Growth performance and plasma insulin-like growth factor I concentrations in sheep selected for high weaning weight1

Abstract

A study was undertaken to determine the effect of selection for high weaning weight on concentrations of plasma insulin-like growth factor I (IGF-I) in sheep and to evaluate the usefulness of measuring IGF-I as an aid in identification of genotypes with a higher growth potential. Lambs from two lines selected for high 120-d weight (HW and DH) and an unselected control (C) were weighed and blood samples collected monthly from birth to weaning (4 mo. of age). A clear differentiation in size occurred after 1 mo of age between lines, between sexes, and between singles and twins. At weaning, selected lines were 3.8 and 5.0 kg heavier than controls. Plasma IGF-I concentrations were 1.5 to 2 times higher (P less than .001) in males than in females after 1 mo of age. There were no significant differences in IGF-I concentration between lines or types of birth. However, line DH and single lambs on average had higher concentrations of IGF-I. Within sex and type of birth correlations between IGF-I concentrations at 0, 1, 2, 3, and 4 mo and 4-mo BW ranged from -.16 to .49 in the three lines, and most were not significant. Coefficients of variation for IGF-I concentrations (36 to 50%) were two to three times higher than those for BW (11 to 15%). Due to the high variability of IGF-I measurements, the low correlations between IGF-I concentration and BW, and the small differences in IGF-I between control and selected lines, measurement of plasma IGF-I is unlikely to be an effective aid to selection for growth rate in sheep.

Growth and carcass characteristics of lambs in relation to plasma IGF-I and some histological traits of Longissimus lumbarum and Biceps femoris as affected by breed and age at slaughter

“…The obtained concentration of IGF-I during P I and P II (105-300 ng/ml) in the two breeds is close to that reported by Medrano and Bradford (1991). The noticeable increase in IGF-I concentration during P III is due to approaching adulthood of the lambs (Jones and Clemmons, 1995;Oksbjerg et al, 2004) as reported by Hamdon et al (2006).…”

“…Also, it increases muscle mass via its action on muscle hypertrophy (Beermann et al, 1987;Mathison et al, 1998) and stimulating muscle cells uptake of amino acids, and protein synthesis (Shimizu et al, 1986). Hence, determination of plasma IGF-I concentration in growing lambs may provide a physiological interpretation of growth feature (Medrano and Bradford, 1991;Gatford et al, 1996Gatford et al, , 1997Whisnant et al, 1997). Studying growth feature in relation to some physiological measures may have a particular importance for understanding factors controlling muscle growth, Livestock Science 124 (2009) …”

Hormones and body size evolution in papionin primates

“…These findings are supported by numerous studies using mouse lines divergently selected on the basis of body weight, growth rate, and IGF-I levels, all of which show that IGF-I levels are positively correlated with growth rates and body size (Kroonsberg et al, 1989;Siddiqui et al, 1992;Hoeflich et al, 1998Hoeflich et al, , 1999. At the same time, other studies on chicken (Goddard et al, 1988), sheep (Medrano and Bradford, 1991), domestic dog breeds (Favier et al, 2001), and humans (Schwartz et al, 1987;Baumann et al, 1991) have not found a clear association between size and IGF-I levels. These seemingly contradictory findings are in line with the result of the present study, and support the idea that the relationship between size and support the hypothesis of complex and variable relationships between size and endocrine factors.…”

Sexual dimorphism of the somatotrophic axis

“…Plasma concentrations of IGF-I are greater in males than females in postpubertal rats (Gabriel et al 1992, Hu et al 1993, mice (Blair et al 1987), pre-and postpubertal sheep (Roberts et al 1990, Medrano & Bradford 1991, Gatford et al 1996, 1997b, cattle (Bishop et al 1989, Hannon et al 1991, Schwarz et al 1992, Röpke et al 1994, Davis et al 1995, late-gestation fetal and postnatal pigs (Owens et al 1990, Lamberson et al 1995, Bauer & Parvizi 1996 and in turkeys from 1 week of age (Bacon et al 1993). In contrast, most, although not all ( Juul et al 1994) studies in primates have found that plasma IGF-I concentrations are greater in postpubertal females than in males (Copeland et al 1985, Merimee et al 1987, Yamamoto et al 1991, Schwartz & Kemnitz 1992.…”