Effects of varying the human-edible fraction of concentrates offered on dairy cow performance and nutrient utilization

With the world's population expected to reach 9 billion by 2050, there are growing concerns about the increasing inclusion of human-edible (HE) feedstuffs in the diets of ruminant livestock. Two experiments (a smaller scale study involving late lactation cows and a larger scale study involving early lactation cows) examined the impact of varying the human-edible fraction (HEF) of the concentrate on the performance of dairy cows offered grass silage-based diets. Changes in HEF were achieved by replacing the cereal and soybean meal component of the concentrate with byproduct feed ingredients, including sugar beet pulp, rapeseed meal, and distillers dark grains. The ingredient composition of the concentrates offered was similar in both experiments. Experiment 1, a 2-treatment, 2-period (duration of 4 wk each) balanced changeover design experiment involved 20 mid lactation Holstein dairy cows (mean 157 DIM, SD 7.0). Diets were offered as a total mixed ration comprising grass silage and concentrates (65:35 DM ratio), with the concentrate component of the diet having either a low HEF (0.18HE) or a high HEF (0.54HE) on a fresh basis. In experiment 2, 32 early lactation Holstein cows (mean 50 DIM, SD 4.9) were used in a 3-period (4-wk duration) partial Latin square design study. Cows were offered grass silage supplemented with 1 of 4 concentrate types (12 kg/d) differing in the proportions of HE ingredients which were offered via an out-of-parlor feeding system. The HEF of these concentrates were 0.17, 0.28, 0.38, and 0.48 (fresh basis). Reducing the HEF of the concentrate in experiment 1 increased total DMI and milk yield and decreased milk fat and protein concentration, but had no effect on ECM yield. Decreasing the HEF of the concentrate had no effect on total feed conversion rate but improved edible food conversion rate (eFCR; daily HE feed output per daily HE input), and net food production (NFP; daily HE feed output - daily HE input). In experiment 2, reducing the HEF of the concentrate tended to decrease feed intake, but increased milk yield and ECM yield. Decreasing the HEF of the concentrate had no effect on either milk fat or protein concentration but increased both milk fat and protein yield. Reductions in the HEF of the concentrate resulted in a linear decrease in the total SFA concentration of milk and a linear increase in the MUFA and PUFA content of milk. Total DM and OM digestibility coefficients showed a linear increase with increases in the HEF in the concentrate. Cows offered concentrate with a lower HEF had a higher eFCR and NFP. In conclusion, reducing the HEF of the concentrate component of grass silage-based diets by replacing cereals and soybean meal with byproduct feeds effectively improved human-edible feed conversion efficiency.