The first experiment on ensiling sweet potato
(SP) included 5 different ratios of sweet potato roots (SPR) and
vines (SPV): 70, 60, 50, 40 and 30% of SPR with 30, 40, 50, 60 and
70% of SPV on a dry matter basis, giving treatments SP7:3, SP6:4,
SP5:5, SP4:6 and SP3:7, respectively. During ensiling all of the
sweet potato silages maintained good quality, with a constant
yellow colour of SPR and a dark green colour of SPV. The silage on
all treatments had a good smell at all times up to 84 days. Dry
matter, crude protein, neutral detergent fiber (NDF), calcium, and
phosphorus contents did not change during the 84 days of ensiling
in all treatments. The pH value in all treatments decreased rapidly
in the first week (from around 6.4 to around 3.8) (P<0.01) and
continued to decrease up to day 14 (to around 3.6), then remained
low until 84 days. Acetic and lactic acid increased quickly in the
first 2 weeks (P<0.01) and then remained constant to 84 days
(P>0.05). As the SPR level of the SP silage increased pH values
decreased (during the 84 days of ensiling) and lactic acid
increased during the 2 first weeks of ensiling (P<0.05). The
NH3-N content in all treatments fluctuated at around
2-3% of total nitrogen during ensiling (P>0.05). All of the
treatments resulted in good quality products.
The second experiment was a digestibility trial
(on-station) to evaluate the digestibility of sweet potato vine
(SPV) and root (SPR) silage and meal, and was done according to a
3*3 Latin Square design with 3 treatments on 3 castrated F1
crossbred fattening pigs with an initial mean live weight of 35 kg.
Treatment SP0 was a basal diet, that was replaced by sweet potato
meal (SPM) or sweet potato silage (SPS) at a level of 50% (DM
basis) to give treatments SPM50 and SPS50. The SPM and SPS were
mixtures of 50% SPV and 50% SPR (DM basis). The digestibility of
DM, CP, CF and NDF in both treatments SPM50 and SPS50 was about 90,
77, 92 and 89%, respectively, of treatment SP0, and all of these
differences were significant (P<0.05). There were
non-significant differences in the digestibility of almost all
nutrients between SPM50 and SPS50 as well as between SPM and SPS
(P>0.05), except for organic matter (OM) digestibility that was
significantly higher for SPS50 and SPS compared to SPM50 and SPM
(P<0.05).
The final experiment was an on-farm feeding trial to determine the effects on performance of including a mixture of SPV and SPR, in both ensiled and dried form, in diets for F1 crossbred fattening pigs (Mongcai sow x Yorkshire boar). The trial was conducted with a total of 40 F1 crossbred pigs (20 females and 20 males) of 15 kg average initial live weight, at 4 farms as replicates. At each farm, 10 pigs were kept in 5 pens (1 male and 1 female in each pen), with each pen representing a treatment. The pigs were fed diets consisting of mixtures of the basal diet (100%, 60%, 40%, 60% and 40%) and the SPM or SPS (0%, 40% SPM, 60% SPM, 40% SPS and 60% SPS) to give treatments SP0, SPM40, SPM60, SPS40 and SPS60, respectively. Dry matter intake decreased when sweet potato silage or meal increased in the diets. However, there was no significant difference in intake between SP0 and SPS40, while differences between SP0 and the other diets were significant (P<0.05). Pigs on the control diet (SP0) performed significantly better than on all other treatments as regards average daily gain (ADG) and feed conversion ratio (FCR). The diets SPM40 and SPM60 resulted in significantly higher ADG and lower FCR compared to the diets SPM60 and SPS60 (P<0.05), while the differences in ADG and FCR between SPM40 and SPS40 were not significant, but between SPM60 and SPS60 were significant (P<0.05). The back fat thickness of the pigs ranged from 1.99 to 2.28 cm but between- treatment differences were not significant (P<0.05). The feed cost was highest for SP0 and lowest for SPS60. The labour cost for processing SPM was higher than for SPS. The feed cost/kg weight gain was the lowest for SPS40 (7,761 VND), that was 93.0, 99.7, 98.5 and 97.3 % of the value for SP0, SPM40, SPM60 and SPS60, respectively.
Key words: Sweet potato roots, Sweet potato vines,
Silage, Dry matter, Crude protein, NDF, Growing F1 pigs, Sweet
potato meal, Sweet potato silage, Digestibility, Feed intake,
Average daily gain, Feed cost.