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Objective: To determine if a pre‐milking teat disinfection protocol would reduce the incidence of clinical mastitis by greater than 50%. Methods: Two pre‐milking routines were compared in a natural exposure trial. Cows from a single dairy herd were randomly assigned to control (n = 246) and experimental (pre‐milking teat disinfection [PMTD]; n = 244) groups. For cows in the control group, the pre‐milking routine involved minimal teat‐washing, except for cows with wet teat contamination. For cows in the PMTD group, the pre‐milking routine involved washing of all teats, dipping with a commercial 0.1% available iodine solution, allowing a minimum of 30 s contact time and then drying of the teats using disposable paper towel. Clinical cases encountered during the trial were recorded and pathogens were isolated from milk samples using standard laboratory methods. Results: The effect of PMTD was determined using multivariable binary logistic regression. Multiparous animals in the PMTD group had higher odds of experiencing clinical mastitis overall and of experiencing clinical mastitis caused by environmental pathogens (odds ratio (OR) 1.97 and 4.11, 95% confidence interval (CI) 1.15–3.38 and 1.49–11.3, respectively). In primiparous animals, pre‐milking teat disinfection did not reduce the odds of clinical mastitis by greater than 50% (OR 1.31, 95%CI 0.52–3.29). Conclusion: In this herd, PMTD increased the odds of clinical mastitis. The effectiveness of PMTD to prevent clinical mastitis in pasture‐based systems is likely to vary greatly between herds. We therefore recommend against the wholesale use of this practice on Australian farms. [ABSTRACT FROM AUTHOR]

Environmental heat can reduce conception rates (the proportion of services that result in pregnancy) in lactating dairy cows. The study objectives were to identify periods of exposure relative to the service date in which environmental heat is most closely associated with conception rates, and to assess whether the total time cows are exposed to high environmental heat within each 24-h period is more closely associated with conception rates than is the maximum environmental heat for each 24-h period. A retrospective observational study was conducted in 25 predominantly Holstein-Friesian commercial dairy herds located in Australia. Associations between weather and conception rates were assessed using 16,878 services performed over a 21-mo period. Services were classified as successful based on rectal palpation. Two measures of heat load were defined for each 24-h period: the maximum temperature-humidity index (THI) for the period, and the number of hours in the 24-h period when the THI was >72. Conception rates were reduced when cows were exposed to a high heat load from the day of service to 6 d after service, and in wk -1. Heat loads in wk -3 to -5 were also associated with reduced conception rates. Thus, management interventions to ameliorate the effects of heat load on conception rates should be implemented at least 5 wk before anticipated service and should continue until at least 1 wk after service. High autocorrelations existed between successive daily values in both measures, and associations between day of heat load relative to service day and conception rates differed substantially when ridge regression was used to account for this autocorrelation. This indicates that when assessing the effects of heat load on conception rates, the autocorrelation in heat load between days should be accounted for in analyses. The results suggest that either weekly averages or totals summarizing the daily heat load are adequate to describe heat load when assessing effects on conception rates in lactating dairy cows. [ABSTRACT FROM AUTHOR]

Plastic sanitary sheaths over artificial insemination (AI) guns have been used at the time of AI to improve hygiene at AI and fertility in cattle, but fertility responses have been variable in studies when AI was performed by professional inseminators. The aims of this study were to investigate whether the use of a sanitary sheath at the time of AI carried out by nonprofessional (do-it-yourself, or DIY) inseminators improves pregnancy rates to AI in pasture-based dairy cows and whether effects of sheaths are greater in cows with contaminated vulvas and in cows at increased risk of extended calving to conception intervals. Lactating dairy cows located in 10 pasture-based herds in a subtropical region of northern Australia were inseminated by herd-based DIY inseminators and assigned to be inseminated with (n = 3,655) or without (n = 3,969) a sanitary sheath, with potential effects assessed using multivariable logistic regression. Overall, use of a sheath at the time of AI did not significantly affect pregnancy rates to AI (36.3% for those inseminated without a sheath vs. 36.8% for those inseminated with a sheath; odds ratio: 1.02; 95% confidence interval: 0.92-1.11). Effects of using a sheath on pregnancy rates to AI varied by herd, with lower pregnancy rates with the use of sheaths in 1 herd and some evidence of increases in 3 herds. Unexpectedly, there was evidence that the effect of sheath on pregnancy rates was less positive (or more negative) when the vulva was classified as dirty before any cleaning of the vulva before insemination compared with when the vulva was classified as clean (interaction odds ratio: 0.75; 95% CI: 0.56-1.00). Interactions between sheath and other explanatory variables that could affect fertility were not significant; thus, there was no compelling evidence that the effect of using a sheath was modified by any of these variables. We conclude that the use of sheaths during AI of pasture-based dairy cows by DIY inseminators does not, on average, markedly improve pregnancy rates to AI. However, responses may vary between herds, and the response to sheaths may be inferior (i.e., less positive or more negative) when a cow's vulva is contaminated with feces or discharge at the time of AI compared with when the vulva is clean., (Copyright © 2019 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This study evaluated the effect of equine chorionic gonadotropin (eCG) on reproductive performance, when incorporated into the first Ovsynch + P4 synchronization following planned start mating (PSM) in pasture-based lactating dairy cows. Two synchrony programs were compared in a randomized controlled trial in Queensland, Australia. Lactating cows from a single dairy herd (n = 782) were randomly allocated to Control and eCG groups. Control cows had their estrous cycles synchronized by treatment with 100 μg gonadotropin releasing hormone (GnRH; im) and insertion of a progesterone (P4) releasing intravaginal device that contained 1.0 g of P4 on Day 0; removal of P4 device and administration of 500 μg of an analogue of PGF2α on Day 7 (cloprostenol; im); 100 μg im of GnRH on Day 9, and fixed-time artificial insemination (FTAI) on Day 10. The eCG group were treated the same as the Control group except for the addition of 400 IU of eCG, im on Day 7 of the first synchronized estrous cycle. Following the first insemination, non-pregnant cows from both groups had their estrous cycles synchronized with the same treatment protocol without using eCG. The effects of eCG on 42d cumulative incidence of pregnancy and pregnancy per AI (P/AI) were determined using logistic regression models. The effect of eCG on time to pregnancy was determined using Kaplan-Meier survival analysis and Cox proportional hazards models. Adjusted 42 d cumulative incidence of pregnancy for eCG and control groups were 47.2 and 39.3% respectively (Odds ratio [OR] = 1.38, 95% CI: 1.01-1.88). Hazard of pregnancy tended to be higher in eCG cows overall (Hazard ratio [HR] = 1.18, 95% CI: 0.99-1.41) and was significantly higher when restricting to the first 42 days after PSM (HR = 1.31, 95% CI: 1.04-1.64). Hazards of pregnancy were not different between groups when restricting to > Day 42 post PSM (HR = 1.00, 95% CI: 0.77-1.31). P/AI tended to be higher in eCG treated cows at the first AI (44.0 vs 37.7%, OR = 1.30, 95% CI: 0.94-1.78). P/AI for second and third AIs were not significantly different between groups. In this herd, a single treatment of eCG at the first synchronized estrus after PSM improved reproductive performance in the short term, but not at subsequent inseminations., (Crown Copyright © 2018. Published by Elsevier Inc. All rights reserved.)

This study investigated the epidemiology of Neospora caninum in three tropical dairy herds in North Queensland, Australia. All animals in the herds were bled, and the sera were tested by ELISA for N. caninum antibodies. Herd records were examined, and the number of calves carried to term and the number of abortions which occurred over the lifetime of each animal were recorded to determine the abortion rate for each animal. Pedigrees were constructed for two of the herds to investigate whether vertical transmission was occurring. The seroprevalence of N. caninum ranged from 23% to 34%. The abortion rate in seropositive animals was significantly (p < 0.001) higher than in seronegative animals in all three herds (12-20.1% cf. 3.6-7%). Overall, the probability of a calf being seropositive was 3.5 times higher when the dam was also seropositive than when the dam was seronegative. Subsequent selective breeding employed by one herd reduced the N. caninum seroprevalence from 23% to 5% over a 9-year period. This study shows that N. caninum infection is prevalent in North Queensland dairy cattle, and both post-natal infection and vertical transmission are common., (© 2010 Blackwell Verlag GmbH.)

Objective: To assess the effectiveness of a gonadotrophin-releasing hormone (GnRH) / prostaglandin program (GnRH-PG-GnRH, Ovsynch) on conception rates and time to conception of lactating dairy cows compared with a PG program (double prostaglandin injection)., Design: A randomised multi-centre cohort study was conducted with 778 cows from nine dairy herds. Cows at different stages of lactation were randomly assigned, after matching for days open at the time of treatment, to either the PG or Ovsynch program., Procedure: Cows on the PG program received two intramuscular injections of prostaglandin (2 mL, Prosolvin) 11 days apart. The Ovsynch program consisted of two intramuscular injections of GnRH (1 mL, Fertagyl) 9 days apart, separated by one injection of prostaglandin 40 h before the second GnRH injection. Milk samples were taken at the time of artificial insemination and assayed for progesterone by radioimmunoassay., Results: The Ovsynch program was not significantly different to PG in achieving conception, with overall conception rates of 37.6% and 41.4%, respectively, for each program. There was, however, a significant interaction between the effects of parity and treatment (P = 0.03), because conception rates were higher in older cows (parity 5 or more) on the PG program than for older cows on the Ovsynch program. There was no significant effect of treatment (P > 0.5) on time to conception after treatment, but older cows were slower to conceive (P < 0.0001). Conception rates differed (P < 0.0001) among herds., Conclusion: The median days to conception for both groups was 22 and mean days from treatment to conception were 36.3 +/- 3.3 and 31.6 +/- 2.7 for the Ovsynch and PG programs respectively, indicating that reproductive performance of cows was not significantly different with Ovsynch program or PG program. There appears to be a need to evaluate causes of reproductive failure in older cows.

All cases of lameness that occurred in cows from three dairy herds between August 198'3 and July 1990 were examined every 2 weeks from the onset of lameness until the lesions resolved. The incidences of herd lameness were 38%, 22% and 2%. Some 186 clinical lesions were identified in 134 cases of lameness in 120 cows. Sole bruising (42%) and white line separation (39%) were the most frequently diagnosed conditions. Lateral digits of the hind limbs were the most affected. The mean time from the onset of lameness to clinical recovery was 27 days and to lesion recovery was 35 days. The peak incidence of lameness occurred during winter for autumn-calving cows and during the late spring for spring-calving cows. The onset of lameness was associated with the stage of lactation and wet weather conditions. Survival analysis revealed that the probability of an individual cow lasting in the milking herd for any specified period of time without becoming lame was highly associated with both her herd environment and her age. Total lactation yields of milk, milk fat and milk protein were lower for cows suffering from lameness than for herd-mates matched on age and proximity on calving date (P<0.05). Reproductive performance was also poorer in lame cows than in their herd-mates.

Herd health records from 1983 to 1985 were analysed for a sample of 19 dairy farms on the Atherton Tableland in tropical north Queensland. Abortion and first service conception rates were calculated for each farm for each year. The association between abortion rate and stage of gestation at pregnancy diagnosis was investigated as well as the association between abortion rate and lactation status. There was a significant linear increase in abortion rate over the 3-year period, during which the mean rate was 7.3 +/- 2.1% (range 4.5% to 10.9%). There was also a significant variation in first conception rates during the same period, when the mean first service conception rate was 51.8% +/- 6.6% (range 42.4% to 65.8%). A significantly higher abortion rate was recorded in first lactation cows. Of 178 abortions in all lactation groups (1984), 20.3% were repeat abortions by the same cows. Of 163 abortions, a majority (80.4%) occurred during months 3 to 7 of gestation. No significant association was found between the timing of pregnancy diagnosis and occurrence of abortion.

An association with a rank correlation of 0.55 (p = 0.06) was obtained between monthly rainfall and monthly abortions for a group of 24 farms in tropical Australia where cows grazed predominantly summer rain-dependent pasture. A similar association was found among cows grazing nitrogen-fertilised, irrigated pasture in winter in the same area. On farms with irrigated pasture the first service conception and abortion rates in herds which grazed intensively during the night (abortion 8.9%; first service conception 42.9%) differed significantly from those which grazed during the day (abortion 6.4%; first service conception 52.9%), and this suggested that increased abortion rates and decreased first conception rates may be part of the one syndrome. An hypothesis was developed that the feeding of immature nitrogen-fertilised pasture, rich in protein and stimulated by rain or irrigation, is associated with an increased abortion rate and a depressed conception rate. Other evidence included an increased susceptibility of first lactation cows to abortion, a lower abortion rate in late pregnant dry cows fed more mature pasture, a 20% repeat abortion rate in the population sampled and the lack of conclusive evidence for infectious and selected non-infectious agents. There were no other observed clinical signs in most aborting cows.

The role of infectious agents on dairy farms on the Atherton Tableland in tropical north Queensland was studied as part of a comprehensive investigation into the causes of bovine abortion. The prevalence of antibody in serums collected from 7 herds whose annual abortion rates ranged from 3% to 21% were as follows: Leptospira hardjo 49.9% (426/853), L. pomona 0.4% (3/851), bovine virus diarrhoea (BVD) 33.7% (35/104). Infectious bovine rhinotracheitis virus (IBR) 11.5% (12/105), Akabane virus 92.2% (95/103), Aino virus 62.1% (64/103), Chlamydia psittaci 3.1% (37/1004), Brucella abortus 0% (0/851), and Toxoplasma gondii 0% (0/105). Testing of serums against a wide range of leptospiral serotypes indicated that reactions occurring in the Hebdomadis and Sejroe serogroups were probably cross reactions with L. hardjo. Infection with L. hardjo and Akabane virus occurred prior to first mating and contact with Aino virus occurred during first pregnancy. Infection with BVD and IBR viruses was sporadic. The pathology and microbiology of 32 aborted foetuses from 24 Tableland herds (10 from the group of 19 farms under more intense study) were performed. Lesions associated with a Sarcocystis-like agent were present in 6, leptospires in 1, suspected toxic hepatosis in 2 and purulent bronchopneumonia (Staphylococcus aureus) in 1 foetus. No diagnoses were made in the remaining 22 foetuses (69%). Evidence for a common infectious cause of abortion in the population was inconclusive.

To provide more evidence for an apparent association between immature, high protein pasture diets and abortion in dairy cows on the Atherton Tableland in tropical north Queensland, pastures and cows on 4 farms were sampled on 5 occasions during a 7-month period. Pasture samples were analysed for dry matter (DM), protein, nitrate and fibre content. Plasma progesterone concentrations were determined in 18 to 20 pregnant cows. Fifty-four pasture samples (38 grass and 16 legume) were analysed and the distribution for 3 DM ranges was: 10% to 14.9% - 20 samples, 15% to 19.9% - 27 samples and 20% to 24.9% - 7 samples, while the distribution for 4 protein ranges was: 15% to 19% - 5 samples, 20% to 24% - 20 samples, 25% to 29% - 21 samples and 30% to 34% - 8 samples. Both pasture protein and DM content fluctuated with time. Pasture nitrate was low and insignificant while fibre (cell wall) levels appeared to be satisfactory for ruminant nutrition. Significant differences occurred between the mean plasma progesterone levels on 3 of the 4 farms. Raised levels in pregnant cows suggested the possibility of increased progesterone production in response to a previous low progesterone crisis or, alternatively, a decreased metabolic clearance rate of progesterone in pregnant cows on a declining plane of nutrition towards the end of the summer wet season. Progesterone data were not available from cows which previously aborted.(ABSTRACT TRUNCATED AT 250 WORDS)