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Automatic shade and solar radiation exposure assessment in dairy cattle using light sensors.

H. L. Sánchez-Rodríguez



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Automatic shade and solar radiation exposure assessment in dairy cattle using light sensors.
H. L. Sánchez-Rodríguez*, I. Colón-Rodríguez, A. Rivera-Camacho, N. Pérez-Rosario, K. Domenech-Pérez, G. Muñiz-Colón. University of Puerto Rico, Mayagüez Campus Mayagüez, Puerto Rico.

Heat stress limits feed intake in cattle, but tropically adapted animals spend more time grazing under direct solar radiation than their temperate counterparts. However, the direct study (i.e., through constant visual observations) of the daily time a cow spends under shade or exposed to solar radiation is time and labor consuming, which may limit its utility in heat stress related research. Thus, the present study aimed to evaluate an automatic light sensor (HOBO MX Temp/Light) as a possible means to determine this variable. For this, 20 Holstein cows (2.8 ± 0.37 lactations, 165.60 ± 27.75 d in milk, and 549.73 ± 21.47 kg of BW) at Lajas, PR, were fitted with a nylon collar containing a light sensor on top. Sensors were programed to record light intensity values every minute. Cows were rotated from artificial shade (0837—0906 h) to direct sunlight (0907—0932 h) and then back to artificial shade (0933—1005 h). The light intensity values recorded during the shade and sun periods were compared by Proc GLIMMIX in SAS. Because the sensors provide light intensity values, a feasible way to convert numeric to behavioral data (i.e., exposure to shade or solar radiation) was also evaluated. The maximum light intensity value observed during the shade periods (4624.62 lx) was used as the cutoff value to create shade or sun categories using the if statement in SAS. The sensitivity of the created categories was determined by Proc FREQ in SAS. Light intensity was smaller during the first (P < 0.01) and second (P < 0.01) shade periods than during sun exposure (2282.40 ± 647.64, 1907.27 ± 626.28, and 51026.00 ± 682.25 lx, respectively). No differences in light intensity were observed between shade periods (P = 0.62). Sensitivity values of 99.37 and 100% were observed for the created shade and sun exposure categories. The evaluated sensors were able to differentiate if the cow was under shade or exposed to direct solar radiation. The obtained numeric light intensity values were easily converted to behavioral data, which may allow for the automatic assessment of this variable in heat stress related studies.

Keywords: solar radiation, light intensity, tropical cattle.