Nutrients digestibility, metabolic parameters and milk production in postpartum Holstein cows fed pomegranate (Punica granatum L.) by-products silage under heat stress condition

Two experiments were conducted to determine the best level of pomegranate by-products silage (PBS) in dairy cows ration and then its effect on transition dairy cows under heat stress condition was studied. In the first experiment, corn silage (CS) was replaced with the incremental levels of PBS [0, 60, 120 and 180 g PBS/kg dry matter (DM)] in total mixed ration (TMR) and then the nutrient digestibility and rumen fermentation parameters were studied using a dual flow continuous culture system. In the second experiment, effects of feeding PBS (120 g PBS addition per kg DM of TMR) on in vivo nutrient digestibility, ruminal fermentation, blood metabolites and milk yield were investigated in 20 postpartum transition dairy cows under heat stress condition [average of temperature-humidity index (THI); 74.3 +/- 2.58]. Fresh pomegranate by-products (PB) including peel and seed were ensiled in a bunker silo with addition 20 g urea/kg DM. Results of the first experiment showed that PBS had about 49 g phenolic compounds/kg DM. Replacing of CS in TMR with 60 g and 120 g PBS improved neutral detergent fiber (aNDF) and acid detergent fiber (ADF) digestibility. TMR supplemented with 120 g PBS produced greatest total volatile fatty acids (VFA) and molar proportion of propionate after fermentation, but molar proportion of acetate and acetate:propionate ratio were lowest. Results of second experiment showed that replacing of CS with 120 g PBS increased total milk production and energy corrected milk (ECM), but it decreased milk protein and lactose content. Feeding fresh cows with 120 g PBS increased their lying behavior compared to the control group (712.1 vs. 572.6 min. d). Cows fed 120 g PBS had higher ADF digestibility and lower crude protein (CP) digestibility than that the control group. Cows fed 120 g PBS numerically had greater serum glucose. It was concluded that replacing of CS with 120 g PBS had potential to increase milk yield in Holstein dairy cows under heat stress condition without any adverse effect on their blood metabolites or health.