Effect of fish oil supplementation and forage source on performance, rumen fermentation, nutrient digestion and chewing behaviour of Holstein bulls

Background: Fat supplementation in ruminants ration often adversely affect dry matter intake (DMI), rumen fermentation and nutrients digestion. Basal diet ingredients is an undeniable determinant of ruminants responses including performance, chewing behaviour and nutrient digestibility to fat supplementation. Objective: Current study was conducted to evaluate the effect of Fish oil (FO) supplementation under different proportion of alfalfa hay (AH) and corn silage (CS) in ration on performance, rumen fermentation, nutrient digestibility and chewing behaviour of Holstein young bulls. Methods: Thirty six Holstein young bulls were used in a 2 × 3 factorial arrangement, with 2 levels of AH proportion (10 and 20 % of AH versus 20 and 10 % of dietary CS) combined with 3 levels of FO supplement (0, 1 and 2.1% of dietary dry matter). Calves were fed TMR consisting of 30 % of forage and 70 % of barley grain-based concentrate mix (dry matter basis). The experiment lasted for 90 days. Results: Dry matter intake was not affected by interaction of AH proportion and FO supplementation. Higher dietary CS proportion caused more DMI regardless of FO supplementation (8.71 versus 8.00 kg/d respectively for treatments with high and low CS proportion; P < 0.01). Highest level of FO reduced DMI regardless of AH proportion (8.65, 8.52 and 7.90 kg/d respectively for 0, 1 and 2.1 % of FO; P < 0.01). Rumen fermentation and nutrients digestibility were not affected by dietary treatments. Rumination times per kg of dry matter (DM) and physically effective neutral detergent fiber (peNDF) > 1.18 were increased in response to FO supplementation regardless of AH proportion (P < 0.01). High AH proportion showed lower total chewing activity and total rumination time (P < 0.01), higher chewing activity per kg of peNDF > 1.18 intake and eating times per kg of DM and peNDF > 1.18 intake (P < 0.01) regardless of FO supplementation. Conclusion: The results demonstrate that AH can be replaced by CS to prevent depression in DMI and stimulate chewing activity in the case of fat supplementation.