Abstract
The world's annual output of rabbits is over 1.2 billion, therefore this sector is also one of the sources of greenhouse gases in livestock production. One hundred-twenty New Zealand rabbits were allocated into four treatments, five replicates in each treatment and six rabbits in each replicate to examine the effect of grinding alfalfa hay to different sizes on growth performance, methane production and cecal archaeal populations. The particle sizes of the alfalfa meal in the four treatment diets were 2500, 1000, 100 and 10 μm, while the other ingredients were ground through a 2.5 mm sieve. The average daily gain (ADG) and average daily feed intake (ADFI) increased (P<0.001) as the particle size decreased, but the feed conversion ratio (FCR) was not affected (P = 0.305). The digestibility of neutral detergent fiber (NDF) (P = 0.006) and acid detergent fiber (ADF) (P<0.006) increased while the greatest digestibility of crude protein (CP) was obtained in 1000 um group (P = 0.015). The rabbits produced more methane (CH4, L/kgBM0.75/d) with decreasing alfalfa particle size (P<0.001). The molar proportion of acetic acid and propionic acid decreased (P<0.001) at the cost of butyric acid (P<0.001). The greatest villus height:crypt depth ratio were obtained in 1000 μm group, and the decrease in the alfalfa hay particle size decreased the jejunum and ilem villus height:crypt depth ratio (P<0.05). The gastric muscular and mucosal thickness decreased with decreasing alfalfa particle size (P<0.05). Archaea diversity decreased with decreasing alfalfa particle size, and the relative abundance of genus Methanobrevibacter increased (P<0.001) while the genus Methanosphaera decreased (P<0.001). It is concluded that a finer particle size favors the growth of genus Methanobrevibacter, which produces more methane but promotes the growth performance of rabbits.
Highlights
The rabbit is an herbivorous animal, and due to its nutritional and physiological characteristics, it depends on fiber to maintain the health of its gastrointestinal tract
During the first 21 days of this experiment, the average daily feed intake (ADFI) of the 100 and 10 μm groups were greater than group 2500 and 1000 μm (P
In the later 21 days, the ADFI of the rabbits increased with decreased alfalfa meal particle size
Summary
The rabbit is an herbivorous animal, and due to its nutritional and physiological characteristics, it depends on fiber to maintain the health of its gastrointestinal tract. The physical structure of the fiber, especially the particle size, is an important feature that has an important effect on the rabbit digestion process: particle size affects the retention time in the gastrointestinal tract [5,6], feed intake [7,8] and nutrient digestibility [2,3,4,5,6,7,8,9]. Most previous studies of feed stuff particles have focused on sizes larger than 1 mm [10,11,12]; the effect of fiber particle size less than 1 mm has mostly been ignored
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