Effect of rumen-protected fat on performance and serum concentration of T3 hormone of Holstein young bulls during hot, humid weather

Abstract

The growth performance and serum concentration of triiodothyronine (T3) of 15 Holstein young bulls with an initial mean live weight of 200±25 kg was studied in response to a dietary rumen-protected fat (RPF) supplementation [3 or 5% of dry matter (DM)] during hot, humid climate (in Guilan, Iran, during summer season) in four sequential 21-d periods. The growth performance and serum T3 concentration were measured at the end of each period. Results showed that there were no differences in the daily DM intake among the treatments in all experimental periods. During all 21-d periods and overall, the bulls fed RPF-containing diet gained significantly more weight than those receiving control diet. The young bulls fed diets containing 5% RPF gained more weight than those receiving 3% RPF-containing diets. The lowest weight gain was observed for young bulls fed the control diet. The highest (P<0.05) feed to gain (f:g) ratios were observed for young bulls fed control diet and the lowest f:g ratios were observed for those fed 5% RPF-containing diet. Serum T3 concentration in the young bulls fed 5% RPF-containing diet was significantly higher than those fed 3% RPF or control diet in all experimental periods and overall. The variations in response to dietary RPF supplements among treatments could be related to lower metabolic heat production of RPFs rather than proteins and carbohydrates, especially in hot, humid conditions. © K. Toufighi et al., 2014.