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ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |


* Department of Animal Science, North Carolina State University, Raleigh 27695; and
and
Merrick Animal Nutrition, Inc., Union Center, WI 53962
6 Correspondence: Box 7621 (phone: 919-513-1117; fax: 919-515-7780; e-mail: bob_harrell{at}ncsu.edu).
Previous research indicates that the neonatal pig does not alter feed intake in response to changes in the energy density of manufactured liquid diets. Also, the limited response of IGF-I to exogenous porcine ST (pST) previously observed in young pigs may be influenced by the source of dietary energy. Our objectives were to 1) determine the effect of a high-fat (HF; 25% fat and 4,639 kcal/kg ME; DM basis) or low-fat (LF; 2% fat and 3,481 kcal/kg ME; DM basis) manufactured liquid diet on pig performance; and 2) determine whether the limited response to exogenous pST in young pigs depends on the source of dietary energy. Two replicates of 60 pigs (n = 120; barrows and gilts distributed evenly), with an initial BW of 4,207 ± 51 g, were weaned from the sow at 10 d of age and used in a randomized complete block design. Pigs were assigned by BW to one of six pens. Diets were formulated to provide a constant lysine:ME ratio and were fed on a pen basis for a duration of 9 d. On d 5, barrows and gilts within a pen were assigned randomly to receive either 0 or 120 µg of pSTkg BW1d1 for 4 d. Pigs gained 336 ± 9 g/d, which resulted in an ending BW of 7,228 ± 120 g, regardless of dietary treatment (P > 0.15). Pigs fed the LF diet consumed 17% more DM per pen daily than pigs fed the HF diet (2,777 ± 67 vs. 2,376 ± 67 g/d, P < 0.01), but calculated ME intake did not differ between dietary treatments (P > 0.20). The G:F was 24% greater in HF- than in LF-fed pigs (P < 0.01). Plasma urea N concentrations were higher in the HF-fed pigs (11.0 ± 0.6 mg/dL) than in pigs fed the LF diet (6.2 ± 0.6 mg/dL; P < 0.05). Treatment with pST increased circulating IGF-I (P < 0.01) and decreased PUN (P < 0.01) concentration 32 and 25%, respectively, regardless of dietary treatment (P > 0.30). Circulating leptin averaged 1.8 ± 0.1 ng/mL and was not affected by dietary treatment (P > 0.35) or pST (P > 0.40). These results suggest that the ST/IGF axis is responsive in the young pig and the increase in circulating IGF-I and growth is independent of the source of dietary energy. Also, young pigs respond to a lower energy density liquid diet with increased feed intake, without altering growth performance, apparently utilizing a mechanism other than circulating leptin.
Key Words: Energy Source Insulin-Like Growth Factor-I Leptin Somatotropin Swine
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