The horse evolved to obtain most of its dietary energy from the hindgut fermentation of
fibrous feeds and so in the interests of health and welfare, the domestic horse should be
fed forage-based diets. However, little information exists on the nutritive value of
different forages that are potentially valuable feeds for horses. The aim of this thesis
was to measure the in vivo apparent digestibility of a range of botanically diverse
fibrous-feeds and to investigate the suitability of ruminant in sacco and in vitro
techniques as routine methods for estimating, degradation kinetics and rates of passage
of fibrous feeds through the gastrointestinal tract of ponies. In the first study, the in
vivo apparent digestibility (AD) of hay (H), haylage (HY), big bale silage (BB) and
clamp silage (CS) were determined in 4 ponies. Dry matter intake was significantly
(P H > CS (2.95 kg/d). For all parameters
measured AD of CS and BB were significantly (P<0.05) greater than for H, with HY
being intermediate. The theoretical digestible energy and crude protein requirements of
the ponies were met or exceeded by all diets except hay. Secondly, the in vivo AD,
intra-caecal fermentation parameters and rates of passage of hay cubes (HC), an oat
hulls:naked oats mix (OH:NO), plain sugar beet pulp (SBF), soya hulls (SH) and a hay
cubes:sugar beet mix (HC:SB) were determined in 3 caecally-fistulated ponies. Total
collection and mobile bag studies produced similar AD values, with SBF being greater
(P<0.05) for all parameters measured than OH:NO and HC, with intermediate values for
SB:HC and SH. All feeds maintained the intra-caecal pH and acetate molar proportions
above 6.5 and 700 mmol/mol respectively. Higher levels of propionate and lactate and
lower levels of butyrate were recorded for ponies fed the OH:NO compared with those
on diets SBF and HC (P<0.05). Pre-caecal losses of total non-starch polysaccharides
(TNSP) from feeds in sacco were highest for SBF (133g/kg) >SH > OH:NO > HC
(51g/kg). In contrast, the highest crude protein (CP) losses were from OH:NO (771
g/kg) which were greater than SH = HC > SBF (296g/kg) (P<0.05). Of the 7 ruminant
models fitted to faecal excretion data, the G3 and G4 time-dependent models of Pond et
al. (1988) best described the passage of both chromium (Cr) and ytterbium (Yb) marked feeds in the three diets. Mean caecal to faecal passage rates measured using Crmordanted feed, were ca. 36 h for OH:NO, which was greater than that of HC at ca. 26
h (P<0.05). Total tract mean retention time (MRT) was measured using orally
administered Yb-marked feeds and averaged 43 h for OH:NO which was greater than
the 30 h noted for the HC (P<0.05). Finally, the in vitro fermentation by pony faecal
inoculum of hay (H) and plain sugar beet pulp (SB) in ratios of 100% H, 75:25 H:SB 1,
50:50 H:SB2, 25:75 H:SB3 and 100%SB, in the presence (+N) or absence (-N) of added
nitrogen was assessed by the manual pressure transducer technique of Theodorou et al.
(1994). DM loss was significantly (P
H:SB3 > H:SB2 > HSB1 > H. Addition of N reduced the time to reach 50% of gas
production (tso), indicating a positive influence of N on degradation rate (P<0.05).
Maximum DM loss {ca. 850 mg/g) from SB occurred within 49 h post-incubation
whereas maximum degradation from the other feeds was attained at ca. 135 h
incubation. A positive associative effect was noted on both the rate and extent of
degradation of H when incubated with HSB3 (-N), indicating an increase in microbial
activity associated with the addition of SB. Results from the experiments described in
this thesis indicate that a
range of botanically diverse fibrous feeds are suitable for
incorporating into equid diets, and offer a valuable relatively energy-dense alternative to
hay as the basal forage for stabled horses. Ruminant techniques for measuring in sacco
AD and the use of markers for determining rate of passage of digesta offer rapid and
reliable methods for measuring digestion of a range of fibrous feeds in ponies. In vitro
gas production showed considerable potential as a routine method for determining DM
loss and degradation rate of fibre feeds for horse
