Effects of dietary inclusion of sunflower soap stocks on nutrient digestibility, growth performance, and ruminal and blood metabolites of light fattening lambs.

Forty-four merino lambs (6 to 8 wk old; BW 15.6 ± 0.21 kg) were used to study the effect of adding different proportions of sunflower soap stock (SS) to pelleted total mixed ration (TMR) for fattening lambs on feed intake, animal growth and dressing percentage, ruminal fluid characteristics, and blood acid-base parameters. Lambs were assigned to 1 of 4 experimental groups (11 lambs per group), each randomly assigned to 1 dietary treatment: 00SS (0 g SS/kg TMR pellet), 15SS (15 g SS/kg TMR pellet), 30SS (30 g SS/kg TMR pellet), and 60SS (60 g SS/kg TMR pellet). Lambs were individually fed the corresponding diet ad libitum. On d 19 to 23, total feces were collected and sampled from 4 lambs per group. When lambs reached 27 kg BW, they were slaughtered. Dry matter intake, ADG, and length of fattening period were not affected by the dietary treatment (P > 0.10). Animals in the 30SS group tended to show the best G:F values (P < 0.10). Dressing percentage tended to linearly decrease as SS increased (P < 0.10). Animals in the 60SS groups showed the lowest DM and fiber digestibility values (P < 0.05). Total VFA contents in ruminal fluid were not affected (P > 0.10), but the propionate proportion linearly increased (P < 0.05), and the acetate to propionate ratio tended to decrease with SS supplementation. Increasing dietary content of SS linearly decreased the cold carcass weight (P < 0.05) but did not affect other measured carcass characteristics. Ruminal fluid pH tended to decrease (P < 0.10) and mucosa color decreased as SS increased in the TMR (P < 0.05). Blood pH and Na concentration increased (P < 0.05), whereas the anion gap, CO2 pressure, and K concentration linearly decreased (P < 0.05) as SS increased. Including more than 30 g SS/kg TMR in the diet for fattening lambs reduces DM and fiber digestibility without affecting feed intake and ADG. The acidotic rumen conditions that induced a darkening of rumen mucosa were counteracted by blood acid-base parameters. The optimum level of inclusion seems to be 30 g SS/kg TMR.