Effect of Feeding Glycerin on Ruminal Environment and In Situ Degradability of Feedstuffs in Young Bulls

SIMPLE SUMMARY: Glycerin (a by-product of the biodiesel industry) can be used as an energetic ingredient in animal feeds, but there are few studies on fattening ruminants that concurrently analyse the effect of glycerin on the ruminal metabolism, ruminal bacterial population and feedstuff degradability. We have studied the effect of feeding glycerin in young bulls that were fed high levels of concentrate. The results showed that the inclusion of glycerin in beef cattle feed (at 20, 40 or 80 g/kg) increased the propionic acid production, and at high levels could reduce the ruminal pH. In addition, the ruminal population of Selenomonas ruminantium (a lactate- and glycerol-consuming and a propionate-producing species) could be increased by glycerin supplementation. In general, no negative effects on the ruminal degradability of feedstuffs (cereals, protein supplements and fibrous materials) are caused by the use of glycerin. In young bulls that were fed high levels of concentrate, glycerin at 20 or 40 g/kg of feed can be included without affecting the ruminal pH. ABSTRACT: This work studied the effect of feeding glycerin in bulls that were fed high levels of concentrate on the ruminal environment and in situ degradability of feedstuffs. Four ruminally cannulated young bulls were assigned to a 4 × 4 Latin square arrangement of treatments. The diets consisted of 15% barley straw and 85% concentrate in dry matter (DM). There were four different concentrates: without glycerin, and with 20, 40 or 80 g of glycerin per kg of DM. Each diet was offered for 24 days, the ruminal fluid was sampled to evaluate the ruminal metabolism and to determine the ruminal bacterial population by quantitative real-time polymerase chain reaction analysis, and the in situ degradability of six different feedstuffs was measured. The treatment with the highest level of glycerin provided the lower pH (p < 0.001), and the acetic/propionic molar ratio decreased (p < 0.001) as glycerin increased. The incorporation of glycerin in the diet did not affect the DNA copies/µL of the total bacteria, Butyrivibrio fibrisolvens and Butyrivibrio proteoclasticus (p > 0.05) in the DNA extract of rumen fluid, but at high levels increased Selenomonas ruminantium (p < 0.01). Very few effects of glycerin incorporation were found for the in situ degradability. In young bulls that were fed high levels of concentrate, glycerin at 20 or 40 g/kg of feed could be included without affecting the ruminal pH and raising the propionic acid, but at 80 g/kg the ruminal pH dropped, despite the increase of Selenomonas ruminantium.