| Quality
Beef from Autumn Grass - 1999
|
| Exp
1: Concentrate Level and Gross Allowance
A previous study carried out during the autumn of 1995 and 1996 at Grange (Drennan et al., 1997), compared feeding 3.5kg of a barley or pulp based ration per head per day to 17 month old continental cross heifers. They achieved an 11:1 carcass response the first year and a 36:1 response the next year. During the first year, heifers were stocked at 4/ha compared with 2.5/ha in the second year. There was no effect of the concentrate type on animal performance. The results of this study would indicate that the carcass response to concentrate supplementation was dependent on grass supply.
In 1996 an experiment was carried out to quantify the relationship between grass supply and concentrate supplementation level on animal performance. The trial lasted 100 days (23 August to 1 December) and 110 continental crossbred steers were used. Three herbage allowances and three concentrate levels were compared. A group was also offered concentrates ad-libitum.
The daily herbage allowances offered were 6, 12 and 18kg DM/head, equivalent to 1, 2 and 3% of bodyweight respectively, while the daily supplementation levels were 0, 2.5 and 5kg (2.5kg twice per day) of concentrates. The concentrate pellet comprised of barley (0.29), unmolassed beet pulp (0.29), maize gluten (0.29), soya bean meal (0.07), molasses (beet) (0.03) and min./vits. (0.03) and was fed individually to all animals. The swards used were re-growths following a series of silage harvests. Kill-out proportion, carcass weight, carcass and liveweight gains are shown in Table 2.
Table 2 : The effect of daily herbage allowance (% liveweight) and concentrate level (kg/day) on liveweight and carcass gain, kill-out proportion, carcass conformation and fat score and internal fat weight. |
| Herbage
allowance (% liveweight) |
1% |
2% |
| Concentrate
level (kg/day) |
0 |
2.5 |
5 |
0 |
2.5 |
5 |
| Grass
DM intake (kg) |
5.29 |
5.40 |
5.23 |
9.28 |
7.98 |
7.34 |
| Final
liveweight (kg) |
583 |
620 |
654 |
619 |
643 |
669 |
| Liveweight
gain (kg/day) |
0.14 |
0.54 |
0.94 |
0.53 |
0.78 |
1.06 |
| Carcass
weight (kg) |
304 |
332 |
352 |
323 |
348 |
361 |
| Carcass
gain (kg/day) |
0.088 |
0.393 |
0.617 |
0.290 |
0.551 |
0.695 |
| Kill-out
rate (g/kg) |
522 |
537 |
538 |
521 |
541 |
540 |
| Carcass
conformation1 |
2.27 |
2.73 |
3.18 |
2.64 |
3.09 |
2.91 |
| Fat
score2 |
3.73 |
3.79 |
3.79 |
3.85 |
4.15 |
3.91 |
| Internal
fat (kg) |
5.05 |
7.35 |
8.82 |
6.79 |
7.57 |
8.92 |
| Internal
fat / carcass (g/kg) |
17 |
22 |
25 |
21 |
22 |
25 |
|
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| Table 2 (cont.): The effect of daily herbage allowance (% liveweight) and concentrate level (kg/day) on liveweight and carcass gain, kill-out proportion, carcass conformation and fat score and internal fat weight. |
| Herbage
allowance (% liveweight) |
3% |
Ad-lib. |
S.E.M. |
| Concentrate
level (kg/day) |
0 |
2.5 |
5 |
conc. |
|
| Grass
DM intake (kg) |
12.95 |
9.41 |
9.27 |
|
0.586 |
| Final
liveweight (kg) |
641 |
668 |
676 |
703 |
14.1 |
| Liveweight
gain (kg/day) |
0.75 |
1.05 |
1.14 |
1.43 |
0.09 |
| Carcass
weight (kg) |
330 |
355 |
363 |
371 |
8.4 |
| Carcass
gain (kg/day) |
0.360 |
0.631 |
0.727 |
0.809 |
0.0344 |
| Kill-out
rate (g/kg) |
515 |
532 |
538 |
528 |
5.3 |
| Carcass
conformation1 |
2.73 |
3.09 |
3.09 |
3.09 |
0.145 |
| Fat
score2 |
4.03 |
3.97 |
4.14 |
4.64 |
0.212 |
| Internal
fat (kg) |
7.93 |
9.19 |
10.25 |
10.69 |
0.746 |
| Internal
fat / carcass (g/kg) |
24 |
26 |
28 |
29 |
0.1 |
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|
Liveweight gain in the absence of concentrates was 0.75 kg/head/day at the high herbage supply. Increased live and carcass weight gains were associated with increased grass supply, however, the response to additional grass supply diminished when concentrates were provided. At current prices (carcass = 170p/kg and concentrates = £130/tonne) there was an economical response to the first 2.5kg of concentrate at all grass supplies and to the second 2.5kg of concentrate at the lowest grass supply. The carcass production responses to concentrate level at the different grass supplies are shown in Table 3. At all grass allowances concentrate supplementation improved carcass conformation score (Table 2). However increased grass supply improved conformation only in the absence of concentrates.
Table 3.Carcass response (kg concentrate/kg carcass)
|
| Herbage
allowance |
Concentrate level (kg/day) |
| (kg
DM/hd/day) |
0
to 2.5 |
2.5
to 5 |
0
to 5 |
| 6 |
8.6 |
10.4 |
9.5 |
| 12 |
8.3 |
22.7 |
15.5 |
| 18 |
10.8 |
20.8 |
15.9 |
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|
To determine the impact of supplementing autumn grass with concentrates on meat quality, the right hand side M. Longissmus dorsi (LD) was excised, post slaughter, from all animals used in Experiment 1. Intra-muscular fat content was determined in all samples. Fat was extracted from 1 g of the LD muscle and the fatty acids were quantified and expressed as g/100 g fatty acid methyl esters (FAME).
Fourteen days post-slaughter, steaks were taken from 6 treatments, shown in Table 4. Warner Bratzler Shear Force (WBSF) which is a mechanical measurement of meat tenderness was measured and a sensory analysis was performed on cooked samples by a group of trained taste panellists. The 6 treatments were selected to give a range of pre-slaughter diets varying from all grass to all concentrates.
Table 4. The effect of daily herbage allowance and concentrate level on intra-muscular fat, fatty acids, WBSF and sensory analysis
|
| Herbage
allowance (% liveweight) |
1% |
2% |
| Concentrate
level (kg/day) |
0 |
2.5 |
5 |
0 |
2.5 |
5 |
| Intra-muscular
fat (g/100g muscle) |
2.85 |
2.82 |
2.32 |
2.20 |
2.54 |
2.77 |
| Saturated
fatty acids(g/kg fat) |
552 |
574 |
522 |
574 |
522 |
581 |
| Monounsaturated
fatty acids (g/kg fat) |
468 |
452 |
498 |
454
|
489 |
445 |
| Polyunsaturated
fatty acids (PUFA) (g/kg fat) |
32 |
28 |
29 |
27 |
36 |
26 |
| Polyunsaturated
: Saturated ratio |
0.06 |
0.05 |
0.06 |
0.05 |
0.07 |
0.05 |
| n-6
PUFA (g/kg FAME1) |
19 |
14 |
18 |
15 |
19 |
13 |
| n-3
PUFA (g/kg FAME) |
10.1 |
5.6 |
6.9 |
8.0 |
11.2 |
6.9 |
| n-6
: n-3 PUFA ratio |
1.9 |
2.5 |
2.6 |
1.9 |
1.7 |
1.9 |
| Warner
Bratzer shear force (kg) |
|
|
4.34 |
|
3.98 |
4.08 |
| Tenderness2 |
|
|
5.74 |
|
5.69 |
5.62 |
| Texture2 |
|
|
3.71 |
|
3.86 |
3.69 |
| Flavour2 |
|
|
3.81 |
|
3.88 |
3.82 |
| Acceptability2 |
|
|
3.76 |
|
3.69 |
3.76 |
|
|
|
Table 4 cont. The effect of daily herbage allowance and concentrate level on intra-muscular fat, fatty acids, WBSF and sensory analysis
|
| Herbage
allowance (% liveweight) |
3% |
Ad.lib |
S.E.M. |
| Concentrate
level (kg/day) |
0 |
2.5 |
5 |
conc. |
|
| Intra-muscular
fat (g/100g muscle) |
2.32 |
2.37 |
2.90 |
4.42 |
0.14 |
| Saturated
fatty acids(g/kg fat) |
517 |
522 |
581 |
507 |
4.8 |
| Monounsaturated
fatty acids (g/kg fat) |
501 |
495 |
496 |
512 |
4.8 |
| Polyunsaturated
fatty acids (PUFA) (g/kg fat) |
29 |
32 |
25 |
30 |
1.6 |
| Polyunsaturated
: Saturated ratio |
0.06 |
0.06 |
0.05 |
0.06 |
0.003 |
| n-6
PUFA (g/kg FAME1) |
16 |
18 |
16 |
23 |
0.8 |
| n-3
PUFA (g/kg FAME) |
8.2 |
9.3 |
6.6 |
4.4 |
0.81 |
| n-6
: n-3 PUFA ratio |
2.0 |
1.9 |
2.4 |
5.2 |
0.60 |
| Warner
Bratzer shear force (kg) |
4.79 |
|
4.16 |
3.85 |
0.279 |
| Tenderness2 |
5.20 |
|
5.80 |
6.15 |
0.325 |
| Texture2 |
3.55 |
|
3.66 |
3.81 |
0.148 |
| Flavour2 |
3.82 |
|
3.83 |
3.89 |
0.185 |
| Acceptability2 |
3.55 |
|
3.88 |
3.94 |
0.170 |
|
|
There was no effect of supplementing grass with concentrates on intra-muscular fat concentration or the concentrations of saturated, mono-unsaturated or PUFA. However the animals offered concentrates ad-libitum produced meat with a higher concentrations of intra-muscular fat and n-6 PUFA and lower concentration of n-3 PUFA. There was no effect of pre-slaughter diet on tenderness as measured by WBSF or on any of the qualities assessed by the taste panellists.
Thus, it has been shown (at Grange) that autumn grass in plentiful supply can maintain a daily liveweight gain of 0.75 kg /day but grass wastage is very high. In practice, at normal stocking rates, such a supply of grass will generally not be available after August. Supplementation of cattle at pasture with concentrates, even at the high grass allowance, will improve carcass gain and carcass conformation. The economical level of supplementation was shown to be 2.5kg/head/day at the high grass supply and 5.0kg of concentrates where grass was scarce (6kg DM/hd/day).
Animals offered concentrate supplemented autumn grass produced meat of similar consumer acceptability as that of animals offered concentrates ad-libitum. However, animals offered concentrates and grass produced an intramuscular fatty acid profile that was more beneficial to human health than that of animals offered concentrates ad-libitum.
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