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Slick-haired Puerto Rican Holstein cows spend more time grazing under sunlight than their wild-type counterparts.

H. L. Sánchez-Rodríguez



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Slick-haired Puerto Rican Holstein cows spend more time grazing under sunlight than their wild-type counterparts.
H. L. Sánchez-Rodríguez*, I. Colón-Rodríguez, A. Rivera-Camacho, G. Vázquez-Arnal, N. Pérez-Rosario, N. Cruz-González, K. Domenech-Pérez, G. Muñiz-Colón. University of Puerto Rico, Mayaguez Campus Mayaguez, Puerto Rico.

Slick-haired (SLICK) cattle have been visually associated with a greater capacity to graze under direct solar exposure than their wild type (WT) counterparts. However, empirical data on this variable is scarce due to the complexity of visually evaluated behavioral research. Thus, the present study employed automatic data loggers to compare solar exposure periods between hair coat groups. Ten SLICK (1.70 ± 0.26 lactations, 95.80 ± 15.24 DIM, and 536.09 ± 19.71 kg of BW) and 10 WT (1.70 ± 0.26 lactations, 92.30 ± 15.29 DIM, and 492.90 ± 13.56 kg of BW) Puerto Rican Holstein cows received a collar with a light sensor (HOBO Pendant MX) tied on top. Sensors recorded light intensity values every 10 s for 2 consecutive days in November 2019, with thermal humidity index ranging from 66.98 to 85.21. Cows were maintained under the farm's management conditions, with natural shade provided at the fences of the grazing paddocks. A cutoff light intensity value of 4624.62 lx (determined in a previous validation trial) was used to differentiate between shade or solar exposure. Daily milk yield (averaged from the week before the study) was also recorded. Data (from 0600 to 1800h; averaged by min) were analyzed by the FREQ and GLIMMIX procedures (SAS). Similar parities (P = 1.00), DIM (P = 0.87), and BW (P = 1.00) were observed between groups. Milk yield was greater in the SLICK than in the WT cows (25.65 ± 2.26 and 21.38 ± 1.76 kg/d, respectively; P < 0.01). The SLICK cows spent a greater proportion of the grazing daily time exposed to solar radiation than the WT (52.67 vs. 47.33%, respectively; P < 0.01). Hair type and solar exposure degree (shade vs. sunlight) interacted (P < 0.01), with greater light intensity values in the SLICK than in the WT cows during solar exposure (24702 ± 106.65 vs. 20518 ± 98.43 lx, respectively), but no differences between groups during shade exposure (1856 ± 7.03 and 1793.2 ± 6.53 lx, respectively). Slick-haired cows spent more time grazing under the sun than their wild type-haired counterparts.

Keywords: slick-haired cows, light intensity, solar radiation.