This study was conducted to investigate the effects of corn addition to Italian ryegrass (IRG) (Lolium multiflorum Lam.) on rumen environment, nutrient digestibility, methane production and energy and nitrogen utilization by goats at two intake levels. Eight castrated Japanese goats were employed in two sequential digestion and metabolism trials. The goats were divided into two groups, offered two diets: Diet 1 consisted of 85% Italian ryegrass pellet (IRG) and 15% soybean meal; and Diet 2 consisted of 42.5% IRG, 7.5% soybean meal and 50% corn. The two intake levels were, high (1.6 times) and low (0.9 times) maintenance requirement of total digestible nutrient (TDN). Rumen ammonia nitrogen (NH3N) level of Diet 1 was lower (p<0.05) than Diet 2. Ruminal pH was higher for Diet 1 (p<0.001) and ranged from 6.32 to 6.85. Diet 2 had higher (p<0.001) concentrations of butyric acid and total VFA but a lower (p<0.05) concentration of propionic acid. Rumen parameters were not significantly affected by level of intake. Dry matter, OM, CF and EE digestibilities were significantly higher for the Diet 2 while the CP digestibility was higher for Diet 1. Both diets had higher (p<0.001) digestibility when fed at lower level of intake. There was no difference (p>0.05) in energy losses as methane (CH4) and heat production between the diets. Urinary energy loss (UE) as a proportion of digestible energy (DE) was higher (p<0.001) for Diet 1 and higher (p<0.01) for lower level of intake. Methane production (g 100 g per DDMI) was similar for both levels of intake. Retained energy (RE) was higher (306 vs. 297 Kcal) for Diet 2 than Diet 1. Nitrogen losses through feces and urine were lower (p<0.001) for Diet 2. Thus, retained N as a proportion of N intake and retained N as a proportion of digested N were higher (p>0.05) for Diet 2. The N loss/unit of N intake was significantly lower (p<0.001) at the high level of intake although it had higher total N losses. Thus, supplementation of IRG diet with corn increased retained energy and retained N through reducing the energy and N losses. The high level of intake reduced the proportion of nutrient losses through feces, urine and methane. Supplementation of IRG with corn and soybean meal at the higher level of intake improved the efficiency of utilization of IRG and increased energy and nitrogen retention.
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