Date Published: June 2, 2011
Publisher: BioMed Central
Author(s): Gretel Ruprechter, Mariana Carriquiry, Juan Manuel Ramos, Isabel Pereira, Meikle Ana.
The present study hypothesized that GH-AluI and IGF-I-SnabI polymorphisms do change the metabolic/endocrine profiles in Holstein cows during the transition period, which in turn are associated with productive and reproductive parameters.
Holstein cows (Farm 1, primiparous cows, n = 110, and Farm 2, multiparous cows, n = 76) under grazing conditions were selected and GH and IGF-I genotypes were determined. Blood samples for metabolic/endocrine determinations were taken during the transition period and early lactation in both farms. Data was analyzed by farm using a repeated measures analyses including GH and IGF-I genotypes, days and interactions as fixed effects, sire and cow as random effects and calving date as covariate.
Frequencies of GH and IGF-I alleles were L:0.84, V:0.16 and A:0.60, B:0.40, respectively. The GH genotype was not associated with productive or reproductive variables, but interaction with days affected FCM yield in multiparous (farm 2) cows (LL yielded more than LV cows) in early lactation. The GH genotype affected NEFA and IGF-I concentrations in farm 1 (LV had higher NEFA and lower IGF-I than LL cows) suggesting a better energy status of LL cows.
The GH and IGF-I genotypes had no substantial effect on productive parameters, although IGF-I genotype affected calving-first service interval in primiparous cows. Besides, these genotypes may modify the endocrine/metabolic profiles of the transition dairy cow under grazing conditions.
Energy balance of dairy cows becomes negative (NEB) during the transition period due to increased nutrient requirements that typically exceed dietary intakes. With the onset of lactation, plasma levels of non-esterified fatty acids (NEFA) and B-hidroxybutyrate (BHB) increase markedly, according to the magnitude of adipose tissue mobilization, to provide additional energy for maintenance and milk production [1-3]. Growth hormone (GH) is known to be responsible for galactopoiesis and persistency of lactation [1,4], and the uncoupled somatotropic axis (GH-insulin-like growth factor I axis, IGF-I) mediates nutrient partitioning for lactogenesis in high producing dairy cows . Concentrations of GH are usually increased during early postpartum and its metabolic effects are antagonistic to insulin by enhancing lipolysis in the adipose tissue and gluconeogenesis in the liver [1,6,7]. Thus, insulin resistance develops to help direct nutrients from insulin-sensitive tissues to the lactating mammary gland . Indeed, genetically-selected dairy cows had increased GH and reduced IGF-I and insulin concentrations during early lactation . Since IGF-I and insulin affect ovarian function, low concentrations of these hormones during the postpartum period are associated with prolonged acyclicity [9-13]. As GH has proven to play a key role on the regulation of metabolism and milk production by modulating the expression of many genes, including IGF-I [14,15], these two genes – GH and IGF-I – could be considered candidate gene markers for productive and reproductive traits.
A χ2 test showed that allele frequency and genotypes of GH and IGF-I were in Hardy-Weinberg equilibrium (P = 0.97) and did not differ between farms (P > 0.28). GH allele frequencies were L (0.84) and V (0.16), while IGF-I allele distribution were A (0.60) and B (0.40). The number of cows for each genotype was LL (n = 122), LV (n = 51) and VV (n = 4) for GH genotypes and AA (n = 63), AB (n = 98) and BB (n = 25) for IGF-I genotypes. Due to the unequal distribution of GH genotypes in our study (dominance of the L allele and low frequency of V allele) we exclude VV genotype from further analysis.
The GH and IGF-I allele frequencies in this study are in agreement with those reported previously in Holstein-Friesian for GH [18,19,27] and in Holstein for IGF-I [29-31].
In summary, the GH – AluI and IGF-I – SnabI genotypes did not have a relevant effect on productive parameters, although the latter genotype affected calving-first service in primiparous cows. On the other hand, this study demonstrated that these genotypes do alter the endocrine and metabolic profiles of the transition dairy cow under grazing conditions.
The authors declare that they have no competing interests.
GR lead the experimental designs, carried out the hormone and the metabolites determinations and genotyping, and drafted the manuscript. IP and JM contributed with the experimental designs. MC contributed with the statistical analysis and helped together with AM on data interpretation and manuscript corrections. All authors read and approved the final manuscript.