Performance, digestibility, and blood acid-base balance of dairy cows in response to the replacement of corn by crude glycerin

Abstract Text:

This experiment evaluated the response of late lactation dairy cows to the partial replacement of corn by methanol rich, crude glycerin. The tallow derived glycerin contained 70.2% DM and 7.3% methanol on an as fed basis. Twelve Holsteins (219±57 DIM), 3 primiparous, were assigned to 35-d periods, 3x3 Latin Squares. The isonitrogenous diets (15.8% CP) contained (DM basis): 11.8% finely ground mature corn and 17.2% soybean meal (T0); 4.9% glycerin, 5.9% corn, and 18.3% soybean meal (T5); or 9.7% glycerin and 19.4% soybean meal (T10). Other ingredients were: 31.9% corn silage, 28.2% sugarcane silage, and 6.2% high moisture corn. Statistical analysis was performed with Mixed of SAS, with a model containing the random effect of cow and the fixed effects of period and treatment. Two contrasts were evaluated: Linear = T0 vs. T10, and Quadratic = T5 vs. (T0+T10). The replacement of corn by glycerin induced linear decreases in milk (22.2, 21.1, 20.0 kg/d, P<0.01) and lactose secretions (P<0.01), without affecting DMI (17.8 kg/d, P=0.53), reducing feed efficiency (P<0.01). Milk contents of fat (4.11, 4.33, 4.37%, P=0.01) and protein (3.47, 3.64, 3.73%, P<0.01) were linearly increased by glycerin, but daily secretions were similar (P>0.86). Milk urea nitrogen was similar (13.8 mg/dL, P=0.51), as well as chewing activity (P>0.32), except the daily ingestion time, reduced by glycerin (P=0.05). Total tract apparent digestibility of the non-NDF organic matter was linearly increased by glycerin (90.3, 91.4, 93.2% of intake, P=0.05), but the intake of digestible organic matter was similar (10.6 kg/d, P=0.66). The ratio of the daily milk energy secretion to the intake of digestible organic matter was linearly reduced by glycerin (1.58, 1.55, 1.42 Mcal/kg, P=0.05). Rumen pH 12-h post feeding was similar (5.67, P=0.72). The intake of crude glycerin was 1.24 kg/d in T5 and 2.5 kg/d in T10, methanol intake was 134 mg/kg of BW in T5 and 269 mg/kg of BW in T10. Health disorders were not observed. However, glycerin reduced the partial pressure of CO₂ (P=0.02) and increased the saturation of hemoglobin with O₂ (P=0.05) in jugular blood samples obtained 6-h post feeding, suggesting an induction of hyperventilation. Venous blood pH, bicarbonate level, base excess, and the partial pressure of O₂ were not affected by treatment (P>0.64). The replacement of corn by crude glycerin reduced milk yield, feed efficiency, and the response was associated to low milk lactose secretion.

Keywords:

Digestibility, glycerin, methanol