Utilização de narasina em dietas para ovelhas: produção e composição do leite e desempenho das crias

Abstract

The objective of this experiment was to evaluate rates of narasin on dry matter intake (DMI), ewes milk production and composition and their lambs performance. The narasin was added to a base diet containing 50% of concentrate and 50% of forage. Forty crossbreeding ewes Dorper vs. Santa Inês (53.6 ± 9.6 kg BW) with their lambs was used with two weeks of lactation (14 ± 4.5 days). The experimental design was in a completely randomized blocks design with 10 blocks and 4 treatments. The treatments consisted of a control diet (0N) based diet, without addition of narasin; 13N - addition of 13 mg of narasin/kg DM; 20N – addition of 20 mg of narasin/kg DM; 27N – addition of 27 mg of narasin/ kg DM. Once a week, from the second to the tenth week of lactation, the ewes was separated from their lambs, stimulated by a 6 IU i.v. oxytocin injection, and mechanically milked to empty the mammary gland. After 3 hours, using the same procedure, the ewes was milked again to measure milk production. The lambs, once a week were submitted to a five-hour food fast and later were heavy to measure the average daily gain (ADG). The experimental period was 56 days.The variables measured was: Consumption of nutrientes, milk production and composition (fat, protein, lactose, total solids, defatted dry extract - DDE, urea nitrogen - UN and somatic cell count - SCC) and performance of the lambs (dry matter intake – DMI, average daily gain - ADG). All data will be analyzed using SAS (2002). The consumption of DM, CP and OM presented a quadratic response (P=0.02, P<0.01 and P=0.02, respectively), where the highest consumption was observed in the diet containing 13 mg of narasin/ kg DM (13N). However, the consumption of NDF (P = 0.04) and MM (P = 0.01) presented a progressive decrease with increasing levels of narasin, the highest consumption being presented by control animals (0N) and the lowest by animals of treatment with 27 mg of narasin/ kg of DM (27N). The milk yield (g/ 3 hours) presented a quadratic response (P=0.03) for those of narasin in the diet, and the animals fed the diet containing 13 mg of narasin/ kg of DM had the highest production of milk (194.91 g/ 3 hours). For the milk composition data, protein, DDE and CCS presented a linear reduction with increased levels of narasin (P=0.01, P=0.03 and P=0.04, respectively). The production of protein and DDE presented a quadratic response (P=0.04 and P=0.03) between the different levels of narasin. All milk production and composition variables presented a week effect (P<0.01), except CCS. The nutrient intake through the initial concentrate by lambs was not affected by treatments, however the ADG of the lambs presented a linear reduction (P<0.01), being lambs of the sheep fed the control diet (without addition of narasin – 0N), those with the highest ADG (269.3 g) and those with the lowest ADG (228.01 g) the lambs of sheep fed the diet containing 27 mg of narasin / kg of MS (27N). The use of 13 mg of narasin / kg of DM in diets for lactating ewes was shown to be effective in increasing milk production. However, the use of diets containing 27 mg of narasin / kg of DM is not recommended.