| Abstrakt: |
Forty eight steers (BW = 296 ± 16.7 kg) were individually fed to evaluate the effects of different growing diets on performance of feedlot cattle. Steers were fed one of four treatments for 56d: 1 - limit fed (LF) high starch, 2 - ad lib (AL) low starch, 3 - AL intermediate starch, and 4 - AL high starch. On d57, steers were placed on treatment 4 for finishing until d140. Orthogonal contrasts were used to compare LF to all other treatments. Linear and quadratic contrasts were applied across increasing starch content of the diets within AL treatments. During d0-56, LF reduced ADG (P < 0.01) compared to AL treatments. Increasing starch concentration increased ADG quadratically in AL treatments (P = 0.04; 1.86, 2.40, 2.32 ± 0.12 kg/d for 2, 3, and 4, respectively). By design, LF resulted in reduced DMI (P < 0.01). Increasing starch content resulted in a quadratic DMI response (P < 0.01; 10.0, 11.6, 10.2 ± 0.28 kg/d). LF tended to increase G:F, and increasing starch resulted in a linear increase in G:F (P = 0.02; 0.17, 0.21, and 0.22 ± 0.01). During d57-140, LF steers had ADG similar to AL treatments (P = 0.9). Increasing starch resulted in a quadratic ADG response in AL treatments (P = 0.06; 1.88, 1.63, 1.70 ± 0.07). DMI was reduced for previously LF steers (P = 0.04) but was not different among AL treatments (P > 0.5; 10.6, 10.5, 10.9 ± 0.4). LF resulted in increased G:F (P = 0.04) and increasing starch resulted in a linear decrease in G:F (P = 0.02; 0.18, 0.15, 0.15 ± 0.004). Across the 140-d trial, LF reduced ADG (P < 0.01), reduced DMI (P < 0.01), and tended to improve G:F (P = 0.07), while minimum separations were observed among AL treatments. LF enhanced feed efficiency at the expense of productivity. These data suggest that growing systems relying on low starch diets do not affect productivity of feedlot cattle when compared to intermediate and high starch based growing systems. [ABSTRACT FROM AUTHOR] |
