The objective of this study was to examine effects of 4 levels of microalgae meal (All-G Rich, CCAP 4087/2; Alltech Inc., Nicholasville, KY) supplementation to the diet of finishing heifers on longissimus lumborum (LL) steak PUFA content, beef palatability, and color stability. Crossbred heifers ( = 288; 452 ± 23 kg initial BW) were allocated to pens (36 pens and 8 heifers/pen), stratified by initial pen BW (3,612 ± 177 kg), and randomly assigned within strata to 1 of 4 treatments: 0, 50, 100, and 150 g·heifer·d of microalgae meal. After 89 d of feeding, cattle were harvested and LL were collected for determination of fatty acid composition and Warner-Bratzler shear force (WBSF), trained sensory panel evaluation, and 7-d retail color stability and lipid oxidation analyses. Feeding microalgae meal to heifers increased (quadratic, < 0.01) the content of 22:6-3 and increased (linear, < 0.01) the content of 20:5-3. Feeding increasing levels of microalgae meal did not impact total SFA or MUFA ( > 0.25) but tended ( = 0.10) to increase total PUFA in a quadratic manner ( = 0.03). Total omega-6 PUFA decreased (linear, = 0.01) and total omega-3 PUFA increased (quadratic, < 0.01) as microalgae meal level increased in the diet, which caused a decrease (quadratic, < 0.01) in the omega-6:omega-3 fatty acid ratio. Feeding microalgae meal did not affect WBSF values or sensory panel evaluation of tenderness, juiciness, or beef flavor scores ( > 0.16); however, off-flavor intensity increased with increasing concentration of microalgae meal in the diet (quadratic, < 0.01). From d 5 through 7 of retail display, steaks from heifers fed microalgae meal had a reduced a* value and oxymyoglobin surface percentage, with simultaneous increased surface metmyoglobin formation (quadratic, < 0.01). Lipid oxidation analysis indicated that at d 0 and 7 of display, as the concentration of microalgae meal increased in the diet, the level of oxidation increased (quadratic, < 0.01). Muscle fiber type percentage or size was not influenced by the inclusion of microalgae meal in diets ( > 0.19); therefore, the negative effects of microalgae on color stability were not due to fiber metabolism differences. Feeding microalgae meal to finishing heifers improves PUFA content of beef within the LL, but there are adverse effects on flavor and color stability.

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We hypothesized that abomasal infusion of glucose would promote de novo fatty acid biosynthesis from glucose in vitro in bovine intramuscular (i.m.) and subcutaneous (s.c.) adipose tissues to a greater extent than ruminal infusion of acetate, propionate, or glucose. Angus crossbred steers (n = 24), 22 mo of age, were fitted with ruminal cannulas, and steers were adapted to another corn/sorghum finishing diet over a 2-wk period while recovering from the placement of the cannulas. After the adaptation period, the steers were fed the second finishing diet at 130% of their voluntary intake and were infused with isocaloric amounts (3.76 Mcal/d) of glucose, propionate, or acetate for 35 d. Glucose was infused either into the rumen or into the abomasum, whereas propionate and acetate were infused into the rumen. Acetate infusion decreased DM and DE intakes (P < 0.05). The 5th to 8th longissimus muscle section was removed immediately and transported to the laboratory within 10 min post-exsanguination in 38 °C, oxygenated Krebs Henseleit buffer containing 5 mM glucose and 5 mM acetate. Intramuscular and s.c. adipose tissues were dissected from the muscle and incubated in vitro in 5 mM glucose plus 5 mM acetate (containing [U-14C]glucose or [1-14C]acetate). Lipid content was lower (P = 0.04) in i.m. adipose tissue of the acetate-infused steers than in the other treatment groups, and i.m. adipocytes from acetate-infused steers were smaller (P = 0.01) than those from propionate-infused steers. The rate of incorporation of acetate into glyceride-fatty acids (GFA) in i.m. and s.c. adipose tissues was greater (P < 0.03) in steers receiving ruminal or abomasal infusions of glucose than in adipose tissues from steers infused with acetate. The greatest rates of GFA synthesis were observed in s.c. adipose tissue from steers infused ruminally with propionate or abomasally infused with glucose (P < 0.001). In i.m. and s.c. adipose tissues, the proportion of acetyl units from acetate incorporated into GFA was greater in steers receiving glucose infusion in the rumen or abomasum than in steers receiving acetate or propionate infusion (P < 0.05). Contrary to our hypothesis, abomasal glucose infusion did not promote greater fatty acid biosynthesis from glucose in i.m. adipose tissue than ruminal glucose infusion. However, glucose infusion caused the greatest production of acetyl units from acetate in i.m. and s.c. adipose tissues.

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