Light sensors assess solar radiation vs. shade exposure of slick- and wild-type Puerto Rican Holstein cows

Anecdotal data suggest that slick-haired cows (SLICK) graze under solar radiation longer than their wild type-haired (WT) counterparts. However, to the authors’ knowledge, empirical data regarding the suggestion is scarce. This study aimed to use light sensors (HOBO Pendant MX) to study solar radiation exposure. Sensors (attached to a collar) were validated in 20 Holstein cows rotated from shade (0837 to 0906h) to sunlight (0907 to 0932h) and then back to shade (0933 to 1005h). After validation, sensors were used to compare the differences in solar radiation exposure between 10 SLICK and 10 WT Holstein cows. Data were analyzed by the GLIMMIX and FREQ procedures (SAS). Light intensity was greater under solar radiation than during the first (P<0.01) and second (P<0.01) shade periods (51,026.00±682.25; 2,282.40±647.64 and 1,907.27±626.28 lx, respectively). No differences were observed between shade periods (P=0.62). The SLICK cows spent more time under solar radiation than the WT cows (52.67 vs. 47.33%, respectively; P<0.01). Hair coat type and period interacted (P<0.01), with greater light intensities in SLICK than in WT cows under solar radiation (24,702±106.65 vs. 20,518±98.43 lx, respectively); but no differences were observed under shade (1,856±7.03 and 1,793.2±6.53 lx, respectively). The SLICK cows showed greater exposure time to direct solar radiation than their WT counterparts.