Izadbakhsh Mohammad-Hossein, Hashemzadeh Farzad, Alikhani Masoud, Ghorbani Gholam-Reza, Khorvash Mohammad, Heidari Mostafa, Ghaffari Morteza Hosseini, Ahmadi Farhad
Department of Animal Sciences, College of Agriculture, Isfahan University of Technology, Isfahan 84156-83111, Iran.
Institute of Animal Science, University of Bonn, 53115 Bonn, Germany.
Animals (Basel). 2024 Jan 16;14(2):275. doi: 10.3390/ani14020275.
This experiment was designed to investigate the effects of feeding diets with different fiber content and forage particle size on the performance, health, nutrient digestion, rumen fermentation, and behavioral and sorting activity of Holstein dairy calves kept under elevated environmental temperature. Sixty weaned Holstein female calves (age = 96.7 ± 7.62 days old; body weight = 82.4 ± 10.4 kg) were randomly assigned to one of 4 treatments arranged in a 2-by-2 factorial design in a 70-day experiment. Dietary forage content (moderate, 22.5%; or high, 40.0% on DM basis) and alfalfa hay particle size (short, 4.39 mm; or long, 7.22 mm as geometric mean) were the experimental factors, resulting in the following combinations: (1) high-fiber (HF) diets with forage-to-concentrate ratio of 40:60 and long particle-sized alfalfa hay (LPS; HF-LPS); (2) HF diets with short particle-sized alfalfa hay (SPS; HF-SPS); (3) moderate-fiber (MF) diets with forage-to-concentrate ratio of 22.5:77.5 with LPS (MF-LPS); and (4) MF diets with SPS (MF-SPS). The temperature-humidity index averaged 73.0 ± 1.86, indicating that weaned calves experienced a moderate extent of heat stress. Fiber level and AH particle size interacted and affected dry matter intake, with the greatest intake (4.83 kg/d) observed in MF-SPS-fed calves. Final body weight was greater in calves receiving MF vs. HF diets (164 vs. 152 kg; < 0.01). Respiration rate decreased when SPS vs. LPS AH was included in HF but not MF diet. Lower rectal temperature was recorded in calves fed MF vs. HF diet. Digestibility of dry matter and crude protein was greater in calves fed MF than HF diets, resulting in lower ruminal pH (6.12 vs. 6.30; = 0.03). Fiber digestibility was greater in calves fed SPS compared with those fed LPS alfalfa hay. Feeding HF compared with MF diet increased acetate but lowered propionate molar proportions. The inclusion of SPS vs. LPS alfalfa hay decreased lying time in HF diet (920 vs. 861 min; < 0.01). Calves fed MF vs. HF diets spent less time eating but more time lying, which is likely indicative of better animal comfort. Dietary fiber level and forage particle size interacted and affected sorting against 19 mm particles, the extent of which was greater in HF-SPS diet. Overall, dietary fiber level had a stronger effect than forage particle size on the performance of weaned calves exposed to a moderate degree of heat stress as feeding MF vs. HF diet resulted in greater feed intake, final body weight, structural growth measures, nutrient digestion, as well as longer lying behavior. The inclusion of SPS alfalfa hay in MF diets increased feed consumption.
本试验旨在研究饲喂不同纤维含量和饲草颗粒大小的日粮对处于环境温度升高条件下的荷斯坦犊牛生产性能、健康状况、养分消化、瘤胃发酵以及行为和挑食活动的影响。60头断奶的荷斯坦母犊牛（年龄=96.7±7.62日龄；体重=82.4±10.4 kg）被随机分配到4种处理之一，在为期70天的试验中采用2×2析因设计。日粮中的饲草含量（中等，22.5%；或高，基于干物质为40.0%）和苜蓿干草颗粒大小（短，4.39 mm；或长，几何平均为7.22 mm）为试验因素，产生以下组合：（1）高纤维（HF）日粮，饲草与精料比为40:60，苜蓿干草颗粒长（LPS；HF-LPS）；（2）HF日粮，苜蓿干草颗粒短（SPS；HF-SPS）；（3）中等纤维（MF）日粮，饲草与精料比为22.5:77.5，含LPS（MF-LPS）；（4）MF日粮，含SPS（MF-SPS）。温度-湿度指数平均为73.0±1.86，表明断奶犊牛经历了中等程度的热应激。纤维水平和苜蓿干草颗粒大小存在交互作用并影响干物质采食量，采食MF-SPS日粮的犊牛干物质采食量最高（4.83 kg/d）。采食MF日粮的犊牛最终体重高于采食HF日粮的犊牛（164 vs. 152 kg；P<0.01）。当HF日粮中使用SPS苜蓿干草而非LPS苜蓿干草时，呼吸频率降低，但在MF日粮中未出现此现象。采食MF日粮的犊牛直肠温度低于采食HF日粮的犊牛。采食MF日粮的犊牛干物质和粗蛋白消化率高于采食HF日粮的犊牛，导致瘤胃pH值较低（6.12 vs. 6.30；P=0.03）。与采食LPS苜蓿干草的犊牛相比，采食SPS苜蓿干草的犊牛纤维消化率更高。与采食MF日粮相比，采食HF日粮增加了乙酸盐摩尔比例，但降低了丙酸盐摩尔比例。在HF日粮中使用SPS苜蓿干草与LPS苜蓿干草相比，躺卧时间减少（920 vs. 861分钟；P<0.01）。采食MF日粮的犊牛与采食HF日粮的犊牛相比，采食时间减少但躺卧时间增加，这可能表明动物舒适度更高。膳食纤维水平和饲草颗粒大小存在交互作用并影响对19 mm颗粒的挑食情况，HF-SPS日粮中这种情况更为明显。总体而言，膳食纤维水平对处于中等程度热应激下的断奶犊牛生产性能的影响强于饲草颗粒大小，因为采食MF日粮与HF日粮相比，采食量、最终体重、体尺生长指标、养分消化率以及躺卧行为时间均更高。在MF日粮中使用SPS苜蓿干草增加了采食量。
