PSXIV-27 Use of narasin in diets for lactating ewes

Abstract

Abstract The objective of this study was to define the ideal level of narasin to be used in diets for lactating ewes. Forty Dorper vs. Santa Inês ewes (53.6 ± 9.6 kg BW and 14 d in milk) were penned individually and used in a complete randomized block design. Ewes were fed a basal diet (16.77 ± 0.35% CP) containing 50% concentrate and 50% coastcross hay. The treatments were: 0N - control diet; 13N - 13 mg of narasin/kg of DM; 20N - 20 mg of narasin/kg of DM; 27N - 27 mg of narasin/kg of DM. Ewes were fed the diets from the wk 2 to 10 of lactation. Milk production was determined every 7 d during the experiment. Ewes were separated from lambs and mechanically milked for emptying of the mammary gland. After 3 hours, using the same procedure, milk production was recorded and samples collected for milk composition analysis. For DMI, there was a quadratic effect of treatments (0N=2.417; 13N=2.491; 20N=2.334; 27N=2.078 kg/d; P = 0.02). The milk production (g/3h) presented a quadratic response to levels of narasin (0N=186.37; 13N=194.91; 20N=194.01; 27N=164.49 g/3h; P = 0.03). In the milk composition, there was a linear reduction in the content of protein (0N=5.31; 13N=5.13; 20N=4.94; 27N=5.00%; P = 0.01) and ESD (0N=11.22; 13N=11.15; 20N=10.84; 27N=10.98 %; P = 0.03). However, the contents of fat, lactose and total solids were not affected by the treatments. As a consequence, the productions (g/3 hours) of fat, lactose and total solids were not affected by the diets. A quadratic response was observed for the productions (g/3 h) of protein (0N=9.86; 13N=9.76; 20N=9.52; 27N=8.29; P = 0.04) and ESD (0N=20.73; 13N=21.45; 20N=21.18; 27N=18.28; P = 0.03). In conclusion, 13 mg/kg of DM is the best concentration of narasin to be used in diets for ewes, values higher than this can compromise milk production and composition.