2.0 The Effect of Peas on the Performance of Pigs
2.1 Growth Performance of Weanling Pigs Fed Peas
The most difficult test for the acceptability of an ingredient is its use in diets for newly weaned pigs. At this critical stage, ingredients need to be not only highly digestible, but also highly palatable. In a recent Canadian trial, peas were included up to 200g kg-1 in a diet for weaned piglets (5.8-6.9 kg). No differences in feed intake (FI),average daily gain (ADG) or feed/gain (F/G) were found in an isoenergetic and isolysine diet containing peas as compared to a SBM based diet (Kehoe et al. 1995 {1280}). Even higher levels (300g kg-1) of peas were successfully incorporated into diets of 10.9 kg liveweight pigs. Results were equal to a SBM control (325g kg-1), however supplementation of the pea diet with 1.2g kg-1 DL-methionine significantly increased all parameters (Gatel et al. 1989 {1404}). Similarly a German experiment concluded that peas could be included up to 300g kg-1 in piglet diets (10-25kg) (Bohme 1988 {1427}). These results indicate that performance of weanling pigs is not adversely affected by the inclusion of peas ( Pisum sativum hortense) in the diet even at relatively high levels.
2.2 Growth Performance of Grower-Finisher Pigs Fed Peas
The performance of grower finisher pigs is, in most cases, unaffected by the inclusion of peas in isocaloric and isonitrogenous diets. In some instances performance is even enhanced over a traditional SBM based diet. In three experiments comparing a total of 12 different diets representative of typical on-farm mixes and more complex commercial diets, the inclusion of peas between 200 and 450 g kg-1 resulted in no significant differences in growth performance when amino acids and digestible energy were balanced. It was noted that in some grower diets, ADG lagged behind that of the control however, this was overcome by significantly (P<0.05) improved growth in the finisher (Gatel et al. 1991 {1386}). This response, possibly indicating a restriction of secondary amino acids (methionine, cysteine), has been observed before and prompted (Jaikaran et al. 1995 {1282}) to establish a pea experiment with or without supplemental methionine and threonine. Even with pea levels of 500g kg-1 for growing pigs (21-53 kg) significant differences were not found between the experimental diets and the control for ADG, FI and F/G. However, significant improvements over the control were seen in ADG and FC with the addition of synthetic methionine but not threonine. Supplementation of the finisher (53-102 kg) diet containing 400 g kg-1 peas resulted in no significant performance differences from the control. Over the entire grower-finisher period no differences were seen among any treatment suggesting that methionine supplementation of pea based diets is only beneficial to about 50 kg liveweight.
The importance of ingredient analysis for proper diet formulation is demonstrated in a trial by Edwards et al. (1987 {1442}). Relying only on published values for pea nutrients, the authors were unable to obtain performance equivalent to a SBM control, especially when peas made up 300 or 450g kg-1 of the diet for grower pigs. Following chemical analysis, diets were reformulated and pigs fed diets containing 300g kg-1 peas performed equally to their SBM counterpart. Since peas rarely undergo processing prior to feeding, their nutrient composition is subject to the natural variability of environment and genetics. To ensure maximum pig performance, it is imperative to ascertain the nutrient composition of peas before feeding.
A natural method for increasing the methionine content
of pea diets is to blend it with canola meal. This combination
offers the benefit of a complementary amino acid profile at a
lower crude protein. A Finnish study using market pigs (25.5
-105 kg) found daily gain and feed conversion ratio unaffected
when protein content was lowered and the diet balanced with synthetic
lysine and threonine in a 1/3 pea 2/3 rapeseed meal diet (Valaja
et al. 1993 {1348}). Matre et al. (1989 {1396})
found better growth rates when pea diets were supplemented with
RSM or herring meal as opposed to synthetic amino acids. A Canadian
study, using pea screenings and CM (Castell and Cliplef 1993 {1331})
found overall growth and feed conversion were not different for
market pigs (25-97 kg) fed either a blend of pea screenings and
CM (124 and 141 g kg-1 or 61 and 283 g kg-1
respectively) or pea screenings alone (424 g kg-1)
or SBM (150 g kg-1) or CM (187 g kg-1).
Poorer performance was observed with the pea and CM diets in
the grower phase (<63 kg), however in the finishing period,
all CM and pea diets were superior to the SBM diet. Using regression
analysis the calculated maximum growth rate (in accordance with
the experimental conditions) would have been achieved with a diet
containing 180g kg-1 peas and 100g kg-1
CM.
Pea screenings are a derivative of the cleaning process
when peas are prepared for human consumption. Composed of undersized,
off-color or broken seeds, pea screenings are an excellent source
of nutrients for pigs and do not vary in composition from peas
unless the sample is diluted with cereal, weed or other seeds.
Using pea screenings composed of only peas (0, 110, 220 and 330g
kg-1) from two Canadian pea varieties (B.C. Blues [green]
and Century [yellow]) no significant differences in the live performance
means or carcass yield between any of the treatments were found.
Daily gains were (878, 887, 828, 857g) B.C. Blues and (899, 863,
859, 832g) for Century for pigs (24-85 kg) (Castell et al.
1988 {1431}). These results lend credence to those interested
in replacing imported SBM with locally grown ingredients.
Although current management systems in intensive
swine production do not readily allow for the feeding of whole
crop (entire plant including seed) ingredients, studies have evaluated
the use of whole crop peas in swine diets. Lund et al.
(1981 {1472}) determined the ME value of whole crop peas to be
10.7 MJ kg-1 DM with a protein content of 125g kg-1
DM. Compositional changes as the crop matures were established
by Graham and Aman (1987 {1445}). They found nutrients in late
harvest originate mainly from the pea cotyledon and are readily
absorbed in the small intestine. However the remaining residue
entering the large intestine contained mainly senesced and lignified
leaves and stems that are very resistant to microbial attack.
In earlier harvest, protein and starch (mainly enclosed within
the cell walls of the stems and leaves) passed the ileum and were
susceptible to fermentation in the large intestine conferring
an undetermined advantage to the pig. The authors advised that
maximum benefit of whole crop peas to pigs was achieved when seeds
are near maturity (Graham and Aman 1987 {1445}).
In a study conducted in Germany where peas were fed
at 3 levels to breeding sows. Ten percent (100g kg-1)
peas had a positive effect on the number of born and reared piglets;
200g kg-1 peas had an indifferent and 300g kg-1
peas had a more or less negative effect on the number of
born (von Leitgeb et al. 1994 {1306}). In contrast, Ogle
and Anner (1993 {1321}) found no significant effects on mean litter
size, piglet mortality or piglet growth rates, and no interaction
between treatment and litter number when 100g kg-1
of white flowered pea varieties replaced soybean meal, barley
and wheat. The diets were balanced so that the calculated lysine
and metabolizable energy contents of the experimental and control
diets were equal and were fed in both gestation and lactation
over four production periods. Mean net gestation weight gains
as well as live-weight losses during lactation were similar for
both groups as were changes in backfat thickness followed the
same pattern. An earlier study using higher levels of peas 240g
kg-1 during lactation and 160g kg-1 during
gestation found similar results with no effect on reproductive
performance (piglet mortality, average number of weaned pigs,
weaning to rebreeding interval and cull rates) or sow body weight
(Gatel et al. 1988 {1437}).
3.0 Carcass Composition of Pigs Fed Peas
Information on carcass composition of pea fed pigs
is varied since little research has been applied to this area.
In two out of the three experiments (8 out of 12 diets) the inclusion
of peas resulted in an increase in dressing percentage (P=0.04)
(Gatel et al. 1991 {1386}). An evaluation of carcasses
found loin lean tissue from pea fed pigs had relatively more (P<0.01)
marbling and saturated fat (lower iodine absorption number) than
SBM or CM fed pigs. Sensory evaluations of the pork were not
different between any of the diets (Castell and Cliplef 1993 {1331}).
This paucity of information and growing consumer concern illuminates
carcass composition as an area for further research.
The versatility of peas as a feed ingredient is evidenced
by the range of diets into which they can be successfully incorporated.
From weanling pigs to sows, pea inclusion in the diet results
in performance equal to or better than a traditional SBM diet.
Even at elevated levels of inclusion (500g kg-1) feed
intakes, weight gain and feed conversion remain unaffected. These
positive performance results, coupled with increasing pea acreage
make peas a desirable and economical alternative to imported SBM.