Effects of monensin supplementation alone or in combination with Methafix on nutrient digestibility, milk production and composition of milking Holstein cows

This study was conducted to evaluate the effect of supplementing diets of milking cows monensin supplementation alone or in combination with Methafix (a commercial product containing malate and fumarate) on nutrient digestibility, milk production and composition and milk fatty acids profile. Using four multiparous Holstein milking cows (657± 12 kg of live weight; 133 ± 41days in milk) in a Latin square design. The cows were randomly assigned to one of the four dietary treatments. The first treatments was the control diet(C), second was control diet supplemented with 24 mg of monensin/kg of DM (M), the third was control diet supplemented with 5 g of Methafix/kg DM (ME) and the fourth treatment was C diet supplemented with 24 mg of monensin in combination with 5 g of Methafix/kg DM (MM). Dietary supplementation with Monensin alone or in combination with Metafix significantly decreased dry matter intake (P<0.05), while the intake of crude protein (CP), neutral detergent fiber (NDF) and non-fiber carbohydrates (NFC) were not affected. The digestibility of organic matter (OM) and CP were significantly lower in M and MM-fed cows than the other cow (P<0.05). Total tract apparent digestibility of NDF and NFC were lowest in the cows fed with MM diet. Dietary treatments had no effect on fat and energy corrected milk production, milk fat, protein and lactose concentrations, utilization efficiency of N and NEL (P>0.05). Utilization efficiency of dry matter for milk production was higher in monensin and Methafix-supplemented cows than in control cows (P<0.05). Supplementing milking cow rations with monensin alone or in combination with Methafix significantly (P<0.05) increased milk fat concentration of conjugated linoleic acid (cis9, trans11). In conclusion, the results of this study showed that supplementing mid-lactating cows with monensin or Methafix would increase milk yield, but had no effect on milk components. Dietary supplementation of milking cows with monensin and Methafix alone or together had no effect on majority of milk fatty acids, but elevated milk concentration of conjugated linoleic acid (cis-9, trans 11).