The effects of the forage-to-concentrate ratio on the conversion of digestible energy to metabolizable energy in growing beef steers

Authors: FULLER, AMANDA - Texas A&M University; WICKERSHAM, TRYON - Texas A&M University; SAWYER, J - Texas A&M University; Hales Paxton, Kristin

Submitted to: Proceeding of Plains Nutrition Council Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 3/21/2018
Publication Date: 3/28/2018
Citation: Fuller, A.L., Wickersham, T.A., Sawyer, J.E., Hales, K.E. 2018. The effects of the forage-to-concentrate ratio on the conversion of digestible energy to metabolizable energy in growing beef steers [abstract]. In: Proceedings of Plains Nutrition Council Spring Conference, April 5-6, 2018, San Antonio, TX. p. 117.

Interpretive Summary:

Technical Abstract: The net energy of a feed, required for beef cattle growth models, is often determined from metabolizable energy using cubic equations established by Garrett (1980). For the determination of these equations, ME was estimated using a fixed efficiency of 82% of the digestible energy. However, methane energy losses can vary greatly across dietary constituents suggesting that the relationship between DE and ME may not be static. The objective of this study was to quantify the effects of decreasing dietary forage and increasing concentrate on the efficiency of conversion of DE to ME. Ten purebred Angus steers (BW 365 ± 15.9 kg) were used in a 5 × 5 replicated Latin square design. The dietary treatments were formulated to contain an increasing proportion of concentrate with a concomitant decrease in forage supplied by corn silage and alfalfa hay. Dry-rolled corn was included in the experimental diets at 0, 22.5, 45, 67.5, and 83.8% on a dry matter basis resulting in a high F:C (HF:C), intermediate F:C (IF:C), equal F:C (EF:C), low F:C (LF:C) and a very low F:C (VLF:C), respectively. Each of the 5 experimental periods consisted of a 21-day diet adaption followed by 5 days of total fecal and urine collections. Additionally, gas exchange was measured over a 24-hour period during each collection period using portable headbox calorimeters. Steers were fed once daily and provided ad libitum access to feed and water. Data were analyzed as a Latin square design using the Mixed procedure of SAS v9.4 (SAS Inst. Inc., Cary, NC). Contrasts statements were used to test the linear and quadratic effects of F:C. There was a tendency (P = 0.06) for DMI to increase linearly as the F:C decreased. Consequently, gross energy intake (GE; Mcal/d) also increased linearly (P = 0.04) as the concentration of grain in the diet increased. Fecal energy loss in Mcal/d (P = 0.02) and as a proportion of GE intake (P < 0.01) decreased as F:C decreased. The digestible energy of the diets (Mcal/d) increased linearly (P < 0.01) and ranged from 20.20 to 26.81 for the HF:C to the VLF:C treatments, respectively. Methane energy loss in Mcal/d and as a proportion of GE intake responded quadratically (P < 0.01) increasing from HF:C to EF:C then decreasing thereafter. The efficiency of the conversion of DE to ME increased linearly (P < 0.01) as the F:C decreased, ranging from 85.82 to 91.87. Heat production increased linearly (P < 0.04) as concentrate grain increased in the diet but was not different as a proportion of GE intake (P > 0.22). Retained energy increased linearly (P < 0.01) as the concentration of grain in the diet increased. Dry matter, OM, and NDF digestibility increased linearly (P < 0.01) as the F:C decreased. Conversely, starch digestibility decreased linearly (P < 0.01) from 99.66 for the HF:C treatment to 93.30% for the VLF:C treatment. In conclusion, the efficiency of conversion of DE to ME increased with increasing dietary digestibility and decreasing methane energy loss.