413 EFFECT OF FLUSHING WITH DIFFERENT DEGRADABILITY PROTEIN SOURCE ON THE PLASMA CONCENTRATIONS OF N-UREA AND PROGESTERONE IN Santa Inês SHEEP

Abstract

Protein excess in diet and or rumen degradable protein (RDP) has been associated with elevated concentrations of N-urea in blood and reduction of the concentration of progesterone (P4) in plasma. The objective of this study was to evaluate the overnutrition (flushing) effects of diets containing different rates of RDP on the plasma concentrations of N-urea and P4 in Santa InÊs ewes. Twelve ewes were assigned in a randomized block design formed by 4 body weight bands. Two isocaloric (3.10 and 2.89 Mcal/day) and isonitrogenous (13.15 and 13.46% crude protein; CP) diets with different proportions of RDP (8.43 and 6.60%) containing soybean meal and corn gluten meal, respectively, and 1 maintenance diet (1.91 Mcal/day; 11.30% CP and 6.31% of RDP) were provided for 28 days before ovulation and during the next estrous cycle. Hence, 3 treatments were compared and 4 replicates were done. On Day 17 after starting the diet treatments, intravaginal sponges containing 60 mg of medroxyprogesterone acetate (MAP-60®, Tecnopec, São Paulo, Brazil) were inserted for 11 days. Nine days after sponge insertion, 240 IU of eCG (Novormon®, Syntex S.A., Buenos Aires, Argentina) and 50 μg of cloprostenol (Prolise®, ARSA S.R.L., Buenos Aires, Argentina) were administered i.m. Blood samples for determination of N-urea were collected on Days 7, 14, 21, and 28 after starting the diets and on Days 3, 6, 9, 12, and 15 after ovulation. Blood samples collected during the postovulatory interval were also analyzed for P4. Data were analyzed by ANOVA and treatment means were compared by orthogonal contrasts, where theF-testwas significant. Contrast 1 =T1 andT2 v. T3, and contrast 2 = T1 v. T2. The N-urea and P4 concentrations in plasma were analyzed according to split plot in time scheme. The sheep dry matter (DM) and CP consumption that were recorded in the flushing diet was higher (P < 0.01) than in ewes receiving the maintenance diet. The DM and CP consumption of ewes did not differ between treatments T1 and T2. The plasma N-urea concentration was not different (P > 0.05) between the ewes that consumed the flushing diet and ewes that received the maintenance diet, but it was higher (P < 0.01) in ewes that were fed the flushing diet containing soybean meal (25.09 mg dL-1) as compared with that of ewes fed the flushing diet containing corn gluten meal (20.81 mgdL-1). The P4 concentration in plasma did not differ (P > 0.05) among animals that received the flushing diet and those that received the maintenance diet, but there was a significant difference (P = 0.05) between flushing diets containing soybean meal (7.28 ngmL-1) compared with those containing corn gluten meal (4.46 ngmL-1). In summary, the nutritional level (flushing v. maintenance) did not alter the concentrations of N-urea and P4 in plasma of ewes, but the supply of a greater protein degradability source did increase their concentrations. Funded by FAPEMIG, CNPq, and TECNOPEC.