Uticaj energetskog dodatka u ishrani na koncentraciju tireoidnih hormona, insulinu sličnog faktora rasta-i i njegovih vezujućih proteina u krvi krava tokom rane laktacije

The objective of this study was to examine the effect of dietary energy supplementation on hormones that are considered to be the main signals of a shift in energy balance around parturition. Sixty dry cows, 15 days before calving, were chosen and divided into two eaqual groups: control and experimental (GLY). Both groups were fed a standard ration balanced in accordance to the stage of the productive reproductive cycle. Additionally, each cow in the GLY group was given glycerol based dietary energy supplementation (250 mL daily during the dry and 300 mL daily during the lactation period), which provided additional 9.30 MJ NEL during the dry and 13.95 MJ NEL during the early lactation period. Milk production was measured on days 30 and 60 of lactation and milk production was significantly higher in GLY compared to control group at day 60 of lactation (p lt 0.05). Service period and insemination index were used as reproductive outcome parameters. Average service period in the control group was significantly longer than in the GLY group (p lt 0.05). Average insemination index in the control group was not significantly different than the index obtained for the GLY group. Blood samples were taken before the begining of the experiment (15 days before parturition), and at days 7, 30 and 60 of lactation. Concentrations of thyroid hormones, IGF-I, relative abundance of IGFBP-2, IGFBP-3 and IGFBP-4, concentrations of total protein and albumin in the blood were measured. Results showed that at days 7 and 30 after parturition, T4 concentrations were significantly higher (p lt 0.001, respectively) in GLY than in the control group, while T3 concentrations were significantly higher in GLY group only at day 7 after parturition (p lt 0.001). IGF-I concentrations and IGFBP-3 abundance were significantly higher in the GLY compared to the control group in all three examined postpartum periods. IGFBP-2 and IGFBP-4 concentrations were higher in GLY compared to the control group in all three examined postpartum periods, but the difference was significant only on day 60 after parturition (p lt 0.01, respectively). Concentrations of total protein and albumin were significantly higher in GLY compared to the control group in all three examined periods after parturition. Based on these results it can be concluded that peripartum dietary energy supplementation prevent cows' exposure to severe negative energy balance, preserves synthetic activity of hepatocytes and consequently has a positive impact on milk production and reproductive performances in dairy cows.Cilj ovog rada je bio da se ispita uticaj energetskog dodatka u ishrani krava na koncentraciju hormona u krvi koji su u periodu oko teljenja glavni pokazatelji promena u energetskom statusu. U tu svrhu, petnaest dana pre teljenja odabrano je 60 krava koje su podeljene u dve jednake grupe: kontrolnu i oglednu (GLY). Obe grupe krava su dobijale identičan obrok usklađen sa proizvodno reproduktivnim ciklusom. Dodatno, kravama GLY grupe je tokom poslednje dve nedelje zasušenja i do 60. dana laktacije dodavan energetski dodatak na bazi glicerola (250 mL dnevno tokom zasušenja odnosno 300 mL nakon teljenja), obezbeđujući dodatnih 9,30 MJ NEL tokom zasušenja, odnosno 13,95 MJ NEL tokom rane laktacije. Kod svih krava je izmerena prosečna dnevna proizvodnja mleka 30. i 60. dana lakatcije, koja je kod GLY grupe bila značajno viša 60. dana (p lt 0,05). Kao pokazatelji reproduktivnog statusa koriščeni su servis period i indeks osemenjavanja. Servis period je bio značajno duži kod kontrolne u odnosu na GLY grupu (p lt 0,05), a vrednost indeksa osemenjavanja se nije značajno razlikovala između grupa. Uzorci krvi krava uzeti su neposredno pre početka ogleda, odnosno 15 dana pre teljenja, kao i 7, 30. i 60. dana laktacije i u njima je određivana koncentracija tireoidnih hormona, IGF-I, relativna zastupljenost IGFBP-2, IGFBP-3 i IGFBP-4, koncentracija ukupnih proteina i albumina. Rezultati su ukazali da je 7. i 30. dana nakon teljenja GLY grupa imala značajno višu koncentraciju T4 (p lt 0,001, pojedinačno) u odnosu na kontrolu, dok je koncentarcija T3 bila značajno viša kod GLY grupe 7. dana nakon teljenja (p lt 0,001). Koncentracija IGF-I i zastupljenost IGFBP-3 je bila značajno viša u krvi krava GLY grupe u odnosu na kontrolu u sva tri ispitivana perioda posle teljenja. Zastupljenost IGFBP-2 i IGFBP-4 je bila viša u krvi krava GLY u odnosu na kontrolnu grupu u sva tri ispitivana perioda postapartalno ali je ova razlika bila značajna jedino 60. dana lakatcije (p lt 0.01, pojedinačno). Koncentracija ukupnih proteina i albumina je, takođe, bila značajno viša u krvi krava GLY grupe u odnosu na kontrolnu grupu u sva tri ispitivana perioda posle teljenja. Na osnovu dobijenih rezultata može se zaključiti da energetski dodatak u ishrani sprečava izloženost krava izrazitom negativnom energetskom bilansu, održava sintetsku funkciju hepatocita i posledično ima pozitivan uticaj na mlečnost i reproduktivne pokazatelje