Studies on the degradation kinetics of botanically diverse fibrous feeds and their apparent digestibility and rate of passage when fed to ponies

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

In vitro fermentation of different ratios of high-temperature dried lucerne and sugar beet pulp incubated with an equine faecal inoculum

An in vitro gas production technique, where equine faeces was the source of microbial inoculum, was used to determine the fermentation kinetics of high-temperature dried lucerne (A) and molassed sugar beet pulp (SB) mixed in the following ratios; 100:0 (A), 80:20 (ASB1), 60:40 (ASB2), 40:60 (ASB3), 20:80 (ASB4) and 0:100 (SB). Total gas pool size increased linearly (P&#60;0.05) with increasing level of SB substitution of lucerne, with values ranging from 148 to 281 ml. Mathematical analysis of the cumulative gas production curves showed significant differences in the fermentation patterns of these feeds (P&#60;0.001). Rate parameter values; fractional rate of degradation (FRGP) and time taken to produce 50 or 95% of the total gas production (T50 and T95, respectively) were all improved by SB addition, which was particularly notable at lower levels of SB substitution (ASB1 and ASB2). Moreover, ASB1 and ASB2 produced rate parameters similar to those observed in bottles containing SB alone. In conclusion, the addition of SB to lucerne at levels of up to 400 mg g−1 dry matter (DM) inclusion appears to significantly increase the rate at which Lucerne is degraded, which has important implications for the overall energy balance in the horse. Furthermore, the gas production technique appears to be a valuable tool for evaluating fibrous feedstuffs and feedstuff combinations, such as lucerne and SB, for equids in vitro, allowing the kinetics of degradation to be studied as opposed to end-point data

The effect of particle size on the in vitro fermentation of different ratios of high-temperature dried lucerne and sugar beet pulp incubated with equine faecal inocula

An in vitro gas production technique, where equine faeces was the source of microbial inoculum, was used to determine the effect of particle size (ground vs. unground) on the in vitro fermentation of high-temperature dried lucerne (L) and molassed sugar beet pulp (SB). Two experiments were conducted; in experiment 1, unprocessed (U) L and SB or ground L and SB (G; to pass through a 1 mm dry mesh screen) were mixed in the following ratios: 100:0, 90:10, 80:20 and 70:30, L and SB, respectively. In experiment 2, unprocessed L or ground L, and ground SB were mixed in the following ratios: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100, L and SB, respectively. Substrate combinations were fermented in vitro with equine faecal inocula using in vitro gas production (GP). In both experiments, total gas pool was unaffected by particle size. Conversely, mathematical analysis of the cumulative gas production curves showed significantly different rates of fermentation in bottles containing ground substrates compared to unprocessed feedstuffs (P&#60;0.001). Rate parameter values, fractional rate of degradation (FRGP) and time taken to produce 50 or 95% of the total gas production (T50 and T95, respectively) were all increased (P&#60;0.001) by grinding the substrates in both experiments. In experiment 2, total volatile fatty acid (TVFA) concentration in the culture fluid post-fermentation was also higher (P&#60;0.001) in bottles containing U material compared to G (82.9 mmol/l vs. 64.0 mmol/l, respectively), with a marked change in the molar proportions of volatile fatty acids (VFA) present, with bottles containing G material containing more propionate and less acetate compared to the U substrates. In conclusion, particle size has a marked effect on the rate of substrate fermentation and TVFA concentration and VFA composition of the culture fluid, which has important implications for predicting in vivo digestibility from in vitro digestibility measurements; therefore, further work is required to determine optimal particle size of substrates evaluated in vitro using equine faecal inocula