Evidence that mastitis can cause pregnancy loss in dairy cows: A systematic review of observational studies

The objective of this study was to conduct a systematic review to identify and assess evidence and knowledge gaps in published observational studies that have investigated the relationship between mastitis and pregnancy loss (PL) in dairy cows. PubMed and ScienceDirect were used to search pertinent peer-reviewed research reports of interest. Screening of research reports was conducted at 3 levels: titles, abstracts, and full-text articles. The search identified 651 records for initial screening. The final screening process identified 8 qualified articles for review after removing 10 duplicate records, 582 titles, 31 abstracts, and 20 full-text articles. Two studies produced strong epidemiologic evidence indicating that (1) exposure to clinical mastitis during early gestation (first 45 d of gestation) is associated with subsequent PL during the following 90 d; and (2) subclinical mastitis 1 to 30 d before artificial insemination (AI) is associated with subsequent PL at 35 to 41 d of gestation. An additional study showed that exposure to clinical mastitis during early lactation in combination with low body condition can increase the risk of PL in dairy cows; however, the interaction effect between clinical mastitis and low body condition on PL was considered weak. Four other studies produced inconclusive evidence indicating that mastitis is a predisposing factor for PL in dairy cows, as the exposure risk period for mastitis overlapped with the follow-up period for diagnosis of PL in dairy cows. Finally, one study failed to identify a relationship between mastitis and PL in dairy cows. Further research is needed to (1) support the hypothesis that mastitis in combination with low body condition score (or other exposure factors) can increase the risk of PL, (2) compare the effect of clinical versus subclinical mastitis on PL, (3) compare the effect of mastitis before breeding and during gestation on PL, and (4) compare the effect of mastitis on PL in dairy cows during different lactations.     

Lying behavior and postpartum health status in grazing dairy cows

Many cows have difficulty making the transition from pregnancy to lactation, as evidenced by the high incidence of disease that occurs in the weeks after calving. Changes in lying behavior can be used as an indicator of illness, yet no work to date has evaluated this relationship in dairy cows on pasture. The objectives of this study were to describe the lying behavior of grazing dairy cows during the first 3 wk after calving and determine the relationships between transition diseases and lying behavior. Our convenience sample included 227 multiparous and 47 primiparous Holstein cows from 6 commercial farms. Cows were recruited as they calved during the spring calving period. Electronic data loggers (Hobo Pendant G Acceleration, Onset Computer Corp., Pocasset, MA) recorded lying behavior at 1-min intervals. Diseases were recorded up to 21 d in milk, and cows were subsequently categorized into 3 health categories: (1) healthy, not lame and had no other signs of clinical (retained placenta, milk fever, metritis, mastitis) or subclinical (ketosis, hypocalcemia) postpartum diseases; (2) lame, identified as being clinically or severely lame with no other signs of clinical or subclinical postpartum disease; and (3) sick, diagnosed as having one or more clinical postpartum diseases (with or without a subclinical disease) but not lame. This last group was further divided into 2 groups: those that were diagnosed with a single clinical health event and those diagnosed with more than one clinical event. Lying behavior differed between primiparous and multiparous cows; primiparous cows divided their lying time into more bouts than did multiparous cows (9.7 ± 0.54 vs. 8.4 ± 0.26 bouts/d) and spent less time lying down than multiparous cows (7.5 ± 0.38 h/d vs. 8.5 ± 0.19 h/d). Lying behavior was also affected by illness; primiparous cows that developed more than one clinical disease, excluding lameness, spent more time lying, and tended to have longer lying bouts in the days following calving compared with healthy cows; multiparous severely lame cows spent more time lying down (1.7 h longer per day) compared with multiparous cows that were nonlame. Clinically lame cows had fewer lying bouts per day and these bouts were of longer duration than healthy nonlame cows. In summary, changes in lying behavior after calving were associated with postpartum health status in grazing dairy cows.     

Effect of interval from timed artificial insemination to initiation of resynchronization of ovulation on fertility of lactating dairy cows

To compare 2 strategies for systematically resynchronizing ovulation, lactating Holstein cows (n = 763) at various days in milk and prior artificial insemination services were assigned randomly at timed AI (TAI) to receive the first GnRH injection of Ovsynch 26 (D26) or 33 (D33) d after TAI to resynchronize ovulation (Resynch) in cows failing to conceive. Cows in the D26 treatment received GnRH 26 d after TAI and continued Resynch only when diagnosed not pregnant by using ultrasonography 33 d after TAI, whereas D33 cows initiated Resynch only when diagnosed not pregnant 33 d after TAI. Cows were classified based on the presence or absence of a corpus luteum (CL) at the not-pregnant diagnosis, and cows without a CL received an intravaginal progesterone-releasing insert during Resynch. When analyzed as a systematic strategy, pregnancy rate per AI (PR/AI) was greater for cows assigned to the D33 than the D26 Resynch treatment (39.4 vs. 28.6%). A treatment × parity interaction was detected for PR/AI after Resynch for nonpregnant cows having a CL in which primiparous cows had a greater PR/AI than multiparous cows when Resynch was initiated 33 d after the initial TAI, and primiparous and multiparous cows when Resynch was initiated 26 d after the initial TAI. Pregnancy loss for Resynch was 6.4% between 33 and 40 d, and 2.6% between 40 and 61 d after Resynch TAI. We concluded that delaying initiation of Resynch until 33 d after TAI increased PR/AI for primiparous cows.     

Association of CXCR2 polymorphisms with subclinical and clinical mastitis in dairy cattle

The ability to identify objectively cows that are more or less susceptible to mastitis has been a long-standing goal. Genetic markers associated with inflammatory responses during mastitis could aid in selection of these cattle. One potential marker is CXCR2, a chemokine receptor required for neutrophil migration to infection sites, which contains single nucleotide polymorphisms (SNP) within the gene. The objective of this experiment was to evaluate the association of CXCR2 SNP genotypes with subclinical and clinical mastitis. Thirty-seven Holstein and 42 Jersey cows that completed at least 2 full lactations were used. Quarter foremilk samples were collected for bacteriological examination quarterly and when cows exhibited clinical mastitis. Subclinical mastitis was defined as the presence of the same pathogen in the same quarter in at least 2 of 3 consecutive samples. A significant association was detected between CXCR2 SNP +777 genotype and percentages of subclinical mastitis cases in Holsteins. Holsteins expressing genotype GG had decreased percentages of subclinical mastitis, but genotype CC cows had increased percentages of subclinical mastitis. Significant differences in clinical mastitis incidence were not detected between genotypes for either breed. This approach of genetically identifying mastitis resistant cows may represent an effective means of marker-assisted selection for mastitis and other inflammatory diseases involving neutrophils.     

Clinical mastitis associated with abortion in dairy cows.

The objective of this study was to assess the association between clinical mastitis and abortion during early gestation in lactating dairy cows. During the study period, there were 2087 cows diagnosed pregnant, 60 cases of clinical mastitis, and 127 cases of abortion. Logistic regression was used to evaluate the association between the occurrence of mastitis and subsequent abortion. This study found that cows that had clinical mastitis during the first 45 d of gestation were at 2.7 (95% confidence interval = 1.3 to 5.6) times higher risk of abortion within the next 90 d than were cows without mastitis. Cows with a calving to conception interval > 174 d were at lower risk (43%) of abortion compared with cows with a calving to conception interval < 79 d (odds ratio = 0.6; 95% confidence interval = 0.3 to 0.9). Conception on a breeding detected by secondary signs of estrus was also significantly associated with increased risk of abortion (odds ratio = 1.7; 95% confidence interval = 1.1 to 2.8). No significant association was found between parity, breeding season, or milk production or use of prostaglandin F2 to induce successful estrus and subsequent abortion.     

Impact of age at calving on lactation, reproduction, health, and income in first-parity Holsteins on commercial farms

The objective was to examine milk production, health, and economic performance among Holstein heifers during first lactation on 3 commercial dairy farms in California. Heifers (n = 1905) were moved to the breeding group between 360 and 390 d of age and grouped retrospectively according to age at first calving (AFC) as low (< or =700 d), medium (701 to 750 d), and high (> or =751 d). Within farm, growing heifers were managed similarly, as were lactating primiparous cows, for the first 310 d in lactation. Heifers were fed to gain 0.70 to 0.80 kg/d from 4 mo of age to breeding, and 0.8 to 0.9 kg/d from breeding to 252 to 258 d of pregnancy. First calving at <700 d was associated with reduced yields of milk and milk components. Cows in the high age group produced more milk fat and true protein than medium and low cows. Incidence of stillbirths was highest for cows in the low group (19.8%), but stillbirths were also a concern for those calving at medium (16.1%) or high age groups (13.5%). Both low and high cows had lower conception rates at first postpartum AI, and abortions averaged 9.8% across groups. Days open and number of inseminations were lower for medium than low cows. Incidence of mastitis and lameness was lowest for cows in the medium group. Culling and mortality rates were not affected by AFC, but among those that died, cows in the low group tended to die earlier postpartum than cows in the high group. Heifers in the medium group had an adjusted income value numerically higher by 138.33 dollars and 98.81 dollars compared with those in the low and high groups, respectively. First calving at <700 d compromised first lactation yields of milk and milk components and impaired reproductive performance. However, extending AFC beyond 750 d did not improve lactation, reproduction, or health of primiparous cows. Although not preassigned to age groups before start of breeding, Holstein heifers managed as in this study had the highest economic return when calving between 23 and 24.5 mo of age.     

Pegbovigrastim treatment resulted in an economic benefit in a large randomized clinical trial in grazing dairy cows

This randomized controlled trial on 4 commercial grazing dairy farms investigated whether pegbovigrastim (PEG) treatment affected partial net return as calculated from milk revenues and costs for feed, medical treatments [clinical mastitis, uterine disease, and other diseases (i.e., any medical treatment that was not intended for clinical mastitis or uterine disease)], inseminations, and culling during a full lactation in grazing dairy cows. We also explored the effect of potential interactions of PEG treatment with parity, prepartum body condition score, and prepartum nonesterified fatty acids concentration on partial net return, milk revenues, and the costs mentioned above. Holstein cows were randomly assigned to 1 of the 2 following trial arms: a first PEG dose 9.4 ± 0.3 (mean ± standard error) days before the calving date and a second dose within 24 hours after calving (PEG: primiparous = 342; multiparous = 697) compared with untreated controls (control: primiparous = 391; multiparous = 723). The effect of PEG treatment on the outcomes of interest expressed per year was tested using general linear mixed models. Results are presented as least squares means ± standard error. Overall, PEG treatment increased the partial net return, resulting in an economic benefit per cow per year of $210 ± 100. The cost of treatment of clinical mastitis was lower for PEG treated cows compared with control cows ($9 ± 3). The largest nonsignificant difference was seen for the cost of culling; additionally, PEG treatment numerically reduced the cost of culling by $145 ± 77.     

Economic performance of lactating dairy cows submitted for first service timed artificial insemination after a voluntary waiting period of 60 or 88 days

The objective of this study was to evaluate the economic performance of dairy cows managed with a voluntary waiting period (VWP) of 60 or 88 d. A secondary objective was estimating variation in cash flow under different input pricing scenarios through stochastic Monte Carlo simulations. Lactating Holstein cows from 3 commercial farms were blocked by parity group and total milk yield in their previous lactation and then randomly assigned to a VWP of 60 (VWP60; n = 1,352) or 88 d (VWP88; n = 1,359). All cows received timed-artificial insemination (TAI) for first service after synchronization of ovulation with the Double-Ovsynch protocol. For second and greater services, cows received artificial insemination (AI) after detection of estrus or the Ovsynch protocol initiated 32 ± 3 d after AI. Two analyses were performed: (1) cash flow per cow for the calving interval of the experimental lactation and (2) cash flow per slot occupied by each cow enrolled in the experiment for an 18-mo period after calving in the experimental lactation. Extending the VWP from 60 to 88 d delayed time to pregnancy during lactation (～20 d) and increased the risk of leaving the herd for multiparous cows (hazard ratio = 1.21). As a result, a smaller proportion of multiparous cows calved again and had a subsequent lactation (?6%). The shift in time to pregnancy combined with the herd exit dynamics resulted in longer lactation length for primiparous (22 d) but not multiparous cows. Longer lactations led to greater milk income over feed cost and a tendency for greater cash flow during the experimental lactation for primiparous but not multiparous cows in the VWP88 group. On the other hand, profitability per slot for the 18-mo period was numerically greater ($68 slot/18 mo) for primiparous cows but numerically reduced (?$85 slot/18 mo) for multiparous cows in the VWP88 treatment. For primiparous cows most of the difference in cash flow was explained by replacement cost, whereas for multiparous cows it was mostly explained by differences in replacement cost and income over feed cost. Under variable input pricing conditions generated through stochastic simulations, the longer VWP treatment always increased cash flow per 18 mo for primiparous and reduced cash flow for multiparous cows. In conclusion, extending the duration of the VWP from 60 to 88 d numerically increased profitability of primiparous cows and reduced profitability of multiparous cows. Such an effect depended mostly on the herd replacement dynamics and milk production efficiency.     

Increased fertility in lactating dairy cows resynchronized with Double-Ovsynch compared with Ovsynch initiated 32 d after timed artificial insemination

The objective was to determine if using a Double-Ovsynch protocol [DO; Pre-Resynch: GnRH-7 d-PGF(2α)-3 d-GnRH, 7 d later Breeding-Resynch: GnRH-7 d-PGF(2α)-56 h-GnRH-16 h-timed artificial insemination (TAI)] to resynchronize ovulation after a previous TAI would increase synchrony and pregnancies per AI (P/AI) compared with an Ovsynch protocol initiated 32 d after TAI (D32; GnRH-7 d-PGF(2α)-56 h-GnRH-16 h-TAI). Lactating Holstein cows at various days in milk and prior AI services were blocked by parity and randomly assigned to resynchronization treatments. All DO cows received the first GnRH injection of Pre-Resynch 22 d after TAI, and cows (n=981) diagnosed not pregnant using transrectal ultrasonography 29 d after TAI continued the protocol. Pregnancy status for all D32 cows was evaluated 29 d after TAI so fertility and pregnancy loss could be compared with that of DO cows. All D32 cows received the first GnRH injection of Ovsynch 32 d after TAI, and cows (n=956) diagnosed not pregnant using transrectal palpation 39 d after TAI continued the protocol. In a subgroup of cows from each treatment, ultrasonography (n=751) and serum progesterone (P4) concentrations (n=743) were used to determine the presence of a functional corpus luteum (CL) and ovulation to the first GnRH injection of D32 and Breeding-Resynch of DO (GnRH1), luteal regression after PGF before TAI, and ovulation to the GnRH injection before TAI (GnRH2). Overall, P/AI 29 d after TAI was not affected by parity and was greater for DO compared with D32 cows (39 vs. 30%). Pregnancy loss from 29 to 74 d after TAI was not affected by parity or treatment. The percentage of cows with a functional CL (P4 ≥1.0 ng/mL) at GnRH1 was greater for DO than D32 cows (81 vs. 58%), with most DO cows having medium P4 (60%; 1.0 to 3.49 ng/ml), whereas most D32 cows had either low (42%; <1.0 ng/mL) or high (36%; ≥3.5 ng/mL) P4 at GnRH1. Ovulation to GnRH1 was similar between treatments but was affected by serum P4 at GnRH. Cows with low P4 (<1.0 ng/mL) had the greatest ovulatory response (59%), followed by cows with medium (≥1.0 to 3.49 ng/mL; 38%) and then high (≥3.50 ng/mL; 16%) P4 at GnRH1. A greater percentage of DO cows were synchronized compared with D32 cows (72 vs. 51%) primarily due to a greater percentage of D32 than DO cows without a functional CL at the PGF injection before TAI (35 vs. 17%) or without complete CL regression before GnRH2 (17 vs. 7%). We conclude that DO increased fertility of lactating dairy cows during a resynchronization program primarily by increasing synchronization of cows during the Ovsynch protocol before TAI.     

Influence of subclinical mastitis during early lactation on reproductive parameters.

Our objective was to determine the effects of mastitis during early lactation on the reproductive performance of Jersey cows. From 1986 to 1997, quarter foremilk samples were collected every 4 to 8 wk during lactation, at drying off, near calving, and when clinical mastitis was diagnosed and were evaluated microbiologically to identify causative bacteria. Services per conception, days open, and days to first service were obtained from DHIA records on 752 cows. Cows were separated by mastitis type (clinical, n = 186; subclinical, n = 240; control, uninfected or infected after confirmed pregnancy, n = 326). Cows were reclassified based on the time of clinical or subclinical mastitis as follows: period 1, before first service (n = 374); period 2, between first service and pregnancy (n = 52); and period 3, after confirmed pregnancy or uninfected (control; n = 326). Milk production did not differ for any group separations. Reproductive performance did not differ between gram-negative or gram-positive mastitis pathogens. Cows with clinical or subclinical mastitis before first service had increased days to first service (77.3+/-2.7 and 74.8+/-2.7 d), days open (110.0+/-6.9 and 107.7+/-6.9 d), and services per conception (2.1+/-0.2 and 2.1+/-0.2) compared with controls (67.8+/-2.2 d, 85.4+/-5.8 d, 1.6+/-0.2; P < 0.05). Days to first service were not increased in cows with clinical or subclinical mastitis during period 2 (70.6+/-3.3 and 61.2+/-7.8 d). However, days open (143.6+/-8.5 d) and services per conception (3.0+/-0.2) were increased (P < 0.05) in cows with clinical mastitis during period 2, but not in cows with subclinical mastitis (90.9+/-20.2 d and 2.1+/-0.5). Cows initially diagnosed subclinical that became clinical during period 2 exhibited increased days to first service (93.9+/-10.1 d), days open (196.0+/-26.2 d), and services per conception (4.3+/-0.7) compared with control animals (P < 0.05). In conclusion, subclinical mastitis reduced reproductive performance of lactating cows similar to clinical mastitis. Subclinical mastitis followed by clinical mastitis resulted in the most severe loss in reproductive performance.     

Comparison of reproductive performance in lactating dairy cows bred by natural service or timed artificial insemination

The objective of this study was to compare reproductive performance of lactating dairy cows bred by natural service (NS) or timed AI (TAI). One thousand fifty-five cows were blocked by parity and enrolled to receive either NS or TAI. Cows in both groups were presynchronized with 2 injections of PGF_2α given at 42 and 56 d postpartum. Fourteen days after the last PGF_2α injection, cows in the TAI group were enrolled in an Ovsynch protocol (d 0 GnRH; 7 d later, PGF_2α; 56 h after PGF_2α injection, second dose of GnRH; and 16 h after second GnRH cows were TAI). Cows in the TAI group were resynchronized with an intravaginal insert containing progesterone inserted 18 d after TAI and removed 7 d later when GnRH was given. Cows were examined by ultrasonography on d 32 after TAI; nonpregnant cows received PGF_2α and GnRH 56 h later followed by TAI 16 h after the GnRH injection. Nonpregnant cows in TAI group were reinseminated up to 5 times using the same scheme. Cows in the NS group were exposed to bulls 14 d after the second PGF_2α injection, and ultrasonography was performed 42 d after exposure to bulls to determine pregnancy status. Nonpregnant cows in the NS group were reexamined by transrectal palpation combined with ultrasound every 28 d until diagnosed pregnant or 223 d postpartum, whichever occurred first. Cows diagnosed pregnant in TAI or NS were reconfirmed 28 d later to determine pregnancy loss. All bulls underwent an evaluation of breeding soundness and were rested for 14 d after 14 d of cow exposure. Health disorders were evaluated up to 70 d postpartum, and body condition score was evaluated at d 70 postpartum. Blood was collected on d 56 and 65 postpartum and analyzed for progesterone to determine cyclicity. The proportion of pregnant cows in the first 21 d of breeding did not differ between groups. The overall 21-d cycle pregnancy rate (PR), which included a total of 8 and 5 service opportunities for NS and TAI, respectively, was not different between groups (25.7 and 25.0% for NS and TAI, respectively). The daily rate of pregnancy was 15% greater for NS than TAI because cows in NS had a greater PR, which resulted in fewer median days open (111 vs. 116 d). Proportion of pregnant cows at 223 d postpartum was greater in the NS than TAI group (84.2 vs. 74.8%, respectively). Cyclicity did not affect reproductive performance. Cows with body condition score ≥2.75 had greater proportion of pregnant cows in the first 21 d of breeding and daily PR in the first 223 d postpartum Primiparous cows had greater proportion of pregnant cows and daily PR than multiparous cows at 223 d postpartum. In conclusion, the greater proportion of pregnant cows in the NS group was attributed to more opportunities for breeding than in the TAI group.     

Association between serum calcium dynamics around parturition and common postpartum diseases in dairy cows

The objective of this study was to compare periparturient serum Ca dynamics (CaDyn) in cows with and without diseases in early lactation. The study enrolled 1,949 cows from a commercial dairy farm in northern Germany. Blood samples were drawn 7 d before expected calving date and on d 0, 1, 3, and 7 after calving and analyzed for serum Ca concentration. Cows were monitored for clinical hypocalcemia (CH), ketosis, left displaced abomasum (LDA), retained placenta, acute puerperal metritis (APM), mastitis, and pneumonia. To evaluate the association between CaDyn and diseases during the transition period, repeated measures ANOVA with first-order autoregressive covariance were performed. Serum CaDyn of healthy cows (i.e., without any of the aforementioned diseases) was compared with CaDyn of cows with one of the aforementioned diseases (CH, ketosis, APM, mastitis, LDA, and pneumonia), and cows with multiple diseases (CH+, ketosis+, APM+, mastitis+, LDA+, and pneumonia+). Separate models were built for primiparous and multiparous cows. For primiparous cows, we evaluated the association between CaDyn and ketosis (healthy cows vs. cows with ketosis vs. cows with ketosis+) and CaDyn and APM (healthy cows vs. cows with APM vs. cows with APM+). The same models were built for multiparous cows. Three additional models were built for multiparous cows to evaluate the association between CaDyn and CH (healthy cows vs. cows with CH vs. cows with CH+), mastitis (healthy cows vs. cows with mastitis vs. cows with mastitis+), or LDA (healthy cows vs. cows with LDA vs. cows with LDA+). In primiparous cows, serum Ca concentrations of cows with ketosis, APM, and APM+ were significantly reduced on d 3 and 7 after calving, compared with healthy cows. Serum Ca concentrations of primiparous cows with ketosis+ were reduced on d 3, but not on d 7 after calving. Multiparous cows with CH had significantly reduced serum Ca concentrations on d 0, 1, and 3 compared with healthy cows. On d 3 and 7, serum Ca concentration of CH+ cows was significantly reduced compared with healthy multiparous cows. Multiparous cows with ketosis and ketosis+ had significantly reduced serum Ca concentrations on d 1 and 3 compared with healthy cows. Cows with APM+ had significantly increased serum Ca concentrations on d 0 and reduced serum Ca concentrations on d 3, compared with healthy cows. Whereas multiparous cows with mastitis had a reduced serum Ca concentration on d 1, mastitis+ cows had a reduced serum Ca concentration on d 1 and 3, compared with healthy multiparous cows. Overall, multiparous cows with LDA+ had reduced serum Ca concentrations. Especially a delayed onset of hypocalcemia (d 3 and 7) was indicative for the development of disease in primiparous cows. In multiparous cows, reduced serum Ca concentrations on d 1 and 3 were associated with occurrence of diseases. Future studies should evaluate whether reduced serum Ca concentrations are a cause or concomitant circumstance of diseases in early lactation.     

Brown Swiss × Holstein crossbreds compared with pure Holsteins for calving traits, body weight, backfat thickness, fertility, and body measurements

Brown Swiss × Holstein crossbred cows and pure Holstein cows were compared in a designed experiment. All cows were housed in a freestall barn at the experimental station of the federal state of Saxony-Anhalt, Germany, and calved from July 2005 to August 2008. Brown Swiss × Holstein crossbred cows were mated to Holstein AI bulls for first calving and mated to Fleckvieh artificial insemination (AI) bulls for second and third calvings. Pure Holstein cows were consistently mated to Holstein AI bulls. At first calving, Holstein-sired calves from Brown Swiss × Holstein crossbred dams (282 d) had longer gestation length than Holstein-sired calves from Holstein dams (280 d). For second and third calvings, gestation length was significantly longer for Fleckvieh-sired calves from Brown Swiss × Holstein crossbred dams (284 d) than for Holstein-sired calves from Holstein dams (278 d). Holstein-sired calves from Brown Swiss × Holstein crossbred dams (43 kg) and Holstein-sired calves from pure Holstein dams (42 kg) were not significantly different for calf weight at birth for first calving. For second and third calvings, Fleckvieh-sired calves from Brown Swiss × Holstein crossbred dams (50 kg) had significantly heavier calf weight at birth than Holstein-sired calves from pure Holstein dams (44 kg). For calving difficulty and stillbirth, Brown Swiss × Holstein crossbred cows were not different from pure Holstein cows at first calving or at second and third calving. Brown Swiss × Holstein crossbred cows (71 d) were not significantly different from pure Holstein cows (75 d) for days to first breeding during first lactation; however, Brown Swiss × Holstein crossbred cows (81 d) had significantly fewer days to first breeding than pure Holstein cows (89 d) during second lactation, and the crossbred cows (85 d) tended to have fewer days to first breeding than pure Holstein cows (92 d) during third lactation. For days open, Brown Swiss × Holstein crossbred cows were not significantly different than pure Holstein cows during any of the first 3 lactations. For body weight, Brown Swiss × Holstein crossbred cows were significantly heavier than pure Holstein cows during first lactation (621 kg versus 594 kg) and second lactation (678 kg versus 656 kg). Also, Brown Swiss × Holstein crossbred cows (18.20 mm) had significantly more backfat thickness than pure Holstein cows (15.81 mm) during first lactation. Brown Swiss × Holstein crossbred cows (48 cm) had significantly greater chest width than pure Holstein cows (46 cm). Furthermore, Brown Swiss × Holstein crossbred cows had significantly longer front heel walls (5.2 cm versus 5.0 cm), significantly longer rear heel walls (4.2 cm versus 4.0 cm), and significantly more depth of the front heel (4.4 cm vs. 4.1 cm) than pure Holstein cows. This study has shown that F₁ of Brown Swiss × Holstein cows are competitive with pure Holstein cows for all traits analyzed here. For fertility, crossbred Brown Swiss × Holstein cows exhibited fewer days to first breeding during second lactation than pure Holstein cows.     

Economic losses associated with mastitis due to bovine leukemia virus infection

Bovine leukemia virus (BLV), which causes enzootic bovine leukosis and immunosuppression, is widely prevalent on Japanese dairy farms. However, in the absence of a national eradication scheme with compensation programs, it is important to estimate BLV-associated economic losses to raise farmers' awareness. Mastitis (includes both clinical and subclinical) is a common disease in the dairy industry and the most common reason for culling. We hypothesized that immunosuppression due to BLV predisposes subclinical mastitis. A retrospective cohort study was conducted to trace Holstein cows at 9 commercial dairy farms in the Nemuro and Kushiro regions of Hokkaido Prefecture, Japan, where monitoring of BLV proviral load is routine. Information regarding Dairy Herd Improvement data, parity number, and delivery day was collected at each farm. Cows with no confirmed infection with BLV during lactation were defined as non-infected. Low-proviral-load and high-proviral-load (H-PVL) cows were defined as those in which proviral load was below and over 2,465 copies/50 ng of DNA, respectively, or 56,765 copies/10⁵ cells, respectively, throughout the lactation period. Survival analysis was performed using the frailty model to estimate the hazard ratio of subclinical mastitis for BLV infection status using data from 1,034 dairy cows after adjusting for parity number and delivery season as confounding factors. Kaplan–Meier survivor curves demonstrated that half of the H-PVL cows developed subclinical mastitis within 52 d after calving. The hazard ratio of subclinical mastitis for H-PVL cows was 2.61 times higher than that of non-infected cows. In 2017, there were 264,443 clinical mastitis cases in Hokkaido. Using field and published data, annual economic losses were estimated using Monte Carlo simulation. The economic loss due to mastitis associated with BLV infection per H-PVL cow was $418.59 (¥43,952), with the annual economic loss in Hokkaido Prefecture due to mastitis caused by BLV infection estimated at $6,097,225 (¥640,208,633). In summary, H-PVL cows were more susceptible to subclinical mastitis than non-infected and low-proviral-load cows, and mastitis due to BLV infection was projected to cause significant economic losses.     

Environmental factors affecting the conception rates of nulliparous and primiparous dairy cattle

Dairy cattle must allocate energy to milk production and reproduction. Therefore, understanding the environmental factors that affect conception rates in nulliparous and primiparous cows is helpful in appropriate feeding management strategies before and after calving. Accordingly, the aim of this study was to investigate the influence of environmental factors before and after the first calving on the conception rate, representing the starting point of milk production. The records of the first artificial insemination (AI) from Holstein nulliparous cows (n = 533,672) and primiparous cows (n = 516,710) in Hokkaido, Japan, were analyzed using separate multivariable logistic regression models. The mean conception rates for nulliparous and primiparous cows from 2012 to 2018 were 55.2 and 39.2%, respectively. In both nulliparous and primiparous cows, the conception rate of crossbreeding using Japanese Black (JB) semen was significantly higher than that for purebred Holstein breeding. The conception rate using sexed semen decreased in the warmer months only in nulliparous cows. Moreover, we grouped primiparous cows according to milk yield during peak lactation (PY; < 25, 25–30, 30–35, ≥35 kg) and the interval from calving to first insemination (CFI; < 60, 60–79, 80–99, ≥100 d), and evaluated their combined effect on the conception rate. Both PY and CFI strongly affected the conception rate in primiparous cows, which decreased with an increase in PY, even for the group with CFI ≥100 d; however, the conception rate increased for a CFI ≥60 d regardless of PY. Taken together, this study demonstrates the long-term effect of PY and an independent effect of CFI on the conception rate of cows. These results provide guidance for management to execute appropriate AI implementation strategies before and after lactation.     

Targeted reproductive management for lactating Holstein cows: Reducing the reliance on exogenous reproductive hormones

Adoption of automated monitoring devices (AMD) affords the opportunity to tailor reproductive management according to the cow's needs. We hypothesized that a targeted reproductive management (TRM) would reduce the use of reproductive hormones while increasing the percentage of cows pregnant 305 d in milk (DIM). Holstein cows from 2 herds (n = 1,930) were fitted with an AMD at 251.0 ± 0.4 d of gestation. Early-postpartum estrus characteristics (EPEC; intense estrus = heat index ≥70; 0 = minimum, 100 = maximum) of multiparous cows were evaluated at 40 (herd 1) or 41 (herd 2) DIM and EPEC of primiparous cows were evaluated at 54 (herd 1) or 55 (herd 2) DIM. Control cows received the first artificial insemination at fixed time (TAI; primiparous, herd 1 = 82 and herd 2 = 83 DIM; multiparous, herd 1 = 68 and herd 2 = 69 DIM) following the Double-Ovsynch (DOV) protocol. Cows enrolled in the TRM treatment were managed as follows: (1) cows with at least one intense estrus were inseminated upon AMD detected estrus for 42 d and, if not inseminated, were enrolled in the DOV protocol; and (2) cows without an intense estrus were enrolled in the DOV protocol at the same time as cows in the control treatment. Control cows were re-inseminated based on visual or patch aided detection of estrus, whereas TRM cows were re-inseminated as described for control cows with the aid of the AMD. Cows received a GnRH injection 27 ± 3 d after insemination and, if diagnosed as nonpregnant, completed the 5-d Cosynch protocol and received TAI 35 ± 3 d after insemination. Among cows in the TRM treatment, 55.8 and 42.9% of primiparous and multiparous cows, respectively, received the first insemination in spontaneous estrus. The interaction between treatment and parity affected pregnancy 67 d after the first AI (primiparous: control = 37.6%, TRM = 27.4%; multiparous: control = 41.0%, TRM = 44.7%). The TRM treatment increased re-insemination in estrus (control = 48.3%, TRM = 70.5%). Pregnancy 67 d after re-inseminations tended to be affected by the interaction between treatment and EPEC (no intense estrus: control = 25.3%, TRM = 32.0%; intense estrus: control = 32.9%, TRM = 32.2%). The interaction between treatment and EPEC affected pregnancy by 305 DIM (no intense estrus: control = 80.8%, TRM = 88.2%; intense estrus: control = 87.1%, TRM = 86.1%). Treatment did not affect the number of reproductive hormone treatments among cows that had not had an intense estrus (control = 10.5 ± 0.3, TRM = 9.1 ± 0.2 treatments/cow), but cows in the TRM treatment that had an intense estrus received fewer reproductive hormone treatments than cows in the control treatment (2.0 ± 0.1 vs. 9.6 ± 0.2 treatments/cow). Selecting multiparous cows for first AI in estrus based on EPEC reduced the use of reproductive hormones without impairing the likelihood of pregnancy to first AI. The use of AMD for re-insemination expedited the establishment of pregnancy among cows that did not display an intense estrus early postpartum.     

The value of the biomarkers cathelicidin,milk amyloid A,and haptoglobin to diagnose and classify clinical and subclinical mastitis

Timely and objective diagnosis and classification of mastitis is crucial to ensure adequate management and therapeutic decisions. Analyzing specific biomarkers in milk could be advantageous compared with subjective or semiquantitative criteria, such as palpation of the udder in clinical mastitis cases or evaluation of somatic cell count using cow side tests (e.g., California Mastitis Test) in subclinical mastitis quarters. The objective of this study was to investigate the diagnostic value of 3 biomarkers; cathelicidin, milk amyloid A, and haptoglobin for the diagnosis of subclinical and clinical mastitis. Furthermore, the suitability of these biomarkers to differentiate between mild, moderate, and severe clinical mastitis and the influence of different pathogens on biomarker levels was tested. A total of 67 healthy cows, 119 cows with subclinical mastitis, and 212 cows with clinical mastitis were enrolled in the study. Although cathelicidin, haptoglobin, and milk amyloid A were measured in all samples from healthy cows and those with subclinical mastitis, haptoglobin, and cathelicidin results were only available from 121 out of 212 cows with clinical mastitis. Milk amyloid A was measured in all samples. In cows with clinical mastitis, the mastitic quarter and a second healthy quarter serving as a healthy in-cow control quarter were sampled. It was possible to differentiate between healthy quarters, quarters with subclinical mastitis, and quarters with clinical mastitis using all 3 biomarkers. Concerning cathelicidin, thresholds were 0.000 [sensitivity (Se) = 0.83, specificity (Sp) = 0.97] and 0.053 (Se = 0.98, Sp = 0.99) for normalized optical density at 450 nm (NOD450) for differentiating between healthy quarters and quarters with subclinical or clinical mastitis, respectively. Thresholds of 1.28 µg/mL (Se = 0.65, Sp = 0.76) and 1.81 µg/mL (Se = 0.77, Sp = 0.83) for milk amyloid A and 3.65 µg/mL (Se = 0.92, Sp = 0.94) and 5.40 µg/mL mL (Se = 0.96, Sp = 0.99) for haptoglobin were calculated, respectively. Healthy in-cow control quarters from cows with CM showed elevated milk amyloid A and haptoglobin levels compared with healthy quarters from healthy cows. Only the level of milk amyloid A was higher in severe clinical mastitis cases compared with mild ones. In contrast to clinical mastitis, cathelicidin and haptoglobin in subclinical mastitis quarters were significantly influenced by different bacteriological results. The measurement of cathelicidin, milk amyloid A, and haptoglobin in milk proved to be a reliable method to detect quarters with subclinical or clinical mastitis.     

Effect of manipulating progesterone before timed artificial insemination on reproductive and endocrine outcomes in high-producing multiparous Holstein cows

Our objective was to evaluate the effect of manipulating progesterone (P4) concentrations before timed artificial insemination (TAI) on reproductive and endocrine outcomes in high-producing Holstein cows. Multiparous lactating Holstein cows (n = 80) were synchronized for first TAI using a Double-Ovsynch protocol and were randomly assigned to receive 25 mg of PGF_2α 1 d after the first GnRH treatment of the Breeding-Ovsynch protocol that included a once-used P4 insert (low-P4 group) or to receive 2 new P4 inserts during the Breeding-Ovsynch protocol (high-P4 group). Blood samples were collected thrice weekly from ?10 to 32 d relative to TAI for all cows and from 32 to 67 d after TAI for pregnant cows and were analyzed for P4 and pregnancy-specific protein B (PSPB) concentrations. Expression of IFNτ-stimulated gene 15 (ISG15) was assessed in blood leukocytes 18 and 20 d after TAI. As expected, P4 concentrations were greater for high-P4 cows than for low-P4 cows from 3 to 8 d before TAI. Incidence of double ovulation was 3-fold greater for low-P4 cows than for high-P4 cows (33 vs. 10%), which resulted in more twin pregnancies 32 d after TAI for low-P4 cows than for high-P4 cows (29 vs. 0%). Low-P4 cows had larger preovulatory follicles at the last GnRH treatment of the Double-Ovsynch protocol and greater P4 concentrations than high-P4 cows after TAI. Relative expression of ISG15 mRNA 18 and 20 d after TAI was greater for low-P4 cows than for high-P4 cows and for pregnant cows than for nonpregnant cows. Overall, PSPB concentrations tended to be greater for low-P4 cows than for high-P4 cows, and pregnant cows had greater P4 concentrations than nonpregnant cows. In summary, cows with low P4 before TAI had increased preovulatory follicle diameter, PSPB concentrations, relative expression of ISG15 mRNA 18 and 20 d after TAI, double ovulations, and twinning compared with cows with high P4 before TAI. Increasing P4 before TAI may effectively decrease double ovulation and twinning in high-producing multiparous Holstein cows.     

Effect of supplemental beta-carotene on incidence and responsiveness of ovarian cysts to hormone treatment

Sixty-two multiparous and 35 primiparous Holstein cows were assigned randomly at 10 days postpartum to receive a ration with or without 300 mg beta-carotene/cow per day. Multiparous and primiparous cows were grouped separately and group-fed complete rations once daily. Incidence of ovarian cysts (26% by rectal palpation) was not affected by beta-carotene fed. Multiparous cows had greater incidence (39%) of ovarian cysts than primiparous cows (11%). Fifty-seven percent of cysts were classified follicular by rectal palpation. Progesterone concentration of milk also was used for diagnosis of type of cyst. Cows with ovarian cysts and with progesterone concentrations in milk less than 1 ng/ml were classified follicular, and those having concentration greater than 1 ng/ml were classified luteal. As determined by milk progesterone, rectal palpation was more accurate for diagnosis of luteal cysts than for diagnosis of follicular cysts. Progesterone concentrations of milk for animals with luteal and follicular cysts were 10.66 +/- 1.29 and .37 +/- .07 ng/ml. beta-Carotene did not affect response or days to respond to treatment with human chorionic gonadotropin or gonadotropin-releasing hormone. Supplemental beta-carotene was not beneficial for reducing incidence of ovarian cysts in cows receiving an adequate supply of beta-carotene in their diet.     

Temporarily decreasing progesterone after timed artificial insemination decreased expression of interferon-tau stimulated gene 15 (ISG15) in blood leukocytes,serum pregnancy-specific protein B concentrations,and embryo size in lactating Holstein cows

Our objective was to evaluate the effects of temporarily decreasing progesterone (P4) after timed artificial insemination (TAI) on embryonic growth in dairy cows. Lactating Holstein cows (n = 80) were submitted to a Double-Ovsynch protocol for first TAI and were assigned randomly to receive 12.5 mg of PGF_2α 5 d after the last GnRH treatment (LowP4) or remain untreated (control). Blood samples were collected thrice weekly from 5 to 29 d after TAI for all cows and from 32 to 67 d for pregnant cows, and were analyzed for P4 and pregnancy-specific protein B concentrations. Expression of interferon-tau stimulated gene 15 (ISG15) was assessed in blood leukocyte mRNA 18 and 20 d after TAI. Pregnancy diagnosis was performed weekly using ultrasound from 32 to 67 d after TAI, and embryonic crown-rump length was measured 32, 39, and 46 d after TAI. Data were analyzed by ANOVA and logistic regression using the MIXED and GLIMMIX procedures of SAS. The LowP4 cows had less P4 than control cows from 6 to 11 d after TAI; however, pregnancy outcomes 32 d after TAI and pregnancy loss from 32 to 67 d after TAI did not differ between treatments. Control cows diagnosed pregnant 32 d after TAI had greater expression of ISG15 20 d after TAI than LowP4 cows diagnosed pregnant 32 d after TAI, and pregnant control cows had greater pregnancy-specific protein B concentrations from 25 to 67 d after TAI than pregnant LowP4 cows. Embryo size did not differ between treatments 32 and 39 d after TAI, but control cows had larger embryos 46 d after TAI. In conclusion, temporarily decreasing P4 after TAI decreased embryonic growth during early pregnancy in lactating Holstein cows but did not affect pregnancies per artificial insemination or pregnancy loss.