Climatização na pré-ordenha de vacas da raça girolando e seus efeitos na produção e qualidade do leite e no comportamento animal

Abstract

This study was conducted to evaluate and quantify the effects of cooling of cows in the pre-milking stable waiting pen on milk production, milk composition, animal behavior, physiological state, thermal environmental adaptation and the cost-benefit of the Adiabatic Evaporative Cooling System (AECS). The research was conducted on a dairy farm producing type B milk located in the state of Pernambuco, Brazil. Sixteen multiparous lactating Girolando cows were used having a genetic composition of 7/8 Holstein-Zebu and an average production of 18 kg of milk per animal per day, divided into four groups with four evaluation periods. A (4x4) Latin square design was used. The Tukey test (P <0.05) was utilized for comparison of the means. The experiment was conducted during the summer season (February-March 2009) and lasted 56 days. The treatments consisted of different periods of exposure (0, 10, 20 and 30 min.) of the animals to the AECS in the pre-milking stable waiting pen before the morning milking sessions (5 to 5:30 a.m.) and the afternoon sessions (2:00 to 2:30 p.m.). Milk production was recorded daily and the collection of samples for analysis of its components was performed twice for each of the 4 study periods. The respiratory rate (RR), rectal temperature (RT) and temperature of the coat (TC) were taken twice during each study period, measured before and after cooling on alternating days and did not coincide with the behavioral assessment days. All animals of each treatment wereobserved at 10 minute intervals, from 7a.m. to 1p.m. and from 3p.m. to 5 p.m. Environmental data consisting of dry bulb temperature (DBT, ºC), relative humidity (RH, %) and black globe temperature (BGT, ºC) were recorded every minute during the time of exposure of animals to the cooling system in the stable waiting pen and out in the external environment using the HOBO® data logger. Wind speed was recorded usingan anemometer at all of the treatment intervals. The thermal efficiency of the system was determined by using the Temperature and Humidity Index (THI), the Wet Bulb Globe Temperature (WBGT), the Radiant Thermal Load (RTL) and enthalpy (h). Exposure of the animals in the stable waiting pen to the AECS for 30 minute periods allowed the environmental variables and the comfort indices to remain below the critical upper limit of thermal comfort for the animals. The 30 minute treatment showed lower RR, TR, and TC values when compared to animals subjected to the 0 min., 10 min. and 20 min. treatments and these values were within acceptable limits. The animals in the 30 minute cooling sessions spent more time on food intake and rumination (277 and 483 observations) compared to the 0 min. treatment (248 and 438 observations), the 10 min. treatment (251 and 437 observations) and the 20 min. treatment (274 and 476 observations) respectively. The 30 min. treatment had a 4.35% increase in milk production compared to the 0 min. treatment. There was no significant effect on milk composition among the treatments. The initial purchase cost of the AECS was R$ 2,147.80, which yielded an increase in milk production of 0.765 kg per animal per day, and an increase in monthly revenue of approximately R$ 1,266.84. Comparing the 0 min. and 30 min. cooling periods, the AECS showed itself to be a profitable investment, with a return on the invested capital within 58 days.