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INTRODUCTION
In contrast with what occurs with other sources of vegetable fat such as canola meal (Myer et al. 1992), palm oil (Ocampo and Lean 1999) and corn oil (Kil et al. 2010), among others, there are scanty information concerning the feeding and nutritive value of diets rich in fat for pigs, due to the use of avocado (Persea americana Mills) products (Grageola 2010 and Grageola et al. 2010), in spite that discarded avocados have envisaged as a potential source of energy for feeding pigs (Carter 2015 and Dione et al. 2015). In this connection, it was found that nutrient digestibility at the rectal site of this type of feed was relatively high, when avocado pulp (Grageola et al. 2010), but not the entire fruit (Ly et al. 2015) was offered to pigs.
In this context, the use of the discarded entire fruit should be an interesting alternative for animal feeding, since the separation of the fruit pulp from seed and peel (Grageola 2010) is not practical. On the other hand, avocado seeds and peels disposal should create a new problem of environmental pollution, in those sites where either fruit processing plants of great markets are placed. Instead, it has been found that the fresh and ground fruit, in form of fresh avocado paste, could be mixed with the other diet components and given as such to pigs (Frànquez et al. 2017). However, in the knowledge of the authors, there are not available data concerning digestibility indices related to the use of the entire, ground and fresh discarded avocado fruits in form of paste, for feeding pigs.
The objective of the present study was to report experimental data concerning rectal digestibility and fecal output of fattening pigs given avocado paste as energy source.
MATERIALS AND METHODS
Sixteen Yorkshire x Landrace pigs, castrated males and females in equal proportion and averaging 67.0 kg initial weight, were allotted at random into two treatments consisting in cereal based diets formulated to contain 0 and 21 % fresh entire avocado (Persea americana Mills) paste. The fruit were of the Hass variety, from Nayarit, Mexico. The paste was composed of the entire, discarded and ripe fruits and contained crude fiber, 14.31 %, ether extract, 49.14 % and crude protein, 9.16 % in dry basis, respectively. The characteristics of the diets are shown in table 1.
Table 1 Composition of the diet (in dry basis)
| Fresh entire avocado paste, % | ||
|---|---|---|
| 0 | 21 | |
| Ingredients, % | ||
| Soy bean meal | 15.5 | 16.6 |
| Sorghum meal | 81.5 | 60.0 |
| Fresh avocado paste | - | 21.0 |
| CaPO4H.2H2O | 1.0 | 0.8 |
| CaCO3 | 0.5 | 0.4 |
| NaCl | 0.5 | 0.4 |
| Vitamins and trace elements1 | 1.0 | 0.8 |
| Chemical composition | ||
| DM | 86.58 | 58.24 |
| DM basis, % | ||
| Ash | 4.23 | 4.38 |
| Organic matter | 95.77 | 95.62 |
| Crude fiber | 3.01 | 5.77 |
| Crude fat | 3.16 | 14.51 |
| Nitrogen free extract | 76.16 | 61.25 |
| Nx6.25 | 13.44 | 13.94 |
| Energy, kjoule/g DM | 18.54 | 20.53 |
1 Following NRC (2012) recommendations
The animals were housed individually in pens with cement floor and provided of a feeding trough and a drinker. These pens were located in a ventilated pig house. The entire avocado fresh paste was mixed with the other dry components during milling the diet every three days, and thereafter was given ad libitum to the animals. After 49 days on test, when the animals attained on average 115 kg live weight, a fecal, sampling was conducted in order to determine rectal digestibility of nutrients by the indirect method (Van Keulen and Young 1977). Fecal samples were conveniently homogenized and frozen at -20ºC until analysis.
In the thawed samples, DM, ash, crude fibre and N were determined in feed and feces following AOAC (2005) recommendations. The acidified ether extract procedure was used to determine crude fat. Acid insoluble ash was estimated following Van Keulen and Young (1977) recommendations. The digestibility per se of the fresh entire avocado paste was calculated by the method of difference (Crampton and Harris 1969) assuming that there were no interactions among the different compounds of the dietary formula. The fecal output of materials was identified taking into account the indigestibility indices of the diets (100 - DM digestibility, in %), following to Ly et al. (1998).
Data corresponding to nutrient digestibility and fecal output of materials of the two diets were compared and subjected to one-way analysis of variance for the means comparison and the level of significance was identified as P<0.05 (Steel et al. 1997). In the required cases, the matrix of correlation of Pearson was utilized to explore the presence of interdependence among several digestive indices. All data were processed using procedures of the statistical package of SAS (1999).
RESULTS AND DISCUSSION
Table 2 lists data concerning rectal digestibility of nutrients. The diet containing 21% of avocados determined a significant (P<0.05) decrease of rectal digestibility of DM, organic matter and crude fibre (81.4, 83.9 and 27.4%, respectively) with respect to the control diet (84.3, 86.9 and 36.4%, respectively) but it was not true neither for rectal N digestibility (78.2 and 83.2%; P>0.10) nor for acidified ether extract digestibility (65.3 and 83.0%; P=0.001). In the particular case of the acidified ether extract, the diet containing 21% of fresh avocado paste showed a very high rectal digestibility.
Table 2 Nutrient rectal apparent digestibility in fattening pigs fed fresh entire avocado paste based diets
| Fresh entire avocado paste, % | SE ± | P | ||
|---|---|---|---|---|
| 0 | 21 | |||
| Number of animals | 8 | 8 | - | |
| Rectal digestibility, % | ||||
| Dry matter | 84.3 | 81.4 | 1.25 | 0.002 |
| Ash | 32.7 | 39.9 | 0.23 | 0.001 |
| Organic matter | 86.9 | 83.9 | 1.34 | 0.002 |
| Crude fiber | 36.4 | 27.4 | 4.15 | 0.049 |
| Acidified ether extract | 65.5 | 83.0 | 4.00 | 0.001 |
| NFE | 90.1 | 85.0 | 1.11 | 0.001 |
| Crude protein | 83.2 | 78.2 | 3.10 | 0.152 |
Since Grageola et al. (2010) did not report any difference between diets containing either 0 or 20% of fresh avocado pulp, the differences encountered in the herein described findings could be attributed to the relatively higher cell wall content of the fresh entire avocado paste, which in turn contained avocado seeds and peels, accounting for some 14.3% crude fibre. In this connection, Ly et al. (2015) noted low rectal digestibility of avocado seeds and peels as compared to avocado pulp, when in situ digestibility of these products were investigated by the mobile nylon bag technique used in pigs. On the other hand, more experimental evidences support the depressive effect caused by peels and seeds from avocados when these materials are included in pig diets (Fránquez et al. 2018 and Grageola et al. 2018).
Calculations of rectal digestibility of nutrients of fresh avocado paste in pigs, as measured by difference (Crampton and Harris 1969) are listed in table 3. These results indicated that the acidified ether extract exhibited a high rectal digestibility in pigs fed on fresh avocado paste. In comparison, N and crude fibre digestibility showed relatively low values.
Table 3 Nutrient digestibility values of fresh entire avocado paste in pigs (in percent)
| x | SE ± | |
|---|---|---|
| n | 8 | |
| Dry matter | 74.0 | 12.1 |
| Ash | 67.1 | 15.5 |
| Organic matter | 77.0 | 13.4 |
| Crude fibre | 31.4 | 18.8 |
| Acidified ether extract | 80.3 | 13.3 |
| N | 50.0 | 7.7 |
The negative influence of crude fibre on rectal digestibility of several nutrients is well known (Le Goff et al. 2002, Hansen et al. 2006, Bindelle et al. 2008 and Wenjuan et al. 2013), and results concerning rectal digestibility of fresh entire avocado paste could be explained by the high level of crude fibre noted in this avocado product. These results were not found by Grageola et al. (2010), in growing pigs fed with fresh avocado pulp, with very low in cell wall content. In the particular case of the rectal digestibility of the fat fraction, pigs fed on fresh entire avocado paste based diets did not appear to be negatively influenced by the fibre fractions in the feed. This contradictory result could be in line with some indications suggesting variable consequences of fat digestibility in dependence of the nature and amount of fibre in the diet (Kil et al. 2010 and Wenjuan et al. 2013).
In this research, it was encountered that all measured digestive indices were significantly (P<0.05) correlated among them, except crude fibre and N rectal digestibility (table 4). In particular, DM and organic matter digestibility had the highest R values as it has been often found elsewhere (Ly 2008), therefore suggesting that rectal DM digestibility can predict more accurately digestive utilization of energy, as compared to that protein.
Table 4 Pearson correlation matrix for digestibility indices of finishing pigs fed diets of fresh entire avocado paste (n = 16)
| DMD | OMD | CFD | |
|---|---|---|---|
| DMD | |||
| OMD | 0.999 | ||
| CFD | 0.732 | 0.729 | |
| ND | 0.711 | 0.711 | 0.377 |
DMD, OMD, CFD and ND express DM, organic matter, crude fibre and N rectal digestibility in the same order. For details, see text
P<0.05 for r>0.502 in absolute values
Table 5 shows rectal output of materials in the pigs. There was a not significant (P=0.050) trend toward an increase in rectal output of fresh materials, 614 and 740 g/kg DM intake. The same effect of the introduction of fresh avocado paste in the diet was observed for dry material and water in feces was noted, whereas fecal N output was significantly (P=0.001) higher in pigs fed the fruit paste when compared to the animals of the other treatment. Overall, this same relationship has been observed in animals fed conventional diets (Van Thi Khanh Vu et al. 2008). The increase in rectal output of materials in pigs fed a fresh avocado paste could be a consequence of the increase in the crude fibre content of the diet. Besides, it has been found that dietary fat may reduce DM, organic matter and energy in the pig (O'Doherty et al. 2002 and Leek et al. 2004), probably due to a decrease in microbial activity in the large intestine (Lewis et al. 2001).
Therefore, the increase in fecal output of materials could be present in individuals fed avocado products, rich in fat and indigestible fiber. In this sense, the manipulation of animal excreta could be of practical interest in order for manure disposal, either in integrated, small farming system or in large populations of pigs subjected to an industrial mode or production.
Table 5 Fecal output of materials in finishing pigs fed fresh entire avocado paste based diets
| Fresh avocado paste, % | SE ± | P | ||
|---|---|---|---|---|
| 0 | 21 | |||
| Number of animals | 8 | 8 | - | |
| Fecal DM, % | 25.78 | 25.12 | 0.79 | ‘0.233 |
| Fecal N, % DM | 1.91 | 2.07 | 0.22 | 0.454 |
| Fecal output, g/kg DM intake | ||||
| Fresh material | 614 | 740 | 61 | 0.050 |
| Dry matter | 157 | 186 | 13 | 0.050 |
| Water | 457 | 554 | 49 | 0.050 |
| N | 3.12 | 4.89 | 0.50 | 0.001 |
The current research revealed that the inclusion of peel and seeds from discarded avocados determines a noteworthy decrease in rectal nutrient digestibility of feeds when pigs are fed on diets containing this type of non-conventional feedstuff. A suggestion is made to study procedures, as those described by De Vriesa et al. (2012), then allowing to increase indices of rectal digestibility in pigs fed on fresh paste of entire avocados.
