Has the soybean oil supplementation effect on milk production, feed efficiency, and grazing behavior of Girolando cows under moderate heat stress in western Amazonia?

Abstract

The effect of soybean oil supplementation in the diet of early lactating Girolando cows under moderate heat stress were studied in a grazing trial. Dry matter intake (DMI), milk yield, feed efficiency, and grazing behavior (during daytime and nighttime) were evaluated in two groups of eight crossbred Girolando (Holstein × Gyr) cows grazing palisade grass (Urochloa brizantha syn. Brachiaria brizantha) with initial means of 53±33 days in lactation and 22.6±3 kg of milk day-1. They were arranged in a 2×2 crossover trial with two supplements (with or without soybean oil), two genetic groups and two periods. During the experimental period, the mean of temperature and humidity index (THI) was 75.11, suggesting moderate heat stress. Total DMI was based on fecal production estimated by LIPE® and the diet in vitro DM digestibility (IVDMD). Grazing behavior was assessed for 48 hours by acoustic data collected with MP3 recorders. Soybean oil supplementation had no significant effects on all variables evaluated in this study. Averages of individual milk yield and total DMI were 19.26 kg day-1 and 15.32 kg DM day-1, respectively. Under moderate heat stress, oil supplementation did not change grazing behavior, dry matter intake, or milk yield in early lactating Girolando cows.