Table 3. A comparison of some recommended particle size distribution of maize silage, lucerne haylage and grass silage North America


> 19 mm 8-19 mm 4-8 mm < 4 mm


1Maulfair et al. (2010); 2


Maize silage1 3-8


45-60 20-30 <10


Heinrichs (2013), 3


Lucerne haylage2 10-20 40-75 30-40 <10


Tayyab et al. (2018)


physically effective (Mertens, 1997). Mertens (1997) proposed that a particle size of 1.18 mm was critical for dairy cows and stimulates rumination (Poppi et al., 1980). More recent studies have reported that a 4 mm sieve size procedure is more suitable for high producing dairy cows (Maulfair and Heinrichs, 2013; Kmicikewycz et al., 2015), whilst others have used 8 mm (Zebeli et al., 2012). Methods of measuring pef have also varied between studies,


although the practical application of the Penn State Particle Separator (PSPS) has resulted in most studies using this technique. The majority of studies that have been conducted on the application of peNDF on rumen metabolism and cow performance have been undertaken in North America, or used North American type diets, with some current recommendations on suitable profiles presented in Table 3. However, these recommendations may not be applicable for the wetter, grass silage based rations commonly fed in the UK. Indeed, in the survey of 50 UK dairy farms, Tayyab et al. (2018) reported that whilst the particle distribution of maize silage was similar to North American recommendations, grass silage was substantially longer (mean particle length of grass and maize silage in the UK was 43 and 11 mm respectively; Tayyab et al., 2018; Table 3). Reasons for the longer chop length in the UK are unclear, but may include a wider variety of forage harvester types (e.g. precision chop, and forage wagon), a more uneven presentation of grass to the harvester cutting mechanism, to avoid clamp slippage, and the belief that a longer particle length is required to maintain rumen pH. As a consequence of the longer mean grass silage particle length,


the particle size distribution of total and partial mixed rations in the UK was considerably greater than that typically recommended in the USA (Table 4). Despite the large variation between farms in the survey of Tayyab et al., (2018), a significant relationship between forage particle length and milk fat content and milk yield was reported (Figure 1), with a longer ration chop length increasing milk fat content, but decreasing milk yield.


Figure 1. Relationship of mean particle size of 0hTMR (Xm, mm)


and butter fat (g/kg/herd) across 50 herds comprising of Holstein Friesian (●=36), Ayrshire (▲=2), Jersey (+=1), Brown Swiss (■=1) and Holstein crossbred (♦=10). Tayyab et al. (2018).


Maize silage3 7


73 13 7


United Kingdom


Grass silage3 80 16 2 2


Recent UK studies on forage particle length and concentrate composition To investigate the effect of grass silage particle length on rumen pH and animal performance under UK conditions, Tayyab et al. (2018), fed a short (within the shortest 5% of grass silages reported by Tayyab et al., 2018) and long (approximately the mean chop length of grass silage reported by Tayyab et al., 2018) grass silage either alone or mixed with maize silage at a ratio of 40:60 (DM basis; Table 5). Reducing grass silage chop length increased DM intake and milk


yield, but only in the grass silage only treatments, and tended to reduce milk fat content and decrease eating time, although total chewing time was little affected, with a mean of approximately 15 h across all treatments (Tayyab et al., 2019). In contrast, reticulo-rumen pH was not affected by the chop length of the grass silage, but was lower in


Table 4. Particle size distribution of mixed diets in North America and the UK. North America


> 19 mm 8-19 mm < 8 mm


Sova et al. (2013) 20 34 46


1Tayyab et al. (2018)


DeVries et al. (2007) 10 40 50


United Kingdom1


Grass silage based TMR 49 39 25


Maize/grass silage based TMR 33 26 29


PAGE 42 MAY/JUNE 2019 FEED COMPOUNDER


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