Performance, Carcass Traits and Meat Quality of Crossbred Lambs Fed Whole Cottonseed Levels

Abstract

Byproduct as whole cottonseed (WCS) and soybean hulls are quite used in finishing diets to feedlot lambs and WCS is a potential source to be included in lambs diet when prices are advantageous. The most part of the studies with WCS is used as a replacement of cereals as corn. Thus, this study was conducted to evaluate the effect of replacing a fibrous byproduct (soybean hulls) with increasing levels of WCS (0, 10 and 20%) on the performance, carcass traits and meat quality of feedlot lambs. Thirty crossbred lambs (15 males and 15 females, 20±1.6 kg) were fed 1 of 3 high concentration diets: CTL (without WCS), WCS10 (with 10% WCS), and WCS20 (with 20% WCS) in a block design (sex) for 56 days. Feeding 10 or 20% WCS significantly (P=0.013) improved the feed conversion without affecting the final weight gain, average daily gain or dry matter intake in kg/d. However, the DMI (in %) of live weight was affected by treatments (P<0.0001): lambs fed the CTL and the WCS10 diet consumed more DMI than the lambs from WCS20 diet (4.19, 4.03 and 3.6%, respectively). The hot carcass weight, dressing percentage, longissimus muscle area and fat thickness were not affected by the WCS levels. The shear force and meat colour were similar among treatments. These results suggested that fattening lambs may benefit from an increase in feed efficiency from 10% WCS up to 20% without negatively impacting carcass and meat quality.

Key Words:

• Byproduct
• Meat
• Oil seed
• Sheep
• Weight gain

Introduction

Whole cottonseed (WCS) is a byproduct of the textile industry that contains high levels of oil, protein and fibre and can be used to reduce ruminal problems in high concentration diets due to its slow nutrient release (Martin, 1990). Moreover, WCS has high levels of fatty acids, which may lead to increased weight gain and greater fat deposition in the carcass (Calkins and Hodgen, 2007).

A major limitation for using cotton by-products in animal nutrition is the presence of high levels of gossypol, which is a toxic compound. However, ruminants have the ability to detoxify large amounts of gossypol within the rumen (Reiser and Fu, 1962). Whole cottonseed is a low-cost byproduct, which can help to reduce feedlot costs. Soybean hulls are also a byproduct and an alternative fibre source that may be used to maintain neutral detergent fibre while increasing the energy concentration of ruminant diets (Araujo et al., 2008). However, when prices are at an advantage compared to soybean hulls, WCS could be potentially used as a feed source for lambs diet.

In some studies concerning the effects of WCS as a replacement of cereals (Cunha et al., 2008; Dayani et al., 2011; Kandalys et al., 1998; Luginbuhl et al., 2000; Moore et al., 1994) on the performance and carcass traits of sheep and goats contradictory results have been reported. Moreover, there is a lack of results about the effects of the replacement of fibrous by-products (as soybean hulls) by WCS on performance and meat quality of lambs. Thus, we hypothesised that through replacing a fibrous by-product like soybean hulls with different WCS levels we can increase the feed efficiency of lambs and meat quality. Therefore, the objective of the current study was to evaluate the effect of the replacement of a fibrous byproduct (soybean hulls) with increasing levels of WCS (0, 10 and 20%) on performance, carcass traits and meat quality of male and female crossbred lambs during feedlot fattening.

Materials and methods

Animals and diets

All animals were managed under approved animal care and use guidelines. The experiment was carried out in Pirassununga, state of São Paulo, Brazil (21°59 45 S; 47°25 32 W; altitude 610 m).

This study was conducted with 15 female and 15 male crossbred lambs (fifty days of age) with an initial mean body weight (BW) of 20±1.6 kg. The crossbreeds were from two genetic groups: i) crosses between a Dorper ewe and Texel ram, and ii) crosses between a Dorper ewe and Santa Inês ram. The animals were allocated in three treatments of ten lambs per treatment in a randomised block design. After completion of the sanitary management against endo- and ecto-parasites, 28 lambs were housed in collective pens (two animals per pen) and 2 lambs were housed in individual pens, with dimensions of 1.20 x 2.00 m with a concrete floor, feed bunk and water trough.

The experimental period was 56 days, preceded by seven days for the management of and adaptation to the diets. The lambs were fed diets ad libitum once a day (07:00), and the amount of feed offered per animal was recorded and adjusted according to daily feed orts and calculated not to exceed 10% of the total weight of the diet. Fresh and clean water was available at all times.

Treatment diets had increasing levels of WCS as follows: i) control (CTL) without WCS, ii) 10% WCS (10WCS), and iii) 20% WCS (20WCS), on a dry matter (DM) basis. The ingredient proportions and the nutrient composition of the experimental diets are presented in Table 1. The experimental diets were formulated and calculated according to the National Research Council (1985).

The feed and orts samples were weighed and sampled three times per week to determine the dry matter, estimated consumption, and feed efficiency. Samples of the concentrate mixtures and forage were collected and stored at -20°C for consequent analyses as follows: DM, organic matter (OM), mineral matter (MM), ether extract (EE), crude protein (CP), neutral detergent insoluble nitrogen (NDIN), acid detergent insoluble nitrogen (ADIN) and lignin according to the methods described by AOAC (2005). The contents of the neutral detergent fibre (NDF), ash- and protein-free neutral detergent fibre (apNDF) and acid detergent fibre (ADF) were obtained according to a method described by Van Soest et al. (1991). The dietary metabolisable energy (ME) was determined using the small ruminant nutrition system, version 1.8.0 (Cannas et al., 2004).

Animal weights were determined every 14 days after complete fasting for 16 hours, for a total of four weightings and four periods. The individual lamb average daily gain (ADG) was calculated as the difference between weights over the period.

The performance evaluation was computed from the measurements taken throughout the trial period. The feed efficiency (G:F) and dry matter intake (DMI) were calculated in kg/day.

Table 1. Ingredient and chemical composition of the treatment diets.

Item	Treatments
	CTL	WCS10	WCS20
Ingredient proportions, % DM
Corn silage	10.00	10.00	10.00
Corn grain (ground)	20.00	20.00	20.00
Soybean meal	2.00	0.00	0.00
Urea	1.00	0.88	0.58
Trace mineralised salt	0.70	0.70	0.70
Whole cottonseed	0.00	10.00	20.00
Soybean hulls (pelleted)	66.00	58.00	49.00
Rumensin	0.03	0.03	0.03
Chemical composition
DM, %	89.90	89.40	89.80
CP, % DM	12.60	12.80	13.80
NDF, % DM	45.30	42.20	42.50
ADF, % DM	39.50	37.10	36.80
EE, % DM	2.50	3.90	5.40
Ash, % DM	3.90	4.10	4.40
ME, Mcal kg^-1	1.92	1.99	2.06

CTL, diet without whole cottonseed; WCS10, diet with 10% whole cottonseed; WCS20, diet with 20% whole cottonseed; DM, dry matter; CP, crude protein; NDF, neutral detergent fibre; ADF, acid detergent fibre; EE, ether extract; ME, metabolisable energy.

Table 2. Effect of whole cottonseed levels on performance of fattening crossbred lambs.

Item	Treatments
	CTL	WCS10	WCS20	SEM	P
IBW, kg	39.4	36.9	41.8	3.13	0.360
FBW, kg	61.1	62.0	67.3	4.68	0.423
ADG, kg day^-1	0.195	0.225	0.210	0.02	0.388
DMI, kg day^-1	2.08	1.95	1.89	0.15	0.339
DMI, % LW	4.19a	4.03a	3.6b	0.09	<0.0001
ME intake, Mcal day^-1	3.99	3.88	3.90	0.29	0.833
G:F, g kg^-1	169b	210a	208a	0.01	0.028

CTL, diet without whole cottonseed; WCS10, diet with 10% whole cottonseed; WCS20, diet with 20% whole cottonseed; IBW, initial body weight; FBW, final body weight; ADG, average daily gain; DMI, dry matter intake; ME, metabolisable energy; G:F: total weight gain divided by total DMI.

^a,b Means with different superscript letters in the same row differ by t-Test. Results were based on the pen.

Table 3. Individual effects of whole cottonseed levels on carcass traits of fattening crossbred lambs.

Item	Treatments
	CTL	WCS10	WCS20	SEM	P
Hot carcass weight, kg	14.9	15.2	16.9	1.03	0.376
Dressing, %	48.7	49.1	50.0	1.03	0.408
Longissimus muscle area, cm^2	13.1	14.3	15.4	0.72	0.090
Fat thickness, mm	2.6	3.2	3.4	0.65	0.738
Renal pelvic and inguinal fat, kg	0.33	0.40	0.42	0.10	0.284
pH 1h	6.2	6.3	6.2	0.08	0.670
pH 24h	5.5	5.5	5.6	0.05	0.407

CTL, diet without whole cottonseed; WCS10, diet with 10% whole cottonseed; WCS20, diet with 20% whole cottonseed.

Table 4. Individual effects of whole cottonseed levels on meat quality of fattening crossbred lambs.

Item	Treatments
	CTL	WCS10	WCS20	SEM	P
WBS, kg	3.74	2.77	2.23	0.32	0.090
L*	38.16	38.60	37.70	1.35	0.986
a*	11.74	11.52	11.59	0.46	0.625
b*	12.95	13.49	12.59	0.51	0.524

CTL, diet without whole cottonseed; WCS10, diet with 10% whole cottonseed; WCS20, diet with 20% whole cottonseed; WBS, Warner-Bratzler; L*, lightness; a*, redness; b*, yellowness.

Carcass and meat quality analysis

At the end of the experiment (56 days) all of the animals (hundred and thirteen days of age) were slaughtered on the same day. After being weighed (fasting prior weighting and free access to water), lambs were transported 2 km, by road, to the abattoir of Faculdade de Zootecnia e Engenharia de Alimentos, where they were directly slaughtered by exsanguination. Thus, slaughter and carcass preparation were carried out following the normal procedures of the Sanitary Inspection Regulations for Animal Products (Ministério da Agricultura, 1997).

Carcasses were immediately weighed to obtain the hot carcass weight, and kept at room temperature (12°C) for 24 h. After that period carcasses were re-weighed, to obtain the cold carcass weight. The carcass pH and temperature were measured at one hour and at twenty-four hours post-mortem using a pH meter equipped with a penetrating glass electrode (using a Hanna Instruments HI8314 device) in the longissimus dorsi muscle between the 12^th and 13^th ribs.

The renal pelvic and inguinal fat were removed from the carcass and weighed for each animal. The dressing percentage was calculated by the ratio of hot carcass weight and carcass weight at slaughter × 100. Carcass (left side) then was divided between the 12^th and 13^th ribs to determine the longissimus muscle area and the fat thickness (FT) through a boxed grid in square centimeters (cm²). The FT was obtained ¾ distance from the medial side of longissimus dorsi to its lateral midline side.

During the deboning, three steaks of longissimus muscle with 2.5 cm of the left half of the carcass of each animal were removed, which were then identified and vacuum-packed. A steak from each animal was frozen at -20°C for a posterior objective analysis of tenderness and colour. After thawing for 24 h at 0°C, the steaks were unpacked and rested with the surface exposed to the environment for 20 min for myoglobin oxygenation (Abularach et al., 1998).

The colour of the steaks was determined with a portable colourimeter (MiniScan XE model; Hunter Lab, Reston, VA, USA), using the scale L*, a*, b* of the CIELab system, where L* is the luminosity associated with the chroma (L*⁼ 0 black, 100 white), a* is the chroma ranging from green (-) to red (+), and b* is the chroma ranging from blue (-) to yellow (+) (Houben et al., 2000). The measurements were taken on the surface of interest in three different areas of each sample, and the averages were calculated. After this procedure, the steaks were wrapped in foil and cooked in an electric oven at 170°C until the meat internal temperature reached 65±5°C (AMSA, 1978), measured by individual analogue thermometers (Good Cook Meat Thermometer; Good Cook, Rancho Cucamonga, CA, USA) with a type sensor and a metal needle that was inserted into the centre of the steaks. Then, the steaks were cooled to 5°C for 12 hours in the refrigerator. Subsequently, six cylinders that were 12 mm in diameter were removed with an electric punch from each steak. The tenderness was determined using a Warner-Bratzler shear (WBS) force equipment (G-R Manufacturing Co., Manhattan, KS, USA) equipped with a WBS blade. The measurement was recorded as the average of a minimum of six replicates of the maximum force needed to shear the samples perpendicularly to the axis of the fibre direction.

Statistical analysis

The experimental unit was the pen for performance data, and the animal for carcass traits and meat quality. The block effect was sex (male and female). The effects of treatments were analysed using the PROC MIXED of SAS (version 9.1) according to the following model:

Y_i= µ + B_i + T_i + e_ijk

where Y_i is the dependent variable, µ is the overall mean; B_i is block effect, T_i is fixed effect of WCS levels (0,10 and 20%), and e_ijk is the residual error.

The effects of treatments were determined with averages calculated by the LSMEANS submitted to the t- Test. The initial BW and carcass weight were included in the model as covariate respectively to performance and carcass variables. Block and covariate effect were removed from the model if no effect were observed for both.

Results and discussion

There were no significant block and covariate effects for any variables analysed.

The lambs presented similar DMI in kg/day (Table 2) although, the DMI in% of LW was affected by treatments: lambs fed the CTL and the WCS10 diet consumed more DM than the WCS20 treatment (4.19; 4.03 and 3.6%, respectively). Luginbuhl et al. (2000) and Moore et al. (1994) also reported an inhibitory effect of increasing levels of WCS on the DMI of meat goats and ewes, respectively, although in both studies Luginbuhl et al. (2000) and Moore et al. (1994) replaced corn by WCS unlike this study, which replaced soybean hulls by WCS. Regardless of the fact that WCS is replacing corn or soybean hulls in diets, the result is an increase in dietary fat content, which can affect negatively the DMI (Palmiquist, 1994).

There were no differences in the ADG (Table 2) among treatments. Nonetheless, the lambs fed the CTL (P=0.013) diet had a lower G:F (169 g/kg) than those fed the WCS10 (209 g/kg) and WCS20 (208 g/kg) diets. Similar to our findings, Cranston et al. (2014) evaluated cottonseed product diets (WCS and cottonseed hulls) with the same percentage of NDF as the control diet (without WCS) and observed lower DMI, similar ADG and better G:F for steers fed the WCS and cottonseed hulls diet compared to the CTL diet (without cottonseed).

Reasons for the increase in G:F by lambs fed the WCS diets compared with those fed the CTL diet are unknown, but possibly this result reflects a greater metabolisable energy (ME) concentration for the 2 WCS diets than for the CTL diet. Based on formulated values (Table 1), the CTL diet had a lower EM concentration (1.92 Mcal/kg) than the WCS diets (1.99 p 2.06 Mcal/kg, respectively). Hence CTL diet was less energy dense than the WCS diets. The EM intake (Table 2) was similar among treatments, probably due to the decrease in DM intake observed, since the intake of EM is the product of DMI and diet EM (DMI*EM).

The observed effects by WCS inclusion could also be explained by the increase of lipid content of the diets (Cunha et al., 2008). The high lipid content of WCS may depress cell-wall degradation (Moore et al., 1986), due to some mechanisms as the physical coating of fibre by lipids, the shortage of cations due to formation of insoluble soaps, the inhibition of rumen microbial activity, and modification of the microbial population (Dayani et al., 2011).

In the current study, the G:F was similar for both levels of WCS. On the contrary, Cunha et al. (2008) fed lambs with increasing levels of WCS (0, 20, 30 and 40%) and found that the ADG decreased, and the G:F showed a decreasing linear effect with the inclusion of WCS. Luginbuhl et al. (2000) also found lower ADG when feeding WCS to meat goats, though they – as Cunha et al. (2008) – used WCS to replace corn (unlike this study).

No carcass traits (hot carcass weight, dressing percentage, longissimus muscle area, fat thickness, renal pelvic and inguinal fat and pH) were affected by treatments (Table 3). Similarly, Cranston et al. (2006) found no differences on carcass characteristics when they evaluated WCS or pelleted cottonseed with the same percentage of NDF in finishing diets to feedlot steers.

The dressing percentage and renal pelvic and inguinal fat were not affected by WCS levels, indicating that most likely the WCS diets did not increase the fat deposition.

Neither WBS nor colour was affected by WCS levels (Table 4). Warner-Bratzler shear force values obtained in both treatments are low (CTL:3.7; WCS10:2.8; WCS20:2.2 kg) and characteristic of very tender meat (Santos-Silva et al., 2002). Few studies examining the inclusion of WCS in the diet of lambs have evaluated its effects on meat quality. Vieira et al. (2010) found that lambs fed increasing levels of WCS (0, 20, 30 and 40%) presented no differences in the WBS of the longissimus muscle area, similar to our findings.

There was no change of L*, a* and b* intensity when WCS was utilised in the diet. This possible similarity may be related to the similar ages of animals in this study, since the slaughter age could affect the colour of the lamb meat (Lanza et al., 2011).

Conclusions

When replacing fibrous byproduct (as soybean hulls) in finishing diet, the inclusion of WCS (10 and 20%) for fattening lambs is seemingly more efficient. These results suggest that fattening lambs may benefit from an increase in feed efficiency from 10% WCS up to 20% without negatively impacting the carcass and meat quality. Furthermore, WCS could be used as a sheep feed source for reduce feedlot costs according to its availability and price.

Acknowledgements

São Paulo Research Foundation (FAPESP; São Paulo, Brazil) provided the first author with scholarship and financial support.