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Pig producers continuously strive to save on feed cost as feed cost constitute 70 – 80% of production cost and even a small saving per tonnage can translate into a large saving per annum. If this saving does not interfere with growth performance it could end up as profit in the pocket of the producer.

Weaning a piglet at 21 or 28 days causes a lot of stress due to dietary, environmental and social changes. This usually results in a post weaning lag phase seen in slow growth, scouring and general unthriftiness (Ravindran & Kornegay, 1993). The piglets immunity is at it’s lowest at around 21 days while the digestive system is not fully developed and it can therefore not fully utilise the feedstuffs generally fed to older animals. This scouring and unthriftiness could also be acounted for by the changes found in the morphology of the small intestine shortly after weaning (Miller et al. ,1986; Van Beers-Schreurs et al., 1998). These changes include reduction of villus height, increased depth of lamina propria, reduced disaccharidase concentrations and reduced absorption (Dunsford et al., 1989). This decrease in villus height can be caused by pathogens (Vellenga et al., 1992), antigens (Miller et al., 1986; Li et al., 1991) or reduced feed intake (Nunez et al., 1996; Pluske et al., 1996; Van Beers-Schreurs et al., 1998). Due to weaning stress and the immature immune system newly weaned pigtlets are more susceptible to infections caused by pathogens, any infections or palatability problems could also lead to decreased feed intake which will further influence gut histology. If, on top of all this, the feed supplied to the animal contains antigens the stress could be such that production losses during this period might not be compensated for during the grower period. This could lead to direct or indirect financial losses to the producer.

The feeding of weaners has therefore been responsible for a lot of debate and controversy in the pig industry. Some producers opt for optimisation of growth while others do for maximisation of growth rate by feeding high levels of milk protein and pre cooked starches. Seve (1985) stated that the early weaning process creates an initial physiological situation requiring a particular nutrient form and balance in the feed. It has thereforee become common practice to use milk products and pre-cooked starches in creep diets (Campbell & Dunkin, 1983; Aherne & Nielsen , 1982; Campbell & Taverner, 1986 and Campbell et al., 1988). Furthermore it has been well documented that growth rate and the efficiency of feed utilisation of early-weaned piglets is appreciably better when milk proteins is used instead of soyabean proteins (e.g. Wilson & Leibholz, 1981; Walker et al., 1986; Zijlstra et al., 1996). Milk products are, however, very expensive and can cost in the order of R 16 000 per ton. The inclusion of these products can therefore lead to complete weaner diet costing up to R 4000 per ton. If a good quality, highly digestible, cheaper protein source could substitute all or part of this milk protein, it could lead to a saving of up to R 400 per ton or more. One such product which shows potential is 48% soyabean oilcake meal, also known as high protein soya bean oilcake meal. Many pig producers are, however, still reluctant to include it in their weaner diets because of problems experienced with quality control during processing and the subsequent danger of the presence of anti-nutritional factors which could lead to additional stress and digestive upsets in the newly weaned piglet.




Soyabeans and byproducts from soyabean processing are recognised as an excellent protein source in pig feeds (Danielson & Crenshaw, 1991). Soyabean oilcake meal contains all of the indispensable amino acids, although the concentrations of cystine and methionine are sub-optimal (Danielson & Crenshaw, 1991) and the digestibility of the first limiting amino acid, lysine, is low (Sohn et al., 1994).

Reduced performance in pigs fed soyabean protein has been associated with reduced digestibility of the amino acids (AA) in the diets fed (Wilson & Leibholz, 1981; Leibholz, 1986 and Viljoen & Ras, 1989). Digestibility is influenced by a number of aspects. These include the presence of anti-nutritional factors (Sauer & Ozimek, 1986; Huisman & Jansman, 1991), inclusion levels (Viljoen et al., 1998), post weaning feed intake (Makkink et al., 1994), the presence of antigens (Li et al. 1991) as well as AA damage due to processing (Marty & Chavez, 1995). Anti-nutritional factors such as trypsin inhibitor will bind to the enzyme trypsin which will render this enzyme inactive and therefore not available for hydrolysis of the protein. Decreased feed intake after weaning will affect pancreatic development and thus enzyme activity (Makkink et al., 1994) while the presence of antigens can cause certain immunological responses in early weaned pigs resulting in, amongst others, decreased villus height and thus digestibility. Another factor which influences digestibility is overheating during processing which leads to the binding of protein to certain sugars rendering it indigestible (Marty & Chavez, 1995). Many of the above mentioned aspects are intrinsic characteristics of soyabean oilcake meal and must be taken into consideration when diets are formulated.

Problems as stated above can be overcome if diets are formulated on digestible amino acid content. Results of Viljoen (1998) showed that weaner diets based on different protein sources can be utilised with equal efficiency (feed conversion) when balanced on digestible amino acid contents and not on total amino acid contents and the palatability of the diets are such that it does not influence intake. It’s good palatability and the composition of high protein soyabean oilcake meal together with modern technology with regard to feed formulation and recent information on amino acid digestibility values could possibly rectify part or all of these limitations.

A study was therefore conducted at the Agricultural Research Council’s Animal Nutrition and Animal Products Institute. The objectives of the trial were two fold. Firstly to test to what extent either milk powder, fishmeal or both as the main protein source in weaner diets, could be substituted by high protein soyabean oilcake meal (48% crude protein) and secondly to measure the effect of the different diets on the histology of the small intestine.

For trial purposes eighty piglets, 40 boars and 40 gilts, of a commercial crossbred strain were used. The piglets were weaned at 28 days and randomly allocated to four different dietary treatments, this design rendered 20 piglets, 10 per sex type, per treatment. Piglets were kept in pairs (a boar and a gilt together), in flat deck type pens (1.5 x 1.0m) with perforated metal floors and equipped with self feeders and automatic water nipples. The piglets had ad libitum access to their allotted diets and clean water.

Treatment diets were formulated to contain either milk powder and fishmeal, milk powder and high protein soyabean oilcake meal, fishmeal and high protein soyabean oilcake meal or high protein soyabean oilcake meal alone as main protein source(s). Treatments diets were further formulated on digestible amino acid basis using the ideal amino acid pattern as described by Kemm et al. (1990) for all amino acids except tryptophan where the value as listed by Wang & Fuller (1989) was used. Digestibility values as described by Rhône-Poulenc (1993) were used for all amino acids except tryptophan where the table of Degussa (1993) was used. Treatment diets and their composition are shown in Table 1.

Table 1 Ingredient and digestible nutrient composition of experimental diets.

	Unit of measure	MP* + FM**	MP + HPS***	HPS + FM	HPS
Ingredient composition (as is)
Maize meal	%	65.11	65.80	71.31	70.13
High protein soyabean oilcake meal	%	-	13.00	5.20	20.80
Skimmed milk powder	%	7.60	11.40	-	-
Fishmeal	%	>9.80		10.00	-
Wheaten bran	%	11.50	2.30	6.90	-
Sunflower oil	%	2.60	2.30	2.57	3.08
Synthetic lysine	%	0.57	0.66	0.65	0.77
Synthetic methionine	%	0.13	0.20	0.16	0.25
Synthetic tryptophan	%	0.12	0.09	0.12	0.09
Synthetic treonine	%	0.24	0.26	0.26	0.29
Monocalcium phosphate	%	0.42	1.46	0.72	1.75
Feed lime	%	1.23	1.70	1.35	1.86
Fine salt	%	0.18	0.33	0.27	0.48
Premix	%	0.50	0.50	0.50	0.50
Digestible nutrient composition
Crude protein	%	15.04	15.01	15.04	15.02
Lysine	%	1.28	1.28	1.28	1.28
Total sulphur containing aminoacids	%	0.69	0.70	0.70	0.73
Tryptophan	%	0.25	0.25	0.25	0.25
Threonine	%	0.81	0.81	0.81	0.81
DE (pig)	MJ/kg	14.50	14.50	14.50	14.50
Fat	%	6.77	5.29	6.76	6.12
Fibre	%	2.73	2.45	2.67	2.71
Calcium	%	1.05	1.06	1.07	1.04
Phosphorous	%	0.44	0.45	0.43	0.41
Sodium	%	0.21	0.20	0.21	0.20
Chloride	%	0.37	0.35	0.35	0.33

*MP – Milk powder

**FM – Fish meal

***HPS – High protein soyabean oilcake meal

The trial continued for four weeks during which time measurements were taken on a weekly basis. These measurements were animal weight, weight of feed supplied during the week and weight of feed residues at the end of the week. These values were used for the estimation of average daily gain and feed conversion ratios. At the end of the four week period five piglets per treatment were selected from the middle weight block and slaughtered. The small intestine was removed and placed in saline solution, the mesenteric web was cut and the intestine laid out straight. Samples were then taken at the terminal duodenum, mid-jejunum and distal jejunum according to the method described by (Dunsford et al., 1989; Healy et al. ,1994). Villus height and lamina propria depth was determined by means of interactive image analysis as described by Dunsford et al. (1989). Ten villus heights and ten lamina propria depth measurements were made from each of three cross sections per sample. These measurements were averaged to result in one observation.

The results obtained from this trial are shown in Table 2 and 3 below. Average daily gain was estimated by fitting a linear model (R2>0.92) to live weight data. The slope of this curve represents the ADG which was used for further data analysis. Average daily gain (ADG) did not differ significantly between sexes (boars - 376 g/d; gilts - 354 g/d) or treatments. These results are in contrast with those reported by Li et al. (1991) who found that pigs fed diets containing soyabean meal had a lower (P < 0.05) rate of gain than the control group. The differences between the current trial and the report of Li et al. (1991) could possibly be attributed to the diets of the current trial being formulated on a digestible amino acid basis. Presumably, that had not been the case in the study of Li et al. (1991).

Total intake as measured per pen and feed conversion ratios did not differ significantly (P<0.05) between treatments. This could be of significance as gut morphology, especially villus heights, is negatively influenced by reduced feed intake (Nunez et al., 1996; Pluske et al., 1996; Van Beers-Schreurs et al., 1998). As intake did not differ between treatments it can be assumed that intake did not influence villus height in this trial and that any differences observed could be attributed to the ingredient composition of the diets.

Table 2 Average daily gain (ADG), feed conversion ratio (FCR) and total intake from 4 to 8 weeks of age for different treatments

Treatment	ADG (g / day)	FCR (kg feed / kg gain)	Total intake(kg)
MP* + FM**	353 + 102	1.56 + 0.05	30.63 + 4.10
MP + HPS***	349 + 106	1.61 + 0.09	31.48 + 7.44
HPS + FM	370 +106	1.58 + 0.13	32.08 + 6.61
HPS	383 + 77	1.49 + 0.08	32.07 + 4.54

*MP – Milk powder

**FM – Fish meal

***HPS – High protein soyabean oilcake meal

Treatment had no significant (P<0.05) influence on gut histology Table 3, the only differences noted were differences between sites of sampling and specifically between samples taken from the terminal duodenum and the other areas of sampling. These differences were, however, anticipated as the histology of different parts of the small intestine is different. These results are in contrast to what was found by Dunsford et al. (1989) and Li et al. (1991) who found that feeding high concentrations of soyabean meal post weaning decreased villus height. This could be attributed to a number of factors which are not known but could include the age of the piglets at sampling, the use of digestibility values for diet formulation in the trial being reported on or differences in anti nutritional factor content of the soyabean oilcake meals.

Table 3 Villus heights (mm) measured at different anatomical sites in the small intestine

Treatment	Terminal duodenum	Mid-jejunum	Distal jejunum
MP* + FM**	1.846 + 0.37	1.670 + 0.20	1.516 + 0.19
MP + HPS***	1.804 + 0.28	1.498 + 0.35	1.416 + 0.16
HPS + FM	1.744 + 0.27	1.608 + 0.35	1.472 + 0.29
HPS	1.598 + 0.19	1.432 + 0.14	1.376 + 0.20

**FM – Fish meal

***HPS – High protein soyabean oilcake meal

From the results of the current study it can be concluded that high protein soyabean oilcake meal can be utilised successfully in diets of weaner pigs, alone or in combination with other protein sources without affecting production parameters or gut histology. This conclusion holds as long as diets are formulated on digestible amino acid basis, the soyabean oilcake meal is processed correctly and the quality known.

Appreciation is expressed to ARC – ANPI and NOPO for the funding of the project.

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C:DATAMatrixSEPTEMBER 2000Protein sources for piglets-elsje p.doc

Author: E. Pieterse – Senior Agricultural Researcher: Agricultural Research Council, Animal Nutrition and Animal Products Institute, Private Bag X 2, Irene, 0062.

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