Feed intake effects upon gain, carcass yield, and ration digestibility in broilers force fed five feed intakes.

Broiler chicks were force fed 75, 100, 125, 140 and 160% of the consumption observed by ad libitum-fed controls to examine feed intake effects upon productivity. Live body weight gain increased with feed intake up to the 140% consumption but was depressed above this point. Feed efficiency and fat, ash, ration (corrected for uric excretion mass), protein (corrected for uric acid excretion nitrogen), and starch digestibility estimates declined by 30, 56, 25, 16, 16, and 2%, respectively, as feed consumption increased from 75 to 160% of ad libitum consumption. Neutral detergent fiber digestibility was not affected by amount of feed consumption. Initial digesta passage rate, estimated by first appearance of ferric oxide in feces, averaged 215 min and was not correlated (P greater than .4) with feed intake. Gastrointestinal tract mass plus contents increased with feed intake and accounted for up to 67% of the increased live body weight gain. Birds apparently adjusted to feed intake level by varying gastrointestinal tract size (mass) and not passage rate. Dressing percentage declined from a high of 73% for birds fed at the lowest feed intake to a low of 63% at the highest feed intake. Carcass gain was 50% greater for the 160 vs 75% group, but most of this (41%) was reached at the ad libitum consumption level. Carcass gain-to-feed ratios were .42, .41, .32, .27, and .21 for the five intakes, respectively. Drumstick, breast, and thigh gains were not (P greater than .01) influenced by increased feed consumption above the ad libitum-fed controls but were depressed (P greater than .05) at the 75% feed intake.(ABSTRACT TRUNCATED AT 250 WORDS)