Effects of adding polyclonal antibody preparations on ruminal fermentation patterns
and digestibility of cows fed different energy sources
ABSTRACT: Nine ruminally cannulated cows fed different energy sources were used to evaluate an avian-derived polyclonal antibody preparation (PAP-MV) against the specific ruminal bacteria Streptococcus bovis, Fusobacterium necrophorum, Clostridium aminophilum, Peptostreptococcus anaerobius, and Clostridium sticklandii and monensin (MON) on ruminal fermentation patterns and in vivo digestibility. The experimental design was three 3 × 3 Latin squares distinguished by the main energy source in the diet [dry-ground corn grain (CG), high-moisture corn silage (HMCS), or citrus pulp (CiPu)]. Inside each Latin square, animals received one of the feed additives per period [none (CON), MON, or PAP-MV]. Dry matter intake and ruminal fermentation variables such as pH, total short-chain fatty acids (tSCFA), which included acetate, propionate, and butyrate, as well as lactic acid and NH3-N concentration were analyzed in this trial. Total tract DM apparent digestibility and its fractions were estimated using chromic oxide as an external marker.
Each experimental period lasted 21 d. Ruminal fluid sampling was carried out on the last day of the period at 0, 2, 4, 6, 8, 10, and 12 h after the morning meal. Ruminal pH was higher (P = 0.006) 4 h postfeeding in MON and PAP-MV groups when compared with CON. Acetate:propionate ratio was greater in PAP-MV compared with MON across sampling times. Polyclonal antibodies did not alter (P > 0.05) tSCFA, molar proportion of acetate and butyrate, or lactic acid and NH3-N concentration. Ruminal pH was higher (P = 0.01), 4 h postfeeding in CiPu diets compared with CG and HMCS. There was no interaction between feed additive and energy source (P > 0.05) for any of the digestibility coefficients analyzed. Starch digestibility was less (P = 0.008) in PAP-MV when compared with CON and MON. In relation to energy sources, NDF digestibility was greater (P = 0.007) in CG and CiPu vs. the HMCS diet. The digestibility of ADF was greater (P = 0.002) in CiPu diets followed by CG and HMCS. Feeding PAP-MV or monensin altered ruminal fermentation patterns and digestive function in cows; however, those changes were independent of the main energy source of the diet.
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RESULTS AND DISCUSSION
An interaction between feed additive and energy source was observed for DMI (P = 0.05; data not shown). In cows receiving no feed additive (CON), DMI was greater (P = 0.01) when HMCS (12.07 kg/d) was fed vs. CiPu (5.69 kg/d). There was no difference be- tween those 2 treatments and CG (9.47 kg/d) in CON group (P = 0.09). In cows receiving MON, DMI was greater (P = 0.03) when HMCS (11.06 kg/d) was fed vs. CG (6.02 kg/d). There was no difference between these 2 groups and CiPu (7.58 kg/d) in the MON group (P = 0.11). Contrary to this observation, a decrease in DMI has been reported in feedlot cattle when HMCS was included in the diet compared with dry-rolled corn (Ladely et al., 1995).
Ruminal fermentation variables are reported in Table 2 and Figure 1. For ruminal pH, a feed additive × time postfeeding interaction was observed (P = 0.04). At 0 h postfeeding, ruminal pH of MON (6.72) was greater (P = 0.03) than PAP-MV (6.47) and CON (6.46). At 2 and 4 h postfeeding, ruminal pH of MON and PAP-MV groups were greater (P < 0.05) than CON. At 6 h post- feeding, pH of the MON group (6.03) was greater (P = 0.04) than CON (5.82), without difference (P = 0.79) between these 2 groups to PAP-MV (6.03; Figure 1a).
Our results agree with in vitro (Schelling, 1984) and in vivo (Nagaraja et al., 1982) data showing that MON is effective in preventing ruminal pH decline after feed- ing. DiLorenzo et al. (2006) observed that steers receiv- ing a PAP against S. bovis (PAP-Sb) in high-grain diets had increased ruminal pH at 5.5 h postfeeding when compared with control (6.08 vs. 5.67). In addi- tion, S. bovis counts were reduced in steers fed PAP-Sb. Blanch et al. (2009) also reported an increased ruminal pH in heifers fed PAP-Sb when compared with control 6 h postfeeding at d 16 (6.70 vs. 6.11), 18 (6.54 vs. 5.95), and 19 (7.26 vs. 6.59) of the experimental period. Moreover, DiLorenzo et al. (2007) observed that a PAP against selected proteolytic, amylolytic, and gram-neg- ative bacteria was effective in maintaining a greater ruminal pH in early lactation dairy cows, where mean daily ruminal pH (6.07 vs. 5.75) and mean daily maxi- mum ruminal pH (6.82 vs. 6.36) were greater for cows receiving PAP when compared with control.
Moreover, for ruminal pH, an energy source × time postfeeding interaction was observed (P < 0.001). At 0 h postfeeding, ruminal pH was greater (P = 0.009) in the group fed HMCS (6.83) when compared with CG (6.38) and CiPu (6.43). Ruminal pH was greater (P = 0.02) at 2 h postfeeding in cows fed CiPu (6.19) vs. CG (5.81); however, HMCS (5.89) did not differ (P = 0.60) from the other 2 energy sources. At 4 h postfeeding, ruminal pH in CiPu cows (6.10) was greater (P = 0.01) than CG (5.69) and HMCS (5.72; Figure 1b).
Mendoza et al. (1999) reported a linear decrease in ruminal pH when increasing amounts of high-moisture corn grain were added in place of dry-rolled grain sor- ghum to sheep diets, probably as a result of an in- creased rate of ruminal degradability of the diet. The findings regarding ruminal pH in ruminants fed pectin- rich diets are mixed. Ben-Ghedalia et al. (1989) and Piquer et al. (2009) observed greater ruminal pH in sheep fed high-pectin diets compared with high-starch diets. Conversely, Leiva et al. (2000) and Assis et al. (2004) did not observe differences in ruminal pH when comparing high-pectin or high-starch diets for lactating dairy cattle.
A significant (P = 0.002) interaction between energy source and time was verified on total SCFA concentra- tion in almost all sampling times. At 0, 8, 10, and 12 h postfeeding, total SCFA concentration was greater (P < 0.05) for CiPu when compared with CG and HMCS. At 4 and 6 h, total SCFA concentration was greater (P < 0.05) for CiPu than CG and not significantly different between these 2 groups and HMCS (data not shown). Absorption rate of SCFA is influenced by dissocia- tion rate, which is determined by ruminal pH. In ba- sic pH, the dissociated form is predominant, reducing the absorption rate. This may explain why in CiPu-fed cows, where ruminal pH was more stable during the day (mean pH = 6.2), total SCFA concentration was greater in relation to the other energy sources (Santos, 2006).
An interaction between feed additive and time (P = 0.03) was verified for acetate:propionate (Ac:Pr) across all sampling times, where Ac:Pr ratio was great- er in PAP-MV than MON, without a difference be- tween these 2 groups and CON (Figure 1c). Although it was not observed in this study, a decrease in Ac:Pr when feeding MON compared with control is expected (Bergen and Bates, 1984; Ramanzin et al., 1997). This decrease is related to changes in microbial population promoted by ionophores that select for gram-negative organisms. These bacteria are the main producers of succinate, which could be a precursor of propionate (Russell and Wallace, 1997). In relation to PAP-MV, Blanch et al. (2009) observed an increase in molar pro- portion of acetate, 6 h after feeding, when a PAP-MV against S. bovis was offered to heifers fed high-grain diets. In our study, feeding PAP-MV did not affect the molar proportion of SCFA in relation to CON.
An interaction between energy source and time was observed (P = 0.004) for acetate molar proportion across sampling times, where cows supplemented with CiPu had greater values compared with CG and HMCS (data not shown). For molar proportion of propionate, an interaction was observed between feed additive and energy source (P = 0.008). In animals fed CG, molar proportion of propionate was greater (P = 0.004) in CON (34.5) vs. MON (23.1) and PAP (26.3). In ani- mals fed HMCS, molar proportion of propionate was greater (P = 0.02) in MON (30.3) vs. CON (22.0) and PAP (20.3; data not shown). An energy source effect (P = 0.0074) was observed for Ac:Pr across sampling times (Figure 1d). At 0, 8, 10, and 12 h postfeeding Ac:Pr was greater (P < 0.05) in CiPu compared with CG and HMCS, which did not differ between them. At 2, 4, and 6 h postfeeding, Ac:Pr was greater (P < 0.05) in CiPu compared with CG and not different between these 2 treatments and HMCS. An interaction between energy source and time was also observed for butyrate (P = 0.001). At 4 and 6 h postfeeding, molar proportions of butyrate were greater in HMCS vs. CG, without a difference between these 2 groups and CiPu (data not shown). These results are in agreement with previously reported effects (Ben-Ghedalia et al., 1989; Nussio et al., 2002; Piquer et al., 2009) of the type of substrate available for ruminal fermentation in each diet. In diets based on dry-ground and high-moisture corn grain where the main carbohydrate being ferment- ed is starch, greater molar proportions of propionate are expected. Conversely, in diets based on citrus pulp, where the main carbohydrate is pectin, a greater molar proportion of acetate is expected (Van Soest, 1994).
The reduced values of ruminal lactic acid reported in this study are in agreement with previous studies reporting similar ranges of ruminal pH (Goad et al., 1998; Mendoza et al., 1998). Up to a ruminal pH of 5.6, lactate is produced, but typically does not accumulate because ruminal lactate-utilizing bacteria are actively fermenting lactate into SCFA. When ruminal pH falls below 5.0, lactate catabolism bacteria are inhibited and lactate begins to accumulate (Nagaraja and Titge- meyer, 2007). No interaction between main factors and time (P > 0.05) as well as main factor effects (P > 0.05) were observed for this variable (Table 2).
No effect was observed for ruminal NH3-N concentra- tion (Table 2). The mean ruminal NH3-N concentra- tion observed in this study was 4.6 mg/dL, which is less than what was recommended by Satter and Slyter (1974) for maximum microbial protein synthesis. How- ever, in high-grain diets, ruminal NH3-N concentrations are typically less than the reported threshold necessary to optimize microbial growth (Ludden and Cecava, 1995; Devant et al., 2000). At 0 h, the values of NH3-N concentration were around 5.3 mg/dL; the peak of con- centration (13.0 mg/dL) was observed at 2 h postfeed- ing. After that, the values fell to 2.6 mg/dL on average and remained at these values until 12 h postfeeding.
Digestibility coefficients for DM and its fraction along with TDN of diets are presented in Table 3. No interaction between feed additive and energetic source was observed (P > 0.05). An effect of feed additive was observed, where starch (P = 0.008) digestibility coef- ficient was less in PAP-MV when compared with CON (P = 0.01) and MON (P = 0.003).
For energy source effect (P = 0.007), NDF digest- ibility was greater in CG (P = 0.01) and CiPu (P = 0.003) than HMCS. This reduction in NDF digestibility in HMCS fed cows could be explained by the inhibitory effect that rapidly fermentable carbohydrates can cause on cellulolytic bacteria and thus on fiber digestion. This effect is probably related to a preference of some bacte- ria species such as Butyrivibrio fibrisolvens, Fibrobacter succinogenes, and Prevotella ruminicola for rapidly fer- mentable carbohydrates fermentation instead of invest- ing energy to produce adhesion factors and cellulases for fiber fermentation (Miron et al., 1996). Moreover, a greater rumen-reticulum passage rate in HMCS fed cows due to greater DMI could have contributed to the reduction in fiber digestibility.
Total tract digestibility of ADF was greater (P = 0.002) in CiPu (P = 0.03), followed by CG (P = 0.005) and HMCS (P = 0.0006). Similar results were observed in previous studies (Bhattacharya and Harb, 1973; Por- cionato et al., 2004) that had partial substitution of corn grain or corn silage by citrus pulp. In the pres- ent study, the increase in ADF digestibility in CiPu diets can be related to stability of ruminal pH near 6.0 throughout the day, which may have promoted cellu- lolytic activity (Russell and Wilson, 1996). Moreover, this increase can be related to fibrous fraction composi- tion of citrus pulp, which has a low lignin content (1% of DM), facilitating its digestion (Ørskov, 1987).
Under the experimental conditions of this study, PAP-MV did not differ from MON in maintenance of ruminal pH 4 h postfeeding. Monensin prevented a de- cline in ruminal pH with a consequent change in SCFA profile (decreased Ac:Pr ratio), whereas PAP-MV pre- vented a decrease in ruminal pH without altering the SCFA profile, independent of energy source used. Di- gestibility of starch was decreased with PAP-MV inclu- sion. Further research is needed to better understand the mechanisms involved in these results.
Different energy source utilization in the experimen- tal diets influenced ruminal fermentation variables. Cit- rus pulp inclusion in the diet prevented a ruminal pH decline at 4 h postfeeding, and increased acetate molar proportion and ADF digestibility when compared with CG and HMCS, regardless of the feed additive used.