Effects of dietary concentrate level on protein feed-food and land use competition indicators

The capacity of dairy cows to use both land and feeds potentially competing for direct human use or not challenges what is their optimal use to maximize milk output and related efficiency. To assess the relationships between these resources and milk output, this study evaluated the effects of dietary concentrate level on efficiency of conversion of dietary protein into bovine milk. Data originated from 336 northern Italy dairy farms, with a wide range in intensification degree, diet composition, milk yield (MY) and milk protein content (MPc), acquired through farm visits and official databases. The net energy requirement of cows and the dietary net energy content were used to estimate dry matter intake (DMI). The crude protein intake (CPI) was computed as DMI x dietary CP content, whereas the milk protein yield (MPY) as MY x MPc. The following protein conversion ratios (PCR = CPI/MPY) of dietary CP into milk were used as indicators of efficiency: a) PCRwd, using the CPI of the whole diet; b) PCRmp, using the CPI from main products of arable land, with exclusion of byproducts; c) PCRco, using the CPI from concentrates; d) PCRhe, CPI from potentially human-edible foods. The PCRs were analyzed with a mixed model testing the fixed effect of the quintile of the percentage of CPIwd covered by CPIco (CPc_p, with average values of 6, 15, 20, 26, and 37% for quintiles from 1 to 5) and the random effect of the dairy system. Herd size averaged 101 lactating cows (range: from 3 to 1009), MY 25.7 kg/cow/d (8.5‒44.5), MPY 0.83 kg/cow/d (0.27‒1.43). Efficiency indicators (mean±standard deviation) averaged 4.38±0.71 (PCRwh), 2.58±1.15 (PCRmp), 0.85±0.41 (PCRco) and 1.12±0.52 (PCRhe). The CPc_p significantly affected MPY, which increased from 1st to 4th quintile. Similarly, at increasing CPc_p we observed a nearly linear decrease of PCRwd (from 4.97 to 3.74 for quintile 1 to 5), whereas PCRmp exhibited best values for CPc_p comprised between 15 to 26%. Increasing CPc_p linearly increased PCRco, with value ≤ 1 kg CPI/kg MPY for CPc_p ranging from 6 to 26%, and quadratically affected PCRhe, with best values for CPc_p ≤ 15%. In conclusion, the use of human-competitive resources has complex interactions with the capacity of dairy cows to convert dietary CP into MP. Anyway, diets with CPc_p close 25% resulted in the best trade-off between MPY and conversion of dietary protein into milk protein, thus supporting the efficiency of dairy farming as source of protein for humans. Research supported by LIVE-GREEN project (REACT EU PON 2014–2021 - Asse IV, azione IV.6) (Dr. Marco Berton)