Diet composed of smaller particles can improve feed intake, digestibility, and animal growth or health, but in ruminant species can reduce rumination and buffering–the loss of which may inhibit fermentation and digestibility. However, the explicit effect of particle size on the rumen microbiota remains untested, despite their crucial role in digestion. We evaluated the effects of reduced particle size on rumen microbiota by feeding long-stem (loose) alfalfa hay compared to a ground and pelleted version of the same alfalfa in yearling sheep wethers during a two-week experimental period. In situ digestibility of the pelleted diet was greater at 48 h compared with loose hay; however, distribution of residual fecal particle sizes in sheep did not differ between the dietary treatments at any time point (day 7 or 14). Both average daily gain and feed efficiency were greater for the wethers consuming the pelleted diet. Observed bacterial richness was very low at the end of the adaptation period and increased over the course of the study, suggesting the rumen bacterial community was still in flux after two weeks of adaptation. The pelleted-hay diet group had a greater increase in bacterial richness, including common fibrolytic rumen inhabitants. The pelleted diet was positively associated with several Succiniclasticum , a Prevotella, and uncultured taxa in the Ruminococcaceae and Rickenellaceae families and Bacteroidales order. Pelleting an alfalfa hay diet for sheep does shift the rumen microbiome, though the interplay of diet particle size, retention and gastrointestinal transit time, microbial fermentative and hydrolytic activity, and host growth or health is still largely unexplored.

24Diet composed of smaller particles can improve feed intake, digestibility, and animal growth or 25 health, but in ruminant species can reduce rumination and buffering -the loss of which may inhibit 26 fermentation and digestibility. However, the explicit effect of particle size on the rumen 27 microbiota remains untested, despite their crucial role in digestion. We evaluated the effects of 28 reduced particle size on rumen microbiota by feeding long-stem (loose) alfalfa hay compared to a 29 ground and pelleted version of the same alfalfa in yearling sheep wethers. In situ digestibility of 30 the pelleted diet was greater at 48 h compared with loose hay; however, distribution of residual 31 fecal particle sizes in sheep did not differ between the dietary treatments at any time point. Both 32 average daily gain and feed efficiency were greater for the wethers consuming the pelleted diet. 33 Observed bacterial richness was very low at the end of the adaptation period and increased over 34 the course of the study, suggesting the rumen bacterial community was still in flux after two weeks 35 of adaptation. The pelleted-hay diet group had a greater increase in bacterial richness, including 36 common fibrolytic rumen inhabitants. The pelleted diet was positively associated with several 37 Succiniclasticum, a Prevotella, and uncultured taxa in the Ruminococcaceae and Rickenellaceae 38 families and Bacteroidales order. Pelleting an alfalfa hay diet for sheep does shift the rumen 39 microbiome, though the interplay of diet particle size, retention and GI transit time, microbial 40 fermentative and hydrolytic activity, and host growth or health is still largely unexplored. 42It has been well established that the nutrient composition of a diet affects the 43 gastrointestinal tract (GIT) microbiota [1,2], yet the physical structure and complexity of the diet 44 may also alter its interactions with the GIT microbiota and host. In cattle, longer fiber particles 45 have been shown to improve rumination [3] and ultimately fiber digestibility [4]. However, shorter 46 or smaller diet particles can change the dynamics of digestion and produce a number of favorable 47 outcomes. Specifically, reductions in particle size associated with mastication or mechanized 48 processing correspond to increases in feed surface area and thus allow for greater microbial 49 attachment and relative fibrolytic and fermentative activities as has been shown in vitro [5]. 50Mechanical breakdown during diet preparation can also physically disrupt waxy plant cuticles and 51 cell walls that can otherwise impede microbial attachment and degradation, thus making plant 52 carbohydrates more available [6] and decreasing the potential confounding effect of forage 53 fragility within the rumen [7]. Hydrolytic activities are also likely further enhanced by the 54 reductions in buoyancy and increased functional specific gravity [8] associated with reduced 55 particle size, that would allow smaller particles to sink beneath the dorsally-located rumen mat ...

A 3 yr experiment was conducted to evaluate the influence of diet and feeding location on animal performance, carcass characteristics, whole blood counts, and internal parasite burden of lambs assigned to 1 of 4 treatments: 1) confinement fed 71% alfalfa, 18% barley pellet, 5% molasses, 0.013% Bovatec, 6.1% vitamin/mineral package diet (CALF), 2) confinement fed 60% barley, 26% alfalfa pellet, 4% molasses, 2.5% soybean-hi pro, 0.016% Bovatec, 7.4% vitamin/mineral package diet (CBAR), 3) field fed 71% alfalfa, 18% barley pellet, 5% molasses, 0.013% Bovatec, 6.1% vitamin/mineral package diet (FALF), and 4) field fed 60% barley, 26% alfalfa pellet, 4% molasses, 2.5% soybean-hi pro, 0.016% Bovatec, 7.4% vitamin/mineral package diet (FBAR). A year × location interaction was detected for ending body weight (BW), average daily gain (ADG), and dry matter intake (DMI); therefore results are presented by year. In all years, cost of gain and DMI were greater for CALF and FALF than for CBAR and FBAR feed treatments (p ≤ 0.03). In yr 2 and 3 field treatments had greater ending BW and ADG than confinement treatments. For all years, diet did not affect ending BW or ADG. In yr 1 dressing percent and rib eye area were greater for field finished lambs than confinement finished (p ≤ 0.02) and Warner-Bratzler shear force was greater for CALF and FALF (p = 0.03). In yr 2 lambs in FALF and FBAR treatments had greater leg scores and conformation than CALF and CBAR (p = 0.09). In yr 1, FALF had a greater small intestine total worm count than all other treatments. In yr 1, ending Trichostrongyle type egg counts were greater for FALF (p = 0.05). In yr 2, ending Nematodirus spp. egg counts were greater for FALF and lowest for CBAR (p < 0.01). Abomasum Teladorsagia circumcinta worm burden was greater in CALF than all other treatments (p = 0.07) in yr 2. While field finishing lambs with a grain-or forage-based diet we conclude that it is possible to produce a quality lamb product without adverse effects to animal performance, carcass quality or increasing parasite burdens.