Nutrient utilisation and enteric methane emissions in female Sahiwal calves of varying residual feed intake

Abstract

Residual feed intake (RFI) is the difference between actual feed intake and predicted feed intake for the animal. The study was conducted with Sahiwal female calves (n=18) of average age 9 months and body weight (BW) 77.97±2.82 to determine RFI value for individual animals and correlate it with nutrient utilization and enteric methane emissions. Experimental animals were fed in form of TMR (Concentrate: Roughage= 40:60) for 120 days including adaptation period of 22 days and RFI value for individual animals were calculated using regression equation and they were designated as low (n= 9; RFI= -0.14 kg/ d) and high (n= 9; RFI= +0.14 kg/d) RFI groups. Low RFI group showed better feed conversion ratio (FCR) compared to high RFI group (5.52 and 6.64 kg DM consumed/kg gain). FCR value was 20.29% lower in low RFI group with low RFI group consuming less (P<0.05) dietary DM compared to high RFI animals (2.56 vs 3.02kg/100 kg BW) while gaining similar body weights (0.48 and 0.47 kg/d) indicating higher efficiency of feed utilizations in the former group. Digestibility of nutrients (DM, OM, EE, NDF, ADF and NFC) were similar in both groups, however, CP digestibility was comparatively higher (P<0.05) in low RFI group. RFI was negatively correlated with digestibility of DM (r= -0.11), OM (r= -0.27), EE (r= -0.28), CP (r= -0.43) and NDF (r= -0.25). Retention of N (22.12 vs. 18.07 g/d; 25.16 vs. 20.57% of N intake; 35.44 vs. 30.07% of N absorbed) was higher (P<0.05) in low RFI group. RFI was negatively correlated (r= -0.51 for g/d; r= -0.71 for % of N intake; r= -0.44 for % of N absorbed) with N retention. RFI was positively related with enteric methane production. Low RFI animals produced less enteric methane compared to high RFI animals when expressed as g/kg DM intake (13.69 vs. 14.89), g/kg DDM intake (21.87 vs. 23.70) or g/kg body weight (0.39 vs. 0.44). Low RFI animals produced 9.40 and 8.08% less methane, when expressed as g/day and g/kg DMI than high RFI animals. RFI was positively correlated with enteric methane emissions whether expressed as g CH₄/kg DMI (r= 0.58), g CH₄/kg body weight (r= 0.75) or g CH₄/ kg DDMI (r= 0.61), indicating that low RFI animals produced less methane compared to high RFI.