The validity of the critical size theory for particles leaving the rumen

Abstract

Three grasses and two legumes, each at two stages of maturity, were fed to three fistulated sheep and samples of the feed, and faeces and contents of the reticulorumen, abomasum and ileum were collected for the determination of particle size by wet sieving. Modulus of fineness (MF) was calculated for all particulate matter that failed to pass a 0-15 mm screen. Resistance to flow from the rumen of feed particles of different sizes was also calculated.The mean MF of the reticulo-rumen contents was 2-56 compared with 5-72 for the feed. Material leaving the rumen and found in the abomasum had a MF of l -67 and subsequent changes were small and not significant; ileum 1-63, faeces 1-80. Particles greater than 1-18 mm passed out of the reticulo-rumen although the quantity was small (1-3 %). The resistance to flow of particles of different sizes from the reticulorumen was closely related to particle size with no difference between grasses and legumes or between young and mature forages.It was concluded that in modelling the flow of particles from the reticulo-rumen a non-compartmentalized approach should be adopted, but if a simple two-compartment model is required then a critical sieve size of about 1-18 mm may be useful, since less than 5 % of the particulate material is retained on this sieve size.

No distinct stratification of ingesta particles and no distinct moisture gradient in the fore-stomach of non-ruminants: The wallaby, peccary, hippopotamus, and sloth

“…Although the physical size degradation of particles beyond the fore-stomach is usually of low 310 magnitude in ruminants and macropods (Poppi et al, 1980; Freudenberger, 1992), we 311 observed finer digesta in rectum than fore-stomach contents in wallabies. 312…”

Effect of stage of maturity of grass at harvest on intake, chewing activity and distribution of particle size in faeces from pregnant ewes

“…Very LP was defined as those equivalent to twice the 95 percentile particle length and width values. Poppi et al (1980) reported that the critical particle size in sheep fed different forage maturities is 1.18 mm; particles larger than this are supposed to be retained in the rumen. However, we found that feeding EH led to a higher proportion of particles longer than 1 mm and a tendency towards a higher 95 percentile particle size value in faeces, compared with MH and LH.…”

“…Advancing -E-mail: alja@life.ku.dk stage of maturity of grass at harvest and increased lignification of forage NDF have been shown to increase both the mean rumination time per kg of NDF and the mean faecal particle size (Shaver et al, 1988;Rustas et al, 2010). The critical threshold for feed particles to leave the rumen in sheep is less than 1 mm (Poppi et al, 1980). Consequently, the physical breakdown of large rumen particles during rumination is important for the clearance of digesta from the rumen and continued feed intake (Ulyatt et al, 1986).…”

Modelagem da redução do tamanho de partículas na alimentação de ruminantes

“…Algumas partículas com mais de 5 mm podem escapar do rúmen, no entanto, Poppi et al (1980Poppi et al ( , 1981 observaram que menos que 5 % das partículas de fezes de ovinos e bovinos passam por uma peneira de 1,18 mm. A maioria dos modelos usa estes valores.…”

“…Poppi et al (1980), porém, sugeriu que um sistema com dois compartimentos para PG e PP oferece melhor quantificação dos processos envolvidos na redução de partículas. Sauvant et al (1996) afirmam que o uso de mais de dois tamanhos prejudicaria o desempenho do modelo, porque aumenta o problema da falta de informação sobre os fluxos entre compartimentos.…”