Evaluation of intervals between observations on estimation of eating behavior of cattle

The effect of different intervals between observations on the estimation of the eating behavior of dairy heifers and lactating cows was evaluated. Twenty Holstein-zebu crossbred dairy heifers were distributed in a completely randomized design, with four levels and five repetitions, fed isonitrogenous diets containing 71% sugar cane and 29% concentrate. Also, 16 dairy crossbred cows were distributed in a completely randomized design, with four levels and four repetitions. They received isonitrogenous diets, containing 85% sugar cane and 1% concentrate. For both heifers and lactating cows, the sugar cane used was treated with doses of 0, 0.75, 1.5 and 2.25% CaO, and corrected with 1% of urea and ammonium sulfate mixture (9:1), at the moment of offering the diets. The experimental period was 21 days long, with observations done on the 19th and 20th days, during 24 hours, at intervals of 5, 10, 15 and 20 minutes. For both heifers and cows, lower values were verified for number of periods (nº/day) and higher values were obtained for average time spent per period of eating, rumination and idle activities, for 10-, 15- and 20-minute intervals. The mean dry matter and neutral detergent fiber with corrections for ash and protein intake per period of eating was also lower for 10-, 15- and 20-minute intervals. The intervals between observations of 10, 15 and 20 minutes lead to underestimation of the number of periods (nº/day) and to overestimation of the average time spent per period of eating, rumination and idle (min) on dairy heifers and cows, resulting in fallacy estimations. The use of 5-minute intervals for studying cattle eating behavior is recommended.