Donkeys (Equus asinus) as well as other herbivores, which are hindgut fermenters are considered to be less efficient than ruminants in utilizing, plant cell wall constituents (Hintz et al., 1978). For most of the part of the year the donkeys are fed on crop residues and mature bush grasses of poor nutrient quality. Comparative studies on voluntary feed intake of donkeys and ponies revealed that donkeys had a higher apparent digestibility, of organic matter and fiber fraction of the forage, than in ponies (Pearson and Merritt, 1991, Pearson et al., 1998). Pearson et al. (2001) also reported that donkeys retained feed residues in gastrointestinal tract longer than did the other equids, irrespective of the diet type. He also reported that donkey can digest fiber more efficiently than other equids.

Many workers have studied on digestibility, gastrointestinal transit time, feed requirement and effect of forage quality. Studies on feed intake and digestibility of fiber have been made by Pearson and Dijkman (1994). Several workers have reported increased digestibility coefficient of feed from 6% to 20%, when fed on good quality diets, as a result of light exercise (Olsson and Ruudvere 1955; Orton et al., 1985, Worth et al., 1987). However, Pearson and Merritt (1991) could not record increased digestibility in working donkeys. Even though all these reports and experiments pertain to either rest condition or for specific objective such as to test the different types of diet formulations, there is no information available in the literature on the digestion coefficient of nutrients during work and its comparison with that of rest. In view of this, the present study was undertaken which may help in developing a standard feeding regime for the working donkeys.

Six adult large white donkeys (average pair weight, 300 kg) were selected and they were housed separately in well-ventilated shed. Two experiments were conducted on same set of animals for 7 days work (1 hr work - ½ hr rest-1 hr work, resulting in 2 hrs work day⁻¹ from 6:30 a.m. to 8:30 a.m., as per Hallikeri et al., 1995) and 7 days rest. After training the animals for general experimental procedures, they were hitched to a rotary mode to operate one hp reciprocating pump to lift water from 2m suction head. In both the experiments, same diet (Table 1) was offered to the animals @ 1kg Concentrate mixture (Groundnut Cake: 17%, Maize: 23%, Deoiled Rice polish: 57%, Mineral mixture: 2% and salt: 1%) day⁻¹ donkey⁻¹, along with dry chopped Sorghum (Sorghum bicolor) fodder at ad libitum. The diet was offered daily at 10:30 a.m. in separate trough in order to reduce wastage of feed and the feed refusals were collected and the actual daily feed intake was recorded.

Digestibility cum metabolic trial was conducted on both the experiments for 8 days preliminary period and 7 days collection and observation period. The donkeys were loosely tied to secure them in places and were fitted with suitable urine collection bags. Faeces and urine voided out during 24 hours duration were properly collected, weighed and measured separately for individual donkeys. All the samples were further processed and proximate analyses viz: Moisture, Ash, Crude Protein, Crude Fibre, Ether Extract, Nitrogen Free Extract, Organic Matter, etc. were done as per AOAC (1995). During work, observations such as draft (kg.), speed (km hr⁻¹), water discharge (kl hr⁻¹) and power output (hp) were recorded as per Michael and Ojha (2006) and digestion co-efficient and apparent digestibility of crude protein (CP), CF, EE and NFE were calculated as per Banerjee (1998) and fatigue score was calculated as per Verma and Singh (1990) and Ram (2007). The Student t test was followed (Snedecor and Cochran, 1989) in this experiment.

Analysis of concentrate mixture and dry sorghum fodder fed to the donkeys during the experiment (Table 1) revealed that the formulated concentrate mixture had 15.95% CP and 66.20% TDN whereas the chopped dry sorghum fodder contained 6.50% CP and 51.14% TDN. Ramachandra et al. (2000) also reported similar composition of dry sorghum fodder. However in the present study, the minor differences observed in some values may be because of the different ingredients used in the preparation of the concentrate mixture. The findings in the present study were also in accordance with the report of Banerjee (1998) regarding the composition of the sorghum hay.

The donkeys had significantly higher digestibility (P<0.05) during work than rest (Table 2). The DM digestibility observed during rest was 55.18%. Cuddeford et al. (1995) observed mean DM digestibility of 58% in donkeys fed on Alfalfa and oat straw diet. However, only on oat straw diet the DM digestibility was 48%. Pearson et al. (2001) also reported that the apparent digestibility of both DM and energy was more when oat straw was offered ad libitum than restricted feeding. Chopped sorghum fodder was offered in the present experiment ad libitum and hence the results can be compared with that of oat straw. Pearson et al. (1998) stated that the donkey was apparently the most successful equid at digesting fiber on low protein diet. This suggested that it may have the best developed mechanism for nitrogen recycling. Izraely et al. (1989) also reported that a decrease in urea filtration rate combined with an increase in the fractional urea re-absorption, resulted in the increased retention of urea nitrogen and recycling of urea nitrogen in to the gut in donkeys fed on low protein wheat straw diet compared to alfalfa.

Donkeys fed on straw diet at ad libitum had a slower rate of passage and higher organic matter digestibility compared to ponies fed on the same diet and this ability was reflected in efficient digestion of fibrous feed. It was concluded that the donkeys would have an added advantage where the food resources are limited (Pearson and Merrit, 1991). Pearson et al. (2001) further reported that the apparent digestibility of DM was higher for the oat straw diet when it was fed ad libitum than restricted feeding particularly in donkeys. Cuddeford et al. (1995) attributed higher DM digestibility in donkeys to the longer retention of feed residues in the GI tract and further suggested that this ability made them superior to other equids with regard to DM digestibility and fiber utilization. Pearson et al. (1998) studied the DM digestibility in donkeys fed on oat straws at restricted and ad libitum intake level. In ad libitum feeding the DM digestibility was 50% and in restricted feeding it was 43%. Higher DM digestibility of 63% was observed in Alfalfa feeding at ad libitum and 66% during restricted feeding. Overall mean DM digestibility observed in the present study is in accordance with the above report. The major feed offered in the present study was chopped sorghum straw and hence the results in the present experiment can be correlated with that of oat straw feeding. However, the differences observed in the DM digestibility with alfalfa can be very well explained, as there is vast difference in the composition of the alfalfa and oat straw. Higher DM digestibility was observed during work in the present experiment. Nengomasha et al. (1999) reported that working animals require more energy during work. This extra energy requirement during work might have resulted in the higher DM digestibility than rest. The differences observed in DM digestibility during work and rest were statistically significant (P<0.05).

CP digestibility (%) during rest and work was 64.65±0.46 and 67.43±0.42 respectively. Cuddeford et al. (1995) reported an overall mean CP digestibility of 52 and 66 with 67 part of alfalfa. The CP supplemented in the feed and fodder in the present experiment may be corresponding with 67 portion of alfalfa as our results are similar with that of the above report. However, Pearson et al. (1992) reported that CP digestibility at 67 and 33 combination of alfalfa and oat straw diet was 66%. Pearson et al. (2001) further reported very high CP digestibility in donkeys fed with alfalfa at ad libitum during rest. The feed combination in there reports might be exactly corresponding with dry sorghum fodder and concentrate mixture offered to the working donkeys in our experiment. They have reported lower CP digestibility when the combination of feed was changed whereas in the present experiment feed offered was constant during work and rest. The difference in the digestibility of CP during work and rest was statistically significant (P<0.05).

Mean CF digestibility (%) observed in the present experiment was 56.20±0.78 during rest and 62.87±0.52 during work. Tisserand et al. (1997) observed elevated digestibility when fed on good quality hay however, on poor quality hay it was 42.00±4.20. Though the hay provided in present experiment was of poor quality, high fiber digestibility was observed which may be due to supplementation of the concentrate mixture. According to Cuddeford et al. (1995), Pearson et al. (2001) and Ramachandra et al. (2000) the difference observed in CF digestibility might be because of different diet combinations. Very high digestibility of CF during work (mean 62.87±0.52) was observed in our experiment and might be attributed to the effect of work. However, the data could not be compared because of paucity of literature in this respect.

Higher digestibility of NFE (67.31±0.98) during work compared to rest (63.58±0.69) was observed (Table 2). Ramachandra et al. (1995) reported slight higher NFE digestibility during work and rest. The EE digestibility during work and rest was 37.78±0.71 and 33.58±1.53 respectively. These results could not be compared because of non-availability of similar works however they are statistically significant at p<0.05.

The parameters recorded during the work (Table 3) were, draft (kg) 52.71±1.54, walking speed of the animal (km hr⁻¹) 3.11±0.06, water discharge (kl hr⁻¹) 2.48±0.05, power output (hp) 0.57±0.0, mean pair weight (kg) 296.67±4.33 and fatigue score 18.00±0.50. During the work the animals were fatigue and hence work was stopped as per Verma and Singh (1990) and Ram (2007). These results are similar to that of Hallikeri (1996) and Hallikeri et al. (2000) during similar kind of work in adult donkeys. The relative humidity (%) and ambient temperature (°C) were 67.16±2.23 and 29.94±2.28 respectively. This range of RH and AT were in the comfort zone for donkeys as suggested by Sastry and Thomas (1976).

The initial and final pair body weight (kg) were 297.43±1.87 & 296.67±4.33 in work group and 296.33±2.44 & 299.24±3.21 in rest group respectively which shows that 2 hr daily work for 7 consecutive days had negligible or no effect on the body weight of the experimental animals. Nengomasha et al. (1999) reported in their findings that the donkeys lost weight during ploughing operation. There was no loss of weight in the present experiment suggesting that proper feeding and management fulfilled the energy needs during work.

It can be concluded that if the nutritional standards are maintained during work there may not be any adverse effect on health of the animal nor there will be any body weight loss. Therefore, it is suggested that, additional concentrates should be provided as work ration for working donkeys along with ad libitum straws. This will help them to maintain their body weight and ultimately the work turnout will also be more. Further research in this direction is required so as to establish feeding standards not only for the work but also for the different types of work viz. heavy, medium and light.

References