Six growing lambs were used to evaluate the feeding value of two forage-based diets in a long-term feeding period by measuring body weight (BW) gain, digestibility, nitrogen (N) retention and microbial N (MBN) yield. The animals were fed imported low-quality timothy hay (TH) with concentrate diet (THD) or imported low-quality Italian ryegrass straw (IR) with concentrate diet (IRD) for 9 months. The forages were offered at 2% BW, and concentrate was fed at 40% of forage intake. The BW gain averaged 82.6 and 66.2 g/day for THD and IRD, respectively, without showing significant difference. Average forage intake (% BW) was significantly greater for IR than for TH, although it was not affected by feeding periods. The digestibility did not differ between diets or periods. The numerically greater (P = 0.06) ratio of retained N to absorbed N for IRD than that for THD was prominent. Neither diet nor period had significant effect on MBN supply and efficiency of MBN synthesis. The results suggest that the IR-based diet can be also used for long-term periods of feeding to growing ruminant animals as a grass hay-based diet without any detrimental effects on nutrient utilization and growth performance.
Keywords: feeding period; forage diet; growing lamb; microbial supply; nitrogen balance.
© 2015 Japanese Society of Animal Science.