The effect of particle size of feed on growth, reproduction and nutrient digestibility of snails (Archachatina marginata)

A J Omole, J A Sansi* and J O Osayomi*

Obafemi Awolowo University, Ile Ife, Nigeria . Institute Of Agricultural Research and Training Moor Plantation
*Federal College of Animal Health and Production Technology, I. A. R. and T., Ibadan, Nigeria
omoleboye@yahoo.com

Abstract

180 growing snails (Archachatina marginata) of mean weight 90.6±3.8g were used to study the effect of feed particle sizes on performance and nutrient digestibility. The treatments were diets that were ground in a hammer mill with 5, 4, 3 and 2mm diameter screen sizes. A completely randomized design was used to compare the four treatments.

All growth and reproductive traits, and digestibility coefficients, were improved or tended to improve as the particle size of the feed was reduced.

Key words: Digestibility, particle size, performance, snails

Introduction

It has been reported that feed processing methods have a significant effect on feed consumption, weight gain and nutrient digestibility in pigs (Ohh et al 1983). In broilers, the digestibility of nutrients was improved and the rate of growth increased as a result of reduction of feed particle size (Behnke 1996). Healy et al (1994) investigated the effect of particle size of maize, hard and soft grain sorghum on growth performance and nutrient utilization in broiler chicks. They concluded that reduced particle size improved growth performance.

In snail production, an effort is being made to use complete balanced feeds (Stievenart 1992; Omole et al 2000; Ejidike 2001). However, there is no information on the effect of feed particle sizes on performance of snail. Moreover, the snail teeth (Radula) are very tiny and delicate, hence the objective of this study was to determine the feed particle size effect on growth, reproduction and nutrient digestibility in the snail (Archachatina marginata).

Materials and methods

The experiment was carried out at the snail unit of the Institute of Agricultural Research and Training (I.A.R.and T.), Ibadan, located on longitude 03⁰51E, latitude 07⁰23N and altitude 650", in the humid zone of South western Nigeria. One hundred and eighty growing snails (Archachatina marginata) of mean weight 90.6±3.8g were used to study the effect of feed particle size on performance and nutrient digestibility. The snails were reared in a cage of 0.5 x 0.5 x 0.5 m³ compartments placed inside a well ventilated open sided house roofed with adex asbestos located under a tree. Sandy loam soil was put inside the cage to a depth of 7cm.

The diet was formulated to contain 24% crude protein (Table 1).

Table 1. Gross composition of the experimental diet
Ingredients, %	%
Maize	22.0
Brewer's dry grain	10.0
Wheat offal	12.6
Groundnut cake	10.0
Soya bean meal.	24.2
Fish meal	4.0
Oyster shell	9.7
Bone meal	2.15
Mineral mixture	5.0
NaCl	0.1
Premix	0.25
Total	100

The diets were ground in a hammer mill with 5, 4, 3 and 2mm diameter screen sizes P5, P4, P3 and P2, respectively. P5 was used as control diet. The treatments were replicated three times and each treatment / replicate contained 15 snails in a completely randomized design. The feed and water were given ad libitum. The feed intake and weight gain were measured on daily and weekly basis, respectively. Shell length and width were measured on weekly basis with the use of vernier callipers. The shell thickness was measured with a micrometer screw gauge on a weekly basis. Records on feed conversion ratio, number of eggs collected and size of the hatchlings were also taken. The experiment lasted for six months. The digestibility trial lasted 10 days, 3 days for adaptation and 7 days for excreta collection. The snails were fed with the same diet as used during the feeding trial. Records on feed intake was taken while excreta was collected daily from each treatment The daily excreta from each treatment was dried to constant weight at105°C in the hot air oven. The dried samples were stored inside a refrigerator for subsequent analysis of proximate composition (AOAC 1990). All data were subjected to analysis of variance (SAS 1995); sources of variation were treatments and error.

Results

The crude protein, calcium and phosphorus contents of the experimental diet (Table 2) were within the range recommended for growing snails (Omole 2003).

Table 2. Chemical composition of the experimental diet
As % of air-dry feed
Dry Matter	87.5
As % of DM
Crude Protein	23.7
Crude Fibre	5.3
Ash	9.1
Ether Extract	3.6
Nitrogen Free Extract	58.3
Calcium	4.5
Phosphorus	0.6

All performance traits improved, or tended to improve, as the particle size of the feed was reduced (Table 3).

Table 3. Mean values for performance traits of snails fed diets with different particle sizes
	P5	P4	P3	P2	± SEM
Weekly dry matter feed intake, g	40.0^b	41.0^b	45.0^a	45.1^a	1.84
Initial weight, g	89.4^a	90.4^a	90.3^a	91.4^a	2.01
Final weight, g	263.4^c	339.8^b	389.8^a	391.2^a	11.94
Weight gain, g/week	7.25^c	10.4^b	12.5^a	12.5^a	1.04
Weekly shell length increment, mm	2.52^c	3.14^b	3.56^a	3.56^a	0.69
Weekly shell width increment, mm	2.13^b	2.23^b	2.61^a	2.62^a	0.15
Weekly shell thickness, mm	0.0324	0.0325	0.0326	0.0326	0.006
Feed conversion ratio	5.52^a	3.95^b	3.60^c	3.61^c	0.38
Total eggs collected	12.0^b	12.2^b	14.3^a	14.4^a	1.41
Weight of the eggs, g	4.38	4.43	4.45	4.45	0.32
Weight of the hatchling, g	4.23	4.23	4.26	4.27	0.3
Means with different superscripts along the same row are significantly different (p<0.05) SEM: Standard Error of Means

The trends in the apparent digestibility coefficients (Table 4) were similar to those recorded for performance traits with positive effects due to reduced particle size.

Table 4. Mean values for digestibility coefficients of snails fed diets with different particle sizes
	P5	P4	P3	P2	± SEM
Dry matter feed intake, g/day	3.68^c	4.16^b	5.19^a	5.25^a	0.84
Apparent digestibility, %
Dry matter	78. 4^c	82.6^b	86.8^a	87.2^a	2.94
Crude protein	84.2^b	88.8^ab	91.7^a	92.1^a	3.41
Crude fibre	81.4^c	85.6^b	89.8^a	90.1^a	3.21
Nitrogen free extract	74.1^c	78.7^b	83.1^a	84.2^a	2.45
Means with different superscripts along the same row are significantly different (P < 0.05) SEM: Standard Error of Means

Discussion

The improvement in feed consumption could be as a result of increase in surface area of the feed which improved the rate of digestion (Ohh et al 1983; Nir et al 1995). Positive effects of reduced feed particle size have been observed in broilers (Behnke 1996) and pigs (Hamilton and Proudfoot 1995). The improvement in nutrient digestibility as the particle size reduced is in line with the observations of Owsley et al (1981) in pigs The zero mortality recorded in all the treatments confirmed that snails can be fed solely on compounded rations without any adverse effect and that the feed particle sizes used in this study had no detrimental effect on health.

Conclusions

When snails are to be fed on complete balanced diets there will be improvements in growth and reproductive performance due to fine grinding down to 2 mm particle size.

References

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