Effects of feeding fish–wheat bran meal on performance and meat quality of Omani sheep

ABSTRACT

Fish wheat bran meal (FWBM) was prepared from ground Indian oil sardines (Sardinella longiceps) using hydrochloric acid and was sun-dried on wheat bran (75:25 w:w). Forty Omani sheep were divided into five groups of eight sheep each and fed with one of five diets for 18 weeks. The diets were formulated from FWBM, soybean meal (SBM), barley, wheat bran, ground date palm leaves, limestone, vitamin and mineral mix, salt and vegetable oil. The objective was to gradually replace soybean with FWBM. The proportions of FWBM in the diet were 0, 50, 100, 150 and 200 g/kg, whereas the parallel SBM ranged from 170 to 0 g/kg. Animals were housed in individual pens and daily feed intake and weekly body weights were recorded. Animals were fed with 500 g/d of the concentrates and allowed ad libitum access to hay, water and trace elements. FWBM diets were well consumed by sheep with no negative effects on feed intake, body weight growth or feed conversion. There were also no negative effects on meat quality parameters. The study indicated that FWBM can be used as an excellent protein and energy source for feeding Omani sheep without compromising performance or meat quality.

KEYWORDS:

• Fish–wheat bran meal
• growth
• meat quality
• sardines
• sheep
• Oman

1. Introduction

Animals in Oman are raised under traditional systems based on grazing range plants plus some supplementation with hay and concentrate stall feeding being essential for successful animal production. There are abundant local non-conventional feed which may be used for feeding livestock, including dried sardines which contain high levels of protein (450–720 g/kg) (Early et al. 2001; Mahgoub et al. 2005) as well as various agricultural by-products including those from date palm.

Fish silage was reported as a useful protein source for swine (Green et al. 1983) poultry (Machin et al. 1990) and to a limited scale in ruminants (Offer & Husain 1987; Samuels et al. 1991). Lambs were successfully reared from one to two days old on synthetic milk composed of silage of white fish (cod fillets), lard and coconut oil, and lactose (Soliman & Orskov 1976). Lambs grew more slowly on the milk replacer during the first 15 days than on a dried skim milk diet. However, their growth was equally good later on.

Shqueir et al. (1984) fed lambs with pelleted diets formulated to contain a control diet (600 g/kg alfalfa hay) with no protein supplement, or supplemented with crude protein (CP) from cotton seed meal (CSM), urea or urea plus liquefied fish (LF) for 43 days. There were no differences in daily gain, total feed intake, feed efficiency, and yield and quality carcass grades among lambs fed with experimental diets. The dressing percentage was higher for lambs fed with fish–wheat bran meal (FWBM) compared to those fed with CSM and control diets. There were no differences in organoleptic evaluation of cooked roasts for tenderness, flavour or overall desirability but CSM increased meat juiciness. In sheep fed with urea + LF, urea aroma score was lower than those in sheep on control diet. Data obtained indicated that LF could be used as a source of supplemental CP for sheep.

During recent years, there has been an increasing interest in healthy foods with respect to fatty acid composition of ruminants’ products. This involves fatty acid composition of dietary fat for humans which is linked to cardiovascular and other lifestyle health problems. Consequently, methods of altering the fatty acid composition of these products are of great interest. It is recommended to increase the intake of unsaturated fatty acids, particularly the omega-3 polyunsaturated fatty acids. These are abundantly found in fish, and they are beneficial to human health especially in reducing the risk of coronary heart disease (Dewhurst & King 1998). Fish which derive their omega-3 fatty acids from marine plankton are extensively used in concentrated animal feeds. Lamb meat with increased levels of long chain omega-3 fatty acids may possibly be produced without altering the sensory quality (flavour or aroma) of the cooked meat (Ponnampalam et al. 2002). This possibility should be explored in animals fed with fish silage in future studies.

This study aimed at feeding FWBM prepared from local fish and incorporated in concentrate diets to native sheep.

2. Materials and methods

2.1. Experimental diets and animals

Experimental feeds, animals and experimental design have been described before (Al-Abri et al. 2014). Briefly, Fish silage was prepared from ground Indian oil sardines (Sardinella longiceps) using hydrochloric acid and was sun-dried on wheat bran (75:25 w:w) before being mixed with other feed ingredients in sheep diets. The aim of this was to determine the drying ratio which can give crude protein percentage close to that of soybean. Forty Omani sheep were divided into five groups of eight sheep each and fed with one of five diets for 18 weeks. The diets were formulated from FWBM, soybean meal (SBM), barley, wheat bran, ground date palm leaves, limestone, vitamin and mineral mix, salt and vegetable oil with the objective of gradually replacing soybean with FWBM. The vitamin–trace mineral pre-mix added to the diet provides per kg of mixed ration: 18,750 IU Vitamin A; 3750 IU Vitamin D3; 7.5 IU Vitamin E; 5 mg Co; 1.25 mg Cu; 75 mg Fe; 1250 mg Mg; 150 mg Mn; 0.375 mg Se; and 100 mg Zn.

The proportions of FWBM in the diet were 0, 50, 100, 150 and 200 g/kg, whereas the parallel SBM ranged from 17% to 0%. Animals were housed in individual pens and daily feed intake and weekly body weights were recorded. Animals were fed 500 g/d of the concentrates and allowed ad libitum access to hay, water and trace elements.

At the end of the feeding trial, animals were slaughtered and processed at Baushar Central Slaughterhouse according to routine slaughterhouse procedures. The weights of the fresh non-carcass organs (head, skin, small and large intestine, lungs and trachea, feet, pancreas, spleen, liver, kidney, heart, bladder, testes) and the hot carcass were immediately recorded. The carcasses were then chilled 4°C for 24 h and weighed to determine cold carcass weight. The weight of the gut content was computed as the difference between the full and empty weight of the whole digestive tract. The empty body weight (EBW) was calculated as the difference between the slaughter weight and that of the gut content.

2.2. Meat quality assessment

Samples from the longissimus dorsi muscle were collected from the loin region of the left side of the carcass. Meat quality-related measurements included ultimate pH, water holding capacity, cooking loose water, tenderness, sarcomere length, myofibrillar fragmentation index and colour (L, a, b) were determined. The ultimate pH was assessed in homogenates (using an Ultra Turrax T25 Homogenizer) of 1.5–2 g of muscle tissue in 10 ml of distilled water using a Metrohm pH meter (model no. 744) with a glass electrode. Chilled muscle samples (13 mm×13 mm cross-section) were used for assessment of tenderness by a digital Dillon Warner–Bratzler shear device after cooking in a water bath at 60°C for 90 min. Sarcomere length was determined by laser diffraction according to procedures of Cross et al. (1981). Expressed juice was assessed by a filter paper method as the total wetted area less the meat area (cm) relatively to the weight of the sample (g). The colour L, a, b light reflectance coordinates of the muscle surface were measured using Minolta Chroma Meter CR – 300 (Minolta Co. Ltd., Japan) with colour measuring area 1.1 cm diameter calibrated using a Minolta calibration plate (L = 97.59, a = −5.00, b = +6.76). The average of two measurements from each sample was recorded as the colour coordinate value of the sample.

Taste panel evaluation of roasted lamb racks was carried out by untrained panellists, including academic, technical staff and students of Sultan Qaboos University. The evaluation included assessment of tenderness, juiciness, flavour, aroma, desirability and overall palatability in the well-equipped Sensory Evaluation Laboratory at the Department of Food Science & Nutrition.

2.3. Statistical analyses

Statistical analysis was carried out using the analysis of variance procedure (Ott 1993), to evaluate the effect of FWBM on sheep performance using SAS Institute Inc. (1991). Significant differences between treatment means were assessed using the least-significant difference procedure. Interaction between the treatments was excluded from the model when not significant (p > .05).

3. Results and discussion

3.1. Feed intake and feed conversion

In general, there were no significant treatment effects on all feed intake measurements, including hay intake, concentrates intake, total feed intake, average daily feed intake or feed intake per body weight (BW) (Table 1). The intake of concentrate feed containing FWBM gradually increased with the progress of the trial and reached its maximum at week 9. This was similar to findings of experiments where fish silage (89 g/kg DM) was fed to calves (Offer & Husain 1987). Animals in all experimental groups consumed similar amounts of hay and therefore had a similar concentrate:hay ratio.

Table 1. Feed intake, BW gain and feed conversion in Omani sheep fed with pelleted concentrate containing various levels of fish silage.

	Diet (fish silage level g/kg)					SEM	Diet effect
Measurement	0	50	100	150	200
Total intake (kg)	83	88	83	85	89	28.2	NS
Average daily hay intake (g)	410	442	400	449	454	23.3	NS
Average daily conc. intake (g)	334	342	342	311	338	11.4	NS
Average daily intake (g)	745	785	742	760	793	25.2	NS
Average BW (kg)	22.8	24	23	23	23	1.44	NS
Total weight gain (kg)	11.8	12.9	11.9	11.3	10.8	0.75	NS
Average daily gain (g)	105	115	106	101	96	7	NS
Feed intake (g/kg BW)	46.5	48.9	48.4	44.3	42.5	4.1	NS
Feed:gain	7.2	6.8	7.0	7.9	8.5	0.49	NS
Gain:feed	0.141	0.147	0.144	0.132	0.121	0.08	NS

Note: SEM, standard error of means; NS = p > .05.

The average daily feed intake ranged between 742 and 793 g/d in sheep fed with the FWBM diets. These were comparable to figures of 770–950 g/kg reported for Omani sheep fed with 50–200 g/kg dried fish sardines (Mahgoub et al. 2005) but lower than 980–990 g/d reported for Tunisian native lambs (Atti et al. 2013). Feed intake per kg BW was not different between experimental animal groups. Feed intake per BW in the current study (42–49 g/kg) was higher than that reported for Omani sheep fed with non-conventional diets (El Hag & Al Shargi 1998). Mahgoub et al. (2005) reported a feed intake of g/kg BW of 33.2, 31.4 and 28.4 g/kg BW in Omani sheep fed with 50, 100 and 200 g/kg dried sardines. Although there was no significant effect of FWBM on feed intake, there was a tendency that the 200 g/kg FWBM group to consume less feed and the 50 g/kg FWBM sheep to consume the highest feed. This trend was confirmed when feed intake was expressed as a percentage of BW.

There was no effect of diet on feed conversion (Table 1). The feed:gain ratio (FGR) of 6.8–8.5 in the current study were comparable to reports on Omani sheep fed with dried sardines (6–7 kg feed/kg BW) reported by Mahgoub et al. (2005) but better than the 13.3 kg feed/ kg BW reported for Omani sheep fed with non-conventional diets (El Hag & Al Shargi 1998). The 200 g/kg FWBM sheep consumed less feed but gained less weight, so they had highest FGR.

3.2. Effect of FWBM on body weight growth of Omani sheep

There were no statistical differences (p > .05) between experimental groups in BW gain (Table 1). Sheep fed with 0, 50, 100, 150 and 200 g/kg FWBM diets gained a total weight of 11.78, 12.90, 11.93, 11.31 and 10.77 kg over the whole experimental period. This was equivalent to average daily BW gains of 105, 115, 107, 101 and 96 g/d, respectively. These figures are comparable to those reported for Tunisian lambs fed with extruded linseed (Atti et al. 2013).

The current study indicated that replacing 200 g/kg of protein sources with FWBM may be achieved. It should significantly reduce feed cost causing no health problems. Daily growth rates of sheep in the current study (96–115 g/day) were relatively lower compared to lambs fed with LF plus urea in a feeding trial carried out by Shqueir et al. (1984) but comparable to that reported for local sheep (122–151 g/d) by Mahgoub et al. (2005).

In fattening sheep, Penedo et al. (1988) demonstrated that growth performance improved by more than 24% when 200 g of molasses fish silage blocks and 300 g of barley replaced 500 g of commercial ration (on DM basis). Feeding trials in Oman have shown that dried sardines substituted at 10% of the diet to replace SBM improved growth rates of growing cattle and goats (El Hag & El Khanjari 1992).

3.3. Carcass and non-carcass components

In general, there were no significant effects of FWBM levels on weights of carcass components (Table 2). Although not statistically different, the non-carcass fat content (Omental and Mesenteric fat) was higher in sheep fed with 50 g/kg FWBM compared to animals fed with other FWBM levels with sheep receiving the 200 g/kg FWBM diet having the lowest values. Similarly, there were no differences between sheep fed with diets containing various levels of dried sardines and those fed with diets containing SBM (Mahgoub et al. 2005). These findings indicate that FWBM may be incorporated into sheep diets up to 200 g/kg without negatively affecting body composition.

Table 2. Mean weights of body, carcass and non-carcass components in Omani sheep fed with pelleted concentrate containing various levels of fish silage.

Body part (g/kg EBW)	Diet (fish silage level g/kg)					SEM	Diet effect
	0	50	100	150	200
Head	62	64.5	65.2	64	66	1.56	NS
Skin	141	121	132	128	118	5.02	NS
Lungs and trachea	17	18	17	17	17	0.88	NS
Heart	3.8	3.8	3.9	4.1	4.0	0.21	NS
Liver	14.6	15.5	14.5	15.2	14.2	0.61	NS
Feet	28.0	27.2	27.5	28.0	30.0	0.63	NS
Alimentary tract-full	185	172	195	218	241	10.7	NS
Alimentary tract-empty	24.3	25.2	26.2	27.7	27.9	1.54	NS
Small and large intestines	63	67	75	66	68	4.99	NS
Spleen	1.2	1.1	1.1	1.2	1.2	0.06	NS
Pancreas	0.93	0.74	1.0	0.67	0.79	0.10	NS
Bladder	0.57	0.42	0.48	0.57	0.62	0.08	NS
Testes	6.9	7.3	7.6	8.8	8.9	0.58	NS
Kidney	2.9	2.9	2.7	3.2	3.4	0.10	NS
Omental fat	15.4	21.3	17.5	14.8	13.7	1.95	NS
Mesenteric fat	13.4	14.0	13.0	12.4	10.2	0.91	NS
Kidney fat	8.1	9.3	9.4	7.5	7.5	0.68	NS

Note: EBW, empty body weight, SEM, standard error of means; NS = p > .05.

3.4. Meat quality and sensory evaluation

In general, there were no significance changes in muscle pH decline between treatments until 24 h postmortem (Table 3) although statistically there was a significant difference in pH after 2 and 8 h of slaughtering. Sheep fed with 50 g/kg FWBM had the lowest meat pH in 2 and 8 h after slaughtering. In general, meat pH value was at an average of 6.3 in all groups and dropped to 5.6 after 24 h of slaughtering. There was a gradual and normal reduction in meat pH in all sheep groups. The pH levels in the current study were comparable to that of Tunisian native sheep fed with extruded linseed (Atti et al. 2013) and local and imported lamb in the Canary Island (Hernández-Castellano et al. 2013b).

Table 3. Meat quality parameters in Omani sheep fed with pelleted concentrate containing various levels of fish silage.

Parameter	Diet (fish silage level g/kg)					SEM	Diet effect
	0	50	100	150	200
pH
40 min	6.2	6.3	6.5	6.3	6.4	0.11	NS
1 h	6.3	6.3	6.4	6.3	6.3	0.06	NS
2 h	6.2^b	6.1^b	6.4^a	6.2^b	6.3^a,b	0.06	**
6 h	6.0	5.9	6.0	5.9	6.1	0.05	NS
8 h	5.9^a	5.6^b	6.0^a	5.7^b	5.8^a,b	0.07	*
10 h	5.7	5.5	5.8	5.6	5.6	0.10	NS
12 h	5.6	5.5	5.7	5.5	5.6	0.10	NS
24 h	5.7	5.5	5.8	5.5	5.6	0.11	NS
Ultimate pH	5.8	5.7	6.0	5.7	5.7	0.2	NS
Colour
L* (Lightness)	29.3^b,c	30.3^b	28.3^c	32.4^a	28.6^c	0.9	*
a* (Redness)	12.5	12.4	11.9	12.4	12.2	0.8	NS
b* (Yellowness)	3.2	3.0	2.7	3.8	3.3	0.4	NS
Cooking loss	10.7	13.6	14.2	13.3	13.9	0.9	NS
Shear force (kg)	7.1	10.6	8.0	7.8	7.1	1.1	NS
Myofibrillar	79.5	78.3	80.9	78.9	78.4	1.0	NS
Express juice	34.6	29.5	30.8	31.9	33.0	3.8	NS
Sarcomere length (µm)	1.8	2.2	2.1	2.1	2.3	0.3	NS
Panel taste scores
Tenderness^1	6.7	5.7	5.3	5.9	6.4	0.443	NS
Juiciness^2	6.2^a	5.6^b	4.5^c	5.4^b	6.1^a	0.370	**
Flavour^3	6.3	6.1	5.2	5.5	6.5	0.391	NS
Aroma^4	6.2^a	6.3^a	4.8^c	5.8^b	6.7^a	0.387	**
Desirability^5	6.3^a	6.2^a,b	4.8^c	5.4^b,c	6.4^a	0.417	*
Palatability^6	6.5^a	6.0^a,b	4.8^c	5.6^b	6.5^a	0.445	*

Notes: SEM, standard error of means; NS = p > .05. Means on the same line denoted with the same superscript do not differ significantly (p < .05). Score range 10 (highest affirmative value) to 1 (lowest value). Total of 27 panellists participated in the evaluation.

¹Scored as 1 = extremely tough, 10 = extremely tender.

²Scored as 1 = extremely dry, 10 = extremely juicy.

³Scored as 1 = extremely undesirable flavour, 10 = extremely desirable flavour.

⁴Scored as 1 = no smell of fish taint, 10 = extremely having fish taint.

⁵Scored as 1 = extremely undesirable, 10 = extremely desirable.

⁶Scored as 1 = extremely unpalatable, 10 = extremely palatable.

There were no effects of FWBM on colour, cooking loss, shear force value, myofibrillar fragmentation index, expressed juice and sarcomere length. Other studies (Smith & Adamson 1977; Van Wyk et al. 1977) have found no changes in the odour or flavour of pork as a result of the feeding of white fish silage. However, feeding diets with herring offal silage (1:1 herring and SBM and barley grain) revealed tainted meat but no effect on eggs (Raa & Gildberg 1982). There were differences in cooking loss and colour values in the current study compared to those reported for Tunisian lambs fed with extruded linseed (Atti et al. 2013) and which may be explained in differences due to breed or pre- and post-slaughter treatment. In general, findings of the current study confirmed lack of correlation between dietary treatment and meat quality (Diaz et al. 2002; Atti et al. 2013).

Factors such as nutrition and ageing can dramatically affect meat quality (Hernández-Castellano et al. 2013a). Therefore, objective and subjective methods are important to assess meat quality. The latter include sensory evaluation which is particularly important in studies using high levels of fish products in animal feeds. Sensory evaluation revealed no differences in tenderness, juiciness, flavour, aroma, desirability and overall palatability between the 200 g/kg FS and the control diet. Similarly, Penedo et al. (1988) reported no effect of fish silage on flavour and taste of sheep meat fed with fish silage. LF fed to lambs did not have a negative effect on the various sensory comparisons or overall desirability compared to the control treatment (Shqueir et al. 1984). High levels of dietary fish oil have been associated with various off-flavour problems when fed to pigs and cattle (Wignall & Tetterson 1977). However, the levels of FWBM used in the current experiment did not cause any detectable off-tastes detected by panel tasters. Kjos et al. (2001) reported that feeding 100 g/kg fish silage to broiler chicks improved carcass quality more than or equal to fish meal.

4. Conclusion

In general, the current study produced evidence that fish silage can be made in a simple way under Omani conditions. It can fully replace SBM in sheep diets without reducing performance. However, more studies are needed to investigate the issue of introducing beneficial fatty acids into mutton through feeding on FWBM.

Acknowledgements

The authors would like to acknowledge the technical assistance of the Agricultural Experiment Station and Department of Animal & Veterinary Sciences, Sultan Qaboos University.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Osman Mahgoub http://orcid.org/0000-0001-8920-6379

Additional information

Funding

This work was carried out as part of Sultan Qaboos University Research Fund [number IG/AGR/ANVS/05/01].