Effects of barley particle size in diets on growth performance, nutrient digestion, and meat quality of fattening Hu sheep

The purpose of this study was to determine the effect of barley particle size in diets on growth performance, nutrient digestion, rumen fluid volatile fatty acids, slaughter performance, and meat quality of fattening Hu sheep. Fifty-four healthy, male (approximately 29.85 ± 0.23 kg) Hu lambs were randomly divided into three treatment groups, each treatment was replicated eighteen times with the sheep being the experimental unit. The three treatments consisted of whole barley that had been ground and passed through a 2 mm sieve small particle size group (SPS group), 3 mm sieve middle particle size group (MPS group), and a 4 mm sieve large particle size group (LPS group). The trial period included a fourteen-day adaptation period, a seven-day pre-feeding period, and a sixty-three-day formal period. The results showed that: 1) There was no significant difference in the final weight, dry matter intake (DMI), average daily weight gain (ADG), and feed to gain ratio (F/G) among the treatments (P > 0.05). 2) There were no significant differences in dry matter (DM), organic matter (OM), and crude protein (CP) digestibilities among the treatments (P > 0.05), but the apparent digestibilities of neutral detergent fiber (NDF) and acid detergent fiber (ADF) were significantly different (P < 0.05). The apparent digestibility of NDF in the LPS group was 14.3 and 7.8% higher than in the SPS and MPS groups, respectively (P < 0.05). The apparent digestibility of ADF in the LPS group was 22.1% higher than that of the SPS group and comparable to that of the MPS group. 3) The total volatile fatty acid (TVFA), acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, and valeric acid were not significantly affected by the treatments (P > 0.05). Similarly, the acetic to propionic acid ratio and rumen fluid pH were not significantly affected by the treatments (P > 0.05). 4) There were no significant differences in live weight before slaughter, carcass weight, dressing percentage and brightness, redness, and yellowness of the rumen ventral sac and dorsal sac among treatments (P > 0.05). 5) There were no significant differences in pH, drip loss, water loss rate, muscle brightness, redness, and yellowness at 0 and 24 h post-slaughter among the treatments (P > 0.05); however, the shearing force in the LPS group was significantly higher than that in the SPS and MPS groups (P < 0.05). In summary, barley particle size in diets does not affect the growth performance, slaughter performance, and volatile fatty acids in the rumen fluid of fattening Hu sheep; however, the apparent digestibility of the LPS group was significantly affected, which might indicate improvement in fiber digestibility.