Effects of fish oil supplementation and supplementation period on adipose tissue generation sites and the gene expression of enzymes involved in metabolizing adipose tissue in Holstein bulls under various forage types

To investigate the effects of alfalfa hay (AH) proportion, fish oil (FO) supplementation, and the length of FO supplementation on lipoprotein lipase (LPL), peroxisome proliferator activated receptorγ (PPARγ) and stearoyl-COA desaturase (SCD) gene expression in various adipose tissue depots, 36 Holstein bulls (initial body weight of 345 ± 61 kg) were randomly assigned to 6 dietary treatments in a 2 × 3 factorial arrangement, with 2 levels of AH (10 and 20% of dietary dry matter) and 3 levels of FO (0, 1.05 and 2.1% of dry matter). Samples of adipose tissue were collected at the middle and end of the period (day 90), after slaughtering. The RT-qPCR technique was used for gene expression analyses. The relative mRNA abundance of lipogenic genes was not correlated with AH proportion and FO interaction. Supplementation of FO increased LPL and SCD gene expression in visceral and subcutaneous adipose tissues regardless of AH proportion (P < 0.05). The gene expression of PPARγ was not affected by dietary treatments. Supplementation of FO increased the mRNA abundance of SCD1 gene more in subcutaneous than visceral adipose tissue (P < 0.01). Gene expression of PPARγ and SCD enzymes increased as a result of prolonged FO supplementation (P < 0.01), whereas LPL mRNA abundance was lower at the end of period comparing to the middle period (P < 0.01). The results demonstrate that FO supplementation increases the abundance of adipose tissue SCD mRNA, which in the case of enhancement in UFAs concentration as a result of higher mRNA abundance and enzyme activity, can benefit both human and animal health. Moreover, the duration of FO supplementation was found to be an important factor in regulating enzymes involved in adipose tissue metabolism.