Noting that recent research has shown that adding alkalizing agents such as calcium oxide were effective at increasing ruminal pH and enhancing fiber digestibility in feedlot steers fed diets containing dried distillers grains plus solubles (DDGS), Purdue University researchers conducted a study to determine the effect of soybean hulls and/or calcium oxide on the performance and nutrient digestibility of cattle fed diets containing 30% DDGS.
In an accepted manuscript published in Translational Animal Science, N.A. Lancaster, C.R. Muegge, A.N. Baird and J.P. Schoonmaker with Purdue University, J.R.R. Carvalho and R.C. Lopes with the Universidade Federal de Lavras in Brazil and R.S. Narumiya and F. Pinese with the University of Sao Paulo in Brazil hypothesized that adding calcium oxide would increase ruminal pH and enhance a potential positive associative effect between stover, soybean hulls and DDGS, resulting in improved fiber digestibility and growth performance of the cattle.
In experiment 1, Lancaster et al. allotted 112 Angus x Simmental steers (initial bodyweight of about 364 kg) to one of four diets arranged as a 2 x 2 factorial and placed in 16 pens, with seven steers per pen, four pens per treatment and 28 steers per treatment. Factors were dietary inclusion of soybean hulls at 0% or 30% of diet dry matter and calcium oxide at 0% or 1%.
The researchers said the basal diets contained 20% corn stover, 30% DDGS and 4% supplement. Diets with soybean hulls contained either 14.1% or 15.0% corn, and diets without soybean hulls contained 43.9% or 44.8% corn.
In experiment 2, the researchers assigned four steers with an initial bodyweight of 510 kg to a 4 x 4 Latin square with 21-day periods to determine the effects of calcium oxide and soybean hulls on ruminal pH, volatile fatty acids (VFAs), nutrient digestibility and digestion kinetics.
According to Lancaster et al., in experiment 1, bodyweight did not differ among treatments (P ≥ 0.46), and overall carcass-adjusted gain did not differ due to soybean hull or calcium oxide inclusion (P ≥ 0.13). However, they noted an interaction (P = 0.01) where calcium oxide improved gain in steers fed no soybean hulls but not in steers fed soybean hulls. Steers fed hulls consumed more dry matter than steers not fed hulls (P = 0.02), and an interaction tended to occur (P = 0.06) where calcium oxide increased dry matter intake in steers fed no hulls, but not in steers fed hulls, the researchers added.
Calcium oxide increased hot carcass weight and yield grade (interaction; P ≤ 0.04) and tended to increase fat thickness (interaction; P = 0.08) in steers fed no hulls, but not in steers fed hulls, Lancaster et al. reported. However, other carcass traits such as dressing percentage, loin muscle area, percent kidney/pelvic/heart fat and marbling score did not differ among treatments (P ≥ 0.14).
According to the researchers total VFA concentrations were greater with soybean hull inclusion and with calcium oxide addition (P < 0.01). Digestibility of dry matter, neutral detergent fiber (NDF) and acid detergent fiber (ADF) were greater with calcium oxide addition (P ≤ 0.04), the researchers said, while NDF and ADF digestibility were greater with soybean hull inclusion (P < 0.001).
For digestion kinetics, Lancaster et al. said soybean hull inclusion did not affect (P ≥ 0.26) the rate of digestion (kd) or rate of passage, while calcium oxide addition tended to increase mean retention time (P = 0.09). An interaction between soybean hull inclusion and calcium oxide addition occurred for kd (P = 0.01), where calcium oxide increased kd in steers fed hulls but decreased kd when steers were not fed hulls.
Total nitrogen excretion tended to be lower with soybean hull inclusion and calcium oxide addition (P = 0.07), the researchers noted.
Lancaster et al. concluded that including calcium oxide in feedlot diets enhanced the performance of cattle fed diets containing corn, DDGS and corn stover, but not when corn was partially replaced by a fiber-based energy feed (soybean hulls).