Abstract
Two experiments were carried out aiming to study the value of whole oats (WO) as a potential source of physically effective fiber (peNDF) in rations for calves. In experiment 1, 24 Hereford calves (177 ± 18 kg) were randomly assigned to eight groups and these into one of four experimental rations (79% concentrate), varying in the replacement level of grass hay (GH) for WO: 0:21, 7:14, 14:7, 21:0% dry matter (DM) basis WO:GH, respectively. Increasing WO level resulted in a quadratic response for peNDF (P= 0.04) with values above 15% of dm. Intake increased quadratically (P= 0.03) and dm digestibility increased linearly (P= 0.03). As a result, feed conversion efficiency tended to improve (P= 0.08). In Experiment 2, four rumen cannulated steers were assigned in a crossover design to one of two experimental rations (65% concentrate) varying in peNDF fiber source: 35% gh or 35% WO, aiming to study the fermentative pattern. Replacing GH for WO reduced mean daily rumen pH (5.9 vs. 6.3, P < 0.01), varying between 6.1 and 5.8, and always below pH values in gh. No differences were observed for the potentially degradable dm fraction, but fermentation rate was higher for WO (35.0 vs. 9.0 %/ h; P= 0.02), hence increasing effective degradability (58.3 vs. 65.4%; P= 0.048). Results from both experiments suggest it is viable to use WO as a peNDF source for concentrated rations.
Highlights
Livestock systems based exclusively on natural grasslands face a low forage supply during winter
The complete replacement of grass hay (GH) with whole oats (WO) represented a reduction of 23% of the total NDF supply in the diet
The reduction of NDF supply by increasing WO was offset by an increase in the content of non-fiber carbohydrates and ether extract in the ration, which would partly explain the linear increase observed in the coefficient of apparent dry matter digestibility (DMD) in calves
Summary
Livestock systems based exclusively on natural grasslands face a low forage supply during winter. Lot feeding in winter and returning to grazing in the spring has been presented in Uruguay and the region(1)(2) as a technological alternative that would be beneficial in areas with no agroecological aptitude for the implantation of pastures or annual crops. This would allow to exploit the growth potential of the calf and decide on the best moment for sale. The total peNDF supply from the diet depends on the total fiber content (NDF) and its effectiveness to promote rumination and mastication This characteristic has been associated with the fiber nature and the particle size(6), and it is maximum in the fiber provided by hay(3). Studies evaluating the replacement of hay with the use of by-products that have low nutritional value but are rich in fiber, such as rice hulls and wood chips from the cellulose industry, showed the viability of removing long fiber from hay without affecting animal performance, providing enough peNDF even when included in a low proportion in the ration (6% to 8%, dry matter basis)(7)(8)(9)
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