Use of thermography and physiological rate to assess heat tolerance in cattle breeds.

Thermography has grown in use in recent years. It is a valuable tool for measuring animal heat tolerance under heat stress conditions since it is a non-invasive, safe and practical methodology. Physiological variables such as respiration rate and eye temperature, and environmental variables such as air temperature and wet bulb temperature were analysed in animals from nine cattle breeds (Angus, Braford, Brangus, Canchim, Charolais, Hereford, Nelore, Simmental and Santa Gertrudis) and one bubaline (Mediterranean) at Rio Grande do Sul, Brazil. Positive correlations were observed between air temperature and respiration rate and eye temperature. Furthermore, the breed strongly influenced the eye temperature and respiration rate of the animals. Eye temperature showed strong correlation with air temperature and wet bulb temperature. Simmental and Nelore animals presented higher eye temperature values. Simmental presented alteration in respiratory rate before the other breeds and Nelore was the last breed to present this alteration. The inflection points in the broken line analysis indicated the environmental temperature limits at which breeds begin to change their respiration to compensate for environmental variation. The use of thermography has proven to be a technique with possible application to evaluate the temperature of animals. Logistic regression analysis allows us to observe how each breed behaves with the temperature change. Using respiration rates and eye temperatures it was possible to identify physiological limits for comfort in different breeds of bovine. In the future it would be interesting to conduct additional studies using other physiological variables and also other indices of climatic conditions.

Different methods of assessing udder temperature through thermography and their relation with rectal temperature.

Infrared thermography of the lateral side portion of the udder was taken from 38 lactating cows in a 6-day experiment. Thermograms were analyzed using specific software with the use of eight different methods. The experiment was aimed at correlating the different methods with each other and with rectal temperature (RT), in order to suggest a method to assess udder side temperature, and also at creating regression equations to enable RT calculation through the use of thermographic data. All methods of analyzing thermograms were highly correlated; correlations between thermograms and RT were significant (P < 0.01) and above 0.840. The highest correlation was between RT and the maximum temperature obtained using a horizontal rectangle placed within the lateral (side) portion of the udder (maximum temperature in a horizontal rectangle (MHR), 0.897). With the exception of the average temperature of a horizontal rectangle, linear regression coefficients were significant (P < 0.05) and coefficients of determination were higher than 75.51%. We suggest the use of MHR to evaluate udder side temperature. The ease of accessing the side of the udder, the welfare advantages of non-invasive observations, and the high correlation with RT suggest the use of thermograms in the lateral portion of the udder to assess animals' temperature.

Natural tree shade increases milk stability of lactating dairy cows during the summer in the subtropics.

This research communication addresses the hypothesis that, during the summer in the subtropics, natural tree shade helps to improve milk functional characteristics such as stability and acidity. Sixteen Holstein lactating cows were enrolled. The study consisted of three periods (pre-stress, heat stress and post-stress) based on allocating grazing cows into two treatments (with and without access to shade during the Heat Stress period). Overall THI during the trial was (mean ± se) 76.0 ± 3.4. Access to shade prevented the heat stress-related decrease in milk stability both in the ethanol and in the coagulation time test, as well as maintained milk acidity within an acceptable range (14 to 18°D).

Mammary gland cell's tight junction permeability from dairy cows producing stable or unstable milk in the ethanol test.

Tight junctions are almost impermeable structures located near the apical border of epithelial cells; increase in the permeability of mammary gland cells' tight junctions may alter milk composition and its suitability for industrialization. Sixteen Holstein dairy cows were studied to evaluate mammary gland cells' tight junction permeability (indicated by plasma lactose levels) from cows producing stable or unstable milk to ethanol at 72 °GL concentration. Rectal temperature, respiratory rate and milk parameters were also compared and weather conditions (temperature-humidity index) monitored. Temperature-humidity index did not vary for cows producing stable or unstable milk, so there were no differences in physiological traits. Cows producing unstable milk presented elevated tight junctions' permeability, probably due to higher days in milk. The odds of cows producing unstable milk (clots formation when mixed with ethanol below or equal 72 °GL) increases according to elevations in days in milk and tight junction permeability.