The sustainability of dairy industry has been challenged due to competition with humans for feed and arable land. We sought to evaluate whether cows could maintain milk yield and improve conversion of human-edible (HE) nutrients in feedstuffs into milk when fed a “zero land use” diet (ZLU) and rumen-protected amino acids (AA). Twelve multiparous cows were assigned to a 3 × 3 Latin square with 21-d periods. Cows were blocked by milk yield and were randomly assigned within block to the following treatments: (1) conventional lactation TMR (CON) with 26% co-products; (2) TMR composed of ZLU feedstuffs; and (3) ZLU with top-dressed AA [ZLU-AA; 77 g/d AjiPro-L (Ajinomoto, Chicago, IL) and 45 g/d MetaSmart (Adisseo, Antony, France)]. ZLU consisted of hay from the winter intercropping of triticale and red clover, wheat middlings, corn gluten feed, corn hominy, spent coffee grounds, whole cottonseed with lint, and molasses. Cows were milked twice/d and milk samples were analyzed on d 18–21 of each period. Maximum HE metabolizable energy (ME) and protein contents were estimated based on sugar, starch, true protein, and fat concentrations in corn grain (including in silage), corn hominy, soybean meal products, wheat middlings, and molasses. Other feedstuffs were considered unsuitable for human consumption. Statistical models accounted for the random effect of cow within square and fixed effects of treatment, period, and square. ZLU diets decreased DMI, milk and solids yields, and feed efficiency (Table 1). ZLU diets did not improve the recovery of HE ME, and worsened HE protein recovery. Avoiding the use of dedicated livestock feed does not necessarily improve recovery of HE nutrients, although assumptions about human ingredient use heavily influence these calculations. Table 1.

Item	Diet			SEM	P-value
CON	ZLU	ZLU-AA
DMI, kg/d	26.2a	22.4b	22.5b	0.63	*
Milk yield/DMI	1.21a	1.06ab	0.99b	0.054	*
Milk yield, kg/d	31.9a	22.9b	22.9b	1.48	*
Fat, kg/d	1.13a	0.87b	0.89b	0.049	*
Protein, kg/d	1.02a	0.70b	0.75b	0.043	*
Lactose, kg/d	1.53a	1.03b	1.05b	0.073	*
Urea N, mg/dL	13.9ab	14.2a	13.7b	0.14	0.03
HE ME recovery in milk, %	0.64	0.65	0.63	0.029	0.90
HE protein recovery in milk, %	0.79a	0.42b	0.41b	0.035	*

*P < 0.001.