Relationships of plasma insulin-like peptide 3, testosterone, inhibin, and insulin-like growth factor-I concentrations with scrotal circumference and testicular weight in Japanese Black beef bull calves

Abstract

This study was conducted to clarify the relationships of plasma concentrations of insulin-like peptide 3 (INSL3), testosterone, inhibin, and insulin-like growth factor-I (IGF-I) with scrotal circumference and testicular weight in Japanese Black beef bull calves (n = 20), from birth to pre-puberty. Monthly blood sampling (0 to 7 months) and scrotal circumference measurements (0 to 7 months) were performed. Testicular weight was recorded immediately after castration at 7 months. Plasma INSL3, testosterone, inhibin, and IGF-I concentrations were measured either by enzyme immunoassay or time-resolved fluorescence immunoassay. The correlation coefficients of these hormonal concentrations with scrotal circumference were significant (P < 0.0001) and it was higher for INSL3 (r = 0.647) than for testosterone (r = 0.597), IGF-I (r = 0.400), and inhibin (r = –0.453). Calves with heavier testes (> 60 g) at castration (7 months) had higher (P < 0.05) plasma INSL3 (from 3 to 7 months) and inhibin (from 1 to 4 months) concentrations than those with lighter testes (< 60 g). The calves with heavier testes at castration had larger (P < 0.05) scrotal circumference than those with lighter testes from 3 to 7 months. In conclusion, blood INSL3 concentrations may be the best functional indicator among the hormones analyzed for determining total testicular volume during pre-puberty in bull calves. In addition, inhibin and INSL3 concentrations in early calfhood may be functional predictors for testicular weight at pre-puberty.

Effect of plane of nutrition during the first 12 weeks of life on growth, metabolic and reproductive hormone concentrations, and testicular relative mRNA abundance in preweaned Holstein Friesian bull calves

“…Moreover, in that study, INSL3 concentration at 4 mo of age correlated well (negatively) with the timing of puberty, as well as with testis size at 18 mo ( Anand-Ivell et al, 2019 ). In agreement, Sakase et al (2018) found that blood INSL3 concentrations may be a robust and repeatable biomarker for determining total testicular volume and degree of sexual maturity in prepubertal bull calves. Thus, our results indicate greater testes development and spermatogenesis potential in calves at 12 wk of age offered an enhanced dietary regimen.…”

Prepubertal nutrition alters Leydig cell functional capacity and timing of puberty

“…Within the bovine testis both in situ mRNA hybridization [20] as well as immunohistochemistry using different antibodies [22,23] confirm that only Leydig cells express INSL3. Moreover, circulating INSL3, as in the present article, correlates closely to the growth of the testes between birth and puberty (present article; [24]).…”

“…INSL3 has been shown to be an accurate measure of Leydig cell development during male puberty in several mammals, including rodents [16], humans [32–34], pigs [35] and ruminants, such as goats [36] and bulls [24,37]. Its value lies both in its more or less constitutive expression pattern, with low intra-individual biological variance, the accuracy of modern assays, with low technical variance, and its significance in effectively measuring Leydig cell functional capacity [2].…”

“…Studies in rats and boars have shown that a lack of INSL3 leads to increased germ cell apoptosis [41,42], and in a male steroidal contraception study in humans residual spermatogenesis was greatest where there was highest circulating INSL3 [43]. Therefore, although Leydig cells comprise less than 10% of the testis, INSL3 production (though not testosterone) in bulls correlates with sperm production, scrotal circumference, and testis weight [24] (Table 1). Moreover, INSL3 concentration is reduced in bulls where there appears to be deficient spermatogenesis [23,37].…”

“…Interestingly, of the parameters measured, INSL3 shows one of the closest correlations with the timing of puberty and is also predictive of total testis weight at 18 months. INSL3 was also shown to correlate closely with total sperm count and testis weight in Japanese Black beef bulls kept on a single feeding regimen [24]. Importantly, if we select the peripheral INSL3 concentration at 4 months, which represents the time within the prepubertal period when the INSL3 profile is increasing most rapidly and consequently shows most discriminatory ability, then this value (and unlike other parameters, except for IGF1) is highly predictive not only of the timing of puberty (Fig 7A), but also of later scrotal circumference, though not of later testis weight nor average sperm density (12–18 months).…”