Supply levels of multiple supplements for beef heifers on pasture during the dry season: ruminal pH and ammonia nitrogen

Abstract Text: This research aimed to evaluate the effect of different levels of multiple supplements for beef heifers that were restricted grazing during the dry season on pH and ruminal ammonia nitrogen. Five Nellore heifers were used, with age and initial weights average of 20 months and 344.0 kg, respectively. The pastures were divided into five paddocks of 0.25 ha each, consisting of Brachiaria brizantha cv. Marandu. The experiment was divided into 5 x 5 Latin square design, composed by five experimental periods of 20 days each and five animals. The strategy adopted was to provide multiple supplements (soybean hulls + ground corn grain + soybean meal + sunflower + urea and mineral mix) at levels of 2, 4, 6, and 8 kg/animal/day. The animals were fed in two fixed hours: 50% of the daily amount at 10 o'clock in the morning and 50% at 3 o'clock in the afternoon, the mineral mixture was offered ad libitum (control). For determination of pH and ammonia concentration in the rumen fluid samples were collected by gavage on the 19th and 20th day of each period, two hours before supplementation (10h - 0h time) and two hours after supplementation of afternoon (15h-2h time).The availability of total dry matter was 2.29 ton/ha. The strategies of supplementation promoted a reduction of ruminal pH (P=0.0343) and increased the concentration of ruminal ammonia nitrogen (NH₃-N) (P=0.0004) before providing supplements, and after the supplementation the NH3 expressed a quadratic effect (P=0.0023). The values observed for ruminal pH varied from 6.44 to 6.78 before supplementation in the morning and from 6.43 to 6.79 two hours after feeding the animals in the afternoon, not harming the ruminal microbiota. Providing high levels of multiple supplements increases the nutritional support for cattle on systems with low level and quality of pasture during the dry season.

Keywords: Brachiaria brizantha, replacement effect, rumen