Effect of non-forage roughage replacement on feeding behaviour and milk production in dairy cows

The objective of this study was to determine whether the partial replacement of roughage from forage with non-forage fiber sources, in a total mixed ration (TMR), could reduce feed sorting by dairy cows without modifying behaviour and milk production. Twelve Holstein cows were fed two TMR maize silage based diets in a cross-over experiment. Compared to the control diet (C-diet), experimental diet (E-diet) was formulated by replacing 8% neutral detergent fibre (NDF) from straw and alfalfa hay with soybean hulls and wheat bran. E-diet had a lower physical effectiveness factor (pef) (0.37 vs 0.34; P<0.001) and physical effective NDF (peNDF) (15.5 vs 14.6%; P<0.01). Feeding and sorting behaviour, ruminal activity, milk yield and composition and blood metabolites were measured. The results indicated that dry matter intake was not affected by diet. Cows fed the experimental TMR spent less time eating (192 vs 178 min/d; P<0.05) but showed the same number of meals per day. C-diet fed cows sorted against peNDF in a greater extent (98.3 vs 100.9%; P<0.05). Treatments did not affect cows time budget of general behaviours, with particular regard to ruminating activity. Despite different forage sources in TMR, no significant differences in milk yield and quality were detected. (NDF) requirement (NRC, 2001) is not met develop metabolic disorders that influence milk production and health status, leading to displaced abomasum, ruminal parakeratosis, laminitis, acidosis and fat cow syndrome (Keunen et al., 2002). Along with NDF content, adequate physical characteristics of fibre, such as particle size and density, are necessary for proper ruminal fermentation, utilisation, metabolism and milk fat production (Mertens, 1997). Reduced forage particle size and non-forage fibre sources have been shown to decrease chewing time and saliva production, which buffers the rumen. Thus, reduced forage particle size and non-forage fibre sources lead to a low ruminal pH (<5.8) (Dohme et al., 2007). However, when fibre is provided in total mixed ration (TMR), and the proportion of particles longer than 19 mm is high, cows are more likely to sort the ration and the diet that is actually consumed by them is very different than the one originally formulated (Leonardi and Armentano, 2007). If cows are allowed to sort their ration, ruminal pH may fluctuate and affect feed intake, fermentation and overall digestion (DeVries et al., 2008). To achieve optimal diet utilisation leading to maximal rumen functionality, health status and milk yield, adequate particle length/size of forage should be maintained (Lammers et al., 1996), and feed sorting by cows should be minimised. In spite of different ration compositions and particle size distributions, many authors found that dairy cows were able to sort out the fibrous component of the feed (Kononoff et al., 2003b; DeVries et al., 2007). Replacing a portion of high-roughage forage in the TMR and a portion of concentrates with short, readily digestible NDF-rich by-products may reduce sorting by animals. Moreover, dry matter (DM) and NDF intake may be more homogenous and improve milk yield through a simultaneous utilisation of energy and proteins by rumen bacteria (Halachmi et al., 2004). The objective of this study was to characterise feeding, sorting, ruminal function, behaviour, milk yield and quality of dairy cows fed a ration with a roughage component based on both forage and readily digestible NDF-rich by-products.