Evaporative tunnel cooling of dairy cows in the southeast. I: effect on body temperature and respiration rate

The techniques used to mitigate the effects of heat stress on lactating dairy cows are often overwhelmed in the southeastern United States, where elevated heat and humidity often persist for extended periods. A model free-stall barn located at the North Mississippi Branch Experiment Station in Holly Springs was used to evaluate the potential of tunnel ventilation with evaporative cooling to alleviate heat stress in lactating dairy cows. Two studies were conducted using 2 groups of 10 lactating Holsteins housed in the tunnel barn (inside) and 2 groups of matched herdmates housed in an adjacent covered free-stall barn (outside), which was cooled by fans and sprinklers during 2001 or by shade and fans alone in 2003. Peak daytime temperatures inside were 5.2 ± 0.18°C below that outside in 2001 and 3.1 ± 0.20°C lower in 2003. Although evaporative cooling increased humidity by 22%, cows housed in the tunnel barn received 84% less exposure to moderate heat stress (temperature-humidity index >80) in both years. Cooling cows with evaporative tunnel ventilation reduced respiration rates by 15.5 ± 0.56 breaths/min and rectal temperatures by 0.6 ± 0.02°C compared with shade and fans alone in 2003. Cooling cows with evaporative tunnel ventilation reduced respiration rates by 13.1 ± 0.78 breaths/min and rectal temperatures by 0.4 ± 0.03°C compared with fans and sprinklers in 2001. Thus, tunnel ventilation cooling dramatically reduced the exposure to heat stress and improved the comfort of lactating dairy cows when compared with traditional cooling technologies under the conditions present in the southeastern United States.     

Forced heat loss from body surface reduces heat flow to body surface

Heat stress is commonly relieved by forced evaporation from body surfaces. The mode of heat stress relief by heat extraction from the periphery is not clear, although it reduces rectal temperature. Radiant surface temperature (Ts) of the right half of the body surface was examined by thermovision in 4 lactating Holstein cows (30 kg of milk/d) during 7 repeated cycles of forced evaporation created by 30 s of wetting followed by 4.5 min of forced airflow. Wetting was performed by an array of sprinklers (0.76 m³/h), and forced airflow (>3 m/s velocity) over the right side of the body surface was produced by fans mounted at a height of 3 m above the ground. Sprinkling wetted the hind legs, rump, and chest, but not the lower abdomen side, front legs, or neck. The animals were maintained in shade at an air temperature of 28°C and relative humidity of 47%. Coat thickness was 1 to 2 mm, so Ts closely represented skin temperature. Mean Ts of 5 × 20 cm areas on the upper and lower hind and front legs, rump, chest, abdomen side, and neck were obtained by converting to temperature their respective gray intensity in single frames obtained at 10-s intervals. Little change occurred in Ts during the first wetting (0.1 ± 0.6°C), but it decreased rapidly thereafter (1.6 ± 0.6°C in the fifth wetting). The Ts also decreased, to a smaller extent, in areas that remained dry (0.7 ± 1.0°C). In all body sites, a plateau in Ts was reached by 2 min after wetting. The difference between dry and wet areas in the first cooling cycle was approximately 1.2°C. The Ts of different body areas decreased during consecutive cooling cycles and reached a plateau by 3 cooling cycles in dry sites (front leg, neck, abdomen side), by 5 cooling cycles in the hind leg, and 7 cooling cycles in the rump and chest. The reduction in mean Ts produced by 7 cycles was 4.0 to 6.0°C in wetted areas and 1.6 to 3.7°C in sites that were not wetted. Initial rectal temperature was 38.9 ± 0.1°C; it remained unchanged during first 5 cooling cycles, decreased by 0.1°C after 7 cooling cycles, and decreased to 38.4 ± 0.06°C after 8 to 10 cooling cycles, with no additional subsequent decrease. The concomitant reduction in Ts in dry and wet areas suggests an immediate vasoconstrictor response associated with heat extraction and later development of a cooler body shell. The reduction in rectal temperature represents a response involving transfer of heat from the body core to the body shell. This response mode requires consideration in settings of heat stress relief.     

Modelling heat-disinfestation of dried fruits on “biological model” larvae Ephestia kuehniella (Zeller)

The effects of heat treatment on the survival of isolated Ephestia kuehniella Zeller larvae were examined. Larvae were treated in a specific device at a temperature range of 46 to 70 °C. Statistical analysis of the data demonstrated that the thermal survival kinetics was best represented by a 2-parameter Weibull model above 50 °C. The mortality of larvae only occurs beyond a critical temperature of 41.6 °C ± 2.5 °C. A 2D axial-symmetric model of heat transfer (convection, microwave at 915 MHz) was developed for cocoa bean and date palm. It was combined with the survival rate of larvae (Weibull model) and some z-values (from literature) are used for calculating a “food quality index” degradation kinetics. The intensive heating/convection process may not be adaptable for food products at low water activity due to high surface product temperatures. The use of microwave heating for date fruits and conventional hot air treatments for cocoa beans is recommended.     

Increasing Heat Stress Relief Produced by Coupled Coat Wetting and Forced Ventilation

Coupling repeated wetting of the coat and forced ventilation is most efficient in removing heat stress in more humid climates. The procedure was initiated approximately 24 yr ago and is widely used, but the impact of air velocity on the efficiency of heat stress relief has not been examined. This study examined the feasibility of using surface temperature for real-time estimation of heat stress relief. It was carried out in midsummer in Israel on 6 mature lactating Holsteins. A 15 × 15 cm area on the right side of the body was thoroughly wetted. Hair surface and skin temperature on the wetted area and adjacent dry area were measured at 1-min intervals for 15 min while air movement was less than 0.1 m/s, and the sequence was repeated with air velocities of 0.5 to 3 m/s perpendicular to the body surface. Because the cooled surface was small, the response to cooling was local. In 3 animals, the whole left side of the body also was wetted and exposed to forced ventilation (1.5 m/s) to combine local cooling with larger body surface cooling. The air temperature was 29.5 ± 0.05°C, and the relative humidity was 56.7 ± 0.2%. Rectal temperature and respiratory frequency indicated minor heat stress. Mean wet hair surface temperature (Thw) and wet skin temperature were 2.1 and 1.5°C lower than the respective dry hair surface temperature (Thd) and dry skin temperature. At an air velocity of 0.5 m/s, Thw was practically identical to that in still air and to Thd. At greater air velocities, Thw decreased immediately after wetting, and minimal values were reached within 1 min, were maintained for 6 to 7 min after wetting, and reached 95% of the mean Thd value by 8 and 11 min after wetting at 1 and 2 m/s, respectively. Wetting the coat had the potential to reduce Thd temperature by 10 to 11°C. The relatively small difference between Thd and Thw probably is due to heat flow from the body. The latter was estimated by comparing enthalpies at Thd, at Thw, and in the wet bulb temperature predicted for Thd. Predicted heat loss rates were 736 and 1,012 W/m² at air velocities of 1 and 2 m/s, respectively, compared with 164 W/m² predicted for the dry surface from the thermal balance model. Increasing heat loss from the left side reduced wet surface temperatures on right side, indicating that larger body surface cooling reduced heat flow to the skin on the right body surface. Heat extraction from the wet body surface is thus reduced by large body surface cooling and depends on the thermal state. The efficiency of heat stress relief may be detected by surface temperature monitoring and may be improved by adjusting the interval between wettings to the changes in surface temperature.     

Strategy to inactivate Clostridium perfringens spores in meat products

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100–200 MPa, 7 min) and elevated temperature (80 °C, 10 min); spore germination at high temperatures (55, 60 or 65 °C); and inactivation of germinated spores with elevated temperatures (80 and 90 °C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 °C, 10 min). Low pressures (100–200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 °C, 10 min), and germinated at temperatures lethal for vegetative cells (≥55 °C) when incubated for 60 min with a mixture of l-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (∼4 decimal reduction) in meat by elevated temperatures (80–90 °C for 20 min) required a long germination period (55 °C for 60 min). However, similar inactivation level was reached with shorter germination period (55 °C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 °C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 °C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 °C in about 20 min and further incubation at 55 °C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 °C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.     

Feasibility assessment of vacuum cooling followed by immersion vacuum cooling on water-cooked pork

Vacuum cooling followed by immersion vacuum cooling was designed to cool water-cooked pork (1.5 ± 0.05 kg) compared with air blast cooling (4 ± 0.5 °C, 2 m/s), vacuum cooling (10 mbar) and immersion vacuum cooling. This combined cooling method was: vacuum cooling to an intermediate temperature of 25 °C and then immersion vacuum cooling with water of 10 °C to the final temperature of 10 °C. It was found that the cooling loss of this combined cooling method was significantly lower (P < 0.05) than those of air blast cooling and vacuum cooling. This combined cooling was faster (P < 0.05) than air blast cooling and immersion vacuum cooling in terms of cooling rate. Moreover, the pork cooled by combined cooling method had significant differences (P < 0.05) in water content, color and shear force.     

Effect of processing temperature on tenderness,colour and yield of beef steaks subjected to high-hydrostatic pressure

Our aim was to achieve a single-step pressure-heat process that would produce tender, juicy beef steaks from meat that would otherwise be tough when cooked. Steak portions (25 mm thick) from hind-quarter muscles were subjected to heat treatment at 60, 64, 68, 72 or 76 °C for 20 min, with or without simultaneous application of high pressure (200 MPa). Control steaks were heated at 60 °C for 20 min with or without pressure and cooked at 80 °C for 30 min. Compared with heat alone, pressure treatment resulted in higher lightness scores at all temperatures and overall yield was improved by pressure treatment at each temperature. Even at 76 °C, the overall water losses were < 10% compared with > 30% for heat alone. Meat tenderness (peak shear force) was improved for the pressure–heat samples at temperatures above 64 °C, and was optimal at 76 °C. Therefore, subject to microbial evaluation, this single-step pressure-heat process could be used to produce tender, high moisture content steaks ready for consumption.     

Effects of processing parameters on immersion vacuum cooling time and physico-chemical properties of pork hams

The effects of agitation (1002 rpm), different pressure reduction rates (60 and 100 mbar/min), as well as employing cold water with different initial temperatures (IWT: 7 and 20 °C) on immersion vacuum cooling (IVC) of cooked pork hams were experimentally investigated. Final pork ham core temperature, cooling time, cooling loss, texture properties, colour and chemical composition were evaluated. The application for the first time of agitation during IVC substantially reduced the cooling time (47.39%) to 4.6 °C, compared to IVC without agitation. For the different pressure drop rates, there was a trend that shorter IVC cooling times were achieved with lower cooling rate, although results were not statistically significant (P > 0.05). For both IWTs tested, the same trend was observed: shorter cooling time and lower cooling loss were obtained under lower linear pressure drop rate of 60 mbar/min (not statistically significant, P > 0.05). Compared to the reference cooling method (air blast cooling), IVC achieved higher cooling rates and better meat quality.     

Comparative study of denaturation of whey protein isolate (WPI) in convective air drying and isothermal heat treatment processes

The extent and nature of denaturation of whey protein isolate (WPI) in convective air drying environments was measured and analysed using single droplet drying. A custom-built, single droplet drying instrument was used for this purpose. Single droplets having 5 ± 0.1 μl volume (initial droplet diameter 1.5 ± 0.1 mm) containing 10% (w/v) WPI were dried at air temperatures of 45, 65 and 80 °C for 600 s at constant air velocity of 0.5 m/s. The extent and nature of denaturation of WPI in isothermal heat treatment processes was measured at 65 and 80 °C for 600 s and compared with those obtained from convective air drying. The extent of denaturation of WPI in a high hydrostatic pressure environment (600 MPa for 600 s) was also determined. The results showed that at the end of 600 s of convective drying at 65 °C the denaturation of WPI was 68.3%, while it was only 10.8% during isothermal heat treatment at the same medium temperature. When the medium temperature was maintained at 80 °C, the denaturation loss of WPI was 90.0% and 68.7% during isothermal heat treatment and convective drying, respectively. The bovine serum albumin (BSA) fraction of WPI was found to be more stable in the convective drying conditions than β-lactoglobulin and α-lactalbumin, especially at longer drying times. The extent of denaturation of WPI in convective air drying (65 and 80 °C) and isotheral heat treatment (80 °C) for 600 s was found to be higher than its denaturation in a high hydrostatic pressure environment at ambient temperature (600 MPa for 600 s).     

Mathematical modeling of the heat transfer process and protein denaturation during the thermal treatment of Patagonian marine crabs

Southern Ocean swimming crab Ovalipes trimaculatus and the Patagonian stone crab Platyxanthus patagonicus are fishing resources with commercial value. Thermal treatment of crabs is necessary to denature muscle proteins, facilitating meat detachment from the crab shell (picking procedure). The proximal composition, protein patterns of crab muscle, thermophysical properties and heat transfer coefficients were determined. Heat transfer during thermal processing of body (i.e., cephalothorax) and claws of both crab species was simulated using a finite element computational code; the simulations were experimentally validated. Color changes in crab muscle during the heating process were measured. Thermal denaturation kinetics of myofibrillar proteins was determined using Differential Scanning Calorimetry (DSC) in small samples previously heated in water under controlled conditions. DSC thermograms of raw crab muscle showed two peaks at 49.0 ± 0.4 and 77.5 ± 0.6 °C corresponding to myosin and actin respectively. Activation energies for the denaturation of myosin (145.70 kJ/mol) and actin (156.42 kJ/mol) were calculated from Arrhenius equation. The degree of denaturation achieved by the myofibrillar proteins at the coldest point of the muscle in body and claws during the heating process was established by considering the protein denaturation kinetics determined by DSC, the activation energies and the heat penetration curves. Adequate conditions for the detachment of meat from the crab exoskeleton were established. The obtained results may help in determining the optimal heating times during the industrialization of these crustaceans.     

Development of an integrated model for heat transfer and dynamic growth of Clostridium perfringens during the cooling of cooked boneless ham

Numerous small meat processors in the United States have difficulties complying with the stabilization performance standards for preventing growth of Clostridium perfringens by 1 log10 cycle during cooling of ready-to-eat (RTE) products. These standards were established by the Food Safety and Inspection Service (FSIS) of the US Department of Agriculture in 1999. In recent years, several attempts have been made to develop predictive models for growth of C. perfringens within the range of cooling temperatures included in the FSIS standards. Those studies mainly focused on microbiological aspects, using hypothesized cooling rates. Conversely, studies dealing with heat transfer models to predict cooling rates in meat products do not address microbial growth. Integration of heat transfer relationships with C. perfringens growth relationships during cooling of meat products has been very limited. Therefore, a computer simulation scheme was developed to analyze heat transfer phenomena and temperature-dependent C. perfringens growth during cooling of cooked boneless cured ham. The temperature history of ham was predicted using a finite element heat diffusion model. Validation of heat transfer predictions used experimental data collected in commercial meat-processing facilities. For C. perfringens growth, a dynamic model was developed using Baranyi's nonautonomous differential equation. The bacterium's growth model was integrated into the computer program using predicted temperature histories as input values. For cooling cooked hams from 66.6 degrees C to 4.4 degrees C using forced air, the maximum deviation between predicted and experimental core temperature data was 2.54 degrees C. Predicted C. perfringens growth curves obtained from dynamic modeling showed good agreement with validated results for three different cooling scenarios. Mean absolute values of relative errors were below 6%, and deviations between predicted and experimental cell counts were within 0.37 log10 CFU/g. For a cooling process which was in exact compliance with the FSIS stabilization performance standards, a mean net growth of 1.37 log10 CFU/g was predicted. This study introduced the combination of engineering modeling and microbiological modeling as a useful quantitative tool for general food safety applications, such as risk assessment and hazard analysis and critical control points (HACCP) plans.     

A 3-D computational fluid dynamics model for forced air cooling of eggs placed in trays

Freshly laid shell eggs must be cooled quickly for controlling Salmonella Enteritidis (SE) growth. To fulfill a research need identified by Food Safety and Inspection Service (FSIS), a 3-D computational fluid dynamics (CFD) model was developed to predict the temperature of eggs placed on a tray (6 rows × 5 columns) under forced air cooling. The continuity, momentum, and energy equations were solved along with standard k − ε turbulence model using PHOENICS software. The model was validated by conducting experiments in a wind tunnel at various air temperatures (7-11 °C) and velocities (0.3-0.7 m/s). Root mean square error for predicting yolk temperatures was within 1 °C. Finally, the CFD model was integrated with a microbial growth model to estimate the risk of SE growth during cooling. This model can be incorporated into the FSIS risk assessment model for more accurate estimation of SE risk in shell eggs.     

Heat sealing of LLDPE films: Heat transfer modeling with liquid presence at film–film interface

Heat sealing is widely used in form-fill-seal packaging of liquid food products. One of the problems often encountered by food companies is the contamination of seal area by the liquid product during heat sealing. In this study, heat transfer models were developed to elucidate the heat transfer during heat sealing of two layers of linear low density polyethylene (LLDPE) films, when a liquid contaminant layer is absent or present at the film–film interface. Thermal contact resistance was incorporated in the models to account for the thermal resistance due to the micro-gaps existed on film surfaces and the heat sink effect of the contaminant liquid. The heat transfer models were validated by using experimental film–film interface temperature data when upper jaw temperatures of 155 and 165 °C were applied. The models predicted the film–film interface temperatures well with root mean square errors (RMSEs) ranging from 1.6 to 2.1 °C for clean seals, and from 1.6 to 2.5 °C for water-contaminated seals. Validation results showed that the heat sink effect of water was counterbalanced by the enhanced heat transfer at the film–film interface, probably due to displacement of air in the micro-gaps by the contaminant liquid.     

Thermophysical properties and thermal behavior of leafy vegetables packaged in clamshells

Little is known about the thermophysical properties of fresh-cut lettuce other than heat of respiration. Empirical correlations based on food composition remain the only way to estimate the thermophysical properties of fresh-cut lettuce. The objectives of this study were (i) to determine the thermophysical properties of several baby-leaf lettuce and brassica greens and (ii) to verify the measured thermophysical properties by using them in a heat transfer model and comparing the predicted product temperatures with measured product temperatures in a simulated interruption of a cold chain. Density, leaf thickness, thermal conductivity, specific heat and water activity from nine varieties of baby-leaf lettuce and brassica greens were measured. A broken cold chain was simulated in a low temperature incubator set at 10 °C for a length of time before readjustment at 2 °C. Results showed that density (1078–1112 kg m⁻³), leaf thickness (0.18–0.54 mm), thermal conductivity (0.55–0.70 W (m °C)⁻¹) and specific heat (3.1–4.3 kJ (kg °C)⁻¹) varied significantly (P < 0.05) between varieties. However, no significant differences were observed for water activity (0.959 ± 0.006). Using thermophysical properties as input in the heat transfer model, experimental and calculated temperatures were well correlated (R² = 0.98) with a root mean square error of 0.57 °C over the 10–40 mg CO₂ (kg h)⁻¹ range of respiration rate. The measured thermophysical properties adequately predicted the temperature of the baby-leaf greens during simulated broken cold chains. A sensitivity analysis performed with the heat transfer model showed that the thermal conductivity, the specific heat and the density were relatively more important on the thermal behaviour of the baby-leaf greens than the heat of respiration.     

Cultured C2C12 cell lines as a model for assessment of bacterial attachment to bovine primary muscle cells

The mechanisms of bacterial attachment to meat tissues need to be understood to enhance meat safety interventions. However, little is known about attachment of foodborne pathogens to meat muscle cells. In this study, attachment of six Escherichia coli and two Salmonella strains to primary bovine muscle cells and a cultured muscle cell line, C₂C₁₂, was measured, including the effect of temperature. At 37 °C, all but one strain (EC623) attached to C₂C₁₂ cells, whereas only five of eight strains (M23Sr, H10407, EC473, Sal1729a and Sal691) attached to primary cells. At 10 °C, two strains (H10407 and EC473) attached to C₂C₁₂ cells, compared to four strains (M23Sr, EC614, H10407 and Sal1729a) of primary cells. Comparing all strains at both temperatures, EC614 displayed the highest CFU per C₂C₁₂ cell (4.60 ± 2.02 CFU/muscle cell at 37 °C), whereas greater numbers of M23Sr attached per primary cell (51.88 ± 39.43 CFU/muscle cell at 37 °C). This study indicates that primary bovine muscle cells may provide a more relevant model system to study bacterial attachment to beef carcasses compared to cell lines such as C₂C₁₂.     

Decomposition kinetics of umami component during meat cooking

We developed a kinetic model for the decomposition reaction of inosine monophosphate (IMP), which is a umami component, and obtained kinetic parameters based on the amount of IMP in an isothermal experiment. The amount of remaining IMP decreased with heating time, and its reduction rate was the highest at 40 °C. We assumed that the activity of IMP decomposition enzyme is temperature-dependent above 40 °C, and constant below 40 °C. The predicted results using this kinetic model are in good agreement with the experimental ones. Unsteady-state three-dimensional heat transfer analysis of meat during sous-vide cooking was conducted, and the distribution of remaining IMP was predicted. By the end of sous-vide cooking, the ratio of the amount of IMP in the interior of the meat decreased, whereas at the surface region, it was almost the same as the initial value, because the surface temperature reached the inactivation temperature immediately.     

A comparison of the effects of 2 cattle-cooling systems on dairy cows in a desert environment

An experiment was conducted to investigate the effects of operation time and size of Korral Kool (KK; Korral Kool Inc., Mesa, AZ) systems on core body temperature (CBT) of dairy cows. Two KK systems were compared: a system with 1.29-m-diameter, 3-hp fans spaced 6 m apart (referred to as small) and a system with 1.52-m-diameter, 5-hp fans spaced 8 m apart (referred to as big). Forty-eight multiparous Holstein cows were assigned randomly to 8 pens (4 big, 4 small), and pens were assigned randomly to a sequence of treatments (KK operated for 21 or 24 h/d) in a switchback design. A complementary calorimetric analysis was developed to investigate the cooling area under the KK units of the big and small systems. Twenty-five sensors distributed equally under the KK units measured ambient temperature at 5-min intervals for 2 h. Average ambient temperature was 35.0 ± 0.6°C and relative humidity was 45 ± 8%. There were significant treatment effects on mean CBT: cows on the small 24-h treatment had a lower mean CBT than cows on the small 21-h treatment (39.22 vs. 39.36 ± 0.14°C), and cows on the big 24-h treatment had a lower mean CBT than cows on the big 21-h treatment (38.95 vs. 39.09 ± 0.13°C). A significant treatment by time interaction was observed. The greatest difference between systems occurred at 0100 h; treatment means at this time were 39.05, 39.01, 39.72, and 39.89 ± 0.16°C for the big 24-h, big 21-h, small 24-h, and small 21-h treatments, respectively. At certain times of day, the big system reduced CBT more than the small system. These results show that CBT of multiparous cows decreased when KK system operational time was increased from 21 to 24 h regardless of the size of the KK cooling system used. The calorimetric analysis showed that even though the big system resulted in lower mean ambient temperatures than the small system, the distance between units in the big system should be decreased to reduce the variation in temperature under the big units.     

Experimental study on the freezing characteristics of four kinds of vegetables

Mushroom, green cauliflower, navy bean and pea pod are four kinds of favored vegetables. Their freezing characteristics are studied in this paper. For fresh samples, the moisture contents of mushroom, navy bean, pea pod and green cauliflower were 88.7±4.9, 92.9±0.4, 87.7±1.0 and 89.7±0.9 g/100 g, respectively. After pre-treating, cooling curve method and differential scanning calorimetry (DSC) were employed to measure the end-points of freezing and glass transition temperatures. The initial freezing points varied from −0.1 to −2.7 °C. The end-points of freezing were all below −20.0 °C. The partial glass transition temperatures varied from −50.3 to −76.1 °C. With a cryomicroscope, the sizes of ice crystals in frozen vegetable saps were found to decrease from 26 to 3 μm when the freezing rates increased from 1.0 to 10.0 °C/min.     

Influence of breed,milk production,season, and ambient temperature on dairy cow reticulorumen temperature

Automatic monitoring of core body temperature in dairy cattle could be useful for identification of illness, heat stress, general physiological stress, and estrus. The SmartBolus (TenXSys Inc., Eagle, ID) system used a reticulorumen bolus to automatically record and transmit dairy cow temperatures. The objective of this research was to characterize the influence of milk yield (MY), time of day, breed, ambient temperature (AT), and season on reticulorumen temperatures (RT) in lactating dairy cows. Continuous RT and AT were collected by SmartBolus transponders every 15 min (96 records per d) from 93 cows (65 Holstein, 18 crossbred, and 10 Jersey) for 615 d. Mean (±SD) daily RT, AT, and MY were 40.14 ± 0.32°C, 12.20 ± 10.61°C, and 33.85 ± 8.67 kg, respectively. The maximum and minimum RT were recorded at 2330 and 1000 h, respectively. Ambient temperature increased RT. Summer RT was significantly greater than spring, fall, or winter RT. The effect of MY on RT varied by breed, season, and AT. Crossbred RT was significantly lower than Holstein RT after adjusting for MY. Crossbred RT responded less to increasing AT than did Holstein RT, potentially indicating improved heat tolerance among these crossbred dairy cows. Reticulorumen temperature increased more dramatically for cows with greater milk yield as AT increased, demonstrating that high-producing cows are more susceptible to heat stress than low-producing cows. These results could be useful in interpretation of automatic temperature system data, heat stress management, and genetic selection of heat-tolerant cows.     

Monitoring the effects of high pressure processing and temperature on selected beef quality attributes

The combined effects of high pressure processing (HPP) and temperature on meat quality attributes were assessed in bovine M. pectoralis profundus, with particular focus on lipid oxidation and fatty acid composition. Beef samples were pressurised at 200, 300 and 400 MPa at two different temperatures 20 °C and 40 °C. Both pressure and temperature regimes had significant effects on colour, cook loss and lipid oxidation. Pressurisation at 200 MPa had a lower impact on colour parameters than higher pressurisation levels. Cook loss also increased when higher levels of pressure were applied. Across all pressure conditions, lower cook loss was observed at 40 °C compared to 20 °C. An increase in TBARS values was observed at the higher pressure levels (300, 400 MPa). While some alterations of individual fatty acids were observed, high pressure had no effect on polyunsaturated/saturated fatty acid (PUFA/SFA) or omega 6/omega 3 (n6/n3) ratio. The temperature at which HPP was applied had a significant effect on the sum of saturated (SFA), monounsaturated (MONO) and polyunsaturated (PUFA) fatty acids. HPP at 40 °C showed higher SFA and PUFA and lower MONO compared to HPP at 20 °C. These results show that high pressure at low or moderate temperatures improves the microbiological quality of the meat with minimal affects on meat quality.