RESEARCH WORK

Digestibility of a sugarcane silage with pig manure, and its evaluation in a double-purpose cattle production system

J. Estrada-Álvarez¹, N. Villa-Duque² and F. J. Henao-Uribe ¹

¹Universidad de Caldas, Calle 65 No. 26-10. Apdo. aéreo 275, Manizales, Colombia
² Universidad de La Paz, Barrancabermeja, Colombia.
E-mail: jestrada@ucaldas.edu.co

ABSTRACT

The in vitro and in situ dry matter digestibility (IVDMD and ISDMD) of a silage elaborated from ground integral sugarcane (GISC) plus 40 % of fresh pig manure (FPM) enriched with VITAFERT, and the effect of replacing corn silage with GISC-FPM silage on the production of milk and ruminal methane (CH₄), were evaluated. The study was conducted at the University of Caldas Colombia in a tropical dairy production system. The IVDMD and ISDMD were each evaluated through completely randomized designs, with eight degradation times. To study the milk production 18 F₁ (Zebu x Holstein) cows were used, between the second and eighth lactation, which grazed star grass (Cynodon plectostachyus) and received 5 kg/animal/day of corn silage. Nine cows, considered control, received corn silage and nine were fed GISC-FPM silage. The CH₄ measurements were conducted on four cows of each treatment. The digestibility of both silages, at 72 hours, reached values higher than 70 %. There were no significant differences in the milk production and silage intake, and no alterations were observed in the sanitary status of the animals. The cows fed GISC-FPM silage produced, significantly, less ruminal CH₄. The digestibility of the silages at 72 h was similar to that of the balanced feedstuffs, which proved the possibility of a partial substitution. There was modulating effect of the GISC-FPM silage, because less ruminal CH₄ was produced (6,9 ppm) than with the corn silage (7,6 ppm). It is concluded that the inclusion of pig manure enriched with VITAFERT in the sugarcane silages can be an alternative in animal feeding.

Keywords: Digestibility, milk production.

The use of byproducts, manure, hair, feathers, blood, foliage, banana pseudo-stems and others, with different levels of processing, constitutes one of the most efficient ways for their strategic utilization.

In this sense, pig production has essayed different options to utilize pig manure, among which the elaboration of silages stands out. Through this way contamination has been prevented and the byproduct can be given added value, as raw material for feeding ruminants (Barrón et al., 2000; Campabadal, 2003).

The strategy that has been most used is mixed silage of pig manure with forage plants, such as sugarcane (Saccharum officinarum), to utilize the contribution of protein and minerals of the pig manure (Campabadal, 2003) and the contribution of easily-fermented carbohydrates from sugarcane (De Lima et al., 2010).

It has been proven that pig manure improves silage digestibility (Pinto et al., 2003), especially if microbial additives are incorporated such as lactic acid bacteria (LAB), which promote the growth of beneficial microorganisms and inhibit the undesirable ones (Martínez-Gamba et al., 2001; Pedroso, 2003).

These silages help to compensate the enzymatic degradation of the fibrous materials in the rumen, because they increase symbiotic microorganisms (Van Soest, 1994). Degradation also provides nitrogen and energy for the synthesis of microbial protein (Bulanget al., 2007).

Among the microorganisms involved in ruminal fermentation it is necessary to mention methanogenic bacteria, in charge of preventing the acidification of the ruminal fluid by eliminating the hydrogen ions produced by the degradation of structural carbohydrates (Berra and Finster, 2010).

The objective of this study was to evaluate the ISDMD and IVDMD of a silage of ground integral sugarcane (GISC) plus 40 % of fresh pig manure (FPM), as well as the effect of replacing corn (Zea mays) silage with GISC-FPM silage on the production of milk and ruminal methane.

MATERIALS AND METHODS

Location. The research was conducted at the farm La Cruz, of the University of Caldas, in Anserma, Caldas, Colombia; which is located in the region classified as tropical dry forest, at 1 050 m.a.s.l., with 1 700 mm of annual rainfall and 24 ºC of mean temperature.

Animals. To evaluate the milk production and silage intake 18 F₁ cows (Zebu x Holstein) were used, with an average weight of 524 kg and 40 days after calving, between the second and eighth lactation. They were selected in a double-purpose herd which consumed star grass (Cynodon plectostachyus) fertilized with 450 kg N/year, in a rotation system per strip/day; the mean pasture availability measured before the entrance of the animals to the grazing area was 15,57 kg DM/animal/day, and the recovery period was 28 days.

The cows remained grazing from 9:00 a.m. to 5:00 a.m. of the next day, time at which mechanical milking started with support of the calf in the barn; after milking, they were supplemented with 5 kg of silage/animal/day, mineralized salt with 8 % of phosphorus and water ad libitum. The trial lasted 18 weeks in the season of moderate rainfall. The CH₄ measurements were performed on a subgroup of eight animals.

The evaluation of the ISDMD was made with three bulls of Zebu x Holstein commercial crossings, of 280 kg, cannulated with ruminal fistulae. They directly grazed C. plectostachyus for a period of 14 days.

Ensiling process. The solid fraction of manually-collected fresh pig manure, from pigs weighing 40-60 kg, fed with a commercial balanced feedstuff, was used (Estrada et al., 2013).

During 21 days a mixture of GISC-FPM (6:4; p/p) enriched with VITAFERT, previously fermented during 48 h, was ensiled in 50-kg containers which were vacuumed for 20 seconds, (Gutiérrez et al., 2012). The microbial additive was added at a rate of 0,4 kg per each kg of pig manure (28,6 % of VITAFERT).

The corn silage was elaborated in black plastic bags, caliber 4.5, from corn plants harvested at 90 days, chopped at 1 cm; lactic acid bacteria (10⁶ CFU/mL) were added, and fermentation lasted 21 days.

Determination of the IVDMD and ISDMD. To determine the IVDMD a strict anaerobic system was used, with agitation at 39 ºC.

Glass tubes of 50 mL were used, with 2 mL of filtered ruminal fluid from three bulls cannulated in the rumen. In each tube a polyester bag of 1 x 6 cm and 53-µm pore was introduced, with sufficient quantity of sample to guarantee 100 mg of dry matter.

The solution used consisted in 7 mL of bicarbonate-phosphate, reducer solution in a 1:2 ratio, 1 mL of boiling water and other 2 mL of ruminal fluid. The incubation times were 0, 3, 6, 9, 12, 24, 48 and 72 h.

The resulting solid residues in each bag were washed with neutral detergent, filtered with light vacuum, washed with ethanol and acetone, and dried at 60 ºC during 48 h (Kiyani Nahand et al., 2011).

The digestibility was quantified through the difference between the weight of the material introduced in the bag and the weight of the corresponding dry residue.

A completely randomized block design with three repetitions per treatment was used; the variable date of the experiment was blocked, the effect of eight fermentation times was tested, and two tubes were used as experimental unit.

In the case of the determination of the ISDMD, through the ruminal cannula a total of 16 polyester bags of 20 x 10 cm and 53-µm pore were introduced in the rumen of each fistulated animal; 5 g of sample were placed in each bag.

To evaluate the digestibility at 0, 3, 6, 9, 12, 24, 48 and 72 h of incubation, two bags were introduced each time, starting by the ones which should remain for 72 hours, in order to withdraw the 16 bags at the same time (Kiyani Nahand et al., 2011).

Once the incubation process was finished the bags were washed with tap water during 20 minutes, until the turbidity disappeared; they were treated for one hour with boiling neutral detergent, to eliminate the adhered microorganisms; and they were dried at 60 ºC for 48 h.

The total digestibility was quantified through the difference in weight between the material introduced in each bag and the dry residue (Van Soest et al., 2000).

For the analysis of the results a completely randomized block design was used with three repetitions per treatment; the variable fistulated bull was block, the effect of eight fermentation times was tested, and two bags were used as experimental unit.

Production essays. The effect of replacing the corn silage with sugarcane plus 40 % of fresh pig manure silage, on the milk production, the silage intake and the ruminal production of CH₄, were evaluated through a unifactorial arrangement with measurements repeated in time for each cow (random effect); the number of lactations and the day of measurement were used as fixed effects.

Nine F₁ (Zebu x Holstein) cows were randomly allocated to each type of silage; the CH₄ production was measured in four of them by direct rumen puncture, using a 7-mL vacutainer®, of red cap and in duplicate.

The CH₄ was quantified with a gas chromatograph coupled with flame ionization detection, with Split-Less injection, following the methodology described by Albarracin et al. (2013).

The health status of each cow was permanently monitored, qualitatively, by the veterinary team of the farm.

All the above-mentioned statistical models were adjusted and analyzed using the program Stata® version 12.0 (2012).

RESULTS AND DISCUSSION

The silage of sugarcane plus pig manure enriched with VITAFERT produced a significant increase (p< 0,05) of the ISDMD (58,1 to 71,7 %) between 0 and 72 h; a similar effect was found in the IVDMD (48,9 to 73,6 %) for the same period (fig. 1).

The difference between the digestibility percentages in the two tests could have been due to the loss of very small particles which can pass through the micropores of the polyester bags (Huhtanen and Sveinbjorsson, 2006).

The apparent digestibility percentages in both tests, higher than 70 % after 72 h of fermentation, were similar to the ones obtained with different balanced feedstuffs (Van Soest, 1994), which supports the possibility of substituting part of the balanced feedstuff supplied to similar animals as the ones in this essay, by this type of silage.

These results coincide with the report by Suárez et al. (2007), who stated that when a better energy-protein ratio is propitiated, through the addition of nutrients to the basal diet, biochemical reactions occur in the rumen which promote a higher microbial growth during the feed permanence time; this increases the ruminal cellulolysis and the degradation of feedstuffs with high fiber content. Additionally, the efficiency of lactic acid producing bacteria has been proven (Galina et al., 2009), because they contribute to the stabilization of the microbial flora present in the rumen ecosystem, and influence the development of fibrolytic microorganisms as delignifying agents (Galina et al., 2010), while the digestibility of the DM and the cell wall increases (Elías et al., 2010).

Figure 2 shows, on the top right, the curve type of milk production for F₁ (Zebu x Holstein) cows reported by Hernández and Ossa (2002) under similar conditions as the ones in this trial, which reaches a peak between the seventh and the tenth week, to descend gradually until week 40; while the lower part synthesizes the information recorded with sugarcane plus pig manure silage as well as with corn silage, without significant differences (p< 0,05).

The two groups of cows totally consumed the 5 kg/day of silage offered. No alterations appeared in the health status of the cows.

These results constitute the first evidences about the possibility of substituting corn silage, traditionally used for milk production, by a fermented mixture with 40 % of solid pig manure, without affecting the milk production and/or generating health alterations in the cows.

The cows fed with GISC-FPM (fig. 3) produced, significantly (p< 0,05), less ruminal CH₄ (6,9 ppm) than those which received corn silage (7,6 ppm).

The low CH₄ levels detected with both silages coincide with the ones found by Ortiz et al. (2009), who stated that the better performance of the animals fed with probiotics can be explained by a decrease of methanogenesis, which contributes to preserve energy for animal growth. Velez-Terranova et al. (2014), in a study conducted in a tropical dairy farm, also found similar results; however, in this work a reduction of 9,21 % was detected when substituting the corn silage by the silage of sugarcane plus pig manure.

The results ratify the modulating effect exerted by the glucose-rich feedstuffs, such as corn and sugarcane; which is due to the fact that they favor the formation of propionic acid through the lactic acid (Galina et al., 2009).

Rodríguez and Valencia (2008) stated that the production of CH₄ is a process performed by anaerobic methanogenic bacteria (Archaea group) which ferment glucose and reduce CO₂ to CH₄. The development of these bacteria can be favored by the diet, when the sources of energy in the rumen are used by the host animal.

In addition, the methanogenic bacteria not only reduce the hydrogen concentration in the rumen, but also benefit the growth of other bacterial species that improve the fermentation process (Johnson and Johnson, 1995).

CONCLUSIONS

The in vitro and in situ digestibility of both silages recorded values over 70 % after 72 h of fermentation.

No significant differences (p< 0,05) were recorded in milk production and silage intake, and no alterations of the health status of the cows were observed, when replacing 100 % of the supplementation with corn silage by a silage of sugarcane with 40 % of pig manure enriched with VITAFERT.

The cows fed the silage of sugarcane and pig manure produced less ruminal CH₄ than the ones which received corn silage, ratifying the modulating effect of glucose-rich feedstuffs, such as corn and sugarcane, on the production of ruminal CH₄.

The incorporation of solid pig manure enriched with VITAFERT to ensiled preparations can constitute an excellent alternative for utilizing a potentially-contaminating byproduct derived from pig production.

ACKNOWLEDGEMENTS

The authors would like to thank the Vice-Rectorate of Research and Postgraduate Studies of the University of Caldas for the resources allocated to this project.

Received: July 24, 2015
Accepted: October 12, 2015