact, amongst the factors that affected the amount of milk needed to cover total extra AI costs, number of days open was the dominant one. Semen, feed and heifer prices had a very small effect. When, hypothetically, use of NS bulls results in a calving interval of 12 months, AI daughters with a calving interval of 13.5 months have to produce about 705 kg of additional milk in order to cover the extra cost. Their actual milk production, however, exceeds this limit by more than 25%. When real calving intervals are considered (13.0 v. 13.7 months for NS and AI, respectively) AI daughters turn out to produce more than twice the additional amount of milk needed. It was concluded that even under less than average management conditions, AI is more profitable than the best NS scenario. The efficient communication of this message should be a primary concern of the AI industry.     

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.     

Does intrauterine site of insemination in cattle really matter?

Two trials were conducted to determine the influence of semen placement on pregnancy rate in dairy heifers and cows. Seventy-two dairy heifers were artificially inseminated (AI) 10 to 12 h after the first detection of estrus. Control heifers (n = 25) were inseminated at the junction of the uterine body and internal cervical os. The remaining heifers were inseminated deep in one uterine horn, 3 to 5 cm anterior to the external bifurcation. Twenty-three heifers were inseminated in the horn ipsilateral to the ovary bearing the ovulatory follicle, and 24 heifers were inseminated in the contralateral horn. Pregnancy rates did not differ for the three groups of heifers. In a second trial, 64 inseminations were performed in 38 nonlactating, adult dairy cattle. Thirty-one inseminations were made deep in the uterine horn ipsilateral to the ovary bearing the ovulatory follicle and 33 in the contralateral horn. Pregnancy rates were similar for both groups. Combining both trials, pregnancy rates for ipsilateral and contralateral inseminations were equal (32 54 = 59% and 34 57 = 60% , respectively). Therefore, placement of semen in one horn of the uterus does not appear to be a cause of decreased or increased pregnancy rate with AI.     

Growth hormone gene polymorphism and reproductive performance of AI bulls

Relationships between the growth hormone gene RFLP polymorphism and bull sperm characteristics were the objects of the present study. DNA was extracted from blood or sperm samples collected from 113 AI bulls and submitted for polymerase chain reaction (PCR) followed by digestion with Alu I restriction enzyme. The bGH genotypes were visualized on 10% polyacrylamide gel. The analyzed population of AI bulls consisted of dairy (Holstein Fresian [HF] crossbred [HF x Polish Black and White]) and beef breeds (Limousine, Charolaise, Piemontese, Angus and Hereford). The frequency of the Leu allele was 0.86 among dairy bulls and 0.38 in beef bulls (0.14 and 0.62 for the Val allele, respectively). Eight sperm characteristics and Day 60 non-return rates (NRR) were analyzed. The 3 genotype groups (LL, VV and LV) and the effect of production type (dairy or beef) on sperm characteristics were considered. None of the traits showed significant variability in relation to the bGH genotype, although a tendency was observed for LL bulls to have a lower ejaculate volume and VV bulls higher NRR. Moreover some statistically significant associations with production type were noticed: beef bulls were superior in sperm concentration and non-return rate, whereas dairy bulls excelled in individual fresh sperm motility.     

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.     

Timing of final GnRH of the Ovsynch protocol affects ovulatory follicle size,subsequent luteal function,and fertility in dairy cows

Synchronization of ovulation (Ovsynch) is an effective method for controlling time of first and subsequent AI in lactating dairy cows. However, validation of the original Ovsynch program did not include testing the optimal time to deliver the final treatment of GnRH. In Experiment 1, the effect of administering the final dose of GnRH on the same day as prostaglandin F2alpha (PGF2alpha) administration was tested. Lactating dairy cows (n = 218) were randomly assigned to receive either Ovsynch (OV; cows were given 100 microg GnRH, then 7 days later cows were administered 25mg PGF2alpha followed by a subsequent treatment of 100 microg GnRH 2 days after the PGF2alpha or the modified version of Ovsynch (MOV; cows were given 100 microg GnRH, then 7 days later cows were administered 25mg PGF2alpha followed immediately with 100 microg GnRH). In both treatment groups, AI took place 16 h after the final administration of GnRH. In Experiment 2, cows (n = 457) were randomly divided into four treatment groups that were administered GnRH 0, 12, 24 and 36 h following PGF(2alpha). The 36 h treatment group served as control. Pregnancy diagnoses were performed by palpation per rectum 36 days post-AI in Experiment 1 and by ultrasonography on Day 28 in Experiment 2. In Experiment 1, pregnancy rate/AI (PR/AI) was greater (P<0.025) in OV versus MOV. In a subset (n = 85), percentage of cows with both synchronized ovulations and regressed CL following administration of PGF2alpha were similar (P>0.1) between OV and MOV, respectively. All cows that became pregnant in the MOV subset group showed regression of the CL in response to the PGF2alpha. Diameter of the ovulatory follicle at the time of final GnRH administration was greater (P<0.05) in OV versus MOV. In Experiment 2, the synchronization rate was once again similar among treatments (P>0.28). There was a linear effect of treatment on follicle size (P<0.05) and PR/AI (P<0.0001) as time increased between administration of PGF2alpha and GnRH, with the greatest PR/AI at 36 h. There was a trend for a greater percentage of cows with short luteal phases in the 0 h group (P<0.10). In summary, delivering the final treatment of GnRH of the Ovsynch program at the same time as PGF2alpha, or in the 24h following PGF2alpha, resulted in lower fertility compared to controls.     

Timed artificial insemination in beef cattle using GnRH agonist, PGF2alpha and estradiol benzoate (EB)

The present work evaluated low-cost protocols for timed artificial insemination (TAI) in beef cattle. In Experiment 1, cycling nonlactating Nelore cows (Bos indicus, n=98) were assigned to the following groups: GnRH-PGF (GP) and GnRH-PGF-GnRH (GPG), whereas cycling (n=328, Experiment 2) or anestrus (n = 225, Experiment 3) lactating (L) cows were divided into 3 groups: GP-L, GPG-L and GnRH-PGF-Estradiol benzoate (GPE-L). In Experiment 4, lactating cows (n=201) were separated into 3 groups: GP-L, GPE-L and G/2PE-L. Animals from Experiment 1, 3 and 4 were treated (Day 0), at random stages of the estrous cycle, with 8 microg of buserelin acetate (GnRH agonist) intramuscularly (i.m.), whereas in Experiment 2 half of the cows received 8 and the other half 12 microg of GnRH (i.m.). Seven days later (D 7) all animals were treated with 25 mg of dinoprost trometamine (PGF2alpha, i.m.) except those cows from the G/2PE-L group which received only 1/2 dose of PGF2alpha (12.5 mg) via intravulvo-submucosa (i.v.s.m.). After PGF2alpha injection the animals from the control groups (GP and GP-L) were observed twice daily to detect estrus and AI was performed 12 h afterwards. The cows from the other groups received a second GnRH injection (D 8 in GPG-L and d9 in GPG groups) or one injection of estradiol benzoate (EB, 1.0 mg, D 8 in GPE-L group). All cows from GPG and GPG-L or GPE-L groups were AI 20 to 24 or 30 to 34 h, respectively, after the last hormonal injection. Pregnancy was determined by ultrasonography or rectal palpation 30 to 50 days after AI. In the control groups (GP and GP-L) percentage of animals detected in heat (44.5 to 70.3%) and pregnancy rate (20 to 42%) varied according to the number of animals with corpus luteum (CL) at the beginning of treatment. The administration of a second dose of GnRH either 24 (Experiment 2) or 48 h (Experiment 1) after PGF2alpha resulted in 47.7 and 44.9% pregnancy rates, respectively, after TAI in cycling animals. However, in anestrus cows the GPG treatment induced a much lower pregnancy rate (14.9%) after TAI. The replacement of the second dose of GnRH by EB (GPE-L) resulted in a pregnancy rate (43.3%) comparable to that obtained after GnRH treatment (GPG-L, 47.7%, Experiment 2). Furthermore, the use of 1/2 dose of PGF2alpha (12.5 mg i.v.m.s., Experiment 4) resulted in pregnancy rate (43.5%) similar to that observed with the full dose (i.m.). Both protocols GPG and GPE were effective in synchronizing ovulation in cycling Nelore cows and allowed approximately a 45% pregnancy rate after TAI. Additionally, the GPE treatment is a promising alternative to the use of GPG in timed AI of beef cattle, due to the low cost of EB when compared to GnRH agonists.     

Influence of sire and sire breed (Gyr versus Holstein) on establishment of pregnancy and embryonic loss in lactating Holstein cows during summer heat stress

Heat stress has negative effects on pregnancy rates of lactating dairy cattle. There are genetic differences in tolerance to heat stress; Bos taurus indicus (B. t. indicus) cattle and embryos are more thermotolerant than Bos taurus taurus (B. t. taurus). In the present study, the effects of sire and sire breed on conception and embryonic/fetal loss rates of lactating Holstein cows during the Brazilian summer were determined. In Experiment 1, cows (n=302) were AI after estrus detection or at a fixed-time with semen from one Gyr (B. t. indicus) or one Holstein sire (B. t. taurus). Pregnancy was diagnosed 80 days after AI. In Experiment 2, cows (n=811) were AI with semen from three Gyr and two Holstein sires. Pregnancy was diagnosed at 30-40 and at 60-80 days after AI. Cows diagnosed pregnant at the first examination but non-pregnant at the second were considered as having lost their embryo or fetus. Data were analyzed by logistic regression. The model considered the effect of sire within breed, sire breed, days postpartum, period of lactation, and AI type (AI after estrus versus fixed-time). There was no effect of the AI type, days postpartum or milk production on conception or embryonic loss rates. The use of Gyr bulls increased pregnancy rate when compared to Holstein bulls [9.1% (60/657) versus 5.0% (23/456), respectively, P=0.008; data from Experiments 1 and 2 combined]. Additionally, in Experiment 2, cows inseminated using semen from sire #4 (Gyr) had lower embryonic loss (10%) when compared with other B. t. indicus (35.3% and 40%) or B. t. taurus sires (18.2% and 38.5%, P=0.03). In conclusion, the use of B. t. indicus sires may result in higher conception rates in lactating Holstein cows during summer heat stress. Moreover, sire can affect embryonic loss and selection of bulls according to this criterion may result in higher parturition rates in lactating Holstein cows.     

Comparison of reproductive performance in Belgian dairy and beef cattle

A computerized program was written to collect, evaluate and compare reproductive performance data of 2004 beef (Belgian Blue breed) and 1649 dairy (Friesian Holstein and German Red) cattle in 35 Belgian herds (6 suckler beef herds, 9 milked beef herds and 20 dairy herds). Reproduction data were collected at monthly herd health visits. No difference in age at first calving was observed. Significant differences were observed among the 3 kinds of herds, and the best results were obtained in dairy herds for the calving interval, interval from calving to the first estrus, interval from calving to the first service and average number of days open. Concerning these parameters, first calvers had lower results than multiparous cows, mainly in suckler and milked beef herds. Significant differences were noted in the number of services per pregnancy. Heifers that had never calved presented the highest fertility. Primiparous beef cows had higher fertility than pluriparous cows. In dairy herds, pluriparous cows had higher fertility than primiparous cows. Estrus detection was better in milked beef herds than in suckled beef and dairy herds. Suckled beef herds had the lowest incidence of metritis and ovarian cysts of the three types of herds. Rates of abortion, overall culling and retained fetal membranes were similar in all the herds. The percentage of animals removed for infertility was highest in milked beef herds and lowest in dairy herds. Because 90% of the 1159 calvings recorded in the beef herds required a caesarean section, the reproductive performance of beef cattle represent results after caesarean section.     

Effect of a single growth hormone (rbST) treatment at breeding on conception rates and pregnancy retention in dairy and beef cattle

Initiation of long-term treatment with rbST (Posilac, Monsanto, St. Louis, MO) coincident with first insemination increased pregnancy rates in dairy cattle, but neither the efficacy of using only the initial injection, nor its effects on retention of pregnancy are known. Lactating dairy cows, dairy heifers, and lactating beef cows were assigned at random to treatment (rbST) or control. Dairy cows, dairy heifers, and beef cows received 500 mg rbST (n = 48, 35, 137 inseminations, respectively) at artificial insemination or were left untreated (n = 62, 33, 130 inseminations, respectively). Pregnancy was diagnosed by ultrasonography at 28-36 days. Treatment with rbST at insemination improved conception rates in dairy cows (60.4% versus 40.3%; P < 0.05), but not in dairy heifers or beef cows. Conception rates did not differ in dairy cows at < or =100 days in milk (DIM), but were improved in cows treated with rbST after 100 DIM (64.3% versus 25.8%; P < 0.05). Retention of pregnancy to approximately 60 days and sizes of CL, diameter of follicles > or =5 mm, and crown-rump lengths of embryos were not affected by treatment. The second objective was to examine the effects of rbST at insemination on birth weight and post-natal calf growth in beef cows. However, birth and weaning weights of beef calves were not affected by treatment. In conclusion, a single treatment with rbST at insemination increased conception rates in dairy cows, specifically in those >100 DIM.     

The effects of feeding broiler litter on microbial contamination of beef carcasses

Two experiments were conducted to test the effects of feeding broiler litter, either directly in the diet or indirectly through pasture-fertilization, to beef cattle on the incidence of Salmonella typhimurium (S) and Escherichia coli O157:H7 (EC) contamination of carcasses and ground beef. In Experiment 1, beef cows (n = 32) were allotted either ad libitum access to grass hay or a formulated diet (80% deep-stacked broiler litter and 20% corn). In Experiment 2, beef cows (n = 32) were assigned to graze on pastures fertilized with a commercial fertilizer or fresh broiler litter. Cows in Experiment 1 were harvested following a 56-d feeding period; whereas, cows in Experiment 2 were harvested after 5, 10, 20, and 40 d of grazing pastures. All samples of muscle, purge, and ground beef were culture-negative for S and EC, suggesting that beef cattle may consume properly handled deep-stacked broiler litter, or pastures fertilized with fresh litter, without increasing the likelihood of carcass/meat contamination with S and (or) EC.     

Postpartum subestrus in dairy cows: comparison of treatment with prostaglandin F2 alpha or GnRH + prostaglandin F2 alpha + GnRH

Two experiments (Experiment 1, 185 cows in 1996/97; Experiment 2, 168 cows in 1997/98) were conducted with Prim Holstein dairy cattle in the Mayenne region of France to investigate subestrus. Cows which had not been observed in estrus since calving were allocated alternately to treatment groups between 60 and 90 d post partum as follows: Experiment 1-Group 1: GnRH (Day 0, 100 micrograms i.m.), PGF2 alpha (Day 7, 25 mg i.m.), GnRH (Day 9, 100 micrograms i.m.) and AI (Day 10); Group 2: PGF2 alpha (Day 0, 25 mg i.m.), AI at estrus, or, if estrus was not observed, a second PGF2 alpha injection on Day 13, and AI on Day 16 and Day 17. Treatments in Experiment 2 were as follows: Group 1: as Experiment 1-Group 1 but AI at the observed estrus after Day 0, or at Day 10 if estrus was not observed; Group 2: as Experiment 1--Group 2, however, if a second PGF2 alpha injection was given on Day 13, AI at the observed estrus. Progesterone was measured in serum at Day 0 and in milk at AI. Pregnancy diagnosis was performed by measuring bovine pregnancy-specific protein B (bPSPB; Day 50 +/- 3) and confirmed by ultrasonography when the result was doubtful. In Experiment 1, farmers observed 47/101 (46.9%) Group 1 cows in estrus, 33/91 cows on Day 10 and 10 cows before Day 10. The progesterone concentrations were compatible with estrus in 69/86 (80%) cows on Day 10. In Group 2, 36/83 (43.4%) cows were inseminated after the first PGF2 alpha injection. After the second PGF2 alpha injection, only 29/43 (67%) cows had a low progesterone concentration at AI. Pregnancy rates were 36.1 and 32.5% for Groups 1 and 2, respectively. In Experiment 2, estrus was observed in 31/93 (33.7%) Group 1 cows. In Group 2, 51/75 (66%) cows were inseminated after the first injection of PGF2 alpha, 13/75 (17.3%) cows after the second injection, while 11/75 (14.7%) were not observed in estrus. Pregnancy rates were 53.7 and 53.3% in Groups 1 and 2, respectively. In conclusion, it is recommended that subestrus be treated with PGF2 alpha followed by AI at the observed estrus when estrus detection is good, while the use of GnRH + PGF2 alpha + GnRH is recommended when estrus detection is poor.     

Factors affecting the fertility of high producing dairy herds in northeastern Spain

Infertility has been often correlated to a rising milk yield in high producing dairy cattle. The aim of the present study was to evaluate, using logistic regression procedures, the effects of several management indicators on the fertility of four dairy herds in northeastern Spain. Data derived from 10,965 artificial insemination (AI). The factors examined were: herd, milking frequency (three versus two milkings per day), lactation number, previous twinning and disorders such as placenta retention and pyometra, milk production at AI, the inseminating bull, season (warm versus cool period) and year effects, AI technician and repeat breeding syndrome (cows undergoing four or more AI). Our findings indicated no effects on fertility of the herd, year of AI, previous twining, placenta retention and pyometra and milk production at AI. Based on the odds ratios, the likelihood of pregnancy decreased: in cows milked three times per day (by a factor of 0.62); for each one unit increase in lactation number (by a factor of 0.92); for inseminations performed during the warm period (by a factor of 0.67); in repeat breeder cows (by a factor of 0.73); and when 3 of the 45 inseminating bulls included in the study were used (by factors of 0.35, 0.43 and 0.44, respectively). Of the 13 AI technicians participating in the study, 3 were related to a fertility rate improved by odds ratios of 1.86, 1.84 and 1.30, respectively, whereas 2 technicians gave rise to fertility rates reduced by odds ratios of 0.64 and 0.49, respectively. Under our study conditions, management practices were able to compensate for the effects of previous twining and reproductive disorders such as placenta retention and pyometra. However, fertility was significantly affected by the factors milking frequency, AI technician, inseminating bull, repeat breeding syndrome, lactation number and AI season.     

Seasonal effects of semen collection and artificial insemination on dairy cow conception

The effects of four seasons of semen collection and of artificial insemination on conception in dairy cows were studied. The solstices and equinoxes (December, March, June and September) defined the beginning and/or end of each season. Semen was collected from 973 progeny-test bulls over 8 years at the two Norwegian AI stations at 60.8 degrees N and 63.4 degrees N where artificial light was used to provide a minimum photoperiod of 10 h/day. The effect of using semen of elite bulls during progeny testing and after selection as elite sires also was investigated. Norwegian Red (NRF) cows were inseminated over a 7-year period using progeny test semen and over the last 4 years of the same period using the semen of the elite sires. The probability of conception to only first inseminations for cows up to, and including, the fifth lactation was assessed by 56-day non-return rate (56d NRR) and calving rate. Two data sets were analysed which excluded cows culled within 270 days of AI or included such cows as non-calving. The reasons for culling were categorised as those for fertility problems or all other reasons. Semen was used for AI irrespective of the season in which it had been collected. Season of semen collection did not affect 56d NRR but calving rate was significantly higher (by 0.5-0.8%, approximately; P < 0.01) for semen collected in the December-March period, when photoperiod was increasing, than at other times of the year. The season in which AI was performed showed a peak of 56d NRR in spring for heifers (P < 0.01) and in summer for parous animals (P < 0.01). For calving rate, however, no seasonal peak was found in heifers, whereas pluriparous cows had much higher calving rates in summer and autumn/early winter than late winter and spring (P < 0.01). Semen of elite sires resulted in higher calving rates by 0.5 (NS) to 1.9% (P < 0.01) when used after selection than when used during progeny testing. The difference between the calving rate achieved when the semen from elite sires was used during progeny testing and after selection indicates that farmers select different classes of cows for submission to AI by progeny test bulls and sires. The 56d NRR was not as good as calving rate for assessing seasonal and other effects on conception 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.