Development and application of an interactive generic physiologically based pharmacokinetic (igPBPK) model for adult beef cattle and lactating dairy cows to estimate tissue distribution and edible tissue and milk withdrawal intervals for per- and polyfluoroalkyl substances (PFAS)

Humans can be exposed to per- and polyfluoroalkyl substances (PFAS) through dietary intake from milk and edible tissues from food animals. This study developed a physiologically based pharmacokinetic (PBPK) model to predict tissue and milk residues and estimate withdrawal intervals (WDIs) for multiple PFAS including PFOA, PFOS and PFHxS in beef cattle and lactating dairy cows. Results showed that model predictions were mostly within a two-fold factor of experimental data for plasma, tissues, and milk with an estimated coefficient of determination (R2) of >0.95. The predicted muscle WDIs for beef cattle were <1 day for PFOA, 449 days for PFOS, and 69 days for PFHxS, while the predicted milk WDIs in dairy cows were <1 day for PFOA, 1345 days for PFOS, and zero day for PFHxS following a high environmental exposure scenario (e.g., 49.3, 193, and 161 ng/kg/day for PFOA, PFOS, and PFHxS, respectively, for beef cattle for 2 years). The model was converted to a web-based interactive generic PBPK (igPBPK) platform to provide a user-friendly dashboard for predictions of tissue and milk WDIs for PFAS in cattle. This model serves as a foundation for extrapolation to other PFAS compounds to improve safety assessment of cattle-derived food products.

An Interactive Generic Physiologically Based Pharmacokinetic (igPBPK) Modeling Platform to Predict Drug Withdrawal Intervals in Cattle and Swine: A Case Study on Flunixin, Florfenicol and Penicillin G

Violative chemical residues in edible tissues from food-producing animals are of global public health concern. Great efforts have been made to develop physiologically based pharmacokinetic (PBPK) models for estimating withdrawal intervals (WDIs) for extralabel prescribed drugs in food animals. Existing models are insufficient to address the food safety concern as these models are either limited to 1 specific drug or difficult to be used by non-modelers. This study aimed to develop a user-friendly generic PBPK platform that can predict tissue residues and estimate WDIs for multiple drugs including flunixin, florfenicol, and penicillin G in cattle and swine. Mechanism-based in silico methods were used to predict tissue/plasma partition coefficients and the models were calibrated and evaluated with pharmacokinetic data from Food Animal Residue Avoidance Databank (FARAD). Results showed that model predictions were, in general, within a 2-fold factor of experimental data for all 3 drugs in both species. Following extralabel administration and respective U.S. FDA-approved tolerances, predicted WDIs for both cattle and swine were close to or slightly longer than FDA-approved label withdrawal times (eg, predicted 8, 28, and 7 days vs labeled 4, 28, and 4 days for flunixin, florfenicol, and penicillin G in cattle, respectively). The final model was converted to a web-based interactive generic PBPK platform. This PBPK platform serves as a user-friendly quantitative tool for real-time predictions of WDIs for flunixin, florfenicol, and penicillin G following FDA-approved label or extralabel use in both cattle and swine, and provides a basis for extrapolating to other drugs and species.

Late-Gestation in utero Heat Stress Limits Dairy Heifer Early-Life Growth and Organ Development

Dairy calves exposed to late-gestation heat stress weigh less, have impaired immunity, produce less milk across multiple lactations, and have reduced productive life. However, less is known about the relationship between in utero heat stress and organ morphology and development. Herein, we characterized the consequences of late-gestation in utero heat stress on body and organ growth trajectories during early-life development. Holstein heifers were either in utero heat-stressed (IU-HT, n = 36, dams exposed to THI &gt; 68) or cooled (IU-CL, n = 37, dams exposed to THI &gt; 68 with access to active cooling) during late gestation (54 ± 5 d prepartum). All heifers were reared identically from birth to weaning. Upon birth, calves were weighed and fed 3.78 L of colostrum followed by 0.87 kg DM/d milk replacer (MR) over two feedings and ad libitum starter concentrate daily. Weaning began at 49 d and ended at 56 d of age. Feed intake was recorded daily, and body weight (BW) and other growth measures were recorded at 0, 28, 56, and 63 d. Blood was collected at d 1 then weekly. Subsets of heifers were selected for euthanasia at birth and 7 d after complete weaning (n = 8 per group each) to harvest and weigh major organs. Reduced BW and stature measures persisted in IU-HT heifers from 0 to 63 d of age with a 7% lower average daily gain and reduced starter consumption relative to IU-CL heifers. IU-HT heifers had lower hematocrit percentages and reduced apparent efficiency of absorption of IgG relative to IU-CL heifers. Additionally, IU-HT heifers had reduced gross thymus, spleen, thyroid gland, and heart weight at birth and larger adrenal glands and kidneys but smaller ovaries relative to BW at 63 d. The mammary gland of IU-HT heifers was smaller relative to IU-CL heifers at birth and 63 d adjusted for BW, suggesting mechanisms leading to impaired milk yield in mature IU-HT cows are initiated early in development. In summary, in utero heat stress reduces whole-body size and limits development of key organs with potential repercussions on dairy calf metabolic adaptation, immune function, and future productivity.

Development and Application of an interactive Physiologically Based Pharmacokinetic (iPBPK) Model to Predict Oxytetracycline Tissue Distribution and Withdrawal Intervals in Market-Age Sheep and Goats

Oxytetracycline (OTC) is a widely used antibiotic in food-producing animals. Extralabel use of OTC is common and may lead to violative residues in edible tissues. It is important to have a quantitative tool to predict scientifically-based withdrawal intervals (WDIs) after extralabel use in food animals to ensure human food safety. This study focuses on developing a physiologically based pharmacokinetic (PBPK) model for OTC in sheep and goats. The model included seven compartments: plasma, lung, liver, kidneys, muscle, fat, and rest of the body. The model was calibrated with serum and tissue (liver, muscle, kidney, and fat) concentration data following a single intramuscular (IM, 20 mg/kg) and/or intravenous (IV, 10 mg/kg) administration of a long-acting formulation in sheep and goats. The model was evaluated with independent datasets from Food Animal Residue Avoidance Databank (FARAD). Results showed that the model adequately simulated the calibration datasets with an overall estimated coefficient of determination (R2) of 0.95 and 0.92, respectively, for sheep and goat models and had acceptable accuracy for the validation datasets. Monte Carlo sampling technique was applied to predict the time needed for drug concentrations in edible tissues to fall below tolerances for the 99th percentiles of the population. The model was converted to a web-based interactive PBPK (iPBPK) interface to facilitate model applications. This iPBPK model provides a useful tool to estimate WDIs for OTC after extralabel use in small ruminants to ensure food safety and serves as a basis for extrapolation to other tetracycline drugs and other food animals.

Physiological parameter values for physiologically based pharmacokinetic models in food-producing animals. Part III: Sheep and goat

This report is the third in a series of studies that aimed to compile physiological parameters related to develop physiologically based pharmacokinetic (PBPK) models for drugs and environmental chemicals in food‐producing animals including swine and cattle (Part I), chickens and turkeys (Part II), and finally sheep and goats (the focus of this manuscript). Literature searches were conducted in multiple databases (PubMed, Google Scholar, ScienceDirect, and ProQuest), with data on relevant parameters including body weight, relative organ weight (% of body weight), cardiac output, relative organ blood flow (% of cardiac output), residual blood volume (% of organ weight), and hematocrit reviewed and statistically summarized. The mean and standard deviation of each parameter are presented in tables. Equations describing the growth curves of sheep and goats are presented in figures. When data are sufficient, parameter values are reported for different ages or production classes of sheep, including fetal sheep, lambs, and market‐age sheep (mature sheep). These data provide a reference database for developing standardized PBPK models to predict drug withdrawal intervals in sheep and goats, and also provide a basis for extrapolating PBPK models from major species such as cattle to minor species such as sheep and goats.

Mycoplasma bovis: Interactions with the Immune System and Failure to Generate an Effective Immune Response

Host responses are often ineffective at clearing Mycoplasma bovis infection and may contribute to the pathogenesis of disease. M bovis possesses a surprisingly large repertoire of strategies to evade and modulate host responses. Unopsonized M bovis impairs phagocytosis and killing by neutrophils and macrophages. Apoptosis of neutrophils and lymphocytes is enhanced, whereas it is delayed in macrophages. Both proinflammatory and antiinflammatory cytokines are stimulated during M bovis infection depending on the cell type and location, and overall systemic responses tend to have a T-helper 2 bias. M bovis reduces proliferation of T cells and, in chronic infection, causes T-cell exhaustion.

Epidemiologic and economic analyses of pregnancy loss attributable to mastitis in primiparous Holstein cows

The main objective of the study reported here was to examine the association between pregnancy loss (PL) and previous exposure to clinical or subclinical mastitis before breeding or during gestation in primiparous Holstein cows. A secondary objective was to estimate the cost of clinical mastitis during gestation, including that of PL attributable to mastitis in study cows. A total of 687 primiparous Holstein cows from 1 dairy farm were included in a matched case-control study. Study cows were declared pregnant via ultrasound on d 33 after timed artificial insemination (TAI). Case cows (n = 78) were those diagnosed as nonpregnant by rectal palpation on d 47 or 75 after TAI. Control cows were those confirmed as pregnant by rectal palpation on d 47 and 75 after TAI. Case cows were matched with eligible controls according to year of calving and calving-to-conception interval ±3 d. Cows were assigned to 1 of 3 groups: (1) cows not affected with clinical or subclinical mastitis; (2) cows affected with subclinical mastitis (Dairy Herd Improvement Association somatic cell score >4.5); and (3) cows affected with clinical mastitis during 2 exposure periods, 1 to 42 d before breeding or during gestation (1 to PL diagnosis day for case cows, and 1 to 75 d for control cows). Conditional logistic regression was used to model the odds of PL as a function of previous exposure to mastitis in study cows. Mastitis before breeding was not associated with PL. The odds of PL were 2.21 times greater in cows affected with clinical mastitis during gestation (95% confidence interval = 1.01, 4.83), compared with cows without mastitis, after controlling for breeding type and lameness. The cost of clinical mastitis during gestation was $149, which includes the cost ($27) of PL attributable to mastitis. In conclusion, this study provides evidence that clinical mastitis during gestation can cause PL in primiparous dairy cows leading to economic losses.

Evaluation of milk components as diagnostic indicators for rumen indigestion in dairy cows

OBJECTIVE To identify milk component alterations that might be useful for detecting cows with rumen indigestion. DESIGN Prospective case-control study. ANIMALS 23 Holstein cows with rumen indigestion (cases) and 33 healthy cohorts (controls) from 1 herd. PROCEDURES Cases were defined as cows between 30 and 300 days postpartum with a > 10% decrease in milk yield for 2 consecutive milkings or > 20% decrease in milk yield from the 10-day rolling mean during any milking, abnormally decreased rumen motility, and no other abnormalities. Each case was matched with 2 healthy cows (controls) on the basis of pen, parity, days postpartum, and mean milk yield. Some cows were controls for multiple cases. All cows underwent a physical examination and collection of a rumen fluid sample for pH measurement at study enrollment. Individual-cow milk yield and milk component data were obtained for the 16 milkings before and after study enrollment. Rumen motility and pH and milk components were compared between cases and controls. RESULTS Rumen motility for cases was decreased from that of controls. Cases had an abrupt increase in milk fat percentage and the milk fat-to-lactose ratio during the 2 milkings immediately before diagnosis of rumen indigestion. Receiver operating characteristic analyses revealed that a 10% increase in the milk fat-to-lactose ratio had the highest combined sensitivity (57%) and specificity (85%) for identifying cows with rumen indigestion. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a positive deviation in the milk fat-to-lactose ratio might be useful for identifying cows with rumen indigestion.

Increasing intake of essential fatty acids from milk replacer benefits performance, immune responses, and health of preweaned Holstein calves

The objective was to evaluate the effect of feeding increasing amounts of essential fatty acids (FA) in milk replacer (MR) during the first 60 d of life on growth, health, and immunity of Holstein calves. Calves were born from dams fed low concentrations of total and essential FA during the lasT2 mo of pregnancy. Newborn calves were blocked by sex and parity of the dam and assigned randomly to receive 1 of 4 MR treatments (T). Hydrogenated coconut oil and soybean oil were mixed with emulsifier and commercial MR powder to prepare the following 4 MR containing 0.119 and 0.007 (T1), 0.187 and 0.017 (T2), 0.321 and 0.036 (T3), and 0.593 and 0.076 (T4) g of intake per kg of metabolic body weight (BW(0.75)) of linoleic acid and α-linolenic acid, respectively. At 30 d of life, concentrations of essential FA (linoleic acid and α-linolenic acid) in liver increased, whereas concentrations of C12:0, C14:0, C16:0, and C20:3n-9 decreased linearly with increasing intake of essential FA. Body weight gain and feed efficiency were optimized when male calves consumed T2, whereas gain by female calves tended to increase linearly with increasing intake of essential FA during the first 30 d of age. However, these responses to treatment were not maintained after initiation of concentrate feeding at 31 d of life. Over the 60-d preweaning period, wither and hip heights were improved in both sexes as intake of essential FA increased up to T3. Some measures of health and immunity were affected by replacing some coconut oil with soybean oil. Severity of diarrhea tended to decrease linearly; plasma concentrations of haptoglobin during diarrhea were lower in T2, T3, and T4; phagocytosis by blood neutrophils tended to peak for calves fed T2; in vitro proliferation of stimulated blood lymphocytes was greater for calves fed T2; in vitro stimulated blood cells produced more IFN-γ (up to T3 for males and T2 for females), concentrations of serum IgG against ovalbumin injections were increased in males fed T2 or T3; and skin-fold thickness increased in response to an intradermal antigen injection of all calves fed up to T4. Across sex and under the conditions of the present study, mean daily intakes of linoleic acid between 3 to 5g/d and intakes of α-linolenic acid between 0.3 and 0.6g/d during the first 30 d of life promoted growth of preweaned Holstein calves, possibly by improving their immune status.

Mycoplasma bovis Infections in young calves

Mycoplasma bovis has emerged as an important pathogen of young intensively reared calves in North America. A variety of clinical diseases are associated with M bovis infections of calves, including respiratory disease, otitis media, arthritis, and some less common presentations. Clinical disease associated with M bovis often is chronic, debilitating, and poorly responsive to antimicrobial therapy. Current control measures are centered on reducing exposure to M bovis through contaminated milk or other sources, and nonspecific control measures to maximize respiratory defenses of the calf. This article focuses on the clinical and epidemiologic aspects of M bovis infections in young calves.

Field evaluation of a Mycoplasma bovis bacterin in young dairy calves

Mycoplasma bovis is an important cause of pneumonia, otitis media and arthritis in young dairy calves, and there is a critical need for improved preventative strategies for this pathogen. We conducted a randomized, placebo-controlled, double-blinded field trial to determine the efficacy of a commercial M. bovis vaccine for the prevention of M. bovis-associated disease in calves. Calves (n = 373) on 3 Florida dairies with a history of M. bovis infection received an M. bovis bacterin or a placebo, administered subcutaneously at 3, 14 and 35 days of age. One of the herds did not experience M. bovis-associated disease; for calves in the remaining 2 herds, the incidence risk for respiratory disease, otitis media and arthritis from 3 to 90 days of age was 0.64, 0.28 and 0.02, respectively. Vaccination had no effect on the age at first treatment for M. bovis-associated disease, incidence of respiratory disease, mortality, weight gain, or nasal colonization with M. bovis in the first 90 days of life. In one herd, vaccination was associated with an increased risk of otitis media. There was no association between M. bovis-specific serum antibody titers and morbidity in vaccinated calves. Under the field conditions in this study, this vaccine was not efficacious for the prevention of M. bovis-associated disease in young dairy calves.

Hematogenous infection of Sprague-Dawley rats with Mycoplasma pulmonis: development of a model for maternal and fetal infection

OBJECTIVES

The specific objective of this study was to conduct a dose response experiment with Mycoplasma pulmonis in Sprague-Dawley rats to develop a reproducible animal model of maternal and fetal infection that would provide a versatile mechanism to address the innate fetal immune response during intrauterine infection.

STUDY DESIGN

Pregnant rats were infected intravenously at gestation day 14 with 0 (control), 10(1), 10(3), 10(5), and 10(7) colony forming units of M. pulmonis and necropsied at gestational day 18. Quantitative culture of maternal and fetal tissues as well as histopathologic examination of the placenta were performed.

RESULTS

We have characterized a rat model of maternal and fetal infection that can be manipulated by alteration of infectious dose. Colonization of Sprague-Dawley rat dam and fetal tissues by M. pulmonis occurred in a dose-dependent manner after intravenous inoculation (P < .001). Placental lesion severity increased with infection dose (P = .0001). The minimum threshold dose required to establish infection of the dam and fetus was at least 10(3) colony forming units, with consistent colonization of maternal and fetal tissues achieved only with 10(7) colony forming units. In some instances, rat fetal tissues could be colonized in the absence of concomitant amniotic fluid colonization. Interestingly, there appeared to be a predilection for colonization of the reproductive tissues.

CONCLUSIONS

In the Sprague-Dawley rat, the infection rate of both the dam and fetus can be controlled by the inoculum dose. Our data support the concept that hematogenous spread of M. pulmonis to the rat fetus can occur without amniotic fluid infection and suggest that the fetus itself can potentially seed the amniotic fluid with microorganisms. Importantly, manipulation of both the route of infection as well as infection dose provide a reproducible way to study both maternal and fetal immune response to infection during pregnancy.

Factors associated with colostral specific gravity in dairy cows

The objectives of this study were to identify factors associated with colostral specific gravity in dairy cows, as measured by a commercially available hydrometer (Colostrometer). Colostral specific gravity was measured in 1085 first-milking colostrum samples from 608 dairy cows of four breeds on a single farm during a 5-yr period. Effects of breed, lactation number, and month and year of calving on colostral specific gravity were determined, as were correlations between colostral specific gravity, nonlactating period length, and 305-d yields of milk, protein, and fat. For 75 multiparous Holstein cows, relationships between colostral specific gravity, colostral IgG1, protein, and fat concentrations, and season of calving were determined. Colostral specific gravity values were lower for Brown Swiss and Ayrshire cows than for Jersey and Holstein cows, and lower for cows entering first or second lactation than third or later lactations. Month of calving markedly affected colostral specific gravity values, with highest values occurring in autumn and lowest values in summer. In multiparous Holstein cows, colostral specific gravity was more strongly correlated with colostral protein concentration (r = 0.76) than IgG1 concentration (r = 0.53), and colostral protein concentration varied seasonally (higher in autumn than summer). Our results demonstrate that colostral specific gravity more closely reflects colostral protein concentration than IgG1 concentration and is markedly influenced by month of calving. These results highlight potential limitations of using colostral specific gravity as an indicator of IgG1 concentration.

Use of mammary gland and colostral characteristics for prediction of colostral IgG1 concentration and intramammary infection in Holstein cows

OBJECTIVE

To determine whether mammary gland or colostral characteristics at calving could be used to predict colostral immunoglobulin G1 (IgG1) concentration or intramammary infection (IMI) and whether leakage of colostrum affects IgG1 concentration.

DESIGN

Prospective study.

ANIMALS

113 multiparous Holstein cows.

PROCEDURE

Cows were examined within 3 hours of calving, and mammary gland and colostral characteristics, colostral volume, somatic cell count, and concentrations of IgG1, fat, and protein were determined. Bacteriologic culture of mammary secretions was performed approximately 14 and 7 days before calving and at calving. Associations of gland and colostral characteristics with colostral IgG1 concentration, colostral volume, and IMI were examined.

RESULTS

Thick or thin colostrum had higher IgG1 concentration than colostrum of intermediate viscosity. Colostrum from mammary glands that were firm had low IgG1 concentration. Colostral IgG1 concentration was weakly correlated with volume. Intramammary infection was likely to be detected if colostrum contained clots or blood or if the California Mastitis Test (CMT) score was > or = 2. Somatic cell count was higher for glands with IMI than for uninfected glands, and CMT score was correlated with cell count.

CLINICAL IMPLICATIONS

Mammary gland and colostral characteristics were of little value in predicting IgG1 concentration. Our findings do not support recommendations that first milking colostrum that is thin (watery) or that is from cows producing large volumes not be fed to dairy calves. Colostral characteristics, particularly CMT score, were of value for predicting IMI.

Effects of mastitis on the volume and composition of colostrum produced by Holstein cows

The effects of mastitis during the late nonlactating period on colostral volume and concentrations and total yields of immunoglobulin (Ig) G1, fat, and protein in colostrum were investigated using matched pairs of mammary glands from multiparous Holstein cows. Samples of mammary secretions were collected at approximately 14 and 7 d prepartum and within 3 h after calving. At each sampling time, the glands and secretions were examined for gross abnormalities, and the California Mastitis Test was performed. Duplicate secretion samples from each gland were cultured, and somatic cell count, pH, and fat and protein concentrations were determined. The volume of colostrum obtained at the first milking of each gland was quantified using a quarter milking device, and its IgG1 concentration was measured. Colostral volume from persistently infected mammary glands was lower than that from matched uninfected glands, as was the total mass of IgG1. However, infection did not alter IgG1 concentration in colostrum. Fat and protein percentages were lower in prepartum secretions but not in colostrum from infected glands. Persistent infection was associated with increased somatic cell count and pH of secretions at all sampling times, and California Mastitis Test scores were higher for colostrum from infected glands. The appearance of secretions was extremely variable, but the presence of flakes or clots in colostrum was associated with infection. We concluded that mastitis during the late nonlactating period alters mammary gland function but is unlikely to be an important contributor to the high rate of failure of passive transfer of immunoglobulins in calves.