RESUMO
This study investigated the influence of day of gestation (DG) and feeding regimens (FR) on the expression of genes responsible for placenta development, nutrient transfer, and angiogenic factors in Holstein × Gyr cows. Forty pregnant multiparous Holstein × Gyr cows with an average initial body weight of 482±10.8kg and an initial age of 5±0.8 yr were allocated to 1 of 2 FR: ad libitum (AL; n=20) or maintenance level (ML; n=20). Maintenance level was considered to be 1.15% of body weight (dry matter basis) and met 100% of the net energy requirements and AL provided 190% of the total net energy requirements. Cows were slaughtered at 4 DG: 139, 199, 241, and 268d. After the cows were slaughtered, the placenta and uterus were separated and weighed. Caruncles and cotyledons were individually separated, counted, and weighed. Placenta expressed as kilograms and grams per kilogram of empty body weight (EBW) was heavier in ML- than in AL-fed cows at 268d of gestation. Placenta expressed as kilograms and grams per kilogram of EBW was the lightest at 139d of gestation, and the greatest mass was observed at 268d in ML-fed cows. However, in AL-fed cows, the heaviest placenta expressed as grams per kilogram of EBW was observed from 199d of gestation. Placentomes expressed as grams per kilogram of EBW were heavier in ML-fed cows during gestation, and the number of placentomes was greater in ML-fed cows at 268d of gestation. We observed that IGFR1 and IGFR2 were involved in placenta adaptations when ML was provided, as their expression in placentome cells was greater in ML-fed cows at 268d of gestation. The genes responsible for angiogenesis were also greater in ML-fed cows: VEGFA, GUCY1B3, HIFA, FGF2, and NOS3 were altered by FR and DG interaction and they were greater in ML-fed cows at 268d of gestation. In addition, VEGFB and ANGPT2 did not show interactions between FR and DG, but they were greater in ML-fed cows. Thus, we suggest that the placenta from an ML-fed cow develops adaptations to the reduced nutrient supply by altering its structure and gene expression, thereby developing mechanisms for potential increased nutrient transfer efficiency to the fetus.
