Effect of abomasal or ruminal supplementation of citrus pulp and soybean oil on nutrient digestibility and ruminal fermentation of dairy cows

The aim of this research was to investigate the effects of supplementing two products, soybean oil (SBO; 0.2 kg/d) or SBO + citrus pulp (CPP; 1.0 kg/d), at two different sites, rumen or abomasum, on intake, total tract apparent digestibility (TTAD) and ruminal fermentation. Four ruminally fistulated lactating Holstein cows were assigned to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments: 1) SBO administered in the rumen; 2) SBO infused in the abomasum; 3) SBO + CPP administered in the rumen; and 4) SBO + CPP infused in the abomasum. Basal DM intake was lower for cows fed SBO + CPP than for those fed SBO only (16.5 versus 17.3 kg/d) and infusion in the abomasum tended (P = 0.07) to decrease it compared to administration in the rumen (16.6 versus 17.1 kg/d). Ruminal pH and ammonia N concentration were similar among treatments. There was an interaction between product and site of supplementation for total volatile fatty acids concentration as administration of SBO + CPP in the rumen increased it compared to that of SBO and infusion of the products in the abomasum had no effect. There was a trend (P = 0.09) for lower TTAD of crude protein with administration of products in the rumen compared to infusion in the abomasum and supplementation with SBO + CPP compared to SBO led to higher TTAD of ether extract. Treatments had no effect on TTAD of dry matter and neutral detergent fiber. Ruminal or post-ruminal supplementation of soybean oil with citrus pulp compared with that of soybean oil had little effects on TTAD of nutrients and ruminal fermentation characteristics. There was no advantage for a source of antioxidants such as citrus pulp to bypass the rumen when cows were supplemented with polyunsaturated fatty acids as SBO.