EFFECT OF FEED PROCESSING ON VOLATILE FATTY ACID PRODUCTION RATES MEASURED WITH 13C-ACETATE IN GRAZING LACTATING DAIRY COWS

The effect of processed cereal grain supplementation on volatile fatty acid (VFA) production rates of grazing, lactating Holstein-Friesian cows were measured in a 5x5 Latin square experiment. The experimental treatments were as follows: control (only grazing, no supplement addition, NS), pelleted barley (PB), pelleted maize (PM), toasted and subsequently pelleted barley (TPB), and toasted and subsequently pelleted maize (TPM) as supplements. An isotope dilution technique using stable isotope of carbon (13C) as an internal marker was employed for the estimation of VFA production. At the beginning of a 3-hour long allowed grazing time, 100 mg of 99% enriched 13C2 Na-acetate were introduced in the rumen and repeated after grazing with 50 mg isotope, after which the cows were starved for 6 hours until evening milking. During grazing disappearance rate (kdis) and production rate (kprod) of acetate, propionate and butyrate were significantly higher (P≤0.05) in supplemented than in NS cows. Moreover the effect of barley grain and pelleting treatment was higher than the effect of maize grain and toasting. During starvation significantly higher (P≤0.05) kdis and kprod of VFAs were observed in PM and TPM treatments. Total VFA production for the experimental period (grazing + starvation) were 49.5, 78.7, 69.9, 88.5, 80.8 mol/day for NS, PB, TPB, PM and TPM, respectively. The higher VFA productions measured in supplemented animals emphasis the extensive digestion that occurs in the rumen after feeding processed grains. In methodological terms, 13C2 Na-acetate labelling appears to be a useful means for examining the VFA acetate production in ruminants

Processed grains as a supplement to lactating dairy cows

Keywords: heat treatment, maize, barley, starch, protein, in sacco, in vivo, dairy, perennial ryegrass, grazing, supplementation, ruminal fermentation, VFA, rumen, degradability, synchrony.In this thesis the effect of different ways of thermal processing (pelleting, expanding, toasting) of barley and maize on the degradative behaviour of their starch and protein in the rumen of lactating dairy cows are described. In situ studies showed that all thermal processing methods increased the ruminal starch and protein availability of maize, while all thermal processing methods decreased ruminal starch availability but only pelleting increased ruminal protein availability of barley. Based on in vivo experiments compared to untreated grains, expander treatment increased the apparent rumen and total tract digestibility of maize starch but did not affect the digestibility of barley starch. Supplementing grazing dairy cows with pelleted and pressure toasted maize and barley slightly (not significantly) decreased the dry matter intake of grass in the first grazing event in the morning after milking, and it decreased ruminal clearence of nitrogen. Supplementing pasture grass with pelleted and pressure toasted cereal grains decreased the pH, the NH 3 -N level in the rumen, the ammonia to total VFA (TVFA) ratio, the isobutyrate proportion, the acetate to propionate ratio and the non-glucogenic to glucogenic ratio in the rumen. Simultaneously it increased TVFA concentrations, propionate, butyrate and valerate proportions as a percentage of the TVFA. All processed grains did affect production responses in dairy cows, by elevating milk protein and decreasing milk fat production, and milk urea nitrogen but no significant differences between these two heat treatments were found. It is concluded that the need of synchrony is specially important with diets based on fresh grass, in which markedly asynchronous rates of release of energy and nitrogen occur in the rumen. It appears that to generate a better ruminal N and organic matter synchrony to improve microbial N yield and N utilization feeding different types of cereal grain that differ by nature in rate and extent of ruminal degradation has more effect than using one of this processing methods on the same type of grain. Responses obtained from cereal grain supplementation are very dependent on the quality and degradation characteristics of the pasture consumed, which changes through the grazing season.</TR

Effect of processed cereal grains as a supplement on grass intake, rumen pool sizes, ruminal kinetics and the performance of grazing lactating dairy cows

Five multiparous lactating Holstein-Friesian dairy cows fitted with rumen cannula were allowed to graze perennial ryegrass swards. Next to a control treatment of grazing only, pelleted barley (PB), pelleted maize (PM), toasted and subsequently pelleted barley (TPB), and toasted and subsequently pelleted maize (TPM) were fed as a supplement in two equal portions. Before and after 3 h of grazing the rumen content was evacuated, weighed, sampled and returned to the animals. Then the cows were kept inside the barn and starved for 6 h, after which rumen evacuations were repeated. The estimated clearance rates of starch showed significant differences (