The objective of this study was to examine effects of feeding microalgae meal (MA; Schizochytrium limacinum CCAP 4087/2) on visceral adipocyte, subcutaneous adipocyte, and Longissimus lumborum (LL) muscle fiber characteristics. Heifers (36 pens; 8 heifers/pen) were blocked by initial pen BW (4014 ± 223 kg) and assigned within strata to 1 of 4 treatments. Treatments consisted of 0, 50, 100, and 150 g·heifer⁻¹·d⁻¹ of MA (Alltech Inc., Nicholasville, KY) added to a basal diet consisting of steam-flaked corn, wet corn gluten feed, alfalfa hay, glycerin, and supplement. Heifers were harvested on d 89 of the study and visceral and subcutaneous adipose tissue were collected from approximately the 13th rib of 3 heifers selected at random from each pen. The strip loin from the left side of the same randomly selected heifers was removed and transported to Kansas State University for analysis. One 1.27-cm steak was removed from the 13th-rib end of each loin for measurement of muscle fiber characteristics of the LL. There were no treatment × depot interactions for cross-sectional area or diameter of subcutaneous and visceral adipocytes (P > 0.33). Increasing MA in the diet did not affect cross-sectional area or diameter of visceral or subcutaneous adipocytes (P > 0.56) and did not affect distribution of LL myosin heavy chain type I, IIA, and IIX muscle fibers or cross-sectional area of fibers (P > 0.16; Table 1). Supplementing microalgae meal does not affect visceral and subcutaneous adipocyte size or muscle fiber characteristics of the LL. Table 1. Cross-sectional area (μm²) of adipocytes and muscle fibers in heifers fed microalgae meal

Item	Algae, g·heifer–1·d–1 DM				SEM
0	50	100	150
Subcutaneous adipocyte	9,962	9,395	9,632	9,899	523
Muscle fiber
Type I	2,601	2,321	2,289	2,521	119
Type IIA	2,794	2,692	2,710	2,676	139
Type IIX	4,171	3,809	3,954	4,020	181