MATERIALS AND METHODS

Study area: The experiment was conducted during the period from September to October, 2021, at the Experimental Unit of the Animal Production Research Department, National Centre for Research located in Soba, Southeast Khartoum. The average daily maximum and minimum temperatures were 29.1±0.89 and 20.1±0.89°C, respectively.

Experimental animals: Six yearling un-castrated males of Sudan desert sheep averaging 19±1.87 kg and six yearling un-castrated males of Sudan Nubian goats averaging 15.8±0.66 kg were used in this study. The animals were purchased from the local market. On arrival at the experimental farm animals were ear-tagged, dewormed with Ivomec against endo-parasite, sprayed with Gamatox to control the ectoparasite and given a prophylactic dose of Oxytetracycline. The animals were left to acclimatize for 14 days, during which the animals were allocated at random to each of the experimental feeds under investigation. Four treatments with three animals to each one: Sheep for (T1, T2) and goats for (T1, T2) were employed in a digestibility trial test.

Feeds: Alfalfa hay (Medicago sativa) and sorghum straw (Sorghum vulgare) were utilized to investigate the digestibility coefficients of the various nutrients, nitrogen balance, rumen fermentation products and blood urea nitrogen and some other physiological parameters related to animal performance. Alfalfa hay was used as T1 for both sheep and goats, whereas, sorghum straw was used as T2 for both sheep and goats. The chemical composition of the experimental feeds is shown in Table 1. Water was served in metal buckets tied to the crates. Animals had free access to water. Water consumed by each sheep and goat was determined by measurement of depletion in the bucket and correcting for evaporation.

Digestibility trial: The animals were harnessed and kept in metabolism cages to allow the collection of faeces and urine separately. After 14 days adjustment period, DMI was recorded for 5 days and dry matter digestibility and nitrogen retention were measured during a 5 days collection period. Faecal and urine collection for nitrogen balance determination were done by using the procedure described by Abubakr et al.¹⁰. Samples of feeds offered were taken daily and bulked at the end of the collection period. The collected composites were divided into two portions: One dried at 60°C and the other at 105°C for chemical analysis and DM determinations, respectively. Digestion coefficients were calculated according to the procedures described by Akinmoladun et al.¹¹.

Samples of feed and faeces were analyzed for their proximate chemical components as described by Abubakr et al.¹². Urine nitrogen was determined as described by Abubakr et al.¹⁰. Rectal temperature was recorded with a telethermometer and respiration rate by counting the flank movement. All the observations were recorded when the animals were resting under shade at 8:00 am.

Rumen liquor and blood samples: At the end of the digestibility trials, the animals fasted for 24 hrs then samples of rumen liquor were obtained using a stomach tube immediately before feeding, 3 and 6 hrs after feeding. The samples of rumen liquor were strained by a mesh cloth and used for the determination of pH and ammonia nitrogen. Rumen pH was determined with a pH meter (ICM model 41600). Ruminal ammonia nitrogen was determined as described by Abubakr et al.¹³. Blood samples were withdrawn from the jugular vein immediately before feeding, 3 and 6 hrs post-feeding. The blood samples were allowed to clot and the serum was separated by centrifugation and stored at -20°C until assayed for blood urea as described by Niyigena et al.¹⁴.

Statistical analysis: Data for the experiment from the digestibility trials as affected by animal species and roughage quality was arranged as a 2×2 factorial. Whereas, ruminal metabolites and blood urea-nitrogen as affected by animal species, roughage quality and sampling time was arranged as a 2×2×3 factorial. Analysis of Variance (ANOVA) was applied to analyze the main effects of animal species, roughage quality, sampling time and interactions at (p<0.05) and (p<0.01) using the GLM procedure of SAS (https://support. sas.com/documentation/onlinedoc/stat/indexchapter.html#stat93). The least significant differences (LSD) test was used for mean separation at p<0.05.

RESULTS AND DISCUSSION

Effect of roughage quality on DMI, WI, DMI ratio, total weight gain, average daily gain, urine volume, RT and RR: Table 2 showed that dry matter intake DMI (kg/day) was higher (p<0.01) in sheep compared to goats (0.54 vs. 0.75 kg/day). Nevertheless, weight gain WG (kg) and average daily gain ADG (kg/day) water intake WI (kg/day) and WI: DMI were not different between sheep and goats. This was following the results obtained by Leon-Tinoco et al.¹⁵ and Li et al.¹⁶, who reported that with little possibility to choose dietary components, goats compared with sheep, showed lower feed intake.

Rectal temperature and respiratory rate were affected significantly (p<0.01) by animal species. In the present study, the values of rectal temperature RT and respiration rate RR were higher in sheep compared to goats being 38.28 and 36.66°C in sheep and goats, respectively. a similar trend was noticed for respiration rates RR (min^–1) values which were higher in sheep (27.20 min^–1) than in goats (23.77 min^–1). Lins et al.¹⁷ stated that under thermo-neutral conditions, RT varies between 38.3 and 39.9°C for sheep and the baseline for goats is between 38.8 and 39.8°C. In this study, the RT in sheep lies within the normal range. Goats showed a significant decrease in DMI and RT compared to sheep. With a low level of intake, the metabolic heat was decreased and resulted in lower RT. Respiration was higher in sheep than in goats which were in line with the data reported by Majeed et al.¹⁸. There was a numerical increase in water intake in sheep compared with goats. It has been reported that the water intake of sheep and goats is influenced by diet types, the composition of rations and the processing of the feeds¹⁹.

In the present study, DMI was higher in animals fed alfalfa hay (0.68 kg) compared to that fed sorghum straw (0.61 kg). This could be explained by the low level of protein contents in sorghum straw (2.28%). Contradicting result was reported earlier by Malik et al.²⁰, who found that forage type did not affect DMI in goats fed either wheat straw or corn stover. The increased DMI seen with alfalfa hay compared with sorghum straw could be explained by the animal’s preference for forage that has greater nonstructural carbohydrate contents^21,22, which results in faster degradation and passage rate. Similar results were obtained by Wang et al.³ who found that Increasing alfalfa supplementation levels increased roughage intake.

In the present study, roughage type had affected significantly (p<0.05) WG (kg) and ADG (kg) feeding alfalfa hay resulted in slightly higher body weight, whereas loss in weight was observed when sorghum straw was fed. One can expect that feeding good quality roughages with high content of protein will result in superior WG and ADG. Recently, Askar et al.²³ reported that sheep had greater feed intake and utilization over goats when a high level of concentrate was offered. Earlier research indicated that both species of small ruminants showed significantly higher weight gain when fed various summer fodders²⁴. Water intake was affected significantly (p<0.01) by roughage quality. The use of alfalfa hay and sorghum straw increased (p<0.01) water consumption (1.55 vs. 0.95 kg/day). The results indicated that there is a strong relationship between WI and digestible energy intake as suggested by Mpendulo et al.²⁵.

The WI: DMI ratio was higher in alfalfa hay compared with sorghum straw (2.42 vs. 1.62). In this study, the water requirements varied with types of feed, indicating that the amount of water that was adequate at one time for a particular diet could be insufficient for another. In the present study, animal species×roughage type interaction did not affect all parameters measured in this study.

Effect of roughage quality on nutrient digestibility coefficient: The effect of roughage quality on nutrient digestibility in sheep and goats is presented in Table 3. In the present study, sheep had superior values over goats for digestibility coefficient of dry matter (DM, 76.b5 vs. 64.82) organic matter (OM, 77.36 vs. 65.68) crude protein (CP, 77.11 vs. 70.66) ether extract (EE, 60.59 vs. 36.59) crude fiber (CF, 79.90 vs. 68.17) nitrogen-free extract (NFE, 75.35 vs. 63.97) and total digestible nutrient (TDN, 70.71 vs. 59.86). This is in line with data reported by Li et al.¹⁶, who compared the digestibility of the pellet diets (grass hay, corn stalk and wheat straw) when fed to sheep and cashmere goats. Similar results were reported when sheep and goat fed maize, millet and sorghum fodders²⁵. They found that the digestibility of various nutrients such as CP, NDF and ADF was significantly higher (p<0.05) in sheep compared to goats. In contrast, Moyo and Nsahlai²⁶ found that goats digested fibre fractions more efficiently than sheep, especially for diets high in cell wall content. Goats are selective feeders and have the advantage over other domestic ruminants of being able to select a relatively high-quality diet when a variety of feeds are available. Therefore, it is expected that the feed consumed by goats may contain high nitrogen and low cell wall contents. It has been documented that goats showed a faster rumen outflow rate when compared to sheep and hens, lower fibre digestion is expected due to insufficient time for rumen microbes to act on plant tissue¹⁶.

Feeding alfalfa hay resulted in higher CF and NFE digestibility when compared to sorghum straw, however, the digestibility of DM, OM, CP and EE, were similar in both alfalfa hay and sorghum straw.

Contrary to this result, Bhatti et al.²⁷ found that forage source did not affect the apparent digestibility of all nutrients except CP, while Wang et al.³ recorded that the nutrient digestibility was significantly decreased with an increase in the level of alfalfa substitution for concentrate in dry ewes’ diet. In this regard, the contradictory data could be explained by the differences in the environment where the experiments took place, different types of diets tested and different breeds of small ruminants used. Nevers less, animal species×roughage type affected nutrient digestibility.

Effect of roughage qual ity on N-balance: The results showed that there were differences (p<0.01) between sheep and goats in N intake in Table 4. Nitrogen intake was higher in sheep than in goats (10.18 vs. 7.27 g/day). Faecal and urinary nitrogen was not affected by animal species, however, nitrogen excreted in urine was higher than that excreted in faeces in both sheep and goat. Similar results were obtained by Moyo et al.²⁸, who reported higher levels of urine nitrogen excretion in sheep. Nitrogen balance values were numerically higher with sheep compared to the goats (0.43 g/day vs. 1.89 g/day). Antwi et al.²⁹ reported that there were no significant differences in N balance between sheep and goats fed on different roughages. Species did not induce a significant (p>0.05) effect on N balance whether it is expressed as a percentage of N intake or as a percentage of digested N. Goats recorded lower values in both cases. The positive N balance observed with both species indicated that N was sufficient to meet the requirements of the animal. Species also failed to induce a significant effect on total N excreted either in faeces or urine.

N intake, was higher with alfalfa hay (15.24 g/day) when compared to sorghum straw (2.21 g/day). Similarly, faecal N and urinary N values were higher in alfalfa hay (3.89 and 9.25 g/day) than in sorghum straw (0.56 and 1.42 g/day). In this study, N balance was higher with alfalfa hay compared with sorghum straw (Table 4). This may be attributed to the significant increase in N intake with alfalfa hay as compared with sorghum straw. In this study, positive N balance was observed with animals fed on sorghum straw. Also, the higher N excretion in faeces and urine with alfalfa hay would reflect the higher CP content and higher N intake. Current results confirmed the finding of Foster et al.²², who found that N intake, faecal N and urinary N increased as CP increased in animals fed on different forage legume hays. The decrease in nitrogen intake will result in lower excretion of urea in urine for maintenance of the pool of urea in the plasma, while the increase in nitrogen intake is accompanied by the increase in the urea production in the liver and subsequently, its excretion in urine²⁸.

The results of the present study showed that there are animal species×roughage type interaction on nitrogen intake. Both goat and sheep fed alfalfa hay had higher values of nitrogen intake when compared to sorghum straw. This could be attributed mainly to the different CP contents of alfalfa hay (14%) and sorghum straw (2.28%).

Effect of roughage quality on rumen fermentation products and blood urea nitrogen: The data for both rumen parameters and BUN as affected by roughage quality are presented in Table 5. Both animal species (sheep vs. goats) and roughage type (alfalfa hay vs. sorghum straw) had affected rumen NH₃-N and BUN but not on ruminal pH. Rumen NH₃-N values were higher in sheep (17.47 mg/100 mL) when compared to goats (14.20 mg/100 mL), similarly, higher values of rumen BUN were recorded in sheep (42.50 mg/100 mL) when compared to goats (33.5 mg/100 mL). Moreover, NH₃-N concentration was higher with alfalfa hay (21.22 mg/100 mL) than that with sorghum straw (10.71 mg/100 mL), while, BUN values were higher with alfalfa hay (57.43mg/100 mL) than those with sorghum straw (17.64 mg/100 mL).

Current results were in line with the data published by Li et al.¹⁶, who found no differences in rumen pH between sheep and goats offered three pelleted diets. Rumen pH was not affected significantly (p>0.05) by the quality of feed. Similar results were reported earlier by Li et al.¹⁶ and Foster et al.²². The higher rumen NH₃-N concentration in sheep could be attributed to the lower efficient utilization of NH₃-N mainly due to the high rate of rumen microbial synthesis in sheep¹⁶. Moreover, diet quality had a significant effect on rumen NH₃-N concentration as evidenced by higher rumen NH₃-N in animals fed alfalfa hay compared to those fed sorghum straws. The crude protein content is superior in alfalfa hay, therefore, higher nitrogen intake could be expected in animals fed alfalfa hay compared to that fed sorghum straw as suggested by Foster et al.²². Additionally, rumen NH₃-N concentration was higher in both sheep and goats three hrs post-feeding compared to 6 hrs post-feeding. The higher BUN concentration with alfalfa hay compared to sorghum straw confirms the results obtained by Kheir and Ahmed³⁰ who found that blood urea concentration increased significantly with feeding Lucerne hay compared to grass hay. Zanton and Heinrichs³¹ found that urea-N excretion increases linearly with N intake. In this study, the alfalfa hay had a higher N intake than sorghum straw (15.24 vs. 2.21 g/day). Both animal species×sampling time and roughage type×sampling time had no effects on rumen pH, BUN and NH₃-N.

CONCLUSION

The results have shown that sheep and goats induced different responses when fed different quality roughages, sheep were better utilized for both low and high-quality roughage. Alfalfa hay had a higher feed intake value than sorghum straw and sorghum straw had higher fibre digestion.

SIGNIFICANCE STATEMENT

This study discovered that the sheep and goats responded differently to different quality feeds which were evidenced by higher nutrient digestibility in sheep compared to a goat. Moreover, high-quality feed had resulted in higher nitrogen intake. This study will help the small ruminant owners to pay attention to the species differences when providing rations containing different roughages.

ACKNOWLEDGMENT

The authors gratefully acknowledge the staff member of the animal production department researchers and technicians for sharing in the fieldwork and laboratory techniques.