It is essential to have accurate data relating sward herbage mass (HM) to voluntary dry matter intake (VDMI) and in vivo organic matter digestibility (OMD_IV) across the year. This will ensure that the production performance of animals grazing differing HM swards can be accurately predicted using in vitro and in situ methods. The objectives of this experiment were to (i) determine the OMD_IV and VDMI of sheep offered perennial ryegrass differing in HM throughout the growing season and (ii) evaluate in vitro gas production (IVGP) and in situ indigestible neutral detergent fibre (iNDF_IS) as methods of predicting OMD_IV. A 3 × 3 Latin square design was used to investigate three HM treatments. The target HM (measured > 4 cm) of perennial ryegrass for the three HM treatments was 1200 kg dry matter (DM)/ha (Low), 2500 kg DM/ha (Medium) and 4000 kg DM/ha (High). The experiment was a Latin square design repeated in three time stages (TS) in 2013 (TS1, TS2 and TS3). A 3 × 2 incomplete Latin square design was used in early spring 2014 (TS4). In TS4 the HM were lower than in the previous TS at 1000 kg DM/ha (Low), 1800 kg DM/ha (Medium) and 2500 kg DM/ha (High). Each experimental period within each TS consisted of a 6 day adaptation phase and 6 day measurement phase; with 12 Texel wether sheep used. Sheep were fed ad libitum to ensure a 10% refusal rate. The interaction between TS and HM treatment had the greatest effect on chemical composition, VDMI and OMD_IV. Low HM swards had the greatest VDMI and OMD_IV. For each 1000 kg DM/ha increase in HM, OMD_IV was reduced by 2.3% on average. This varied from 0.9% in TS4 to 2.7% in TS3. There was no difference between HM treatments in the rate of digestion of digestible NDF using the IVGP technique. In situ indigestible NDF concentration and OMD derived from IVGP (OMD_GP) were highly correlated with OMD_{IV (}r² = 0.901 and 0.895 respectively) and moderately correlated with digestible organic matter intake (DOMI) (r² = 0.633 and 0.652 respectively). It can be concluded that the interaction between HM and TS will greatly affect OMD_IV and VDMI. Secondly OMD_IV can be predicted by both iNDF_IS and OMD_GP with acceptable accuracy to allow for their use in future feed evaluations.

至关重要的是，必须获得全年准确的数据，这些数据将草皮草质量（HM）与自愿干物质摄入量（VDMI）和体内有机物消化率（OMD _IV）相关联。这将确保使用体外和原位方法可以准确地预测放牧不同HM草地的动物的生产性能。本实验的目的是（i）确定在整个生长季节提供的多年生黑麦草的HM有所不同的绵羊的OMD _IV和VDMI，以及（ii）评估体外产气量（IVGP）和原位难消化的中性洗涤剂纤维（iNDF _IS）作为预测OMD _IV的方法。3×3拉丁方形设计用于研究三种HM治疗。三种HM处理的多年生黑麦草的目标HM（测得> 4厘米）为1200 kg干物质（DM）/ ha（低），2500 kg DM / ha（中）和4000 kg DM / ha（高）。该实验是2013年按三个时间阶段（TS1，TS2和TS3）重复进行的拉丁方设计。2014年初春（TS4）使用了3×2不完整的拉丁方形设计。在TS4中，HM分别比以前的TS低，分别为1000 kg DM / ha（低），1800 kg DM / ha（中）和2500 kg DM / ha（高）。每个TS内的每个实验阶段都包括6天的适应阶段和6天的测量阶段。与12只特克塞尔绵羊一起使用。随意喂羊以确保10％的拒绝率。TS和HM处理之间的相互作用对化学成分，VDMI和OMD _IV影响最大。低HM草地的VDMI和OMD _IV最高。HM每增加1000 kg DM / ha，OMD _IV平均减少2.3％。从TS4的0.9％到TS3的2.7％不等。使用IVGP技术的HM处理之间，可消化NDF的消化速率没有差异。源自IVGP（OMD _GP）的原位消化NDF浓度和OMD与OMD _IV高度相关_（ 分别为r ² = 0.901和0.895），与可消化有机质摄入量（DOMI）中等相关（r ² 分别为0.633和0.652）。可以得出结论，HM和TS之间的相互作用将极大地影响OMD _IV和VDMI。其次，iNDF _IS和OMD _GP都可以以可接受的精度预测OMD _IV，以便在将来的饲料评估中使用它们。