Asda has developed a range of beef which it says has a carbon footprint over a third lower than the standard 24 month beef. "The ASDA low carbon scheme uses dairy bulls, which would ordinarily be exported or slaughtered, and rears them for between 9-11 months so they can be sold as low carbon beef. Technically classified as a "by-product" of milk production, the CO₂ emitted by the calf is offset against the existing dairy farming process. What's more, as ASDA's low carbon beef is slaughtered at 9-11 months, it emits significantly less CO₂ during its lifetime than cattle more typically reared until 14-30 months of age. As it is smaller in size, portions are easier to manage, and it is available at a lower price point than standard beef." Note that many dairy bulls are already reared for beef - the difference with the ASDA scheme is that they are slaughtered at a younger age, which means that over their lifetime they emit less methane, eat less, use less energy and so forth. You can download the press release here.