Molecular epidemiology of Streptococcus uberis intramammary infections: Persistent and transient patterns of infection in a dairy herd.

A longitudinal observational study was carried out to explore transmission dynamics and duration of infection of Streptococcus uberis. Quarter milk samples were collected aseptically for bacterial culture from all lactating cows once a month over a 10-mo period. Molecular typing of S. uberis mastitis was performed using pulsed-field gel electrophoresis (PFGE). Molecular typing was used to determine episodes of S. uberis intramammary infection (IMI). Comparisons of spontaneous cure among PFGE types were performed using Fisher's exact chi-squared tests. Differences of duration among PFGE types and between periods of lactation were tested with Kaplan-Meier survival curves and Cox's proportional hazard model. Among a total of 851 quarter samples, 145 milk samples were detected with S. uberis presence. Based on results of PFGE, 66 episodes of S. uberis IMI were determined. From the 8 main PFGE types (A-H), PFGE type D, E, F1, F2, G, and H had only one episode indicating no evidence for transmission, subsequently defined as environmental S. uberis strains. In contrast, PFGE types A1, A2, B, C1, and C2 had at least 2 infection episodes caused by the same strain in different quarters or cows, indicating that these strains would be able to transmit to other quarters or cows. These strains were defined as contagious strains. The majority of IMI were attributable to PFGE type A1 (55%), B (17%), and A2 (11%). Spontaneous cures were observed in 35 IMI episodes. Of these 35 IMI cures, 91.4% were in IMI with duration of infection of 1 mo, n = 25, and 2 mo, n = 6. The remaining 8.6% was in IMI with duration of infection >2 mo, n = 4. Based on results from Cox's proportional hazard model, environmental S. uberis episodes were likely to have spontaneous cure with shorter duration compared with contagious S. uberis with PFGE type B (hazard ratio = 8.4). Quarters infected with S. uberis strain PFGE type A in early lactation were more likely to persist compared with those infected in late lactation (hazard ratio = 7.57). In conclusion, the majority of S. uberis IMI in this herd were transient and showed spontaneous cure. In addition to environmental S. uberis IMI, at least 3 types of contagious IMI S. uberis can be defined as (1) short duration of IMI and likely to have spontaneous cure, (2) long duration and unlikely to have spontaneous cure, and (3) wide range of duration of IMI either transient or persistent where spontaneous cure may occur depending on host defense capacity.

In vitro maturation of class I oocytes of bovine during different tropical seasons.

The aims of this study were to determine the effects of seasonality on yields and quality of bovine abattoir-derived oocytes and their in vitro maturation (IVM) competence in Thailand, a tropical country. Ovaries were collected monthly from a slaughterhouse, from January to June 2017, separated into cool (January to February), summer (March to April), and rainy (May to June) seasons. Cumulus oocyte complexes (COCs) were obtained by follicular aspiration, and subsequently, oocyte yield and quality were examined. Selected class I and II COCs were cultured under IVM condition, and their maturation capacity was also evaluated. Results showed that average numbers of COCs and class I COCs per ovary were highest in summer. However, no significant seasonal difference in oocyte maturation rates was found. The higher numbers of COCs and class I COCs in summer might be caused by their follicular development during the cool season, and might be a reason why the pregnancy rate in summer is better than in the rainy season.

Isolation and screening of aflatoxin-detoxifying yeast and bacteria from ruminal fluids to reduce aflatoxin B1 contamination in dairy cattle feed.

AIMS: To obtain yeast and bacteria from ruminal fluids that possess aflatoxin B1 (AFB1 ) detoxifying ability for use in animal feed. METHODS AND RESULTS: Sources of isolation were ruminal fluids of three nonfistulated dairy cows, fed diets containing cassava pulp, rice straw or distillery yeast sludge. The isolation was carried out to screen for the isolates that were active in both anaerobic and aerobic conditions. Three yeast and three bacteria isolates were selected. Up to 85% of AFB1 was detoxified by yeast isolates and up to 60% AFB1 reduction was evident by bacteria isolates. Two yeast isolates were identified as Kluyveromyces marxianus and one isolate as Pichia kudriavzevii. The three bacteria isolates were identified as Enterococcus faecium, Corynebacterium phoceense and C. vitaeruminis. All strains showed high biomass production when cultivated in medium with 80 g l-1 glucose. CONCLUSIONS: The isolated yeast and bacteria with AFB1 detoxifying ability showed a good potential to be applied as an aflatoxin-detoxifying agent to ingredients used to feed dairy cattle. SIGNIFICANCE AND IMPACT OF THE STUDY: The abilities of isolates to survive and be active in anaerobic and aerobic conditions rendered them to be active in cattle's rumen. Their biomass could be produced in bulk and used as feed supplement for aflatoxin detoxification in dairy cattle.

Increases of antibiotic resistance in excessive use of antibiotics in smallholder dairy farms in northern Thailand.

Antibiotic resistance patterns of bacterial isolates from both quarter teat-tip swabs and their quarter milk samples were evaluated in smallholder dairy farms in northern Thailand with excessive use of antibiotics (HIGH) compared with normal use (NORM). Results from teat-tip swab samples showed that the percentage of Bacillus spp. resistance to overall antibiotics was significantly lower in the NORM group than that of the HIGH group, whereas, the resistance percentage of coagulase-negative staphylococci in the NORM group was higher than that of the HIGH one. The overall mastitis-causing bacteria isolated from milk samples were environmental streptococci (13.8%), coagulase-negative staphylococci (9.9%), Staphylococcus aureus (5.4%), and Corynebacterium bovis (4.5%). Both staphylococci and streptococci had significantly higher percentages of resistance to cloxacillin and oxacillin in the HIGH group when compared to the NORM one. An occurrence of vancomycin-resistant bacteria was also observed in the HIGH group. In conclusion, the smallholder dairy farms with excessive use of antibiotics had a higher probability of antibiotic-resistant pattern than the farms with normal use.

Hyperketonemia and the impairment of udder defense: a review.

The objective of this study was to review the possible relationships between hyperketonemia and the function of phagocytes with respect to the bovine udder defense mechanism. We hypothesize that an increased incidence of clinical mastitis in high-producing cows is caused by the impairment of the udder defense mechanism during hyperketonemia. First, we review the acute phase of udder defense mechanisms after intramammary infection. The physiological changes of cows in negative energy balance are subsequently discussed. Finally, possible relationships between udder defense and physiological changes during negative energy balance, especially hyperketonemia, are reviewed. The three stages of an acute phase of udder defense are: (1) immediately eliminating invading pathogens by phagocytes, (2) releasing inflammatory substances, especially chemoattractants, and (3) migration of polymorphonuclear leukocytes into the infected udder. Leukocytes from hyperketonemia subjects show a lower capacity of the phagocytic defense mechanism. In addition, the phagocytic and bactericidal capacities of neutrophils are reduced when these cells are acting in the presence of high concentrations of ketone bodies. Lower amounts of cytokine production after bacterial infection are observed in ketotic subjects. The chemotactic capacity of blood leukocytes is impaired in leukocytes obtained from ketotic cows. Lower numbers of blood leukocytes are observed in ketotic cows. In conclusion, the impairment of the udder defense mechanism in negative energy balance cows seems related to hyperketonemia.

Low somatic cell count: a risk factor for subsequent clinical mastitis in a dairy herd.

A case-control study was conducted to evaluate factors measured at the udder inflammation-free state as risk factors for subsequent clinical mastitis. The factors including somatic cell count (SCC), body condition score, milk yield, percentages of milk fat and milk protein, and diseases were evaluated for their association with the results of udder inflammatory response. The results of the response were specified as presence (case) and absence (control) of clinical signs of mastitis. Data on Holstein Friesian cows calving from January 1984 to November 1996 from a commercial farm with low bulk milk SCC were used. Univariable and multivariable random-effect logistic models were used to evaluate the effect of those factors on the risk of clinical mastitis. The following variables were associated with increased odds of case versus control events in the univariable analysis: early lactation period, low SCC, high milk yield, high percentage of milk protein, high percentage of milk fat, low body condition score, retained placenta, and milk fever. For the final multivariable model of all variables used for analysis, only low SCC remained significantly associated with increased risk of subsequent clinical mastitis. The authors concluded that very low SCC during the udder inflammation-free state are associated with increased risk of clinical mastitis.

Beta-hydroxybutyrate levels in peripheral blood and ketone bodies supplemented in culture media affect the in vitro chemotaxis of bovine leukocytes.

The role of ketone bodies on chemotactic capacities of leukocytes was characterized in two experiments. Experiment I was performed to investigate the association between serum beta-hydroxybutyrate concentrations (BHB) and in vitro chemotaxis of leukocytes. Cows were divided into low-BHB, medium-BHB, and high-BHB ones and classified according to their BHB. Leukocytes from high-BHB cows had a significantly lower chemotactic differential than leukocytes from low-BHB cows (p < 0.01). The effect of adding ketone bodies into in vitro chemotaxis cultures on leukocytes chemotaxis was studied in Experiment II. Either individual or a combination of commercial ketone bodies - sodium salts of BHB (BHBA), lithium salt of acetoacetate (ACAC), and acetone (Acetone) - were diluted in culture media and divided into eight concentrations corresponding to concentrations of bovine subclinical and clinical ketosis. For leukocytes from medium- and high-BHB cow, the chemotactic indexes of leukocytes were reduced by ACAC and Acetone. Chemotactic differentials of cultures with ACAC and acetone supplementation from both sources of leukocytes were significantly lower than that of the control culture (p < 0.05). For leukocytes from high-BHB cows, chemotactic indexes were suppressed in a ketone-body environment. In conclusion, leukocytes from naturally-occurring ketotic cows have lower chemotactic differentials than those from non-ketotic cows, and a chemotactic capacity indicated by a chemotactic differential is impaired when leukocytes migrate in an environment with ketone bodies in vitro.

A Cox proportional-hazards model with time-dependent covariates to evaluate the relationship between body-condition score and the risks of first insemination and pregnancy in a high-producing dairy herd.

The objective of this study was to determine the relationship between body-condition score and postpartum reproductive efficiency in dairy cattle. Data on body-condition score, reproduction, diseases, and production from 1404 lactations of 639 cows, calving between January 1984 and November 1996 on a commercial farm, were used. The Cox proportional-hazards model with time-dependent covariates was used to qualify the relationship between body-condition score on a scale of 1 to 5 and risks of first insemination and pregnancy. Cows with body condition at calving < 3 had lower first-insemination risks. Loss of body-condition score between calving and 45 days after calving was associated with increased days open and days-to-first insemination. Cows with body-condition scores < 2 after Day 45 and before first insemination were less likely to be inseminated and become pregnant compared with cows that had higher body condition. Milk yield, mastitis, lameness, milk fever and genital infection were associated with a reduction in reproductive efficiency. The results indicated that loss of body-condition and actual body-condition scores before conception or first insemination or both can be used as a prognosis for days open and days-to-first insemination in dairy herds.