Influência de diferentes níveis de sombreamento sobre a sanidade de bovinos leiteiros na Amazônia Meridional

Abstract

Brazil stands out for having one of the largest cattle herds in the world, ranking first in terms of commercial herds on the whole planet. Within cattle farming, dairy farming stands out for its importance within the national economy due to the representativeness of small family properties that develop a large part of the national milk production. However, despite the extensive area available for agricultural production, much of Brazil is located within the tropical zone of the planet. This region stands out for its high temperatures and high intensity of incident solar radiation. This condition tends to lead the animals to thermal stress, thus leading to a decrease in meat production, but mainly milk production; especially on properties that make use of European breeds. One of the alternatives to overcome the impact of heat stress in tropical regions is to cross European breeds with zebu breeds with dairy aptitude, as well as to seek measures to reduce the incidence of solar radiation on these animals through integrated systems, such as the silvopastoral system. Therefore, the objective of this study was to evaluate the impact of different levels of shading in a Silvipastoral System on various health issues of dairy cows of different blood degrees raised in the field within the southern Amazon region of Mato Grosso. This study was carried out at the Brazilian Agricultural Research Corporation (EMBRAPA - Agrossilvipastoral), located in the municipality of Sinop - MT, during two seasons, the months of August and September of 2020, which correspond to the dry season; and March and April of 2021, which correspond to the rainy season. Forty-seven Dutch + Gir crossbred cows were used, in lactation, with blood degrees of ½, ⅝ and ¾, divided into four experimental herds; according to shading intensity: TYPE I - thinning lateral shading (pasture with a density of 130 trees/ha distributed along the edges of the paddock); TYPE II - dense lateral shading (pasture with a density of 260 trees/ha distributed along the edges of the paddock); TYPE III - simple intense shading (simple rows of eucalyptus spaced by 21 m, with a density of 120 trees/ha); and TYPE IV - intense triple shading (triple rows of eucalyptus spaced by 15 m, with a density of 340 trees/ha). The animals were evaluated weekly for eight weeks in each experimental period, totaling 16 collections throughout the experiment. Among the parameters evaluated, it was found that animals ½ blood were more susceptible to subclinical mastitis, making cows ⅝ better for management, with the most favorable type IV shading level. Regarding the parasitological aspects of the animals evaluated, ¾ cows were the most affected by helminths, and animals with ½ blood had lower means of ticks and flies; and they also had type IV as the best shading level with the lowest average of fly counts, with the rainy season as the period with the lowest average of flies and the highest average of egg counts per gram of feces (EPG). From the hematological and biochemical aspects, the dry season had excellent hematological indices and the rainy season had a lower level of cortisol, also having satisfactory results in the shading of lower levels.