Judul: Uji Kecernaan In vitro Silase Campuran Rumput Gajah (Pennisetum purpureum) dan Lamtoro Merah (Acacia villosa)
Abstrak: The aim of this experiment was to study in vitro digestibility of mixed Pennisetum purpureum and Acacia villosa silage in different proportion. The experiment used factorial block randomized design 3x6 with three replicates. Factor A was the ratio between P. purpureum and A. villosa i.e. A1 = 60% P. purpureum : 40% A. villosa, A2 = 50% P. purpureum : 50% A. villosa, and A3 = 40% P. purpureum and 60% A. villosa. Factor B was incubation times i.e. B1-B6 for 4, 8, 12, 24, 48, and 72 hours. Data were analyzed using analysis of variance (ANOVA), the difference between treatments were tested with polynomial and Duncan test. The result showed that bacterial population, and organic digestibility were influenced by treatments (P<0.05). Ammonia concentrations, and dry matter digestibility were influenced by incubation time (P<0.05). Protozoa populations was influenced by treatments and incubation time (P<0.05). Interaction between two factors was detected (P<0.05) on total VFA concentrations. Methane was reduced by the increased of A. villosa. It is concluded that the addition of 40% of A. villosa cause the highest digestibility and total VFA production but produce the highest methane.
Keyword: P. purpureum, methane, digestibility, A. villosa

Judul: Utilisasi Silase Jerami Jagung dengan Suplementasi Kulit Matoa terhadap Penurunan Produksi Gas Metan secara In Vitro
Abstrak: Penelitian ini bertujuan untuk menganalisis pengaruh jerami jagung dengan suplementasi kulit matoa terhadap fermentabilitas dan kecernaan rumen secara in vitro. Penelitian menggunakan rancangan acak lengkap (RAL) dengan 4 perlakuan dan 4 ulangan. Perlakuan meliputi P0 = 1 kg jerami jagung; P1 = 1 kg jerami jagung + 20% kulit matoa; P2 = 1 kg jerami jagung + 30% kulit matoa; P3 = 1 kg jerami jagung + 40% kulit matoa. Parameter yang diamati yaitu analisis proksimat, gas total, gas metana, pH rumen, volatile fatty acid (VFA), NH3, sintesis protein mikrobial (SPM), kecernaan bahan kering (KcBK), kecernaan bahan organik (KcBO), total bakteri, dan populasi protozoa. Data dianalisis menggunakan analysis of variance (ANOVA) dan diuji lanjut dengan Uji Duncan menggunakan program SPSS 25. Perlakuan tidak berpengaruh nyata terhadap pH rumen, kadar NH3, SPM, KcBK, dan KcBO. Namun, berpengaruh nyata pada total produksi gas total, penurunan gas metan, dan konsentrasi VFA. Silase jerami jagung dengan suplementasi kulit matoa efektif menurunkan gas metan, tetapi tidak mempengaruhi fermentabilitas dan kecernaan rumen., This study aimed to analyze the effect of corn straw silage with matoa peel supplementation on fermentability and rumen digestibility in vitro. This study used a completely randomized design (CRD) with 4 treatments and 4 replications. The treatments consisted of P0 = 1 kg corn straw; P1 = 1 kg corn straw + 20% matoa peel; P2 = 1 kg corn straw + 30% matoa peel; P3 = 1 kg corn straw + 40% matoa peel. Parameters observed were proximate analysis, gas production, methane gas, rumen pH, volatile fatty acid (VFA), NH3, microbial protein synthesis (MPS), dry matter digestibility (DMD), organic matter digestibility (OMD), total bacteria, and protozoa population. Data were analyzed using analysis of variance (ANOVA) and further tested with Duncan's test using the SPSS 25 program. The treatment had no significant effect on rumen pH, NH3 levels, MPS, DMD, and OMD. However, the treatment had a significant effect on total gas production, methane gas reduction, and VFA concentration. Corn straw silage with matoa peel reduced methane gas but it did not affect on rumen fermentability and digestibility.
Keyword: fermentabilitas, in vitro, jerami jagung, kulit matoa, Metan

Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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