This study aimed to investigate the effects of insulin resistance (IR) during the
close-up dry period on the metabolic status and performance of dairy cows as well as to
determine the effects on body weight (BW) and metabolic status of their calves. An insulin
tolerance test (ITT) was conducted by administering 0.05 IU/kg BW of insulin to 34
multiparous Holstein cows at 3 weeks prepartum. Blood samples were collected at 0, 30, 45
and 60 min after insulin injection, and cows were divided into two groups based on the
time required for glucose to reach the minimum levels [non-IR (NIR), 45 min (n=28); and
IR, 60 min (n=6)]. Blood or milk sampling and body condition score (BCS) estimation were
performed twice weekly during the experimental period. Blood samples from calves were
collected immediately after birth. Cows with IR showed lower BCS
(P<0.05) and serum urea nitrogen (P<0.05) and
glucose concentration (P=0.05) before calving, and lower serum
non-esterified fatty acid concentration (P<0.05) and milk yield
(P<0.05) and earlier resumption of luteal activity
(P<0.05) after calving; their calves showed lower BW
(P<0.05) and plasma insulin-like growth factor-I concentration
(P<0.001) and higher plasma insulin concentration
(P<0.05). In conclusion, IR at 3 weeks prepartum in dairy cows is
related to postpartum metabolic status and performance along with growth and metabolic
status of their calves.
Insulin-like growth factor-1 (IGF-1) is one of the important factors for growth, milk production and reproductive functions and mainly released from the liver in response to growth hormone (GH) via GH receptor (GHR) in cattle. Recently, some single nucleotide polymorphisms (SNPs) were identified in the bovine GHR gene. Some GHR-SNPs were shown to be related to plasma IGF-1 concentration in cattle. Hence, the capacity to IGF-1 production in the liver might be affected by GHR-SNP and associated with performance in the future. This study examined whether GHR-SNP is associated with IGF-1 production in the liver of pre-pubertal heifers. In 71 Holstein calves, blood samples for genomic DNA extraction were obtained immediately after birth. To genotype the GHR-SNPs in the promoter region, polymerase chain reaction (PCR) products were digested with restriction enzyme NsiI (cutting sites: AA, AG and GG). All heifers at 4 months of age were intramuscularly injected with 0.4 mg oestradiol benzoate. Blood samples were obtained from the jugular vein just before (0 h) and 24 h after injection. The number of AA, AG and GG at the NsiI site was 0, 17 and 54 respectively. In AG and GG, plasma GH concentrations were higher pre-injection than 24 h post-injection (p < 0.01). Moreover, plasma GH concentrations in AG post-injection were higher than in GG (p < 0.05). In contrast, the GG genotype exhibited higher plasma IGF-1 concentrations in pre-injection than post-injection (p < 0.01), although oestradiol did not change IGF-1 concentration in the AG genotype. We conclude that the GG polymorphism in the promoter region of GHR is associated with a higher potential capacity of IGF-1 production in the liver of cattle.
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