Effects of distillers dried grains with solubles and forage dietary concentration in precision-fed dairy heifer diets: Mineral apparent absorption and retention

Objective: The objectives were to determine the effects of feeding different forage-to-concentrate ratios (F:C) and corn distillers dried grains with solubles (DDGS) inclusion rates on mineral apparent absorption (_AAb) and retention in precision-fed dairy heifer rations. Materials and Methods: A split plot design with F:C as whole plot [50:50 (LF) or 75:25 (HF)] and DDGS concentration as subplot (0, 7, 14 and 21%) was administered in a 4 × 4 Latin square using 8 ruminally cannulated Holstein heifers (12.5 ± 0.5 mo of age and 344 ± 15 kg of BW), and targeted an ADG of 800 g/d. Results and Discussion: Mineral intake was affected by F:C and DDGS; there was a linear interaction in DMI. Fecal excretion of Mg, S, and Mn was greater for heifers fed HF diets, and fecal Ca, Mg, P, S, and Mn decreased linearly with increasing DDGS. Urinary excretion of Mg was greater for LF and decreased as DDGS increased. The _AAb of Mg, S, and Mn was greater for LF. Linear and quadratic interactions between F:C and DGGS in _AAb were observed for S and Mg, respectively. Retention of Mg was greater in LF; no differences were detected for Ca, K, Na, and S retention with F:C or DDGS. Linear interactions between F:C and DGGS were observed in the retention of Mg, P, and S. Linear and quadratic interactions in _AAb for Mg and S, respectively, and a linear interaction for Mg, P, and S rentention demonstrate the importance of digestion kinetics when different F:C are used to evaluate dietary manipulations. Implications and Applications: There was a linear reduction of Ca, Mg, P, S, and Mn fecal excretion in response to the linear reduction of DMI as DDGS were incorporated in diets. Heifers fed high forage diets had greater DMI and rate of passage resulting in small increases in Mg, S, and Mn excretion in feces. Absorption and retention of most minerals, notably Ca, K, Na, and P, were not affected by dietary levels of DDGS.