Changes in rumen digesta of cows during a restricted feeding period when offered fresh red clover, lucerne, or lucerne hay

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Abstract
Three cows were offered fresh red clover (Trifolium pratense L. cv. Pawera - RC), fresh lucerne (Medicago sativa L. cv. Wairau - FL), or lucerne hay (LH) ad libitum during two 2 h periods per day. Total removal of rumino-reticulum (RR) contents was used to determine changes in digesta mass, particle size distribution of dry matter (DM), volatile fatty acid (VFA) and ammonia concentrations before, during, and after the morning feeding period. Particle size distribution was measured in faecal DM of the cows given RC and LH, and in DM from the omasum and abomasum of 8 hayfed cows in a separate experiment, and showed that few particles larger than 2 mm leave the RR. Consumption of 4.2-4.8 kg DM during the morning feeding period increased RR digesta mass from 28 to 62 kg with RC, 36 to 59 kg with FL, and 47 to 48 kg with LH. Particles retained on a 2 mm sieve ( > 2 mm) increased from a pre-feeding value of7- 14% to 26-29% ofRR DM after eating, so chewing during eating reduced 64-69% of feed DM to less than 2 mm. Molar proportions of VFA did not change during eating, but molar proportions of VFA differed for RC and FL. Differences and similarities in particle size reduction and fermentation of the 3 feeds are discussed in relation to bloat.