Does Replacing Maize with Barley Affect the Animal Performance and Rumen Fermentation, including Methane Production, of Beef Cattle Fed High-Concentrate Diets On-Farm?

SIMPLE SUMMARY: The mitigation of greenhouse gas (GHG) emissions is a must in order to fight the climate emergency. Ruminants are responsible for over 75% of GHG emissions from livestock, with enteric methane being of paramount importance. Animals consuming high-concentrate diets produce less enteric methane than those fed high-forage diets, but the predominant grain in the concentrate may have an influence. On these grounds, the objective of this study was to assess, in commercial farm conditions, the effects of a partial substitution of maize with barley on animal performance and rumen fermentation in intensively reared beef calves. The predominant grain in the concentrate had no effect, in general, on animal performance or rumen fermentation. The general population and environmentalists should then be aware that a partial substitution of maize with barley in the concentrate offered to beef calves does not seem a promising strategy to decrease the emissions of enteric methane on-farm. ABSTRACT: Ruminants fed high-concentrate diets produce less enteric methane than those fed high-forage diets, but not all grains are equally effective in reducing methane production. This study aimed to examine, in farm conditions, the effects of a partial substitution of maize with barley on animal performance and rumen fermentation, including methane production, of intensively reared beef calves (ca. 0.9:0.1 concentrate to forage ratio). Ninety-six beef calves were fed a concentrate with 45.5% maize and 15% barley (n = 48; M) or a concentrate with 15.5% maize and 45% barley (n = 48; B). Both the concentrate and barley straw were offered ad libitum. The type of concentrate did not have a significant effect (p > 0.05) on final live weight, average daily gain, carcass dressing percentage or intake of concentrate and straw. Dry matter and organic matter digestibility were higher (p < 0.05) for the M (75.4% and 76.6%) than for the B (71.0% and 73.1%) treatment, but with no effect on digestible organic matter intake. In general, the majority cereal in the concentrate did not affect rumen fermentation, including methane production, or the degradability of dry matter and starch. A partial substitution of maize with barley in the concentrate offered to beef calves does not seem a promising strategy to decrease the emissions of enteric methane on-farm.