Abstract
BackgroundThe 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.MethodsHolstein 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.Results and DiscussionFrequencies 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.There was no effect of IGF-I genotype on productive variables, but a trend was found for FCM in farm 2 (AB cows yielded more than AA cows). IGF-I genotype affected calving first service interval in farm 1, and the interaction with days tended to affect FCM yield (AB cows had a shorter interval and yielded more FCM than BB cows). IGF-I genotype affected BHB, NEFA, and insulin concentrations in farm 1: primiparous BB cows had lower NEFA and BHB and higher insulin concentrations. In farm 2, there was no effect of IGF-I genotype, but there was an interaction with days on IGF-I concentration, suggesting a greater uncoupling somatropic axis in AB and BB than AA cows, being in accordance with greater FCM yield in AB cows.ConclusionThe 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.
Highlights
The present study hypothesized that Growth hormone (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
A c2 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)
While no effect of the interaction between GH genotype and dpp on productive variables was observed in farm 1, a trend was observed on 4%FCM yield (P = 0.07) in farm 2, as LL cows presented greater FCM yield than LV cows during early lactation (15 and 75 dpp, Figure 1B)
Summary
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. 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]. Genetically-selected dairy cows had increased GH and reduced IGF-I and insulin concentrations during early lactation [8]. Since IGF-I and insulin affect ovarian function, low concentrations of these hormones during the postpartum period are associated with prolonged acyclicity [9,10,11,12,13]. 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 IGFI - could be considered candidate gene markers for productive and reproductive traits
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