Effects Of Optimal And Sub-Optimal Feeding On Apparent Digestibility, Nitrogen Balance And Methane Emission In Boran Steers Fed Rhodes Grass Hay

Abstract

The objective of this study was to determine effects of optimal and suboptimal feed intakes on apparent digestibility, nitrogen balance and methane emissions in Boran steers fed Rhodes grass hay. The study was carried out at the International Livestock Research Institute (ILRI), Nairobi campus using Boran steers (n=12; 150.0 ± 12.5 kg LW) in a completely randomized design. The steers were stratified by live weight and allocated to four treatments replicated three times. The experimental diet was made of Rhodes grass (Chloris gayana) hay (CP: 7.1%) with 4 levels of intake. The four experimental diets (treatments) were; Diet 1; calculated at 120% Maintenance Energy Requirement (MER), Diet 2; 100% MER, Diet 3; 80% MER and diet 4; 60% MER and were fed for five weeks. Daily feed intake, fecal, urine and methane outputs were monitored. Samples of the diet and fecal matter were collected and analysed for dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF) and nitrogen (N) content. Urine samples were analysed for total N. The results from the study showed that methane production increased with increase in energy intake: 64.13, 55.1, 52.9 and 38.63 g CH4/100kg LW per day at 120% MER, 100% MER, 80% MER, 60% of MER respectively. Nitrogen efficiency (%) was significantly different between the treatments 28.6, 41.74, 48.16 and 51.9 for 120% MER, 100% MER, 80% MER, 60% of MER respectively. Apparent digestibility of DM, OM, CP, NDF and ADF was not affected (P>0.05) by the treatment. The steers on the 60% MER and 80% MER treatment groups lost weight; -500 g/100kg LW and -245 g/100kg LW respectively. The steers on 100% MER and 120% MER treatment groups gained mean weight of 284g and 565 g/100kg LW daily during the five weeks of the trial. It was concluded that restricted feeding affects nitrogen efficiency and enteric methane gas production but had no effect on apparent digestibility of the Rhodes grass hay.