Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs.
Exogenous insulin-like growth factor (IGF)-I has been shown to increase growth rate in neonatal pigs while an analogue of IGF-I, long arginine (LR3) IGF-I, has been shown to be more potent than IGF-I in the rat. Therefore, two studies were conducted to determine whether IGF-I and LR3IGF-I increase growth in the artificially-reared neonatal pig. Expt 1 involved forty-two (2 kg initial weight) pigs infused with either control, IGF-I (2, 4 or 8 microg/h) or LR3IGF-I (2, 4 or 8 microg/h) infusions for 8 d. Pigs were weighed and then offered 1.7 MJ (gross energy) milk replacer/kg0.75 per d. Expt 2 involved eighteen pigs (2 kg initial weight) treated with control saline, IGF-I (8 microg/h) or LR3IGF-I (8 microg/h) infusions. After 9 d an additional pump was inserted to increase the infusion rates of each of the growth factors (16 microg/h) for a further 9 d. Cows' milk was provided ad libitum. In Expt 1 there was no overall effect of growth factors on daily weight gain or slaughter weight. However, milk intake was greater in pigs infused with growth factors (909 v. 867 g/d, P=0.027), with an apparently greater milk intake by the pigs infused with IGF-I compared with LR3IGF-I (920 v. 898 g/d, P=0.12). Infusion of LR3IGF-I decreased plasma IGF-I concentrations, but had no effect on plasma IGF-II concentrations. In Expt 2, neither IGF-I nor LR3IGF-I infusion had any effect upon daily weight gain over the first 9 d of the study. However, over the second 9 d of the study, daily weight gain was increased in LR3IGF-I-infused pigs (457 v. 386 g/d, P<0.01), but not in pigs infused with IGF-I (413 v. 386 g/d, P=0.15). Milk intake was not different during the first 9 d of the study but was significantly greater in pigs infused with growth factors over the second half of the study (3407 v. 2905 g/d, P<0.01). Plasma IGF-binding protein-3 concentrations were highly correlated (R=0.85) with average daily gain over the 3 d preceding blood sampling. In conclusion, exogenous IGF-I and particularly LR3IGF-I can increase growth rate and milk intake in artificially-reared pigs fed ad libitum but not in limit-fed piglets.
Dunshea
Frank R
FR
Victorian Institute of Animal Science, 600 Sneydes Rd., Werribee, Australia. Frank.Dunshea@nre.vic.gov.au
Chung
Chung S
CS
Owens
Phil C
PC
Ballard
John F
JF
Walton
Paul E
PE
D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008297:Male; D008892:Milk; D009929:Organ Size / Q000187:drug effects; D011994:Recombinant Proteins / Q000494:pharmacology; D013552:Swine / Q000254:growth & development*; D015430:Weight Gain / Q000187:drug effects*
D018972:Insulin-Like Growth Factor Binding Protein 3; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II