INTRODUCTION
Soybean meal (Glycine max) is a widely used ingredient in livestock feed for its excellent protein content. Its production in Mexico is for use in the livestock industry, and is limited by the small scale of domestic soy bean production. Only 3 % of soybean meal demand is met by domestic production, the remaining 97 % coming from imported raw material(1). Despite its excellent protein content, its antinutritional factor content means soybean meal can only be used as an alternative protein source at low levels in poultry diets(2). Often, it is used together with canola (Brassica rapa) meal since they complement each other’s nutritional properties. Canola meal has lower protein and lysine contents than soybean meal, but higher methionine and cysteine contents(3).
Antinutritional factors have been an issue in development of canola. Rapeseed (Brassica napus) is the parent species to canola, but has not been widely used in livestock applications due to its erusic acid and glucosinolates content, which negatively affect productive performance. Modifications to canola created the new “00” varieties, so called for their extremely low glucosinolate content (<20 µg/g) and trace erusic acid content(2,4,5).
Canola meal has been used successfully in diets for hens at up to 20 % to replace from 25 to 30 % of soybean meal, without affecting egg yield or quality(6). However, sensory evaluations of eggs from hens fed diets containing 12 or 20 % canola meal identified a fishy odor in 28 % (range = 15-40) of raw brown eggs and 18 % (range 10-30) of raw white eggs(7). When cooked, the odor in the brown eggs was noticeably more intense than in a control treatment or in white eggs. In a study of canola meal (10, 15 and 20 %) used in diets for ISA Brown hens, no effects were observed on egg production or animal mortality(8). A fishy odor was present, however, at the 15 and 20 % substitution levels, but diminished after storage at 10 °C for two to five weeks. No differences between treatments were observed in the sensory analysis. Presence of the alkaloidal amine sinapine in canola is the cause of the fishy odor. It is problematic in a small percentage of semi-heavy hens that lack the enzyme trimethyl amino oxidase needed to degrade this compound and prevent its deposition in the egg(2).
Use of canola meal in laying hen diets has been shown to affect egg quality parameters. In a study of 8, 10 and 20 % inclusion levels of canola paste in diets for ISA Brown hens, overall egg weight was found to decrease (62.9, 61.8, 60.7 g, respectively), and yolk weight was greater than albumin weight at the 20 % level(9). Values for Haugh units (HU), and shell strength and thickness were unaffected. Sensory analysis in the same study found egg flavor and acceptability to be lower in the canola meal treatments. Use of 10 % canola meal in diets for hens was reported to increase shell weight and lower yolk weight, but had no effects on Haugh units, or shell thickness and resistance(10). Lower canola meal inclusion levels (0, 4, 6 and 8 %) produced no effects on egg production yield and internal and external quality characteristics(11).
The present study objective was to evaluate the effect of three canola meal inclusion levels (6.6, 13.2 and 26.4 %) in sorghum-soya based diets for semi-free range ISA Brown laying hens on egg production yield, yolk pigmentation and organoleptic quality.
MATERIAL AND METHODS
Two experiments were run using ISA Brown hens in a semi-free range production system. Animals were housed in experimental pens in a natural environment at the Center for Poultry Production Teaching, Research and Outreach (Centro de Enseñanza, Investigación y Extensión en Producción Avícola) at the National Autonomous University of Mexico (Universidad Nacional Autónoma de México – UNAM). Each corral was divided into two sections, one containing straw beds and the other an open area with grass. Access to the grass area was restricted to 0900 to 1200 throughout the experimental period. Each pen contained four feeders and two bell drinkers. Photoperiod was 16 h light: 8 h dark. Both feed and water were made freely available throughout the experimental period.
Both experiments involved 405 red semi-heavy ISA Brown laying hens. Exp 1 lasted for 49 d
and hens began the experiment at 30 wk of age. Exp 2 lasted for 56 d and hens began at 45 wk of age. In each experiment, the design was completely random, with three treatments including three replicates of 45 animals each. The animals were housed in pens with an enclosed area providing 0.73 m2 per animal and a grazing area providing 1.3 m2 per animal.
Diets were formulated using sorghum and soybean meal (SP), with different canola meal
substitution levels (Tables 1, 2). Replacement of SP was done based on percentage of protein content (25, 50 and 90 %). Based on canola protein content, the resulting substitution levels were 6.6, 13.2 and 26.4 % canola. The treatments in each experiment were as follows:
Experiment 1:
Treatment 1) Sorghum-soya diet (ME= 2,750 kcal/kg, 16 % CP).
Treatment 2) Sorghum-soya diet + 13.2 % canola (ME= 2,750 kcal/kg, 16 % CP).
Treatment 3) Sorghum-soya diet + 26.4 % canola (ME= 2,750 kcal/kg, 16 % CP).
Experiment 2:
Treatment 1) Sorghum-soya diet (ME= 2,750 kcal/kg, 16 % CP).
Treatment 2) Sorghum-soya diet + 6.6 % canola (ME= 2,750 kcal/kg, 16 % CP).
Treatment 3) Sorghum-soya diet + 13.2 % canola (ME= 2,750 kcal/kg, 16 % CP).
Weekly data were collected on laying percentage, average egg weight, egg mass, feed intake, feed conversion and percentage mortality. At the end of each experiment, 30 eggs per treatment were collected to evaluate quality characteristics, including Haugh Units, shell thickness, and yolk pigmentation (using the DSM colorimetric fan).
Organoleptic evaluations were also made of the eggs. Ten eggs per treatment were taken to the Animal Nutrition Area of the Salvador Zubirán National Institute of Medical and Nutrition Sciences (Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán), Mexico City. Tests were run using 29 untrained panelists who confirmed they were regular egg eaters. They evaluated the eggs while seated in individual cubicles under white light, in the institute’s sensory evaluation laboratory. Panelists expressed their like or dislike of yolk color and egg flavor using two questionnaires of categorized scales per panelist. Each category was divided into scores of 1 to 5: 5= like very much; 4= like; 3= indifferent; 2 dislike; 1= dislike very much. Yolk color was evaluated by presenting each panelist with a tray (corresponding to a treatment) of four transparent molds each containing a yolk, and the corresponding questionnaire. Egg flavor was evaluated by presenting the panelists with a plate containing three samples of egg prepared by cooking scrambled without salt or oil. They were also given white bread and water to eat after each tasting. Questionnaire data was entered into a database and a Friedman test applied to them with the SPSS statistics package(12).
Production behavior data from both experiments were processed with a completely random ANOVA, and a Tukey test to compare the means of statistically different (P<0.05) treatments. All statistical analyses were done with the SPSS statistics package(12).
RESULTS
Performance variables (i.e. laying percentage, egg weight, feed intake, egg mass and feed conversion) did not differ (P>0.05) among treatments (Tables 3, 4). The same held true for the egg quality variables (Haugh Units, yolk pigmentation and shell thickness), with no differences (P>0.05) observed among treatments (Tables 5, 6).
In contrast, some differences between treatments were observed in the sensory tests. In Exp 1, yolk color did not differ (P>0.05) between treatments, but egg flavor in the 0 and 13.2 % canola treatments was more widely accepted (P<0.01) than in the 26.4 % canola treatment (Table 7). For Exp 2, no differences (P>0.05) were observed for either variable in either of the canola treatments (6.6 and 13.2 %) (Table 8).
DISCUSSION
Addition of canola at different concentrations (6.6, 13.2 and 26.4 %) to the sorghum-soya meal diet had no effect on productive parameters. This coincides with previous studies such as one evaluating Dekalb SCWL hens fed a wheat-soya diet with 10 or 20 % added canola, in which neither egg production nor animal mortality were affected(13). However, feed intake did decrease (102.2 vs 99.8 g) in the 20 % canola treatment. In another study involving Bovans Brown hens fed corn-soya diets with 4, 6 or 8 % added canola, no effect (P>0.05) was observed on performance compared to a control(11).
Other studies using ISA Brown hens have reported variations in some parameters. Using corn-soya diets with 8 or 10 % added canola one study found no differences in laying percentage but egg weight dropped significantly in the 10 % canola treatment(14). Addition of salt (3 mg/kg feed) to the 10 % canola treatment somewhat improved egg weight compared to the 10 % canola containing no added salt (62.1 vs 60.7 g). In another study using ISA Brown hens, addition of 10, 15 or 20 % canola to sorghum-soya diets had no effect on egg production, although average egg weight did decrease (P<0.05) in the 15 and 20 % treatments(8).
Much more variable results than observed in the present study have been reported elsewhere.
In a study of addition of 5, 10 or 15 % canola to sorghum-soya diets fed Leghorn hens, the 15 % treatment was found to negatively affect (P<0.05) laying percentage and egg weight(15). Another study using Leghorn hens fed diets containing 5, 7.5 or 10 % non-genetically modified canola showed that egg production dropped (P<0.05) in the 10 % treatment, although egg weight exhibited no changes.
In both Exp 1 and Exp 2, Haugh Units, yolk pigmentation and shell thickness values did not vary (P>0.05) among treatments. This agrees with other studies in which addition of 5, 7.5 or 10 % non-genetically modified canola had no effect on Haugh Units values(16), and addition of 5, 10 or 15 % canola did not affect Haugh Units values or shell thickness(14). In a study using Hy-Line W36 hens fed diets containing 5, 10 or 15 % canola, no effect was observed on Haugh Units values or shell thickness(10).
Unlike the productive parameters, egg flavor clearly varied between treatments in Exp 1: the control and 13.2 % canola treatment were preferred (P<0.01) to the 26.4 % canola treatment. This coincides partially with egg flavor results in a study of Bovans Brown hens fed diets containing 4, 6 or 8 % canola in which the 8 % canola treatment eggs had inferior (P<0.05) flavor compared to the other treatments(11). Using boiled eggs from hens fed diets containing 8 or 10 % canola, another study found differences in flavor and aroma between the control treatment and the canola treatments(14). The fishy odor that lowers consumer acceptance was also notable in cooked and raw eggs from Hy-line Brown hens fed diets including 12 or 20 % canola(7); the aroma was less pronounced in cooked eggs than in raw ones.
Sinapine is known to be the primary form of choline in canola, and is a precursor of trimethylamine, which can produce the fishy odor and flavor in eggs from semi-heavy hens fed diets containing canola(17,18,19). In an effort to determine how much sinapine is needed to cause this phenomenon, it was found that inclusion of more than 1 g sinapine per kilogram feed in diets for semi-heavy hens will cause eggs to have this undesirable odor and flavor(20).
Yolk color was unaffected and no fishy odor or flavor was reported in eggs from Exp 2, in which the highest inclusion was 13.2 %. The yolk color results agree with a study in which ISA Brown and White Leghorn hens were fed diets containing 10, 15 or 20 % canola(8); no changes in color perception were noted in any of the treatments. This study did not include flavor evaluations.
CONCLUSIONS AND IMPLICATIONS
Inclusion of canola meal at three levels (6.6, 13.2 and 26.4 %) in replacement of the protein (25, 50 and 90 %) in soybean meal in isoproteic and isocaloric diets fed ISA Brown hens had no effect on performance, Haugh Units values, yolk color and shell thickness. However, replacement of 90 % of the soybean meal protein (26.4 % canola meal replacement level) imparted a fishy odor to the eggs.
This article was originally published in Revista Mexicana de Ciencias Pecuarias 2016;7(2):173-184.
