Prevalence of shiga toxin-producing Escherichia coli in dairy cattle and their products

The main objective of this review was to assess the role of dairy cattle and their products in human infections with Shiga toxin-producing Escherichia coli (STEC). A large number of STEC strains (e.g., members of the serogroups O26, O91, O103, O111, O118, O145, and O166) have caused major outbreaks and sporadic cases of human illnesses that have ranged from mild diarrhea to the life-threatening hemolytic uremic syndrome. These illnesses were traced to O157 and non-O157 STEC. In most cases, STEC infection was attributed to consumption of ground beef or dairy products that were contaminated with cattle feces. Thus, dairy cattle are considered reservoirs of STEC and can impose a significant health risk to humans. The global nature of food supply suggests that safety concerns with beef and dairy foods will continue and the challenges facing the dairy industry will increase at the production and processing levels. In this review, published reports on STEC in dairy cattle and their products were evaluated to achieve the following specific objectives: 1) to assemble a database on human infections with STEC from dairy cattle, 2) to assess prevalence of STEC in dairy cattle, and 3) to determine the health risks associated with STEC strains from dairy cattle. The latter objective is critically important, as many dairy STEC isolates are known to be of high virulence. Fecal testing of dairy cattle worldwide showed wide ranges of prevalence rates for O157 (0.2 to 48.8%) and non-O157 STEC (0.4 to 74.0%). Of the 193 STEC serotypes of dairy cattle origin, 24 have been isolated from patients with hemolytic uremic syndrome. Such risks emphasize the importance and the need to develop long-term strategies to assure safety of foods from dairy cattle.     

Estimation of quantitative trait loci effects in dairy cattle populations

Standard animal model programs can be modified to include the effect of a quantitative gene, even if only a fraction of the population is genotyped. Five methods to estimate the effect of a diallelic quantitative gene affecting a quantitative trait were compared to a standard animal model (model I) on simulated populations, based on mean squared errors and bias. In models II, III, and IV complete linkage between a single genetic marker and the quantitative trait gene was assumed. In models II and III the elements of the incidence matrix for the gene effect were 0 or 1 for genotyped individuals, and the probabilities of the possible candidate gene genotypes for individuals that were not genotyped. In model III segregation analysis was used to compute these probabilities. If only some of the cows were genotyped, the model III estimates were nearly unbiased, while model II underestimated the simulated effects. When only sires were genotyped, model II overestimated the simulated effect. In models V and VI two markers bracketing the quantitative gene with recombination frequencies of 0.1 and 0.2 with the quantitative gene were simulated, and the algorithm of Whittaker et al. (1996) was used to derive estimates of gene effect and location. In model V marker allele effects were included in the animal model analysis. In model VI, the model I genetic evaluations were analyzed. Model V estimates for both effect and location of the quantitative gene were unbiased, while model VI estimates were only 0.25 of the simulated effect.     

Photoperiodic effects on dairy cattle: a review

Since the initial report in 1978 of galactopoietic effects of a photoperiod of 16 h of light:8 h of darkness, numerous studies have confirmed long-day stimulation of milk yield. The endocrine factor(s) responsible for increased milk yield, however, has eluded identification. Recent studies suggest that insulin-like growth factor-I (IGF-I) may mediate the galactopoietic response to long day photoperiod. Indeed, long days increase IGF-I in heifers and lactating cows; in the latter case, the response preceded an increase in milk yield. In heifers and cows, the increase in IGF-I is independent of changes in circulating growth hormone. Melatonin feeding to mimic a short-day photoperiod suppressed the increase of IGF-I in heifers induced by long days. However, melatonin feeding had no effect on milk yield in cows. Despite lack of resolution of the endocrine mechanism, dairy producers are interested in how photoperiod management can be integrated with current practices throughout the lactation cycle. There is strong evidence that milk yield responses to long days persist through an entire lactation. Also, long days can be combined with bovine somatotropin (bST) to produce additive increases in milk yield. During the dry period, long days increase the periparturient surge of prolactin. However, relative to long days, short-day treatment during the dry period produces the largest magnitude of response in milk yield during the subsequent lactation. The response to short days during the dry period may be due to a priming effect on the photoperiodic response system. In summary, IGF-I has emerged as a possible mediator of the increase of milk yield in response to long-day photoperiod. Photoperiod can be combined effectively with other management techniques such as bST. Consideration of photoperiod management during the dry period is essential to maximize responses during the subsequent lactation.     

The effects of heat stress in Italian Holstein dairy cattle

The data set for this study comprised 1,488,474 test-day records for milk, fat, and protein yields and fat and protein percentages from 191,012 first-, second-, and third-parity Holstein cows from 484 farms. Data were collected from 2001 through 2007 and merged with meteorological data from 35 weather stations. A linear model (M1) was used to estimate the effects of the temperature-humidity index (THI) on production traits. Least squares means from M1 were used to detect the THI thresholds for milk production in all parities by using a 2-phase linear regression procedure (M2). A multiple-trait repeatability test-model (M3) was used to estimate variance components for all traits and a dummy regression variable (t) was defined to estimate the production decline caused by heat stress. Additionally, the estimated variance components and M3 were used to estimate traditional and heat-tolerance breeding values (estimated breeding values, EBV) for milk yield and protein percentages at parity 1. An analysis of data (M2) indicated that the daily THI at which milk production started to decline for the 3 parities and traits ranged from 65 to 76. These THI values can be achieved with different temperature/humidity combinations with a range of temperatures from 21 to 36°C and relative humidity values from 5 to 95%. The highest negative effect of THI was observed 4 d before test day over the 3 parities for all traits. The negative effect of THI on production traits indicates that first-parity cows are less sensitive to heat stress than multiparous cows. Over the parities, the general additive genetic variance decreased for protein content and increased for milk yield and fat and protein yield. Additive genetic variance for heat tolerance showed an increase from the first to third parity for milk, protein, and fat yield, and for protein percentage. Genetic correlations between general and heat stress effects were all unfavorable (from −0.24 to −0.56). Three EBV per trait were calculated for each cow and bull (traditional EBV, traditional EBV estimated with the inclusion of THI covariate effect, and heat tolerance EBV) and the rankings of EBV for 283 bulls born after 1985 with at least 50 daughters were compared. When THI was included in the model, the ranking for 17 and 32 bulls changed for milk yield and protein percentage, respectively. The heat tolerance genetic component is not negligible, suggesting that heat tolerance selection should be included in the selection objectives.     

Anti-methanogenic effects of monensin in dairy and beef cattle: A meta-analysis

Monensin is a widely used feed additive with the potential to minimize methane (CH₄) emissions from cattle. Several studies have investigated the effects of monensin on CH₄, but findings have been inconsistent. The objective of the present study was to conduct meta-analyses to quantitatively summarize the effect of monensin on CH₄ production (g/d) and the percentage of dietary gross energy lost as CH₄ (Y_m) in dairy cows and beef steers. Data from 22 controlled studies were used. Heterogeneity of the monensin effects were estimated using random effect models. Due to significant heterogeneity (>68%) in both dairy and beef studies, the random effect models were then extended to mixed effect models by including fixed effects of DMI, dietary nutrient contents, monensin dose, and length of monensin treatment period. Monensin reduced Y_m from 5.97 to 5.43% and diets with greater neutral detergent fiber contents (g/kg of dry matter) tended to enhance the monensin effect on CH₄ in beef steers. When adjusted for the neutral detergent fiber effect, monensin supplementation [average 32 mg/kg of dry matter intake (DMI)] reduced CH₄ emissions from beef steers by 19 ± 4 g/d. Dietary ether extract content and DMI had a positive and a negative effect on monensin in dairy cows, respectively. When adjusted for these 2 effects in the final mixed-effect model, monensin feeding (average 21 mg/kg of DMI) was associated with a 6 ± 3 g/d reduction in CH₄ emissions in dairy cows. When analyzed across dairy and beef cattle studies, DMI or monensin dose (mg/kg of DMI) tended to decrease or increase the effect of monensin in reducing methane emissions, respectively. Methane mitigation effects of monensin in dairy cows (–12 ± 6 g/d) and beef steers (–14 ± 6 g/d) became similar when adjusted for the monensin dose differences between dairy cow and beef steer studies. When adjusted for DMI differences, monensin reduced Y_m in dairy cows (–0.23 ± 0.14) and beef steers (–0.33 ± 0.16). Monensin treatment period length did not significantly modify the monensin effects in dairy cow or beef steer studies. Overall, monensin had stronger antimethanogenic effects in beef steers than dairy cows, but the effects in dairy cows could potentially be improved by dietary composition modifications and increasing the monensin dose.     

Evaluation of associative effects of total mixed ration for dairy cattle using in vitro gas production and different rumen inocula

BACKGROUND: Current feed evaluation systems for dairy cattle assume that nutritive values of feed components can be added, but do not take into account possible interactions among feed components. The main objective of this study was to investigate associative effects on in vitro gas production from total mixed ration (TMR), based on grass silage and cereal concentrate, and separate TMR components. TMR was incubated with inocula of free rumen liquid (FRL) and particle‐associated rumen liquid (PAL) for 48 h and donor cows were fed TMRs with three different particle sizes to evaluate their influence on associative effects. RESULTS: Associative effects on gas production largely occurred at 2 and 4 h of incubation and dissipated with time of incubation. Incubation of TMR with PAL increased (P < 0.01) gas production compared to FRL at all incubation times; however, associative effects were not different between rumen inocula. Dietary particle size affected associative effects on gas production when TMR was incubated with FRL (P < 0.05) compared to PAL, particularly at early hours of incubation. CONCLUSIONS: Associative effects at early incubation hours emphasise that summing the nutritive values of feedstuffs may underestimate fermentation intensity of TMR which may have implications for prediction of ruminal fermentation yield. Copyright © 2012 Society of Chemical Industry     

Major advances associated with environmental effects on dairy cattle

It has long been known that season of the year has major impacts on dairy animal performance measures including growth, reproduction, and lactation. Additionally, as average production per cow has doubled, the metabolic heat output per animal has increased substantially rendering animals more susceptible to heat stress. This, in turn, has altered cooling and housing requirements for cattle. Substantial progress has been made in the last quarter-century in delineating the mechanisms by which thermal stress and photoperiod influence performance of dairy animals. Acclimation to thermal stress is now identified as a homeorhetic process under endocrine control. The process of acclimation occurs in 2 phases (acute and chronic) and involves changes in secretion rate of hormones as well as receptor populations in target tissues. The time required to complete both phases is weeks rather than days. The opportunity may exist to modify endocrine status of animals and improve their resistance to heat and cold stress. New estimates of genotype × environment interactions support use of recently available molecular and genomics tools to identify the genetic basis of heat-stress sensitivity and tolerance. Improved understanding of environmental effects on nutrient requirements has resulted in diets for dairy animals during different weather conditions. Demonstration that estrus behavior is adversely affected by heat stress has led to increased use of timed insemination schemes during the warm summer months to improve conception rates by discarding the need to detect estrus. Studies evaluating the effects of heat stress on embryonic survival support use of cooling during the immediate postbreeding period and use of embryo transfer to improve pregnancy rates. Successful cooling strategies for lactating dairy cows are based on maximizing available routes of heat exchange, convection, conduction, radiation, and evaporation. Areas in dairy operations in which cooling systems have been used to enhance cow comfort, improve milk production, reproductive efficiency, and profit include both housing and milking facilities. Currently, air movement (fans), wetting (soaking) the cow's body surface, high pressure mist (evaporation) to cool the air in the cows’ environment, and facilities designed to minimize the transfer of solar radiation are used for heat abatement. Finally, improved understanding of photoperiod effects on cattle has allowed producers to maximize beneficial effects of photoperiod length while minimizing negative effects.     

Defining ruminal and total-tract starch degradation for adult dairy cattle using in vivo data

Literature was searched for studies performed in adult dairy cattle that simultaneously measured starch degradability in the rumen (RSDeg) and starch digestion in the total tract to compute postruminal starch digestion (PRSDig). Forty-one studies with 161 dietary treatments were used to form the data set. Of these diets, the major starch source was corn for 83 diets, small grain for 58 diets, and sorghum for 8 diets. Corn RSDeg was more variable than other sources. As measured in vivo across all starch sources, the percent RSDeg was influenced only by the amount of starch consumed, with the amount of degradation being approximately 75% at low starch intakes and decreasing to about 60% when 4 kg or more of starch were consumed. Small grain starch had greater RSDeg than corn or sorghum starch, which were approximately equal. The PRSDig of corn and small grain starches were approximately equal, but sorghum was about 15% less. Across all diets, models derived from the Cornell Net Carbohydrate Protein System predicted percentage of total-tract digestibility of starch very accurately, but overpredicted RSDeg and, as a result, underpredicted percent PRSDig. Calculation of RSDeg using a French model predicted the mean RSDeg with greater accuracy but less precisely. The relative differences in RSDeg percent among starch sources was correctly predicted by these models. A model using a revised rate of digestion as a way of combining effects of starch type and processing was developed, which predicted corn starch RSDeg and PRSDig with greater accuracy than nutrition models but only slightly better than using the mean observed degradation or the French calculation. Inaccuracies in prediction of RSDeg may be due mainly to processing effects and particle sizes, but these were not well reported in literature studies and were difficult to estimate. More accurate assessment of RSDeg and PRSDig will require better and more consistent reporting of grain processing. Based on this study, the French calculation is the most accurate of the models examined, although adjustments will be required to improve accuracy.     

Hoof discomfort changes how dairy cattle distribute their body weight

Lameness is a costly and widespread health and welfare problem in intensive dairy production, and reliable automated methods to detect lameness are needed. Lameness may be detected through the measurement of how cattle distribute their weight among their 4 legs, but this requires an understanding of how cattle redistribute their weight in response to pain in one or more limbs. In 3 experiments, 13, 12, and 15 Holstein dairy cows were trained to stand on a platform that measured the weight placed on each limb. We replaced the soft rubber surface under either 1 or 2 hooves with an uncomfortable concrete surface. Cows placed less weight on a back hoof that was placed on an uncomfortable surface, and they redistributed the majority of the weight onto the contralateral back hoof but did not change the distribution of weight on their front hooves. When the same surface was placed under a front hoof, cows placed less weight on that hoof and placed more weight on the contralateral front hoof and the ipsilateral back hoof. The variation in weight the cow placed on both contralateral hooves increased when one of the hooves was on the uncomfortable surface. Cows placed more weight on the back hooves when both front hooves were standing on uncomfortable surfaces, although no change was observed when back hooves were on uncomfortable surfaces. Dairy cows remove weight from a limb in response to limb discomfort and redistribute this weight primarily to the contralateral limb. The variation in weight over time applied to a pair of contralateral limbs increases in response to discomfort in one hoof. Cows have only limited ability to shift weight from front to back. Measures of weight distribution may provide useful on-farm techniques for the detection of lameness.     

Freestall maintenance: effects on lying behavior of dairy cattle

In a series of 3 experiments, we documented how sand-bedding depth and distribution changed within freestalls after new bedding was added and the effect of these changes on lying behavior. In experiment 1, we measured changes in bedding depth over a 10-d period at 43 points in 24 freestalls. Change in depth of sand was the greatest the day after new sand was added and decreased over time. Over time, the stall surface became concave, and the deepest part of the stall was at the center. Based on the results of experiment 1, we measured changes in lying behavior when groups of cows had access to freestalls with sand bedding that was 0, 3.5, 5.2, or 6.2 cm at the deepest point, below the curb, while other dimensions remained fixed. We found that daily lying time was 1.15 h shorter in stalls with the lowest levels of bedding compared with stalls filled with bedding. Indeed, for every 1-cm decrease in bedding, cows spent 11 min less time lying down during each 24-h period. In a third experiment, we imposed 4 treatments that reflected the variation in sand depth within stalls: 0, 6.2, 9.9, and 13.7 cm below the curb. Again, lying times reduced with decreasing bedding, such that cows using the stalls with the least amount of bedding (13.7 cm below curb) spent 2.33 h less time per day lying down than when housed with access to freestalls filled with sand (0 cm below curb).     

Adhesion of dairy propionibacteria to intestinal epithelial tissue in vitro and in vivo

Adhesion to the intestinal mucosa is a desirable property for probiotic microorganisms and has been related to many of their health benefits. In the present study, 24 dairy Propionibacterium strains were assessed with regard to their hydrophobic characteristics and their autoaggregation and hemagglutination abilities, since these traits have been shown to be indicative of adherence in other microorganisms. Six strains were further tested for their capacity to adhere to ileal epithelial cells in vitro and in vivo. The results of the study showed that propionibacteria were highly hydrophilic, and hemagglutination and autoaggregation were properties not commonly found among these microorganisms. No relationship was found between surface characteristics and adhesion ability, since hemagglutinating, autoaggregating, and nonautoaggregating bacteria were able to adhere to intestinal cells both in vitro and in vivo. Microscopic examination revealed that autoaggregating cells adhered in clusters, with adhesion being mediated by only a few bacteria, whereas the hemagglutinating and nonautoaggregating strains adhered individually or in small groups making contact with each epithelial cell with the entire bacterial surface. The in vitro assessment of adhesion was a good indication of the in vivo association of propionibacteria with the intestinal epithelium. Therefore, the in vitro method presented here should be valuable in screening routinely adhesive properties of propionibacteria for probiotic purposes. The adhesion ability of dairy propionibacteria would prolong their maintenance in the gut and increase the duration of their provision of beneficial effects in the host, supporting the potential of Propionibacterium in the development of new probiotic products.     

Reduced stocking density mitigates the negative effects of regrouping in dairy cattle

In freestall systems, cows are frequently moved among pens and regrouped. This practice involves mixing unfamiliar cows, and can result in changes in stocking density after regrouping. Both regrouping and changes in stocking density can affect cow welfare, but no study to date has assessed the combined effects. The aim of this study was to test if reductions in stocking density can mitigate the responses to regrouping. By manipulating group size (6 vs. 12 cows) and pen size (12 vs. 24 stalls), 3 different stocking densities were created (25, 50, and 100%). Four groups of Holstein cows were regrouped weekly for 4 wk and the stocking density changed at regrouping. The change in density varied as follows: a decrease by a factor of 4 (100 to 25%), a decrease by a factor of 2 (100 to 50% or 50 to 25%), no change (50 to 50%), an increase by a factor of 2 (25 to 50% or 50 to 100%), and an increase by a factor of 4 (25 to 100%). Displacements at the feeding area, feeding time, and lying time were scored. The daily means for each group were used to calculate the differences in responses from 1 d before to 1 d after each regrouping. The number of displacements at the feed bunk decreased and lying time increased when stocking density decreased at regrouping. In conclusion, increases in competitive behavior and the associated decrease in lying times can be mitigated by reducing stocking density when regrouping dairy cows.     

Dietary choline effects on milk yield and duodenal choline flow in dairy cattle

In Experiment 1, the effect, in early lactation, of 0 or 3 g of supplemental choline/kg of total diet DM on milk yield and composition was tested in 20 first lactation and older Holstein cows. In Experiment 2, 30 first lactation and older Holstein cows between 45 and 200 d postpartum were assigned to treatments of 0, 2.5, and 5.0 g of supplemental choline/kg of total diet DM to test the effect of dietary choline with diets based on corn and soybean meal. In Experiments 1 and 2, added choline had no effect on either milk yield or fat-corrected milk yield. In both experiments, fat yield and fat percentage tended to increase with choline supplementation, but protein yield and protein percentage were unaffected. In Experiment 1, choline had no effect on serum lipids. Ruminal dosing of steers with 27 g/d supplemental choline in Experiment 3 increased duodenal choline flow by only 3 g/d. The apparent rumen degradability of choline tended to be higher (77.1 vs. 70.6%) in the supplemented steers. Choline concentration in rumen fluid and duodenal chyme were higher in the supplemented steers. Choline supplementation in Experiments 1 and 3 had no effect on rumen VFA or rumen pH. Dietary choline supplementation apparently is ineffective because of rapid degradation of choline in the rumen.     

Psychrotrophs in dairy products: Their effects and their control

Health concerns and technological effects of psychrotrophic bacteria in dairy products are reviewed, as well as methods to control their presence and development. The various Gram‐negative and Gram‐positive psychrotrophic species are listed and, with respect to pathogenic psychrotrophs, emphasis is given on Listeria monocytogenes, Yersinia enterocolytica, and Bacillus cereus. The influence of psychrotrophic bacteria on the quality of raw milk, pasteurized and UHT milks, butter, ice cream, cheese, and powders is examined. Public health considerations of Listeria monocytogenes, Yersinia enterocolytica, and Bacillus cereus of these various dairy products are also presented. Methods that can be used to eliminate or control the development of psychrotropic bacteria include low or high temperatures, chemicals, gases, the lactoperoxidase system, lactic acid bacteria, microfiltration, bactofugation, lactoferrin‐related proteins, sanitation, flavors, and naturally occurring spore germinants.     

Gastrointestinal nematodiasis in dairy cattle

Infection with gastrointestinal nematode parasites appears to be widespread in the cattle population. The pathologically important genera of worms all belong to the family Trichostrongylidae. The most pathogenic species is Ostertagia ostertagi, which can produce profound changes in abomasal mucosa of affected animals. These nematodes show developmental adaptations, such as seasonally arrested development, that are of prime importance to their survival and persistence on a year to year basis. Whereas nematode prevalence in cattle is high, their association with outbreaks of clinical disease is lower. This has focused attention on their so-called subclinical effects, particularly reduction of milk production in lactating cows. Evidence for this effect is still equivocal, but constant exposure to low infection apparently can depress milk production. Subclinical effects also have been demonstrated in young animals and include depressed rates of gain and interference in energy and nitrogen metabolism. Evidence suggests that these effects may be partly due to hypersensitivity reactions at the mucosal level in sensitized animals.     

Tail docking dairy cattle: effects on cow cleanliness and udder health

To determine whether tail docking would influence cow cleanliness and udder health in a free-stall system, we monitored milking cows after half the animals in a herd were docked. A sample of 223 docked and 190 undocked cows (reducing to 169 and 105 over the study as cows were dried off) were monitored for 8 wk. Cow cleanliness was scored in two areas: along the spine, and the rump adjacent to the tail at 1, 2, 3, 5, and 8 wk after docking. Cleanliness was evaluated by counting squares that were soiled (0 to 14 on a 5- x 17.5-cm grid) and judging soiling severity on a scale from 0 (clean) to 3 (thickly caked). Udder cleanliness was scored with the same scale (0 to 3) and by counting the number of teats with debris on them. Udder health was assessed by measuring SCC of two milk samples and the number of animals diagnosed as mastitic by the on-farm veterinarian. No treatment differences were found in four measures of cow cleanliness, two measures of udder cleanliness, or udder health. However, cow cleanliness did differ over time, and analysis of a subsample of cows illustrated individual differences in cleanliness.