Detoxification of castor meal

Three methods described by Anandan et al⁷ were used to detoxify the castor meal:

Autoclave method (A), chemical method (Ch), and their combination (ACh).

Autoclave method

Forty samples of castor meal of 1,000 g each were placed in a Felisa autoclave, applying one atmosphere of pressure for 60 min, at 121 ºC. They were sun-dried 48 h and stored at room temperature⁷.

Chemical method with calcium hydroxide Ca(OH)₂

Twenty castor meal samples of 1,000 g each were treated with calcium hydroxide at a concentration of 40 g/kg, for 8 h and then they were sun dried 48 h, grounded with a hand mill (Estrella®, Mexico), and stored at room temperature. The calcium hydroxide was diluted in water before being mixed with the castor meal⁷.

Combination of autoclave and chemical methods

The autoclave and calcium hydroxide methods described by Anandan et al⁷ were used in consecutive order.

Birds and treatments

The experiment was conducted at the poultry facilities of the Postgraduate College (Colegio de Posgraduados), Campus Montecillo, Texcoco, State of Mexico. Located at an altitude of 2,247 m asl¹¹. Five treatments (experimental feeds) were evaluated: control diet corn and soybean meal (SM), non-detoxified castor meal (NDC), autoclaved castor meal (AC), chemical method treated castor meal (ChC) and autoclave and chemical methods treated castor meal (AChC). Each treatment was randomly assigned to seven experimental units with 10 chickens each. The birds were housed in 1.5 m² pens with wood litter shavings. A 23 h light regime was provided during the first two weeks and then decreased to 12 h. The ambient temperature at the beginning of the experiment was 33 °C, which was reduced by 2 °C per week to a temperature of 21 °C. This study was conducted in accordance with the Guide for the Care and Use of Experimental Animals approved by the General Academic Council of the Postgraduate College.

The feeding program was divided into two phases: starter diet (1-21 d) containing: 3,025 kcal of metabolizable energy (ME) kg^-1, 22 % of crude protein (CP), 0.96 % of Ca and 0.48 % of available P, and finisher diet (22-42 d) containing: 3,100 kcal of ME kg^-1, 19 of CP, 0.80 % of Ca and 0.40 % of available P (Table 1). The diets were formulated to cover or exceed the nutritional recommendations of the Ross 308 line¹².

Productive performance, animal welfare and carcass yield traits

Feed consumption, weight gain, and feed conversion ratio were recorded from day one through d 42. At d 43, 35 birds per treatment were randomly selected to evaluate walking ability, valgus-varus angulation, and prostrate latency. Walking ability was evaluated according to the methodology described by Kestin et al¹³ as modified by Garner et al¹⁴. The measurement was carried out simultaneously by two assessors who rated each bird on a scale of 0 to 5 where: 0. Birds that walk normally; 1. Birds with a slight difficulty for walking; 2. Birds with a defined and identifiable defect in their gait, but whose injury or damage does not impair movement or consumption of food and water; 3. Birds with an obvious defect that affects the ability to move; 4. Birds with a severe defect, and 5. Birds incapable of walking.

Valgus-varus angulation was evaluated according to the methodology described by Leterrier and Nys¹⁵. Depending on the tibia-metatarsal angle, 4 scores were defined: 0, normal chicken; 1, chicken with low angulation (tibia-metatarsal angle between 10 and 25 °); 2, bird with evident angulation (angle between 25 and 45 °) and 3, severe angulation (angle greater than 45 °).

The birds were subjected to the latency-to-lie-down test as described by Berg and Sanotra¹⁶. This test is based on the chicken's body contact with water, which is a novel and adverse experience for broilers. The birds were placed in a plastic container with water at 32 °C at a height of 3 cm. The time elapsed in seconds until each bird lay down was recorded. If the bird stood up after 600 seconds, the test was stopped. The birds were assessed individually, without visual contact among them.

At 42 d of age, seven birds per treatment were randomly selected in order to assess the carcass yield, breast weight and leg-to-thigh weight. Feed was withdrawn 8 h before slaughter, and the chickens were slaughtered using a stun knife (model VS-200, input power 120 V-1 A, output power 50 V-0.1 A, Midwest Processing Systems, Minneapolis, MN, USA), according to the Mexican Official Standard NOM-033-SAG/ZOO-2014¹⁷.

Development of the digestive system and accessory organs

The chickens selected for the evaluation of carcass yield were used to assess the development of the digestive system. The length of the small intestine and the cecum was obtained with a measuring tape, and the empty weight of the proventricle, gizzard, small intestine and cecum were determined. The weight of liver, spleen, bursa of Fabricius, pancreas and heart was also estimated. The small intestine and the cecum were measured on a wet cloth in order to prevent them from contracting.

Statistical analysis

Feed consumption, weight gain, and feed conversion ratio were analyzed with a completely randomized design with a significance level of 0.05, using the SAS GLM procedure¹⁸. Treatment means were compared using the Tukey adjusted test (P<0.05). The variables walking ability and angulation were analyzed with a completely randomized design using PROC GLIMMIX (for non-parametric data) and SAS PROC FREQ¹⁸. The relative weights of the digestive system, accessory organs and prostrate latency were analyzed with a completely randomized experimental design with five treatments and seven repetitions per treatment using the GLM procedure of the SAS¹⁸. Treatment means were compared using the Tukey test and presented as mean ± standard error.

Productive performance and carcass yield

Chickens in the NDC and ChC treatments had lower (P<0.05) feed consumption and weight gain, compared to birds in the other treatments. No differences (P>0.05) were observed between treatments in feed conversion ratio. (Table 2). There were no differences between treatments in the carcass, breast, and leg and thigh yield variables.

Walking hability

Differences were found (P<0.05) by effect of the treatments on the walking ability; broilers fed the NDC and ChC diets exhibited a higher proportion of healthy birds (rating 0) compared to the birds of the other treatments. Birds rated 4 and 5 were not observed in this experiment (Table 3).

Valgus-varus angulation

Valgus/ varus angulation was affected by treatments (P<0.05) on the degree of valgus-varus angulation. The highest proportion of birds with a 0 rating was found in the NDC and ChC treatments and, to a lesser proportion, in birds with a score of 1. No broilers with a degree of angulation rated 3 were observed (Table 3).

Latency to lie down

There was no difference (P>0.05) between treatments in latency to lie down (Table 3).

Development of the digestive system and accessory organs

There were not differences (P>0.05) in terms of relative weight of spleen and heart; however, the relative weight of liver was lower (P<0.05) in broilers fed the SM diet, compared to birds fed the treatments that included castor meal. Relative weight of bursa of Fabricius was lower (P<0.05) in chickens fed the NDC and ChC diets compared to chickens fed the SM, AC and AChC diets (Table 4).

Relative weight of pancreas, gizzard, and small intestine and length of small intestine were greater (P <0.05) in chickens fed NDC and ChC diets, with respect to SM, AC and AChC. Relative weight of cecum of chickens fed SM, AC and AChC diets were lower (P <0.05) compared to the chickens of the ChC treatment and the length of the cecum was greater (P <0.05) in the chickens fed with NDC compared to AChC.