Ruminant Nutrition: By-Products and Supplements

A study was conducted to determine the effects of dietary glycerol on dry matter intake (DMI), milk yield and components, blood metabolites, and efficiency in the transition cow. The study was conducted from Feb. to Oct. of 2008 using 48 cows (25 primiparous and 23 multiparous). The study ran from 3wk prepartum to 8wk postpartum with a randomized block design using a 2 × 2 factorial. Treatments were prepartum control and postpartum control (CC); prepartum control and postpartum 400g/h/d glycerol (CG); prepartum 200g/h/d glycerol and postpartum control (GC); prepartum 200g/h/d glycerol and postpartum 400g/h/d glycerol (GG). Cows were assigned to treatment by previous or predicted production values, parity, and estimated calving date. Diets were corn silage based and balanced to be isocaloric and isonitrogenous. Data was analyzed using Proc MIXED of SAS with contrasts and 2 and 3 way interactions. Postpartum DMI (P = 0.15) was 16.1, 17.3, 18.7, and 16.7 kg/d (±0.81) for CC, CG, GC, and GG respectively. Milk yield (P = 0.59) was 32.4, 34.4, 35.0, and 34.8(±1.70) for CC, CG, GC, and GG respectively. Milk protein percentage (P = 0.08) was 3.4%, 3.9%, 3.8%, and 4.0% (±0.18) for CC, CG, GC, and GG respectively. Efficiency defined as (ECM/DMI) [P = 0.15] was 2.11, 2.09, 1.98, and 2.25 (±0.08) for CC, CG, GC, and GG respectively. No statistical effect on serum glucose (average 66.1 mg/dl) or blood urea N (average 15.2 mg/dl) was observed. Non-esterified fatty acids and B-hydroxybutyrate concentrations were not affected by treatment averaging 0.62 mEq/L and 8.0 mg/dl respectively. The inclusion of glycerol in the diet resulted in a numerical improvement in milk yield and components compared with CC. GG resulted in a numerical improvement on efficiency compared with CC, CG, and GC. Researchers observed that the use of dietary glycerol as an energy source may be useful in improving production and efficiency in the transition cow though further research is needed to determine the optimum levels.