This study determined the effectiveness of convective cooling at different times of day when air temperature (T) was cycled from day to night. Mid-lactation Holstein cows (n = 12) were placed in 3 environmental chambers (4 cows per chamber) and acclimated to T 19.9°C (thermoneutral; TN) for 7 d followed by an incremental increase over 3 d to a heat stress (HS) condition. Conditions were maintained for 11 d at high and low daily T of 33 and 23°C, respectively. To determine adaptive HS response, the HS period was divided into early (E: d 11 to 14) and late (L: d 17 to 20) periods. During HS, cows were exposed to continuous fan (convective) cooling (CC), 8-h day fan cooling (1100 to 1900 h; DC), or 8-h night fan cooling (2300 to 0700 h; NC). Compared with DC, the NC treatment maximized the thermal gradient during the convective cooling. Each animal received all treatments within 3 trials using a repeated 3 × 3 Latin square design. Cows were fed a total mixed ration and milked twice daily. Thermal status was assessed by using thermal conductance and average daily values for mean, minimum, and maximum rectal temperature (T), skin temperatures, and respiration rate. Percent reduction in dry matter intake from TN to HS was less for CC than DC and NC, with no change from E to L periods. The DC group exhibited the greatest trend for a percent reduction in total milk yield below CC due to the significantly lower morning milk production. All values for total daily milk production decreased from E to L periods, with E to L reductions in both morning and afternoon milk production. Minimum T for CC and NC cows was 0.4°C below DC. In contrast, maximum T was similar for NC and DC groups, at 0.5 to 0.6°C above the CC group. Skin temperature for CC cows was always less than DC cows. Skin temperature for NC cows was equal to CC for minimum skin temperature, but exceeded both CC and DC cows for maximum skin temperature. Average skin temperature decreased from E to L, which suggested heat adaptation. The thermal advantage of night (lowest T and greatest thermal gradient) versus day cooling (greatest T and lowest thermal gradient) was increased heat transfer via thermal conductance with NC. The higher thermal strain of DC cows caused a larger percent decrease in morning milk yield than for NC cows. In contrast, use of convective cooling at night in the absence of elevated humidity could sufficiently reduce heat strain beyond DC to maintain milk production at a level that is closer to that of CC cows.

Download full-text PDF

Source
http://dx.doi.org/10.3168/jds.2017-14283DOI Listing

Publication Analysis

Top Keywords

convective cooling
20
skin temperature
20
thermal gradient
16
milk production
16
cows
13
thermal
9
cooling
8
reduce heat
8
heat stress
8
fan cooling
8

Similar Publications

Homogeneous boiling over melting ice.

Sci Rep

January 2025

Mechanical Engineering Department, University of South Florida, Tampa, FL, 33620, USA.

We report on discovering the homogeneous boiling within a liquid film residual resting in equilibrium over a melting ice block. This phenomenon was induced via longwave infrared radiation generated by a continuous wave [Formula: see text] laser. This investigation employed a high-speed camera and the Schlieren visualization technique.

View Article and Find Full Text PDF

The application of a pulsed magnetic field (PMF) during a metallurgy solidification process has proven to be an effective method in refining the grain size and improving the mechanical performance of the material. However, fewer works were reported in the realm of laser additive manufacturing (LAM) and the mechanism of grain refinement consequent to the PMF is still unclear. In this work, numerical models were developed to study the thermal-fluid characteristics in the Ti-alloy melt pool generated during the laser scanning process under the effect of a combined direct current (DC) electric field and PMF.

View Article and Find Full Text PDF

Exposure to high temperatures during indoor and outdoor activities increases the risk of heat-related illness such as cramps, rashes, and heatstroke (HS). Fatal cases of HS are ten times more common than serious cardiac episodes in sporting scenarios, with untreated cases leading to mortality rates as high as 80%. Enhancing thermal comfort can be achieved through heat loss in enclosed spaces and the human body, utilizing heat transfer mechanisms such as radiation, conduction, convection, and evaporation, which do not require initial energy input.

View Article and Find Full Text PDF

The hydrodynamic and thermal interactions between neighboring vapor bubbles on hot surfaces play a crucial role in heat transport and flow characteristics. To investigate these interactions, we conducted numerical simulations of saturated vapor bubbles in a two-dimensional square enclosure filled with liquid water. The water was heated at the bottom and cooled at the top to replicate boiling at 100^{∘}C and normal atmospheric pressure.

View Article and Find Full Text PDF

A Warm Environment Reduces Exogenous Glucose Oxidation and Endurance Performance during Cycling with Facing Airflow.

Med Sci Sports Exerc

December 2024

National Centre for Sport and Exercise Medicine, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM.

Unlabelled: Exercise in warm environments increases thermal/cardiovascular strain and decreases gastrointestinal (GI) integrity and endurance performance. However, laboratory-based studies have provided little to/no facing airflow, potentially exacerbating these effects, particularly for cycling, where convective cooling may be a major contributor to thermal balance.

Purpose: This study investigated the effect of cycling in a warm vs temperate environment with sufficient facing airflow on exogenous glucose use, performance, and GI responses.

View Article and Find Full Text PDF

Want AI Summaries of new PubMed Abstracts delivered to your In-box?

Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!