The seasonal lack of availability of lush green forages can force dairy farmers in developing nations to rely on crop residues such as wheat and rice straw as the major feed source. We tested whether ammonia fiber expansion (AFEX) treatment of wheat straw would increase the energy available to Murrah buffalo and Karan-Fries cattle consuming 70% of their diet as wheat straw in India. Forty lactating animals of each species were blocked by parity and days in milk and randomly assigned to 1 of 4 treatment diets (n = 10). Treatments were a nutrient-rich diet with 0 to 20% straw (positive control; PC) and 3 high-straw diets with various levels of AFEX-treatment: (1) 70% untreated straw (no AFEX), (2) 40 to 45% untreated straw with 25 to 30% AFEX-treated straw (low AFEX), and (3) 20% untreated straw with 50% AFEX-treated straw (high AFEX). The AFEX-treated straw was pelleted. Urea was added to the no and low AFEX diets so they were isonitrogenous with the high AFEX diet. Animals were individually fed the PC diet for 14 d followed by 7 d of adaptation to treatments, full treatments for 28 to 35 d, and finally PC diets for 21 d. Compared with buffalo fed the PC diet, those fed high-straw diets consumed 29% less feed dry matter, put out 16% less milk energy, and lost 0.8 kg/d more body weight; the AFEX treatment of straw did not alter intake or milk production but greatly ameliorated the body weight loss (-1.0 kg/d for no AFEX and -0.07 kg/d for high AFEX). In Karan-Fries cattle, high-straw diets decreased dry matter intake by 39% and milk energy by 24%, and the high AFEX diet increased intake by 42% and milk energy by 18%. The AFEX treatment increased digestibilities of organic matter, dry matter, neutral detergent fiber, acid detergent fiber, and crude protein by 6 to 13 percentage points in buffalo and 5 to 10 points in cattle. In conclusion, AFEX treatment increased the digestibility and energy availability of wheat straw for lactating buffalo and cattle and has commercial potential to improve milk production and feed efficiency when high-quality forages or grains are not available.

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AFEX treatment of crop residues can greatly increase their nutrient availability for ruminants. This study investigated the concentration of acetamide, an ammoniation byproduct, in AFEX-treated crop residues and in milk and meat from ruminants fed these residues. Acetamide concentrations in four AFEX-treated cereal crop residues were comparable and reproducible (4–7 mg/g dry matter). A transient acetamide peak in milk was detected following introduction of AFEX-treated residues to the diet, but an alternative regimen showed the peak can be effectively mitigated. Milk acetamide concentration following this transition was 6 and 10 ppm for cattle and buffalo, respectively, but also decreased over time for cattle while tending to decrease (p = 0.08) for buffalo. There was no difference in acetamide concentration in the meat of cattle consuming AFEX-treated residues for 160 days compared to controls. Further investigation is necessary to determine the metabolism of acetamide in ruminants and a maximum acceptable daily intake for humans.

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