Use of narasin in diets for lactating ewes

ABSTRACT The objective of the present study was to evaluate the effect of different doses of narasin on dry matter intake (DMI), milk production and composition in ewes and also on growth performance of their lambs. Forty crossbred lactating ewes Dorper vs. Santa Ines (54.4 ± 1.7 kg of initial BW; mean ± SD) were penned individually with their lambs and used in a randomized complete block design with 10 blocks and 4 treatments. Ewes were fed a basal diet (168 ± 0.003 g/kg DM of CP) containing 50% concentrate and 50% Brachiaria brizantha hay. The treatments were as follows: 0 N - control diet (basal diet without addition narasin); 13 N - addition of 13 mg/kg DM of narasin; 20 N - addition of 20 mg/kg DM of narasin; 27 N - addition of 27 mg/kg DM of narasin. Once a week, from the second to tenth week of lactation (weaning time), ewes were separated from their lambs, injected with oxytocin, and mechanically milked to empty mammary gland. After 3 hours, the same procedure was repeated, milk production was recorded and samples collected for milk composition analysis. Ewes were weighed for 3 consecutive days at the beginning and end of the experiment. Lamb’s growth performance was evaluated weekly. The data were analyzed using a linear or quadratic polynomial contrast in SAS. There were quadratic responses for DMI (P = 0.02) and milk production (g/3 h) according to the increasing doses of narasin (P = 0.03). Narasin inclusion decreased linearly the percentage of protein (P = 0.01), non-fat solids (P = 0.03), and SCC (P = 0.04). The fat, lactose and total solids content were not affected by treatments. There was a quadratic effect (P = 0.05) of narasin doses on concentrate intake by the lambs, in which the lowest intake was observed for lambs from ewes fed N13. The supply of narasin did not affect the ADG and final BW of the lambs. In conclusion, the inclusion of 13 mg/kg DM of narasin improves the milk production, resulting in lower concentrate intake by lambs. On the other hand, higher narasin inclusions negatively affected dry matter intake and, consequently, the milk production of the ewes, increasing the dependence of lambs on concentrate intake.