Derivation of the maintenance energy requirements and efficiency of metabolizable energy utilization for dry and lactating Jersey cows

摘要

Maintenance energy is the energy required to conservethe state of an animal when no work is completed.Dietary energy must be supplied to meet maintenancerequirements before milk can be produced. The objectivesof the current experiment were to quantify themaintenance energy requirement of Jersey cows whenlactating or dry. Energetic measures were collected on 8Jersey cows and evaluated across 3 physiological phasesand nutritional planes: lactation, dry cows fed at maintenance,and fasted dry cows. Through total collectionof feces and urine as well as using headbox-style indirectcalorimeters, energy balance and heat productiondata were measured across all phases. Lactation datawere collected across four 28-d periods. Data for cowsfed at maintenance were collected after 14 d and fastingheat production was measured during the last 24 h ofa 96-h fast. Net energy for maintenance (NE_M) requirements,and the efficiency of converting metabolizableenergy (ME) into net energy were compared betweenlactating and dry (maintenance or fasting phase) cows.Heat production of dry cows fed at maintenance, whichrepresents ME for maintenance, was 0.146 ± 0.0087Mcal per unit of metabolic body weight (BW~(0.75),MBW). Fasting heat production, which representsNE_M, was 0.102 ± 0.0071 Mcal/MBW. Energy balancewas calculated as tissue energy plus milk energy. Whenestimated via regressing energy balance on ME intake,NE_M was not different between dry and lactating cows(0.120 ± 0.32 vs. 0.103 ± 0.0052 Mcal/MBW). However,the slope of the regression of energy balance onME intake was greater for dry compared with lactatingcows (0.714 ± 0.046 vs. 0.685 ± 0.010) when evaluatedwith a fixed intercept. This suggests that dry cowswere more efficient at converting ME into net energyand that the efficiency of utilizing ME for maintenancemay be greater than for lactation. Our measurementsof NE_M and the slope of ME on energy balance weregreater than the value used by the National ResearchCouncil (2001), which are 0.080 Mcal/MBW for NE_Mand approximately 0.64 for the slope. Results of thisstudy suggest that NE_M and the efficiency of convertingME into NE_M of modern lactating Jersey cows are similarto recent measurements on modern Holstein cowsand greater than previous measurements.