Risk Factors for Peripartum Mastitis in Pasture-Grazed Dairy Heifers

A longitudinal observational field study was conducted using 708 heifers in 30 spring-calving dairy herds in the Waikato region of New Zealand. The aim of the study was to investigate risk factors for subclinical and clinical mastitis (CM) in the peripartum period using path analysis methods and to find the factors most important at the population level as a basis for potential control programs. Body condition and udder hygiene scores, blood samples, and quarter mammary secretion samples for bacteriology were collected approximately 3 wk before the planned start of the seasonal calving period and again within 5 d following calving. Additionally, milk samples were collected from quarters diagnosed with CM within 14 d of calving. Significant risk factors for subclinical mastitis postcalving were precalving subclinical mastitis (3.32 incidence risk ratio; IRR), low minimum teat height above the ground (1.32 IRR), and unhygienic udder postcalving (1.32 IRR). Significant risk factors for clinical mastitis postcalving were precalving subclinical mastitis (2.14 IRR), Friesian breed (1.94 IRR), low minimum teat height above the ground (2.05 IRR), udder edema (1.81 IRR), and low postcalving nonesterified fatty acid serum concentration (1.55 IRR). Control of precalving subclinical mastitis and udder edema by producers, and enhancement of breed immunity by geneticists were important factors at a population level, and hence, are likely the most rewarding areas to target in any heifer mastitis management program.

Clinical and bacteriological response to treatment of clinical mastitis with one of three intramammary antibiotics

AIM

To compare the proportions of clinical and bacteriological cure of glands of dairy cows diagnosed with clinical mastitis, following treatment with one of three different intramammary antibiotic preparations.

METHODS

Cows from dairy cow herds (n=28) across New Zealand which were diagnosed with clinical mastitis in one or more glands at any stage of lactation were randomly assigned at the cow level within sequentially presented groups of three animals to be treated with one of three intramammary antibiotics. The treatments were 1 g procaine penicillin, 0.25 g cefuroxime, and a combination of 1 g procaine penicillin and 0.5 g dihydrostreptomycin (DHS). All treatments were infused on three occasions at 12-hourly intervals. Duplicate milk samples were collected for bacteriology before initial treatment, and 21-42 days later. Logistic regression or generalised linear mixed models were used to analyse the proportion of cows or quarters retreated for mastitis within 30 days of initial treatment ('clinical treatment failure'), and the proportion of glands from which bacteria were isolated initially but from which the same bacterial species was not re-isolated ('bacteriological cure').

RESULTS

The annual herd average cumulative incidence rate of clinical mastitis was 12.7 cases/100 cows. The incidence rate was higher in young (2-year-old) and old (> or = 9-year-old) cows relative to 3- and 4-year-old cows, and was higher in Friesian than Jersey or crossbred cows. Streptococcus uberis was the pathogen most commonly isolated, and its relative prevalence declined with time postpartum. Cows treated with cefuroxime were more likely (p<0.01) to be re-treated for clinical mastitis in the 30 days after initial treatment than cows treated with procaine penicillin or procaine penicillin and DHS. Bacteriological cure occurred in 74% of treated glands and there was no difference in the proportion of cures among the treatments (p=0.4). The proportion of cures was lower when treatment occurred 28-72 days after calving (p<0.01) and if a major pathogen was isolated (p<0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

There was no benefit in terms of clinical or bacteriological cure rate in treating clinical mastitis cases with the combination of procaine penicillin and DHS compared to treatment with procaine penicillin alone. The proportion of clinical mastitis cases re-treated differed among herds, and more cows treated with cefuroxime were retreated within 30 days of initial treatment. However, the bacteriological cure proportion was the same among the treatments. Cure proportions were lower in cows from which major mastitis pathogens were isolated and when treatment commenced 28-72 days after calving.

Parenteral Treatment of Clinical Mastitis with Tylosin Base or Penethamate Hydriodide in Dairy Cattle

The objective of this study was to compare the clinical and bacteriological cure rates of cows with clinical mastitis following treatment with either tylosin base (5 g injected 3 times at 24-h intervals; n = 306) or penethamate hydriodide (5 g injected 3 times at 24-h intervals; n = 289). Duplicate milk samples were collected before treatment and again 14 +/- 3 and 21 +/- 3 d later for microbiological analysis. Only those quarters from which gram-positive mastitis pathogens were isolated before treatment were included in the analyses. Streptococcus uberis was the most prevalent isolate. The number of cows with clinical failure (i.e., retreated within 21 d of enrollment) did not differ between treatments (64 vs. 63, respectively). At the quarter level, there was no difference in the proportion of bacteriological cure between treatments (81.2 vs. 83.8% for penethamate hydriodide or tylosin, respectively). The proportions of clinical and bacteriological cure were influenced by age, herd, severity of mastitis, number of glands within the cow with clinical mastitis, bacterial species, and days postpartum at enrollment. There was no difference between treatment groups for SCC (4.46 vs. 4.44 +/- 0.08, mean +/- standard error of the difference in ln SCC for cows treated with penethamate hydriodide or tylosin, respectively) or production of milk solids (1.45 vs. 1.48 +/- 0.02 kg/d of milk fat + protein, for the penethamate hydriodide or tylosin treatment, respectively). Overall, there was no difference in the proportions of clinical failure (17.3 vs. 16.5% of cows treated with penethamate hydriodide or tylosin, respectively) or bacteriological cure (79.8 vs. 82.0% of cows treated with penethamate hydriodide or tylosin, respectively), or in SCC or milk production between dairy cows with clinical mastitis and those treated for clinical mastitis with 1 of 2 parenteral antibiotic therapies.

Subclinical and Clinical Mastitis in Heifers Following the Use of a Teat Sealant Precalving

This study investigated the effect in heifers of infusion of a bismuth subnitrate teat-canal sealant and bacterial intramammary infection (IMI) precalving on prevalence of postcalving IMI and incidence of clinical mastitis in the first 2 wk postcalving. Glands (n = 1,020) from heifers (n = 255) in 5 seasonally calving, pasture-fed dairy herds were randomly assigned within heifer to 1 of 4 treatment groups (no treatment; mammary gland secretion collection; infusion of a teat sealant; or sample collection with infusion of teat sealant). Heifers within a herd were enrolled on one calendar day, 31 d on average before the planned start of the seasonal calving period. Duplicate milk samples were collected from each gland within 4 d after calving for bacterial culture. Herd owners collected duplicate milk samples, before treatment, for bacterial culture from glands they defined as having clinical mastitis. The gland prevalence of IMI precalving was 15.5% and did not differ between herds. Bacteria isolated precalving included coagulase-negative staphylococci (76.9% of all bacteriologically positive samples), Streptococcus uberis (14.1%), Staphylococcus aureus (5.1%), Corynebacterium spp. (3.8%), and others (0.1%). The presence of an IMI precalving increased the risk of an IMI postcalving 3.6-fold and the risk of clinical mastitis 4-fold, relative to no IMI precalving. Infusion of the teat sealant reduced the risk of postcalving IMI due to Strep. uberis by 84%, and of clinical mastitis by 68%. Sampling the glands precalving had no effect on postcalving IMI or on clinical mastitis incidence. Use of an internal teat canal sealant in heifers precalving may be a useful tool for reducing the risk of subclinical and clinical mastitis in heifers.

Pharmacokinetic profile of a new modified release formulation of zolpidem designed to improve sleep maintenance

The aim of this study was to compare the relative bioavailability and the pharmacokinetic profile of a single oral dose of a zolpidem modified-release (MR) 12.5-mg formulation with those of the standard 10-mg zolpidem immediate-release (IR) formulation. Absolute bioavailabilities of oral formulations were evaluated using intravenously (i.v.) administered zolpidem as a reference. Twenty-four healthy, Caucasian, male volunteers (18-45 years old) received single doses of three oral formulations (zolpidem-MR 12.5 mg, zolpidem-IR 10 mg and an experimental form) and zolpidem i.v. infusion (8 mg) in a randomized, open-label, crossover trial. Blood samples (18 time-points) were collected up to 16 h post-dose after oral administration and up to 12 h post-dose after i.v. administration. Pharmacokinetic parameters were determined by non-compartmental analysis, allowing comparisons between treatments based on estimated ratios and differences, with 90% confidence intervals. The initial absorption phase of the zolpidem-MR formulation was as fast as that of zolpidem-IR with no significant difference in t(max). With zolpidem-MR 12.5 mg, C(max) was moderately lower than with zolpidem-IR (ratio of 0.82), and plasma zolpidem concentrations were maintained above those observed with zolpidem-IR for a longer period of time, particularly from 3 to 6 h post-dose. This was confirmed by an increase in half-value duration (HVD) from 2.3 h with zolpidem-IR to 4.6 h with zolpidem-MR 12.5 mg. The mean terminal half-life was similar between formulations. Zolpidem-MR 12.5 mg provides the appropriate pharmacokinetic characteristics to extend plasma zolpidem concentrations into the middle of the night (3-6 h post-dose), while retaining the same t(max) and terminal half-life.

Reproductive performance in the subsequent lactation of dairy cows previously treated for failure to be detected in oestrus

AIM

To describe the effect of treatment of cows not detected in oestrus (NDO) with progesterone (P4) and oestradiol benzoate (ODB) in one lactation, on the reproductive and productive performance in the subsequent lactation.

METHODS

Cows (n=770 from nine herds) which were NDO 10 days before the planned start of the seasonal breeding programme (PSM) were blocked by herd, age (2 or >2 years old) and ovarian status (i.e. with or without a palpable corpus luteum; CL), and treated either with an intravaginal progesterone-releasing device and ODB and resynchrony, or were left as untreated controls. In the following lactation, data were collected on the occurrence of endometritis, NDO, breeding dates, pregnancy test results and milk production. The effect of treatment and ovarian status in the previous lactation on the incidence of disease, and the proportions submitted for service, conceived and pregnant in the subsequent lactation were analysed. Calving dates and intervals from start of breeding to first insemination and conception were analysed using Kaplan Meier survival analysis. Additional multivariate analyses were undertaken to include known confounders such as age, breed, herd, calving date and milk production, as well as the cyclic status (i.e. previously cycling, NDO, or "late-calving") in the previous lactation, to examine the potential "carryover" effects of previous status on the reproductive performance in the subsequent lactation.

RESULTS

Treatment of NDO cows resulted in an earlier calving date (Julian calving date 214, 95% CI=207-221, vs 224, 95% CI=220-228; p=0.005), more female calves reared (31.4% vs 23.3%; p=0.01), and reduced risk of being NDO (33.9% vs 46.1%; p=0.002) in the subsequent lactation compared with controls. There were no differences in the incidence of peripartum disease, or the proportion of cows submitted, conceived or pregnant between the Treatment and Control groups in the subsequent lactation (p>0.2). Previously CL-positive (+ve) NDO cows were less likely to produce a female calf that was reared (19.0% vs 29.9%; p=0.005), more likely to be treated as NDO (26.4% vs 18.6%; p=0.02), less likely to conceive by the end of the subsequent lactation's breeding programme (82.2% vs 87.8%; p=0.09), and took longer to conceive (41 vs 33 days from the PSM to conception) than cows that were NDO-CL-negative (-ve) in the previous lactation. There was no interaction between ovarian status and treatment for any of the outcome variables (p>0.05). Cows that were NDO or late-calving in the previous lactation were more likely to be NDO (p<0.005), treated as NDO (p<0.005), and have longer PSM to conception intervals (p<0.005) in the subsequent lactation than cycling herdmates, despite inclusion of factors known to confound reproductive performance in analyses.

CONCLUSIONS

Treatment of NDO cows resulted in more female calves reared, earlier calving and a reduced risk of being NDO in the subsequent lactation. Status (i.e. NDO-CL+ve or NDO-CL-ve) affected some reproductive measures in the subsequent lactation, and the effect of treatment in the subsequent lactation differed between the two groups for some measures. Reproductive performance in the subsequent lactation was not improved despite the earlier calving date and longer calving to PSM intervals. Additionally, the previous season's status was still important in the subsequent season's reproductive performance, despite adjusting for known confounders of fertility.

CLINICAL RELEVANCE

The economic benefits from treatment of NDO cows are likely limited to effects of an earlier calving date and potential for longer lactation and increased milk yield, increased number of calves derived from artificial insemination and from a reduced number of NDO cows in the subsequent lactation. Effects of improved reproductive performance in the subsequent lactation were not demonstrated and hence should not be included in any economic analysis of therapy of NDO cows.

Association between endometritis diagnosis using a novel intravaginal device and reproductive performance in dairy cattle

Endometritis reduces reproductive performance in dairy cattle. Diagnosis of endometritis is undertaken using a variety of techniques including vaginoscopy, manual examination, cytology and ultrasonography. The current studies compared a novel test device ("metricheck") that is inserted into the vagina with vaginoscopy and then examined the relationship between the metricheck test score at 35 days before the start of the seasonal breeding programme and subsequent reproductive performance. Cows (n = 191; Study 1) with a history of a peripartum disease were examined by both vaginoscopy and the metricheck device and any material viewed within the vagina (using vaginoscopy) or retrieved (by the metricheck device) was scored on a 0 (no material) to 5 (grossly purulent and with an odour) scale. Within each herd the order of examination was randomized with sequentially presented pairs of cows. All cows (n = 2793; Study 2) from nine herds were examined and scored using the metricheck device 35 days before the start of the seasonal breeding programme. All cows were pregnancy tested to determine date of conception. In Study 1, more cows were defined as infected (i.e. score > 1) following metricheck than vaginoscopic examination (60% versus 43%, respectively; P < 0.05) and the level of agreement between the two tests was moderate (kappa = 0.45). The metricheck device had a higher sensitivity, but lower specificity, than vaginoscopy. Endometritis (i.e. score > 1) was detected in 21.2% of cows examined in Study 2. The prevalence of endometritis varied among herds, declined with time postpartum (P < 0.05) and was higher in cows recorded as having a peripartum disease (P < 0.01). Cows diagnosed with endometritis were at higher risk of not being detected in oestrus before the start of breeding (P < 0.01), took longer to be inseminated after the start of the seasonal breeding programme (P < 0.01), had a lower first service conception rate (P < 0.01), had lower 56-day and final pregnancy rates (P < 0.05) and took longer to conceive than cows without endometritis (P < 0.05). It is concluded that examination with the metricheck device is more sensitive in detecting endometritis than vaginoscopy. Diagnosis of endometritis with the metricheck device was associated with poorer subsequent reproductive performance.

Factors affecting conception and expression of oestrus in anoestrous cows treated with progesterone and oestradiol benzoate

Nutrient balance affects the resumption of ovarian cyclic activity following calving in dairy cattle. However, few data are available about the relationships between nutrient balance and expression of oestrus or conception. It was hypothesised that previously anoestrous cows that conceived to first insemination and cows that expressed oestrus at the subsequent expected return to oestrus would be less likely to be in negative energy balance (i.e. would have higher body condition score, higher glucose, insulin-like growth factor (IGF), leptin or insulin concentrations, and lower non-esterified fatty acids (NEFA), blood urea nitrogen (BUN), beta hydroxy butyrate (BOH) concentrations 12-15 days after insemination) than herd mates not conceiving or expressing oestrus. Anoestrous cows were treated with progesterone and oestradiol benzoate (Day 0 = end of treatment period) and retrospectively categorised as conceiving (n = 108) or not conceiving (n = 108) to insemination. A subset of cows not conceiving to insemination were categorised as expressing (n = 44) or not expressing (n = 44) oestrus between Days 14 and 28 after initial insemination. Cows conceiving had a lower NEFA concentration (P = 0.014) than non-conceiving cows. Cows subsequently detected in oestrus had higher body condition scores (P = 0.016), IGF concentrations (P = 0.008) and milk protein percentages (P = 0.038), and lower BOH concentrations (P = 0.018) than cows not expressing oestrus. No difference in concentrations of leptin, insulin, glucose, blood urea nitrogen or milk yield were found between cows conceiving or not conceiving and those detected in oestrus or not detected in oestrus (P > 0.1). It is concluded that some measures of metabolic status at the time of pregnancy recognition affects the probability of pregnancy and of subsequent expression of oestrus in those treated, anoestrous cows not conceiving.

Pregnancy loss in dairy cattle in the Waikato region of New Zealand

AIM

To define the incidence rate of pregnancy loss and risk factors for those losses in pasture-fed dairy cattle in the Waikato region of New Zealand.

METHODS

Cows (n=2,004) from 10 pasture-fed, spring-calving dairy herds in the Waikato were enrolled following confirmation of pregnancy 29-45 days after insemination, for inseminations that occurred within the first 16 days of the seasonal breeding period. Transrectal ultrasonographic examinations for pregnancy were conducted at approximately 6, 8, 10, 14 and 22 weeks gestation, and subsequent calving data were recovered. Pregnancy loss was defined as having occurred when a confirmed pregnancy was not re-diagnosed, when gross abortion was detected, or when a cow calved <265 days after the confirmed conception date. Data were analysed using reverse stepwise logistic regression and Cox's proportional hazards analysis.

RESULTS

A total of 128 (6.4%) pregnancy losses were detected. The incidence rate was higher in early compared to late gestation (10.9 vs 2.8 losses/10,000 cow-days between Weeks 6-10 vs Weeks 10-14, respectively; p<0.001). Higher rates of loss were associated with the occurrence of clinical mastitis (Hazards ratio (HR)=1.57; p=0.071), being treated for anoestrus (HR=1.69; p=0.007), and in cows that had calving-to-conception intervals < or =63 days compared with those that had calving-to-conception intervals >92 days (HR=2.49; p=0.06). In addition, the rate of pregnancy loss differed between herds (p=0.05).

CONCLUSIONS

The highest rate of pregnancy loss occurred in early gestation. Clinical mastitis, anoestrus and calving late in the calving season were risk factors for pregnancy loss.

CLINICAL RELEVANCE

Pregnancy diagnosis using ultrasonography can be undertaken from 28 days post-insemination. However, due to the high rate of pregnancy loss at this stage of gestation, herdowners need to be warned of possible losses, and cows should be re-examined to confirm pregnancy before certification of pregnancy status is given.

Gross abnormalities, bacteriology and histological lesions of uteri of dairy cows failing to conceive or maintain pregnancy

AIM

To describe the gross pathology, bacteriology and histopathology of the reproductive tracts of dairy cows that failed to conceive or maintain pregnancy.

METHODS

The reproductive tracts of 105 cows that were not pregnant at the end of the seasonal breeding programme were retrieved following slaughter. The tracts were examined grossly, both horns of the uterine lumen were swabbed for bacteriology, and tissue was collected from each horn and the body of the uterus for histopathology. Grossly enlarged uteri and tracts containing purulent vaginal content were excluded. Histopathology was performed on three sections of uterine tissue from each of three cows in which no gross pathological changes were detected and from which no bacteria were isolated, from three cows in which no gross pathology was detected but from which bacteria were isolated, and from three cows in which gross pathological changes were detected but from which no bacteria were isolated.

RESULTS

Thirty-six (34%) cows had one or more gross lesions which involved the ovary, uterine tube, uterus or vagina. Bacteria were isolated from the uteri of 22 (21%) cows. Isolates included Arcanobacterium pyogenes (n = 1), Escherichia coli (n = 1), Fusobacterium spp (n = 1), Haemophilus somnus (n = 5), Streptococcus acidominimus (n = 12), S. bovis (n = 2), S. uberis (n = 1) and S. salivarious (n = 1). In only five cows were both gross pathology and bacteria detected. There was no relationship between the isolation of bacteria and the diagnosis of gross pathology of the uterus. There were no differences in the degree of histopathological changes in the uteri from the three groups of cows examined, and lesions present were minor.

CONCLUSIONS

Gross pathological changes and intra-uterine bacteria were found in 34% and 20% of cows, respectively, but the correlation between the two was poor. Histopathological changes were unremarkable, suggesting the bacteriological findings were coincidental, that causative agents of infertility were not present at the time of examination, or that unrelated causes such as nutritional anoestrus may have been responsible for the failure of some cows to conceive.

Reproductive Performance of Anestrous Dairy Cows Treated with Progesterone and Estradiol Benzoate

Anestrus is a major reproduction problem in pasture-based dairy operations that results in poorer reproductive outcomes than herdmates detected in estrus before the start of the seasonal breeding program. The objective of the current study was to assess a combined progesterone and estradiol benzoate treatment program including resynchrony with no treatment. Anestrous pasture-fed dairy cattle (n = 756) in 9 herds were blocked by herd and age and assigned within sequentially presented pairs of cows to be treated with an intravaginal progesterone-releasing insert for 8 d plus 2 mg of estradiol benzoate injected i.m. at insert insertion and 1 mg of estradiol benzoate injected 1 d after insert removal (d -1). Those cows detected in estrus from 0 to 3 d had a used progester-one-releasing insert reinserted for 6 d commencing on d 16 with 0.5 mg of estradiol benzoate injected i.m. 1 d after insert removal (treatment). The other cow within the pair was left as an untreated control (control). Treatment increased the risk of insemination and pregnancy by 28 d into the breeding program and resulted in conception 15 d earlier compared with controls. In contrast, treatment did not increase the risk of pregnancy after 56 d into the breeding program or at the end of the breeding season. It is concluded that treatment of anestrous dairy cattle with progesterone and estradiol benzoate combined with reinsertion of the progesterone insert resulted in earlier conception, but no difference in the final pregnancy rate compared with no treatment.

Reproductive performance in anestrous dairy cows following treatment with two protocols and two doses of progesterone

The objectives of this study were to evaluate the effect using two doses of progesterone (P4) releasing devices in two different programs on reproductive performance of anestrous dairy cows. Cows (n = 1555) not detected in estrus by 10 d before the planned start of the seasonal breeding program and in which no CL was palpable were treated with an intravaginal P4-releasing device ('Single'; approximately 1.56 g of P4) or a modified device with triple the normal P4 dose ('Triple'; approximately 4.7 g of P4). The devices were in place for either 6 d ('Short') or 8 d ('Long'), with 1mg estradiol benzoate (EB) given 24 h after device removal. The 'Long' program also included treatment with 2 mg EB at device insertion. The Long program resulted in a higher first service conception rate (RR = 1.18 (95% CI = 1.03-1.33); P = 0.02), but had no effect on the 28-d, 56-d or final pregnancy rate compared to the Short program. There were no effects of dose of P4 on any outcome. In conclusion, the Long compared to the Short program, but not the dose of P4, improved first service conception rates in anestrous cows.

Effect of exogenous progesterone and oestradiol on plasma progesterone concentrations and follicle wave dynamics in anovulatory anoestrous post-partum dairy cattle

The effect of exogenous progesterone (P4) and of oestradiol benzoate (ODB) on plasma progesterone concentration and follicle dynamics was studied in anovulatory anoestrus (AA) post-partum pasture-fed dairy cattle. Cows (n=32) were defined AA based on not detecting a corpus luteum upon transrectal ultrasonography of the ovaries. Cows were randomly assigned to treatment with an intravaginal P4-releasing device containing 1.56 g of P4 (1Q; Cuemate, Pfizer Animal Health, Auckland, NZ; n=11) or with modified devices with double (2Q; n=11) or triple (3Q; n=10) the normal P4 dose for 8 days. Half of each group received 2 mg ODB at device insertion (Day 0) while the other half did not receive ODB at this time. All cows were treated with 1 mg ODB 1 day after intravaginal device removal (Day 9). Ultrasonography occurred daily until either ovulation or Day 15 whichever occurred sooner. Blood samples were drawn on Days 0, 1, 3, 5, 7, 8, 9, 15 and 22 for plasma P4 determination. Increasing P4 dose was associated with an increase in plasma P4 concentration during the time of device insertion (P <0.05). The highest P4 dose was associated with a delay in emergence of, but a shorter interval from emergence to maximum diameter and ovulation of, the subsequent dominant follicle (DF2) compared to the lowest P4 dose. Treatment with ODB resulted in a delay in emergence of DF2 (4.2 (0.4) versus 2.0 (0.4) days (S.E.M.) to emergence for ODB versus no-ODB; P=0.01), a smaller maximum diameter of DF2 (15.2 (0.5) versus 17.9 (0.6)mm (S.E.M.) for ODB versus no-ODB; P <0.01), a shorter interval to maximum DF2 diameter (5.0 (0.3) versus 6.8 (0.3) days (S.E.M.) for ODB versus no-ODB; P=0.03), a shorter interval from DF2 emergence to ovulation (6.3 (0.4) versus 8.5 (0.4) days (S.E.M.) for ODB versus no-ODB; P=0.02) and a tendency for a lower average plasma P4 concentration post-ovulation (i.e. average of Days 15 and 22; 2.5 (0.4) versus 3.4 (0.4) ng/ml plasma P4 for ODB versus no-ODB, respectively; P=0.08). The DF present at device insertion, was still present at device removal in three (9%) cows of which two were treated with 1Q + no-ODB and one with 3Q + ODB. It is concluded that increasing P4 dose and ODB treatment are associated with a delay in subsequent follicle wave emergence and more rapid follicle growth. Oestradiol benzoate treatment also tends to reduce the plasma P4 concentration in the subsequent luteal phase in post-partum, anoestrous dairy cattle.

Production and Health of Pasture-Fed Dairy Cattle Following Oral Treatment with the Ionophore Lasalocid

The aim of the study was to evaluate the effect of feeding the ionophore lasalocid on the productivity and health of seasonally calving, pasture-fed dairy cows. Dairy cows (n = 1020) from 4 herds were enrolled in a split-herd, prospective intervention study. Cows were blocked by breed and age, ranked on previous production, and then assigned to 2 treatment groups. Treatment cows were each exposed to 300 to 350 mg of lasalocid/d commencing 3 wk before and ending 18 wk after the start of the seasonal calving period. Milk production was determined on 3 occasions for each cow at approximately monthly intervals (herd tests 1 to 3), body condition score was determined fortnightly, and all disease occurrences were recorded. Lasalocid treatment increased milk volume milk protein and milk fat production by approximately 2%, without altering milk composition. Fewer lasalocid-treated cows than control cows (7.3 vs. 11.6%, respectively) were diagnosed with clinical mastitis. Lasalocid treatment of pasture-fed dairy cows resulted in reduced mastitis incidence and increased milk production without changes in body condition or negative effects on metabolic processes as monitored by metabolite concentrations.

The use of hormonal treatments to improve the reproductive performance of lactating dairy cows in feedlot or pasture-based management systems

Hormonal interventions have been used to increase the probability of estrous detection and insemination, and to increase pregnancy rates of dairy cattle under a variety of management systems. The present review addresses the basic principles of hormonal intervention and presents typical examples that illustrate the methodology. The hormones used to control the estrous cycle mimic the reproductive hormones found within the normal cow. Most estrous synchronization systems employ a method for controlling follicular wave development, promoting ovulation in anestrous cows, regressing the corpus luteum in cyclic cows, and synchronizing estrus and (or) ovulation at the end of treatment. A wide range of reproductive systems are in place on dairy farms. In most herds, a non-intervention period is practiced where postpartum cows are observed estrus estrus. Cows not observed in estrus are then treated. A number of studies in pasture-based and confinement systems have demonstrated net benefits of whole-herd synchronization. Despite the advantages of whole-herd reproductive programs, their uptake has been inconsistent globally. The benefits of a timed artificial insemination (AI) system increase under conditions of poor estrous detection rate and poor conception rate. The unpopular nature of timed AI programs in pasture-fed cows relates to high rates of estrous detection and conception for pasture-based dairying. Regardless of production system, some cows must be re-inseminated because they are not pregnant after first insemination. The presence of "phantom cows" (non-pregnant cows that do not return to estrus) creates a serious reproductive challenge for both pasture-based and confinement-style operations. Early pregnancy diagnosis and second insemination timed AI may reduce the effects of phantom cows on dairy herds. Fundamental research into anestrous, the hormonal control of the estrous cycle, and early pregnancy detection should elucidate new methods that can be used to strengthen reproductive programs on dairy farms.

Duration of Infection and Strain Variation in Streptococcus uberis Isolated from Cows’ Milk

The duration of infection and pulsed-field gel electrophoresis (PFGE) types of bovine intramammary Streptococcus uberis isolates were examined. Milk samples were collected in duplicate from all 4 glands of 503 cows from 5 herds within 1 to 3 d of parturition and from 113 cows with clinical mastitis in the same herds throughout lactation. Glands from which S. uberis was isolated were resampled at 28-d intervals.The prevalence of S. uberis was 12% for cows around parturition, and the median duration of infection was 16 d. Cows >2 yr old had a longer duration of infection than 2 yr old cows, and duration varied among herds. A total of 173 different PFGE types were identified from a total of 234 S. uberis isolates. Each farm had a unique set of PFGE types. Only 3 PFGE types were common to each of 3 pairs of cows, and these occurred on the same farm. Where S. uberis was isolated on more than one occasion from a gland, only 55% of the PFGE types were the same across time. For cows with multiple glands infected, only one-half (9 of 18) had the same PFGE type in more than one gland. No predominant PFGE type was identified in any herd. It is concluded that there was wide heterogeneity of PFGE types, that the environment rather than other cows was the likely source of S. uberis infections, and that glands may be infected with multiple S. uberis PFGE types over a lactation.

Intramammary treatment of clinical mastitis of dairy cows with a combination of lincomycin and neomycin, or penicillin and dihydrostreptomycin

AIM

To compare clinical and bacteriological cure rates of clinical mastitis following treatment with intramammary preparations containing either lincomycin and neomycin or penicillin and dihydrostreptomycin.

METHODS

Cases of clinical mastitis were sourced from four seasonal-calving dairy herds in the central Waikato region of New Zealand during the first 120 days of lactation. Affected quarters were infused three times at 12 h intervals with either 333 mg lincomycin plus 100 mg neomycin (lin/neo; 197 glands),or 1,000 mg penicillin plus 500 mg dihydrostreptomycin (pen/DHS; 207 glands). Milk samples were collected for bacteriology from each quarter immediately before and approximately 21 days after initiation of treatment. Additionally, a composite milk sample from each cow was collected, on average, 54 days after enrolment for assessment of milk yield, composition and somatic cell count (SCC). The probability of bacterial cure was initially analysed using Chi-squared analysis, and factors that were associated (p<0.2) were offered to a reverse stepwise logistic regression model. Continuous variables (e.g. milk solids production and log10 SCC) were analysed using general linear models.

RESULTS

A total of 404 quarters diagnosed with clinical mastitis, from 282 cows in the first 120 days of lactation, were included. Streptococcus uberis, coagulase-negative staphylococci and Staphylococcus aureus were isolated from 56.5%, 18.8% and 10.0% of the bacteriologically positive quarters. There was no difference in the bacteriological cure rate (76.7% vs 76.7%, OR=0.94; p>0.8), the log10 SCC (2.1, SE 0.1, vs 2.0, SE 0.1; p>0.3) or milk production (1.2, SE 0.1, vs 1.2, SE 0.1, kg milksolids/cow/day; p>0.7) between lin/neo vs pen/DHS treatments, respectively. However, the proportion of cows re-treated following initial treatment was higher for the lin/neo compared to pen/DHS-treated group (16.3% vs 5.2%, OR=3.46; p<0.05).

CONCLUSIONS

No difference in bacteriological cure rate, milk production or SCC was evident between lin/neo and pen/DHS intramammary treatments for clinical mastitis in dairy cows during the first 120 days of lactation.

Resynchrony of previously anoestrous cows and treatment of cows not detected in oestrus that had a palpable corpus luteum with prostaglandin F2𝛂

AIMS

To determine if resynchrony, using a progesterone (P4) / oestradiol benzoate (ODB) regime, of previously treated, anovulatory anoestrous (AA) cows would increase the probability of oestrus, conception and pregnancy compared to no resynchrony. Additionally, the effect of prostaglandin F2alpha (PG) treatment of cows not detected in oestrus, but in which a corpus luteum (CL) was palpable transrectally (NDO/CL+), was compared with no treatment.

METHODS

Cows not detected in oestrus by 1 week before the start of the seasonal breeding programme were categorised as AA or NDO/CL+, based on absence or presence of a palpable CL, respectively. All AA cows were treated with an intravaginal device containing 1.36 g P4 (CIDR-B) for a period of 6 days, and with 1 mg ODB by intramuscular (I/M) injection 1 day after the device was removed (Day 0). Half the AA cows that were detected in oestrus between Days 0 and 3 were randomly assigned to be resynchronised by reinsertion of a clean used CIDR-B device on Day 15, for a period of 6 days, followed by an I/M injection of 0.5 mg ODB, 1 day after the device was removed (resynchrony, RS), while the other half were not resynchronised (no-RS). NDO/CL+ cows were alternately assigned to be either treated with 25 mg of the PG, dinoprost tromethamine, on Day 0 or left as untreated controls (Con).

RESULTS

Resynchrony increased the percentage of cows detected in oestrus between Days 14 and 28 (212/282 = 75.2% vs 155/285 = 54.4%, for RS vs no-RS, respectively; p<0.001), but had no effect on conception rate to a service within the first 3 days of the mating period (146/397 = 36.8% vs 148/399= 37.1%, for RS vs no-RS cows, respectively; p>0.9), or to a service between Days 14 and 28 (84/159 = 52.8% vs 114/217 = 52.5%, for RS vs no-RS cows, respectively; p>0.9). Resynchrony increased the Day 28 pregnancy rate (264/432 = 61.1% vs 237/435 = 54.5%, for RS vs no-RS cows, respectively; p=0.03), but had no effect on the Day 56 or final pregnancy rates (p>0.1).Prostaglandin treatment of NDO/CL+ cows did not affect the percentage of cows detected in oestrus by Day 7 (43/106 = 40.6% vs 51/101 = 50.5%, for Con vs PG, respectively; p=0.15), or Day 28 (92/106 = 86.8% vs 91/101 = 90.1%, for Con vs PG, respectively; p>0.4). Treatment did not affect the Day 28 pregnancy rate (55/103 = 53.4% vs 54/98 = 55.1%, for Con vs PG, respectively; p>0.9), the Day 56 pregnancy rate (81/103 = 78.6% vs 74/98 = 75.5%, for Con vs PG, respectively; p>0.6), or the final pregnancy rate (98/103 = 95.1% vs 89/97 = 91.8%, for Con vs PG, respectively; p>0.3).

CONCLUSIONS

Resynchrony of AA cows treated using the present protocol increased the proportion of non-pregnant cows detected in oestrus between Days 14 and 28 and increased the Day 28 pregnancy rate. This resynchrony protocol may be useful for increasing the proportion of the herd pregnant in the first month of the breeding programme, especially in herds that have a history of a low proportion of non-pregnant cows detected in oestrus between Days 14 and 28. There was no benefit in treating NDO/CL+ cows with PG compared to no treatment.

Invited review: Treatment of cows with an extended postpartum anestrous interval

Cows with an extended interval from calving to first ovulation (PPI) have increased intervals from calving to conception and are more likely to be culled compared with cows with a short PPI. In year-round calving dairy herds, between 11 and 38% of cows are reported as anestrus by 50 or 60 d after calving. In seasonally calving dairy herds, between 13 and 48% of cows are diagnosed as anovulatory anestrus at the start of the breeding period. Ovulation and estrus after calving are delayed when the positive feedback effects of estradiol on release of LH from the pituitary, and circulating concentrations of metabolic hormones such as insulin and insulin-like growth factor-I, are reduced by a variety of environmental factors. The main factors are limited energy intake, lower body reserves, increased partitioning of energy to milk production, suckling, and peripartum disease. Treatment options for cows with an extended PPI include hormonal and management strategies. Hormonal treatments that include a period of progesterone supplementation result in the majority of treated animals displaying estrus with a subsequent luteal phase of normal duration and improved pregnancy rates compared with untreated controls. Hormonal interventions also tend to have more predictable outcomes compared with management changes, such as manipulating body condition or dietary intakes after calving, and usually have some estrous synchronization effect, thus facilitating the use of artificial insemination. However, responses to any treatment are variable and are related to those factors that influence duration of the PPI, such as body condition and parity.

Management factors associated with the incidence of clinical mastitis over the non-lactation period and bulk tank somatic cell count during the subsequent lactation

AIM

To evaluate associations between management decisions related to the control of mastitis, including the infusion of antibiotics at the end of lactation (dry-cow therapy; DCT), on the incidence of clinical mastitis over the non-lactating period and the bulk tank somatic cell count (BTSCC) in the subsequent lactation.

METHODS

Dairy herd owners (n=158) provided information via a retrospective survey about (a) the proportion of their herds treated with DCT; (b) DCT management, including: number of occasions on which cows were dried off; manipulation of feed and water intake around drying off; infusion technique (partial vs full depth insertion of cannula); and hygiene before and after DCT infusion; (c) occurrence of mastitis and frequency of occurrence following drying off and in the subsequent lactation; (d) number of cows culled for mastitis-related conditions; (e) reasons for culling; (f) incidence of clinical mastitis; and (g) stock purchase policy with regard to mastitis. The BTSCC for each vat of milk supplied for the 1999/2000 and 2000/2001 seasons, and records of antibiotic purchases were collated for each herd. The probability that >2% of cows within a herd were diagnosed with clinical mastitis over the dry period was initially examined using univariate analysis (i.e. chi2 or logistic regression) and associated factors (p<0.2) were offered to a reverse stepwise logistic regression model. Factors hypothesised as being associated with the average lactation log10 BTSCC for the 2000/2001 season were initially examined using univariate analysis (i.e. ANOVA or linear regression analysis) and associated factors (p<0.2) were then tested using a forward manual model-building approach.

RESULTS

Increasing the percentage of the herd treated with DCT at the end of lactation was associated with reduced probability that >2% of a herd would be diagnosed with clinical mastitis over the non-lactating period and with a lower BTSCC in the subsequent lactation (p<0.01). A lower BTSCC was associated with small herds (<150 cows; p<0.05), not reducing feed intake around drying off (p<0.05), checking for clinical mastitis over the dry period in the milking parlour rather than at pasture (p<0.05), partial insertion of the DCT cannula (p<0.01), and use of 'change in udder shape' during lactation as a diagnostic criterion for mastitis (p<0.05). The incidence of clinical mastitis over the dry period was positively associated with reduced feeding around drying off (p=0.05) and the estimated volume of milk being produced at the time of drying off (p=0.014).

CONCLUSIONS

Use of dry cow therapy was associated with fewer cases of clinical mastitis over the non-lactating period and reduced BTSCC over the subsequent lactation. Reduced BTSCC was also associated with smaller herds, use of partial (compared with full depth) insertion of the DCT cannula, not reducing feed intake at the time of drying off, checking for clinical mastitis over the dry (non-lactation) period in the milking parlour, and use of udder shape for diagnosis during lactation. Control of clinical mastitis and BTSCC involves a range of management practices that need to be used in conjunction with DCT.

KEYWORDS

Dairy cows, mastitis, dry-cow therapy, somatic cell count, management practices.

Influence of estrus on somatic cell count in dairy goats

The effect of estrus on the somatic cell count (SCC) of goat's milk was examined by inducing estrus in 24 of 48 seasonally anestrus, lactating dairy goats. Goats were blocked by infection status and ranked on SCC from three preceding herd tests and randomly allocated (within block) to the following three treatment groups: a) "Short," in which an intravaginal progesterone-releasing device was inserted for 12 d plus equine chorionic gonadotropin and dinoprost tromethamine 2 d before device removal (n = 12), b) "Long," in which an intravaginal progesterone-releasing was inserted for 17 d plus equine chorionic gonadotropin on the day of device removal (n = 12), or c) "Control," in which the goats were left as untreated controls (n = 24). Bacteriological status of each gland of each goat was determined before and after synchronization (d -23 and +13) and SCC and milk volumes were determined on d -2, 0, 1, 2, 3, 4, 14, and 25, where d 0 was the day of intravaginal device removal. Goats in the Short group were in estrus before those of the Long group, who were, in turn, in estrus before the Control group. The log10 and log10 absolute SCC (SCC cells/ml x volume) were higher in the Short than in the Control group on d 1, 2, 3, and 4, whereas those of the Long group were higher than those of the Control group on d 2 and 4. These data indicate that estrus resulted in an increase in SCC, and that the increase in SCC was independent of the decline in milk volume at estrus.

Preferential recognition of a fragment species of osteoarthritic synovial fluid fibronectin by antibodies to the alternatively spliced EIIIA segment

OBJECTIVE

To characterize the species of synovial fluid (SF) fibronectin (FN) bearing the alternatively spliced EIIIA segment.

METHODS

SF from patients with osteoarthritis (OA) and rheumatoid arthritis (RA), as well as corresponding affinity isolation products, were subjected to 1-dimensional and 2-dimensional electrophoresis followed by Western blot analysis.

RESULTS

Regardless of the clinical type of arthritis, a polyclonal antibody that recognizes antigenic determinants throughout the FN molecule produced staining of predominantly approximately 200+ and approximately 170-kd species in reduced 1-dimensional electrophoresis. Despite the overall prevalence of the larger species, 4 monoclonal antibodies (mAb) reactive with sequences lying near the center of the EIIIA segment exhibited a relative failure to recognize the larger of these 2 species in OA, but not RA, SF. The absence of recognition of EIIIA sequences within the approximately 200+ kd forms of OA SF FN was unrelated to their derivation from dimers, since anti-EIIIA mAb recognized the smaller fragment species in preference to both monomeric and dimeric forms. The approximately 170-kd EIIIA+ fragments were observed to have minimal gelatin-binding capacity and appeared on 2-dimensional electrophoresis to extend from the N-terminus of FN through at least the center of the EIIIA segment. Similar results were obtained for samples obtained by needle aspiration or arthroscopic lavage, suggesting a widespread applicability of these findings.

CONCLUSION

The approximately 170-kd EIIIA+ species of FN could potentially constitute a soluble "vehicle" by which chondrocyte-regulating EIIIA sequences, liberated from inhibitory flanking C-terminal sequences, could reach cells in the arthritic joint. Additionally, "FN species-specific" recognition of this segment within OA SF could constitute a marker by which to gauge the activity of the OA disease process.

Treatment of anovulatory anoestrous postpartum dairy cows with a gonadotropin-releasing hormone (GnRH), prostaglandin F2𝛂, GnRH regimen or with progesterone and oestradiol benzoate

AIM

To compare 2 treatments for anovulatory anoestrus (AA) in postpartum dairy cows. The treatments were combinations of gonadotropin-releasing hormone (GnRH) and prostaglandin F2 (PG) or progesterone (P4) and oestradiol benzoate (ODB).

METHODS

Forty AA cows from each of 5 herds were blocked by age (2 or 2 years old) and randomly assigned to 1 of 2 treatments. The first group (GPG) were treated with 250 mug of a GnRH analogue, gonadorelin, followed 7 days later by 15 mg of the PG analogue, luprostiol. Two days later the cows were injected with 250 mug of gonadorelin. Cows were artificially inseminated 16-24 h after the second GnRH injection. The second group (P4+ODB) were treated with an intravaginal P4 releasing device for 6 days, followed 24 h after device removal by injection of 1 mg of ODB. Cows were pregnancy tested 35-40 days after the initial insemination and twice again at 6-8 week intervals thereafter.

RESULTS

There was no significant difference between P4+ODB and GPG groups in the percentage of cows submitted for insemination in the first 7 days (94.0% vs 100% for P4+ODB vs GPG, respectively; p>0.3), in conception rate to first insemination within the first 7 days (43.6% vs 35.0% for P4+ODB vs GPG, respectively; p>0.2), in the percentage of cows conceiving in the first 28 days of the breeding period (68.0% vs 58.3%, P4+ODB vs GPG, respectively; p>0.1), or in median interval from the end of treatment to conception (20 vs 21 days; p>0.1).

CONCLUSIONS

No differences in the reproductive performance of AA cows treated with either P4+ODB or GPG were detected. However, given the small number of animals enrolled, further data are required before the GPG protocol can be recommended for treatment of AA cows.