Diet and Nutrition Management

Introduction

Bongos (Tragelaphus eurycerus) are one of a number of ruminants which are kept in captivity. A ruminant digestive system consists of a single compartmentalised stomach in which the esophageal region expands into four distinct diverticula known as; the rumen, reticulum, omasum and abomasum (Cheeke & Dierenfield, 2010). This is a specialist form of digestion, which relies heavily on microbial assistance and rumination (Baldwin, 1995). Ruminants also include bovine, antelope, sheep and deer (Baldwin, 1995).

The diets and nutrition for ruminant livestock has been well researched and is now well understood, however, there is a lack of research regarding the diets of ruminants kept within the zoo environment (Clauss et al., 2003a). When zoo nutrition was originally devised, it was believed that all ruminants thrived on a singular formula (Clauss et al., 2003a). Further research later discovered that there was differences in nutritional requirements dependant on whether the animal was a grazer or browser (Clauss et al., 2003b), with browsers often requiring more protein and less fibre than grazers (Clauss et al., 2003b).

It has been observed in the wild that bongos are herbivorous browsers. Their diet consists primarily of leaves, vines, roots and fruits (Wright et al., 2011). Despite this knowledge, their natural diet is still poorly understood, resulting in a number of zoos struggling to supply their bongos with the correct nutritional needs (Wright et al., 2011). Research has also shown that the diets of bongos vary throughout different zoos, with a significant difference in browse nutrient composition and digestibility. An issue that was also highlighted throughout this research was that the browse was of low nutritional value (Wright et al., 2011). To combat this it is recommended to further analyse their nutritional needs and to carry out further research regarding what food is nutritionally optimal.

Formulated Captive Diet

Due to the lack of literature, the formulation for this diet is heavily based on what the okapi (Okapi johnstoni) require which is also a browser ruminant that is often kept in captivity (Nijboer, 2017). Other gaps were based on what is known of nutrition required in livestock ruminants such as sheep and goat (Baldwin, 1995).

Ingredients and Comparative Nutrition

The formulated diet below is based on an individual weighing 235kg. The tables below outline the ingredients and the weight of each of the ingredients of the formulated diet, including a comparison of the nutrients in the recommended diet and formulated diet. Some nutrients are below the recommended guideline. Due to these deficiencies it is recommended to monitor as to whether these lower levels are impacting the health of the bongo and possibly include supplements. The inclusion of a salt lick can help increase the sodium levels that this diet does not reach, which is suggested in previous research (Wright et al., 2011). Vitamin D can also be increased with exposure to UVB (Schutowski et al., 2010). Although this diet can be used as a base, nutrients may vary dependent on the life stage of the Bongo. For a Bongo of this weight, the calorie intake during late pregnancy will need to rise to 61526kj daily, and further in late lactation to 70315kj daily. It may also be necessary to increase the amount of feed available in winter, as the drop in temperature will require more kilojules to maintain body temperature. It is important to remember that these needs are based on an individual weighing 235kg, and adjustments will need to be made depending on weight using the Klieber equation (Heusner, 1982) as was used to work out the daily kilojule allowance for this individual.

It is also important to further make allowances for the pasture that the animal may graze on, as different grass contain differing amounts of nutritional value (Hackman et al., 2007). As the bongo is a browser (Wright et al., 2011) it may be recommended to limit the grass intake and only offer browse. However, browse can also have varying levels of nutritional value (Wright et al., 2011). Although the diet below only includes typical browse, as the browse offered will vary dependant on the location of the zoo and seasonality. Browse is an important part of the diet, and research has shown that Bongos are less able to break down the fibrous qualities of hay than grazers (Wright et al., 2011). It has been found that lucerne and ash have the highest in-vitro digestibility (Wright et al., 2011). It is recommended to feed mostly good quality browse without too much concentrate, as concentrated feed has been shown to lead to obesity and acidosis (Krause & Oetzel, 2005). No fruit or vegetables were included in this diet as they are shown to have a different composition to wild fruit and vegetables, which can lead to a build up of volatile fatty acids, causing the pH in the rumen to drop and leading to acidosis (Whright et al., 2010). Micronised full fat linseed was also included in this diet as it has been found to be beneficial to giraffes in captivity (Clauss et al., 2011) and is high in protein.

Table 1: the ingredients and weight fed per gram daily in the desiged diet for a bongo weighing 235kg.

Table 2: the nutrients available in the recommended diet (of what is known through literature) and the nutrients available in the formulated diet for a bongo weighing 235kg.

Feeding Schedule

The feeding schedule for this diet is based off, although not exactly the same as a schedule that has been found to be previously successful (Wright et al., 2011). The 1670g of dry feed (1665g Dodson and Horrel browse cubes and 5g micronised full fat linseed) will be offered to the bongo once daily in the feeding trough to ensure the animal gets the vitamins that it needs. The browse should be offered throughout the day with the alfafa hay, grass hay and bamboo leaves throughout the enclosure. This will help mimic the natural browsing behaviour and aid digestion as ruminants need to keep eating throughout the day (Baldwin, 1995). This will allow them to ruminate correctly (Baldwin, 1995). A mineral or salt lick should also be offered daily (Wright et al., 2011)

Critical Evaluation of the Formulated Diet

There are a number of benefits to this formulated diet. The diet is high in protein which is beneficial to the bongo as it is a browser and requires more protein than ruminants that are grazers (Clauss et al., 2003b). It is also high in neutral detergent fibre (NDF) which is the percentage of the food which is made of the structural components of plant cells such as hemicelluose and lignin (Baldwin, 1995). This is considered to be the fibre which is difficult to digest, however due to this property it is believed that it may reduce the possibility of acidosis as it will prevent the rumen pH from dropping below 5.5 (Baldwin, 1995). Unfortunately, the diet is also higher than recommended in acid detergent fibre (ADF) which is the percentage of plant material made of lignin and celluose (Gressley & Armentano, 2011) this is harder to digest than ADF which may impact the bongo as they are not able to digest fibre as efficiently as grazers (Clauss et al., 2003b ). Although there is a limited amount of research to suggest the impact that this may have, therefore, it may be suggested to monitor and keep a body condition score of the animal.

The diet is also higher than the recommended amount in other nutrients such as copper and calcium, as with the ADF it is best to monitor the animal in regards to the impact it may have. The formulated diet also contains no fruits and vegetables which may cause acidosis (Wright et al., 2011) and is high in forage. The level of forage is beneficial as it closely mimics the natural diet and provides enrichment as the bongo is able to forage throughout the day.

Ease of Management of the Diet

The diet is easy to manage, as it is relatively cheap and easy to source. The dry feed can be ordered from within the UK and requires minimal preparation. The dry feed can also be stored easily in containers that are pest proof. The hay and bamboo leaves can also be sourced from the UK and also requires minimal preparation. The hay and bamboo leaves are also relativity easy to store, as it can be stored in a barn that is pest proof and does not let in water as that will increase mould (Class et al., 2003b). The amount of forage may be difficult to supply, however it can be collected from on site and surrounding areas, although it will require man hours to collect it, cut it down to size and place within the enclosure. The browse is also unfortunately difficult to store, and loses much of its nutrients after is has been cut (Clauss et al., 2003b). Although it can be stored with the hay it will need to be changed more frequently.

Conclusion

This diet mostly meets the bongos nutritional and behavioural requirements. Although there may be some issues with the diet, these should not be too detrimental. The diet is also easy to manage and requires sources that are readily available. However, further research does need to be further carried out in the nutritional requirements of the bongo to better formulate a diet that is more ideal for the species, as there are many issues with basing the diet on alternate species.