Effect of crude glycerin on dry matter and nutrient digestibility of feed ingredients in dairy cows

Abstract Text: Rumen-cannulated Holstein cows (n = 6; 587 ± 39 kg BW; 114 ± 29 DIM; 20 ± 1.5 kg milk/d), were used to evaluate the effects of crude glycerin on in vitro digestibility of dry matter, and nutrients (CP and NDF) of feed ingredients. Cows were assigned to a replicated 3 × 3 Latin square. The three isoenergetic and isonitrogenous diets composed of corn silage, cracked corn grain, sunflower meal, corn gluten, urea, mineral premix, and 0 (G0), 15 (G15), or 30% (G30) crude glycerin. The experiment lasted 69 d, with three periods of 23 d each. For in vitro determinations, the Daisy II fermenter was used. The ingredients were ground (1 mm), and placed in F57 bags (0.5 g/bag; 25 bags/treatment). At d 20 of each experimental period, rumen content was manually collected and strained with cheesecloth. Then, 400 ml of strained rumen content were placed in each fermentation jar, with 1330 ml buffer A and 266 ml buffer B. The jars were purged with CO₂, and incubated at 39^oC for 72 h. When the incubation was completed 48 h, 8 g pepsin and 40 ml HCl 6N were added to each jar. The pH and ammonia-N (NH₃-N) were determined at 0, 48, and 72 h of incubation. Data were analyzed as mixed model with fixed effects of diet and period, and random effects of cow (diet) and residuals. Crude glycerin inclusion did not affect pH and NH₃-N concentration (pH = 6.5, 6.4, 3.4; NH₃-N = 20.5, 8.3, and 8.5 mg/dl, respectively for 0, 48, and 72 h incubation). The addition of 15% crude glycerin decreased (P<0.05) IVDMD and IVCPD of sunflower meal, and corn grain. When 30% crude glycerin were added, a decrease in IVDMD was observed for corn gluten (P<0.05), and in vitro NDF digestibility for corn silage (P<0.01). No differences were observed on IVDMD and IVCPD of corn silage. The addition of up to 30% crude glycerin in lactating cows diets affected digestibility of feed ingredients. Caution should be taken when combining glycerin with roughages, due to the negative effect on NDF digestibility.

Keywords: dairy cow, digestion, glycerol.