Contents lists available at ScienceDirect Journal of Thermal Biology journal homepage: www.elsevier.com/locate/jtherbio The impact of hair coat color on physiological variables, reproductive performance and milk yield of Holstein cows in a hot environment F. Anzures-Olvera a , F.G. Véliz a , A. de Santiago a , J.E. García b , J. Mellado b , U. Macías-Cruz c , L. Avendaño-Reyes c , M. Mellado b, ⁎ a Department of Animal Nutrition, Autonomous Agrarian University Antonio Narro, Saltillo, Coah, Mexico b Department of Veterinary Science, Autonomous Agrarian University Antonio Narro, Torreon, Mexico c Institute of Agricultural Sciences, Autonomous University of Baja California, Mexicali, Mexico ARTICLE INFO Keywords: Heat stress Milk yield Panting score Body surface temperature Hematological variables ABSTRACT Vulnerable animals to heat stress have been described as ones with dark or black hides due to increasing ab- sorption of solar radiation. The effect of coat color in pluriparous contemporary Holstein cows in a hot en- vironment (mean annual temperature 24.6 °C), on body surface temperature (infrared thermography), physio- logical and hematological variables as well as milk yield and reproductive performance was assessed using 178 Holstein pluriparous cows (74 predominantly white and 104 predominantly black). Data were collected in the morning and afternoon in July (mean temperature-humidity index 82 units). Body condition score at mid-lac- tation (128 ± 32 days in milk at the start of the experiment) was higher (P < 0.01) in predominantly white than in black cows (3.3 vs. 3.2). Respiration rate did not differ between groups (72 ± 23 vs. 73 ± 20 breaths/ min for white and black cows, respectively, sampling time combined). In contrast, rectal temperature of black cows was 0.1 °C higher (P ≤ 0.01) than white cows, regardless of sampling time. The only significant hemato- logic change was a slight increase in mean corpuscular volume in black cows (54.7 fL, P < 0.01) compared to white cows (53.8 fL), but it remained within the reference range. Differences due to coat color did not alter body surface temperatures at any time of the day. Conception rates, services per conception, calving intervals and fetal losses were not associated with hair coat color, but cows with predominantly white coat produced 394 kg more (P < 0.01) fat-corrected milk in 305 days compared to cows with predominantly black coat. It was concluded that in this hot-arid environment with cows housed in facilities with extensive cooling, black hair coat mod- erately reduces 305-d milk yield without affecting milk composition, body surface temperature, and re- productive performance. 1. Introduction Maximum ambient temperature > 30 °C in arid zones of northern Mexico extend for about 8 months. Thus, intense radiant energy is prolonged in this environment causing a chronic heat stress for dairy cows, with little relief from heat during the evening hours. Lactating Holstein cows create a large quantity of metabolic heat which make them particularly susceptible to heat stress due to the high metabolic load of milk synthesis and visceral metabolism associated with high feed intake needed to sustain lactation (Dunshea et al., 2013) and ac- cumulate additional heat from radiant energy (West, 2003). Under these climatic conditions, cows produce and accumulate heat which increases heat load in the cow due to the compromised cooling cap- ability of Holstein cows (Baumgard and Rhodas, 2013). Temperatures higher than the cow's comfort zone have a negative effect on feed intake (Wheelock et al., 2010), postabsorptive metabo- lism (Rhoads et al., 2009), nutrient partitioning (Baumgard and Rhoads, 2013), reduced milk yield (West et al., 2003; Bohmanova et al., 2007), reduced milk components (Garner, 2017), reproduction (Mellado et al., 2013) and growth (López et al., 2017). Additionally, acute heat stress has a negative effect on the cow's well-being. These declines are associated with physiological changes in the stressed cows, including increased sweating, respiration and panting rates, core body temperature, metabolic and endocrine-system changes that are im- portant to dairy cow health and productivity (Wheelock et al., 2010). While much is known about the effects of high ambient temperature on production of dairy cows, there are some shortfalls in knowledge on this topic. For example, it is required a better understanding of the https://doi.org/10.1016/j.jtherbio.2019.02.020 Received 23 October 2018; Received in revised form 18 January 2019; Accepted 26 February 2019 ⁎ Correspondence to: Autonomous Agrarian University Antonio Narro, Department of Animal Nutrition, Saltillo, Coahuila 25315, Mexico. E-mail address: miguel.mellado@uaaan.edu.mx (M. Mellado). Journal of Thermal Biology 81 (2019) 82–88 Available online 27 February 2019 0306-4565/ © 2019 Elsevier Ltd. All rights reserved. T