The effects of growth modifiers and health status on appetite and growth regulatory mechanisms in swine
The objective of the first experiment was to determine the effects of an anti-GnRF vaccine and porcine ST (pST) in group housed boars and gilts. A total of 224 pigs were used in a 2x2x2 factorial design, with the factors being a GnRF vaccine (Improvac, 0 or 2 mL at 13 and 17 wk of age), pST (0 or 5 mg/d from 17 wk of age), and gender. Daily gain was increased by pST (P=.03) and Improvac (P<.001). Feed intake was lower in gilts than boars (P=.01), was decreased by pST (P=.01) and increased by Improvac treatment (P<.01). Lean tissue deposition rate was lower in gilts than in boars P<.01), increased by pST (P<.01) and by Improvac (P=.014). Fat deposition rate tended to be lower in gilts than in boars (P=.06), decreased by pST (P<.01) and increased by Improvac (P<.01). In conclusion, Improvac increased growth rate through increased lean and fat deposition, but concomitant use of Improvac and pST increased lean gain above either alone, while negating the increase in fat deposition in pigs treated with Improvac. The objectives of the second experiment were to determine: 1) the effect of a high (25% fat, HF) or low (2% fat, LF) fat liquid diet on pig performance, and 2) if the limited response to exogenous pST in young pigs is dependent on the source of dietary energy. Diets were formulated to provide a constant lysine:ME ratio and were fed on a pen basis for 9 d. On d 5, pigs within a pen were randomly assigned to receive 0 or 120 mg pST·kg BW ?1·day ?1 for 4 d. Pigs gained 335±9 g/d, which resulted in an ending body weight of 7225±95 g (P>.42). Pigs fed the LF diet consumed more feed than pigs fed the HF diet (P<.01), but calculated ME intake did not differ (P>.20). Pigs fed the HF diet had higher PUN concentrations than pigs fed the LF diet (P<.01). Treatment with pST increased circulating IGF-I (P<.01) and decreased PUN (P<.01) concentration, regardless of dietary treatment (P>.65). Circulating leptin was not affected by dietary treatment (P>.26) or pST (P>.54). These results suggest that the ST/IGF axis is responsive in the young pig and the response is independent of the source of dietary energy. The objectives of the third experiment were to determine: 1) the effect of porcine reproductive and respiratory syndrome virus (PRRSv) and M. hyopneumoniae (M. hyo.) and 2) if exogenous ST can stimulate the IGF system in health-challenged pigs. Pigs were randomly assigned to one of three treatments: 1) Non-infected, ad libitum intake (C); 2) Challenged with PRRSv and M. hyo., ad libitum intake (HC); and 3) Non-infected, pair-fed to HC pigs (PF). HC pigs were infected with M. hyo. during jugular catheterization surgery and with PRRSv 8 d later (d 0). On d 14, pigs within a treatment group were randomly assigned to receive 0 or 120 mg pST·kg BW ?1·day ?1 for 4 days. Initial body weight did not differ (P>.64), but C pigs were heavier than HC and PF pigs on d 21 (P<.01). Disease challenge reduced feed intake beginning on d 7 of infection (P<.04). Basal circulating IGF-I levels averaged 322±22 ng/mL (P>.15) and ST administration increased circulating IGF-I (P<.01). Circulating leptin was not different between treatment groups (P>.29). The mRNA abundance of IGF-I and its receptor were not different between groups in liver or muscle (P>.29). These results indicate that the ST/IGF-I system was not responsible for the growth reduction found in PRRSv and M. hyo. infected pigs.
Advisor:Dr. Glen W. Almond; Dr. C. Scott Whisnant; Dr. Jack Odle; Dr. Robert J. Harrell
School:North Carolina State University
School Location:USA - North Carolina
Source Type:Master's Thesis
Date of Publication:03/17/2003