The effects of replacing dietary carbohydrate with calcium salts of fatty acids on finishing lamb feedlot performance, blood metabolites, muscle fatty acid composition, and carcass characteristics

Sixty finishing lambs (BW = 41.6 ± 1.4 kg) were utilized to investigate the effects of replacing carbohydrate-based energy with calcium salts of fatty acids (CSFA) on finishing lamb feedlot performance, blood metabolites, muscle fatty acid composition, and carcass characteristic. Upon arrival, lambs were weighed on 2 consecutive days and randomly assigned to 1 of 4 dietary concentrations of CSFA. Treatments included: (1) 0% CSFA (control); (2) 4% CSFA; (3) 7% CSFA and (4) 11% CSFA on a DM basis. Diets were formulated to be isoenergetic (TDN basis) and isonitrogenous (DIP and UIP) and consisted of 75% concentrate, and 25% roughage (corn silage). Rations had comparable levels of dietary TDN; rations with less corn had a higher concentration of CSFA-pellet. Intake was controlled to balance TDN per kg of BW across treatments; all treatments met 2006 NRC requirements for growing lambs. Lambs were weighed and bled every 14 ± 2 d. Blood samples were analyzed for glucose, lactate and insulin concentrations. On d 62, lambs were transported to a commercial abattoir and slaughtered. Hot carcass weight (HCW) was determined at the time of slaughter, and longissimus muscle (LM), and liver and subcutaneous adipose tissue samples were collected and snap-frozen for later analysis. Longissimus muscle area (LMA) and back fat (BF) carcass measurements were determined after a 48 h chill at 4 °C. There was a treatment effect for ADG, DMI and gain to feed efficiency (P < 0.01). Lambs receiving 11% CSFA had lower ADG (P < 0.05), lighter HCW (P < 0.001) and smaller LMA (P < 0.01) than all other treatments. Control lambs had greater BF (P < 0.05) than lambs receiving 11% CSFA, but had similar BF when compared to lambs receiving 4 and 7% CSFA. Dressing percentage was similar across treatments. There was a treatment by time interaction observed for blood glucose (P = 0.02), with lambs fed the control diet having higher blood glucose concentrations than those fed 11% CSFA. Plasma insulin and the insulin:glucose ratio were similar across all treatments at all time points measured. Fatty acid profiles for LM, liver and subcutaneous adipose were similar across treatments. Overall, data suggest that CSFA can be used to replace carbohydrate from corn at rates up to 7% DMI before performance is negatively affected.