by Jude (Judith) Capper
Published in the Journal of Dairy Science, 2012
The objective of this study was to compare the environmental impact of Jersey or Holstein milk production sufficient... more
The objective of this study was to compare the environmental impact of Jersey or Holstein milk production sufficient to yield 500,000 t of cheese (equivalent cheese yield) both with and without recombinant bovine somatotropin use. The deterministic model used 2009 DairyMetrics (Dairy Records Management Systems, Raleigh, NC) population data for milk yield and com- position (Jersey: 20.9 kg/d, 4.8% fat, 3.7% protein; Holstein: 29.1 kg/d, 3.8% fat, 3.1% protein), age at first calving, calving interval, and culling rate. Each population contained lactating and dry cows, bulls, and herd replacements for which rations were formulated according to DairyPro (Agricultural Modeling and Training Systems, Cornell, Ithaca, NY) at breed- appropriate body weights (BW), with mature cows weighing 454 kg (Jersey) or 680 kg (Holstein). Resource inputs included feedstuffs, water, land, fertilizers, and fossil fuels. Waste outputs included manure and green- house gas emissions. Cheese yield (kg) was calculated according to the Van Slyke equation. A yield of 500,000 t of cheese required 4.94 billion kg of Holstein milk compared with 3.99 billion kg of Jersey milk—a direct consequence of differences in milk nutrient density (fat and protein contents) between the 2 populations. The reduced daily milk yield of Jersey cows increased the population size required to supply sufficient milk for the required cheese yield, but the differential in BW between the Jersey and Holstein breeds reduced the body mass of the Jersey population by 125 × 103 t. Consequently, the population energy requirement was reduced by 7,177 × 106 MJ, water use by 252 × 109 L, and cropland use by 97.5 × 103 ha per 500,000 t of cheese yield. Nitrogen and phosphorus excretion were reduced by 17,234 and 1,492 t, respectively, through the use of Jersey milk to yield 500,000 t of Cheddar cheese. The carbon footprint was reduced by 1,662 × 103 t of CO2-equivalents per 500,000 t of cheese in Jersey cows compared with Holsteins. Use of recombinant bovine somatotropin reduced resource use and waste output in supplemented populations, with decreases in carbon footprint equivalent to 10.0% (Jersey) and 7.5% (Hol- stein) compared with non-supplemented populations. The interaction between milk nutrient density and BW demonstrated by the Jersey population overcame the reduced daily milk yield, thus reducing resource use and environmental impact. This reduction was achieved through 2 mechanisms: diluting population maintenance overhead through improved milk nutrient density and reducing maintenance overhead through a reduction in productive and nonproductive body mass within the population.
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