Dairy cattle can convert human-inedible by-products, or leftovers, into food for humans. When cows are fed diets high in by-products, they can more than double the amount of food available for humans. Our goal was to evaluate the effects of feeding a diet of 70% by-products on milk production and net food production. Multiparous Holstein cows (n=31; 90 23 DIM, 51 8 kg milk/d, 730 60 kg BW) were used in a crossover design of 2 diets. Diets were composed of 20% by-products (CON) or 70% by-products (BYP). BYP diet consisted of 25% corn silage, 18% corn gluten feed, 15% bakery waste, 10% whole cottonseed, 10% wet beet pulp, 8% wheat straw, and 13% supplements (DM basis). CON contained 36% corn silage, 13% haylage, and 25% corn grain. Data were analyzed using PROC GLIMMIX of SAS 9.4 with treatment, treatment sequence, and period as fixed effects and cow as random. Cows fed BYP consumed less DM (30.1 vs 30.9 kg/d, P < 0.01) and produced less milk (46.9 vs 49.1 kg/d, P < 0.01) with more fat (3.68 vs 3.55%, P < 0.01), less protein (3.07 vs 3.09%, P = 0.01), and less lactose (4.91 vs 4.95%, P < 0.01) than cows fed CON. Energy-corrected milk was decreased 3% (P < 0.01; 47.5 for BYP and 48.9 kg/d for CON). Cows fed BYP were considerably more efficient in converting human-edible feed energy into milk energy using Atwater energy values (171 vs 54%, P < 0.01). Cows fed BYP were also more efficient in converting human-edible feed protein into milk protein (202 vs 72%, P < 0.01). Adding more by-products in dairy cattle diets presents tradeoffs for sustainability with decreased production levels but increased net food production.
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