EFFECT OF OSCILLATING CRUDE PROTEIN CONTENT ON NITROGEN UTILIZATION, MILK PRODUCTION AND PERFORMANCE OF SHEEP

The objective of this study was to determine the effects of oscillating dietary crude protein on milk yield, composition, and N metabolism in ewes, and lambs performance. Twenty Barki ewes rearing single lamb (36.7 ± 1.78 kg and 6.38 ± 0.12 kg initial body weights of the ewes and their lambs, respectively) were used in a completely randomized design during a 10-week period of lactation. Ewes were fed a diet containing different levels of crude protein, 11.2% (low), 14.1% (Medium), 17.3% (High), or oscillating (Low and High crude protein diets oscillated for 3 days and 4 days, respectively). Dry matter intake did not differ among diets, but CP intake (g/d) differed (P<0.05) from 179 (low) to 230 (medium), 272 (high), and 229 (oscillating) g/ d. However, dry matter digestibility was not varied among diets, while that of crude protein was significantly differed (P<0.05) in which the highest value was for the high diet (69.6%) and the lowest one for the low crude protein diet (56.5%). An intermediate value was recorded for ewes fed the medium and oscillating crude protein diets (64.7%). Nitrogen retention was higher (P<0.05) in ewes fed high (14.6 g/d) and oscillating (12.8 g/d) diets than that in the ewes fed medium (10.0 g/ d) and low (8.0 g/d). Urinary urea N not differed (P<0.05) between ewes fed medium (12.1 g/d) and oscillating (11.6 g/d) but was lowest for those fed low (8.2 g/d) and greatest for those fed high (16.1 g/d). The pH and total VFA values did not differ among diets, but ammonia-N differed (P < 0.05) from 5.11 (low) to 10.63 (medium), 14.95 (high), and 12.37 mg/dl (oscillating). Microbial protein synthesis was higher (P < 0.05) in ewes fed oscillating (1.69) and high (1.64) than that reported in the ewes fed medium (1.49) or low (1.27 g/ 100 ml rumen liquid). Milk yield and composition did not differ among diets. Initial and final body weights of lambs are similar, but average daily gain (g/ d) significantly (P<0.05) differed (186, 194, 203 and 208 g/d for low, medium, high and oscillating, respectively). In conclusion, these data indicated that ewes fed oscillating diet varying in crude protein concentrations had an improvement in the crude protein digestibility, microbial protein synthesis and N retention compared with those fed low and medium dietary protein diets.