Growth and reproductive performance of West African Dwarf sheep fed endophyte-infected maize stover supplemented with soybean meal

F A Gbore^*, E O Ewuola and J T Ogunlade^**

Animal Physiology Laboratory, Department of Animal Science, University of Ibadan, Ibadan, Nigeria
dejiprecious@yahoo.com
^*Present Address: Department of Environmental Biology and Fisheries, Adekunle Ajasin University,
Akungba, Akoko, Ondo State Nigeria
^**Department of Animal Production and Health, University of Ado-Ekiti, Nigeria

Abstract

An experiment was conducted to investigate the effect of feeding endophyte-infected maize stover on growth and reproductive parameters of West African Dwarf (WAD) sheep. In a six weeks feeding trial, twenty-one individually caged growing WAD sheep were randomly allotted to three dietary treatments in a Randomized Complete Block Design. Treatment 1 (NF = control) consisted of diet with healthy maize stover without Fusarium inoculation while treatments 2 and 3 consisted of diets with slight (SF) and high (HF) Fusarium-infected maize stover respectively.

The mean daily dry matter intake was significantly (P<0.05) higher in animals fed the control diet when compared with animals fed the test diets. The mean daily weight gain of the animals fed diet HF was significantly (P<0.05) lower. The feed conversion ratio revealed that it will take 3.76 kg of the highly-infected stover (HF) to produce the same unit weight of meat that was produced by 2.12 kg of healthy maize stover (NF). The mean relative kidney weight tended to decline with an increase in the level of Fusarium infection. The reproductive parameters examined were not significantly different among the treatments. 

The results suggest that ingestion of Fusarium-infected maize stover by sheep for a short time will depress dry matter intake and weight gain without adverse effect on the organ traits and reproductive potential.

Key Words: Endophyte-infected maize stover, growth, reproductive performance, sheep

Introduction

Recent studies have shown that the disease status of crop stovers such as maize can have a large impact on the digestibility of crop tissues and on animal performance. Maize particularly has been reported (Cardwell et al 1999) to be vulnerable to degradation by mycotoxigenic fungi, such as Fusarium species that is prevalent in maize worldwide especially in the humid tropics.

Fusarium species, which are ubiquitous in roots and stalks of maize and most other plants, exist as saprophytes in moribund tissues of living host or as opportunistic pathogens awaiting stress in the host (Kommedahl et al 1978). It was ascertained in the same study that infection of roots and stalks by Fusarium spp occurred independently and that the inoculum appeared to be disseminated primarily from above ground sources. Inoculum of F. verticillioides disseminated either by wind or rain (Ooka and Kommedahl 1977), and spore dispersal by the corn borer (Chiang and Wilcoxson 1961) and Picnic beetle (Windels et al 1976) are considerable factors in infection of stalks other than from roots. Kommedahl et al (1978) concluded that after anthesis, irrespective of the hybrids, most if not all stalks, are naturally infected or colonized internally by one or more species of Fusarium and other fungi without apparent symptoms of stalk rot, and that damage from these fungi depends on the degree of stress subsequently imposed on the plant by the environment.

Since F. verticillioides has been reported to be predominant in both stover and grain of maize both in early and late maize growing seasons obtainable in humid tropics (Cardwell et al 1999), it was therefore hypothesized that there should be correlation between the nutritive value of such infected stovers and degree of Fusarium infection, which has not been investigated. Thus far, studies have only concentrated on the effect of Fusarium infection on crops yield with possible interaction with other fungi, and feeding infected grains to livestock with attention to fumonisin produced by the fungi. No study has been reported to determine the effect on ruminants exposed to endophyte levels reported in stovers.

The current study was therefore conducted to assess the feeding value of Fusarium-infected maize stover on the performance and reproductive parameters of sheep.

Materials and methods

Experimental site

The experiment was carried out in the ruminant unit of the Livestock Research Farm of the International Livestock Research Institute (ILRI), IITA, Ibadan, Nigeria (7⁰30¹N; 3⁰54¹E)

Generation of infected stover

Infected stover was generated by the plant pathology team at the International Institute of Tropical Agriculture (IITA). Fusarium verticillioides isolate, obtained from a naturally-infected ear found in a farmer's field within Ibadan metropolis, Nigeria, was grown on acidified Potato Dextrose Agar (PDA) and microconidia were washed into a suspension with distilled water. At 10 and 15 days past mid-silk, 2ml of F. verticillioides inoculum (1x10⁶/ml) was atomized on maize stalk using tooth picks at two insertion points at first internode for slightly infected stover and four insertion points at first and third internodes for highly infected stover during the actively growing stage of the plants to generate two levels of infection for the test stovers and the control inoculated with water, thus, constituting a control (diet MS), a slightly Fusarium-infected maize stover (diet SF) and a highly Fusarium-infected maize stover (diet HS). The fungus was allowed to grow with the maize plants till maturity and the stovers harvested when dried for the feeding trial.

Feeding trial

Twenty-one West African Dwarf (WAD) sheep (18 males and 3 females) were sourced from the ILRI Farm, treated for internal and external parasites and brought indoors after the pens had been properly washed and disinfected. Animals were blocked on live weight and randomly allocated to three treatments: zero infection (NF), slight infection (SF) and high infection (HF), each having 6 males and 1 female. The maize stovers were chopped and fed to the animals for six weeks, after a two-week physiological adjustment period. All animals were fed ad libitum (80g/kg BW ^0.75) at 0800h and 1600h. Basal diet for each animal was supplemented with 200g soybean meal per day to ensure adequate protein intake. Feed refusals were collected prior to feeding every morning. The feed intake was monitored daily and animals weighed weekly for the 42 days of experimental period.

At the end of the feeding trial, 3 male animals per treatment were sacrificed, dissected and their organs (kidneys, liver and testes) were carefully removed and weighed. The evaluation of the sperm storage potential of the experimental male animals involved direct haemocytometric count after 1:100 (v/v) dilutions in 0.154 M NaCl (Egbunike et al 1976).

Statistical analysis

The data collected were subjected to statistical analysis using analysis of variance procedure of SAS (1999). The treatment means were compared using the Duncan procedure of the same software.

Results and discussion

Performance of sheep

The mean dry matter intake was significantly influenced by the dietary treatments (Table 1). Weight gain also decreased significantly (P<0.05) with increase in the infection levels in the stover while the feed conversion ratio increased in mean value as the levels of endophyte infection increased.

Animals fed highly infected stovers compared favourably in dry matter intake with those fed the control diet. This may probably be attributed to the reduction in the quality or nutritive value of the highly infected stover since the fungus also fed on the nutrients in the stover for its growth. The animals on highly-infected stovers tended to eat more of the diet in an attempt to meet their daily nutrient requirement. However, the weight gain was significantly lower in animals fed diet HF compared to the others. This result corroborates the report of Ewuola et al (2003) observed  in rabbits fed Fusarium-cultured diets. The feed conversion ratio revealed that it will take 3.76kg of the highly-infected stover to produce the same unit live weight that is produced by 2.12 kg of healthy stover (control).

Organs traits

The average gross and relative weights of liver and kidneys (relative to live weight) were not significantly influenced by the dietary treatments. However, the mean relative kidney weight (relative to live weight) tended to decrease apparently with an increase in the level of Fusarium infection in the stover (Table 2).

The results show that the relative liver and kidney weights of animals that were fed test diets compared favourably with those fed control diet. This is an indication that the dietary qualities of the experimental diets promote identical organ traits among the treatments. This may probably be attributed to the protective action of the  protein supplementation of the basal diets of the endophyte-infected stovers.

Reproductive performance

The weights of testes, testicular sperm production per testis and gram testis, epididymides weights and epididymal (caput, corpus and cauda) sperm reserves were not significantly influenced by the experimental diets.  The mean value of these reproductive parameters from animals fed the experimental diets compared favourably with the control. This indicates that the diets possessed the same dietary quality that promotes identical daily sperm production and gonadal and extra-gonadal sperm reserves. The weight of testes relative to live weight was highest for animals fed diet NF and least for animals on diet SF. This is a confirmation of findings in earlier studies by Swierstra (1966) and Egbunike (1973) that testicular size and sperm production are highly related.

Conclusions

This study has demonstrated that feeding highly Fusarium-infected maize stovers to WAD sheep solely resulted in the poor performance of the experimental animals in terms of low feed intake and weight gain because of reduction in the feeding value of the maize stovers. The study further shows that the basal diet (maize stovers) supplemented with soybean meal promoted identical organ triats and reproductive parameters in all the treatments. From the foregoing, it can be suggested that highly Fusarium-infected maize stovers should be avoided in sheep diet or not fed solely as this, due to feed refusal effect, will depress intake with resultant effect on weight gain without any adverse effect on organ traits and reproductive potential of sheep when fed for a short time.

References

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Received 22 March 2006; Accepted 21 June 2006; Published 13 September 2006

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