Different forms and frequencies of soybean oil supplementation do not alter rumen fermentation in grazing heifers

Abstract

Over the productive cycle, the performance of cattle in grazing systems may be compromised, and feed supplementation is a strategy to establish nutritional balance and maximise the performance of grazing animals. The objective of this study was to evaluate the effect of different supplementation frequencies (i.e. daily supplementation (DS) versus Monday, Wednesday and Friday (MWF)) with different forms of soybean oil (i.e. soybean grain (SG), soybean oil (SO) and rumen-protected fat (RPF)) on the nutrient digestion and rumen fermentation of heifers grazing Brachiaria brizantha cv. Marandu pastures. Twelve crossbred heifers (1/4 Nellore × 1/4 Santa Gertrudis × 1/2 Braunvieh) with an initial bodyweight of 236.3 ± 27.6 kg were distributed in a completely randomised design with a factorial arrangement 3 × 2 (three diets and two supplementation frequencies). There was no interaction among the SO form or supplementation frequency on dry matter intake and dry matter digestibility (P > 0.05). The animals supplemented with SG exhibited lower nitrogen intake and absorption compared with animals that were fed SO (P < 0.05). The efficiency of microbial synthesis was not influenced by the diet or supplementation frequency (P > 0.05). Forms of SO affected the rumen pH; animals fed SO showed pH values similar to those of animals receiving SG but lower values than animals fed RPF (P < 0.05). Animals supplemented with DS exhibited higher levels of rumen ammonia nitrogen relative to those supplemented MWF. The reduction of supplementation frequency (from DS to MWF k) in our experimental conditions can be used to increase the efficiency of pasture utilisation without effects in fermentation activity of the rumen microbial population. Supplementation with SO is a strategy to increase propionic acid concentration and reduce A:P ratio, which is an indicator of improvement of the efficiency of the ruminal energy utilisation.