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This study was conducted to evaluate the utilisation of the residual feed intake (RFI) as a feed efficiency selection tool and its relationship with methane emissions. Eighteen Murrah buffalo (Bubalus bubalis) heifers were fed ad libitum with total mixed ration (TMR) for 120 days. Based on linear regression models involving dry matter intake (DMI), average daily gain (ADG) and mid-test metabolic body size (MBW 0.75 ), heifers were assigned into low and high RFI groups. The RFI varied from -0.09 to +0.12 kg DM/day with average RFI of -0.05 and 0.05 kg DM/day in low and high RFI heifers respectively. Low RFI heifers ate 11.6% less DM each day, yet average daily gain (ADG) and feed utilisation were comparable among low and high RFI groups. Low RFI heifers required significantly (p < .05) less metabolizable energy for maintenance (MEm) compared to high RFI heifers. Apparent nutrient digestibility showed non-significant difference (p > .05) among low and high RFI groups. Although the nitrogen balance was similar among heifers of low and high RFI groups, nitrogen metabolism was significantly higher (p > .05) in high RFI heifers. Comparison of data from heifers exhibiting the low (n = 9) and high (n = 9) RFI showed that the low RFI heifers have lower enteric methane production and methane losses than high RFI heifers. In conclusion, results of this study revealed that selection of more efficient buffalo heifers has multiple benefits, such as decreased feed intake and less emission of methane., (© 2017 Blackwell Verlag GmbH.)

The aim of this study was to evaluate differences in efficiency of feed utilisation between buffalo calves with low and high residual feed intake (RFI) by comparing feed intake, nutrient digestibility, growth traits and blood metabolites. Eighteen male Murrah buffalo calves (aged 4-6 months; 70 ± 1.0 kg body weight) were fed ad libitum with a total mixed ration for 120 d. Based on linear regression models involving dry matter intake (DMI), average daily gain (ADG) and mid-test metabolic body size, calves were assigned into low and high RFI groups. The RFI varied from -0.33 to +0.28 kg DM/d with an average RFI of -0.14 and 0.14 kg DM/d in low and high RFI calves, respectively. Calves had a mean DMI of 1.9 and 2.4 kg/d and an ADG of 0.5 and 0.6 kg/d in low and high RFI groups, respectively. Low RFI calves ate 19.0% less DM each day and required significantly less metabolisable energy for maintenance compared with high RFI calves (12.5 vs. 16.7 MJ/d). Nutrient digestibility and nitrogen balance did not differ among low and high RFI calves. In more efficient animals (low RFI calves) higher (p < 0.05) plasma level of growth hormone, insulin-like growth factor-1 (IGF-1), triiodothyronine (T3) and lower concentration of thyroxin hormone were detected. No significant differences in levels of insulin, hydroxyproline, plasma and urine creatinine, total protein and albumin between high and low RFI groups were found. Blood metabolites showed significant (p < 0.05) differences at initial and final stages of study in both groups. At final stage of study, RFI showed negative correlations with growth hormone, IGF-1, T3, urine creatinine and albumin. Low RFI buffalo calves are more efficient in feed utilisation and the differences in blood metabolites are probably due to differences in feed intake and body metabolism.

To evaluate different levels of energy and protein for optimum growth of Murrah male buffalo calves, a growth trial (150 days) was conducted on 30 calves (body weight 202.5 ± 6.8 kg). Six diets were formulated to provide 90, 100 and 110% protein level and 90 and 110% energy level requirements for buffalo calves, derived from ICAR 2013 recommendations for buffaloes. The crude protein (CP) intake was increased with higher dietary CP, whereas no effect of energy levels or interaction between protein and energy was observed on CP intake. There were significant effects (P < 0.01) of the interaction between protein and energy (P < 0.05) on metabolizable energy (ME) intake. The digestibility of dry matter (DM), organic matter (OM) and non-fibrous carbohydrate (NFC) was higher (P < 0.0001) in high-energy groups compared to low-energy groups. The CP digestibility increased with the increased CP and ME of the rations. The absorbed N was improved linearly with an increased level of dietary CP, whereas the N retention was similar among all the groups distributed as per different energy or protein levels. The nutrient intake (protein or energy) per kg body weight (BW)(0.75) at various fortnight intervals was regressed linearly from the average daily gain (ADG) per kg BW(0.75). By setting the average daily gain at zero in the developed regression equation, a maintenance requirement was obtained, i.e. 133.1 kcal ME, 6.45 g CP and 3.95 g metabolizable protein (MP) per kg BW(0.75). Requirement for growth was 6.12 kcal ME, 0.46 g CP and 0.32 g MP per kg BW(0.75) per day. Metabolizable amino acid requirement was estimated from partitioning of MP intake and ADG. The ME requirements were lower, whereas the MP requirement of Murrah buffaloes was higher than ICAR (2013) recommendations.

Fifteen male Murrah buffalo calves (15-18 months, 227.98 ± 4.44 kg body weight) were distributed randomly in to three equal groups and fed solely on either berseem (G1), oats (G2), or chicory fodder (G3). A digestibility trial followed by methane measurement using SF6 tracer technique was conducted. No significant difference was observed in nutrient intake; however, crude protein (CP) intake was lower in G2 (0.35 kg) than G1 (0.7) and in G3 (0.71) and non-fibrous carbohydrates (NFC), and neutral detergent insoluble CP (NDICP) intake was significantly (p < 0.05) higher in G3 (1.54 and 0.31 kg) followed by G2 (1.27 and 0.2 kg) and G1 (1.06 and 0.18 kg). The digestible dry matter, organic matter, neutral detergent fiber, and ether extract intake was similar in all the groups, whereas the digestible CP and NFC intake was lower in G2 compared to G1 and G3. Chicory- and berseem-fed groups emitted 12.2 and 5.2 % less methane than oats-fed group. However, no significant difference was observed in the absolute methane loss and methane loss as percentage of energy intake (p > 0.05) among the groups. There was positive correlation between nutrient intake and total methane production. However, an inverse relationship was observed between total digestible carbohydrate intake and methane production (g/kg dry matter intake). The following regression equations were developed to estimate methane production: methane (g/kg BW) = 128.8553 + (167.7456 × dNDFI) + (216.32 × dCPI) - (40.3313 × dNFCI) and methane (g/d) = -1.7494 + (41.42 × NDFI) + (39.8686 × CPI) + (0.5197 × NFCI).