Changes in neck muscles in Swedish reindeer bucks during rutting season.

Three neck muscles in Swedish reindeer bucks have been studied before and during the rutting season. These were M. splenius, M. sternocephalicus and M. brachiocephalicus. For comparison, M. longissimus dorsi was chosen. Fibre composition and fibre size were studied in the four muscles as also was the metabolic potential of three enzymes, representing respiratory chain (cytochrome oxidase), beta-oxidation of fatty acids (3-hydroxyacyl-CoA dehydrogenase) and anaerobic glycolysis (lactate dehydrogenase). The extreme increase in size of certain muscles in the neck in connection with the rutting season (e.g. sternocephalicus, which increases from 250 g to 1,500 g) was to a great extent due to an increase in fibre size. In splenius, all three fibre types studied increased (I, IIA, IIB); in brachiocephalicus, mainly IIA and IIB; and in sternocephalicus, only the IIB. No corresponding fibre increase could be found in longissimus dorsi. In splenius and sternocephalicus from bucks older than 54 months, 60-70% of the fibres were of type I, and in brachiocephalicus, only about 40%. In all muscles but one, oxidative capacity (cytochrome oxidase) and beta-oxidation of fatty acids (3-hydroxyacyl-CoA dehydrogenase) decreased significantly during the rutting season. This indicates that purposes other than the enhancement of energy production by fatty acid oxidation must account for the enlargement of the neck muscles.