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The Impact of Size, Performance and Farming System on Feed Requirements

In the previous section it has been shown that there have been major changes in animal size and productivity over the last 20 years. It is also evident that there is greater diversity of farming system than previously was the case. The challenge in relation to stock unit calculations is to determine which variables should be incorporated within stock unit tables. If important variables are assumed as being single value then the calculations lack credibility. However, if all variables are included then the number of combinations becomes unmanageable.

Spreadsheet modeling of energy requirements for different situations, undertaken as part of this project, shows that in relation to breeding systems there are three key variables. These are:

• maternal liveweight;
• weaning percentage;
• weaning weight of progeny.

The most important of these is maternal liveweight (Figures 2 & 3).

In relation to finishing systems, the three most important variables are:

• average liveweight;
• liveweight gain;
• length of the finishing period.

The most important of these is length of the finishing period (Figure 4).

The implications of these relationships, which have been summarised in Table 10, are that for breeding systems the average liveweight of the female has 2-3x the effect on annual ME requirements as the reproductive rate. However, it is the reproductive rate that is more often considered explicitly in stock unit calculations. Also, annual ME requirement of the breeding female is just as sensitive to progeny weaning weight as it is to the reproductive rate, yet weaning weight is not considered a variable in any existing stock unit tables.

In finishing systems, variation in the length of the finishing period, and therefore the number of days of ‘maintenance’ is the most important variable that affects total ME requirements and hence stock unit values. The second most important variable is average liveweight and the third most important is livweight gain. In existing stock unit tables the length of the finishing period is not given any consideration.

STORE LAMBS

Coop’s (1965) ‘standard ewe’ included the proportion of the lamb energy requirement from pasture only up to weaning. The assumed weaning weight was 22.5-27.5kg. At that time a high proportion of lambs were sold ‘FOM’ (fat off mothers, i.e. at weaning) at light carcass weights. Coop (1965) did not include a stock class to account for lambs grown on from weaning until slaughter (before winter). A high proportion of lambs now fall into the latter category and specialist ‘lamb finishing’ properties turn over a number of intakes of such lambs over the year. Estimates of the energy requirements of a range of finishing lambs options are shown in Table 11:

Figure 2: The relative effect of altering major production variables on the annual ME requirement of breeding ewes, breeding cows and finishing cattle

Proportional Change in Cow variable

Figure 3: The relative effect of altering major production variables on the annual ME requirement of breeding cows .

Figure 4: The relative effect of altering major production variables on the annual ME requirement of finishing cattle

Table 10. The percentage change in annual ME requirements of breeding ewes, breeding cows and finishing cattle for a 10% change in input variable

Percentage change in annual ME requirements
Breeding ewes		Breeding cows		Finishing cattle
Liveweight (kg)	6.2	Liveweight (kg)	5.5	Liveweight(kg)	7.5
Weaning (%)	2.2	Weaning %	2.6	Live wt gain (kg/day)	4.1
Weaning wt (kg)	2.1	Weaning wt(kg)	2.5	Finishing period (days)	10.2

Table 11 The estimated metabolisable energy requirement of lambs post-weaning to slaughter

Liveweight (kg) In Out		Liveweight gain (g/day)	Days	GJ ME per lamb	RSU (6 GJ ME)
25	38	232	56	0.96	0.2
22	38	230	70	1.13	0.2
27	40	220	60	1.03	0.2
20	36	160	100	1.24	0.2
Average				1.09	0.2
for mixed sex lambs, 75 kg mature liveweight, producing 3.5 kg fleece/annum

BEEF CATTLE SYSTEMS

There is considerably more diversity of beef farming systems than was the case in 1965 and the per animal energy requirements of these systems span a considerable range (Table 12). Comparing these figures with those of Coop requires considerable caution given that there are some issues of terminology as to how Coop defined particular classes. However, assuming a stock unit value of 6000 MJME, then some of these systems have stock unit values more than 40 % higher than those proposed by Coop (1965).

Table 12: The energy requirements for some current beef cattle production systems

Growing/Finishing cattle				Activity = medium
Time period	Annual		Apr - Mar
Sex	Start wt		Final wt	Mature Lwt	LWG	GJ ME/year	RSU5
6 to 18 months
Steer	180		400	550	0.60	29.5	4.9
Heifer	160		360	500	0.55	56.8	9.5
Bull	150		420	600	0.74	31.4	5.2
18 to 30 months
Steer	400		560	600	0.44	36.3	6.1
Heifer	360		460	550	0.27	32.4	5.4
Bull	420		560	700	0.38	42.3	7.1
High performance systems:
Yearlings slaughtered before 2nd winter
Steer	250		540	600	0.80	42.6	7.1
Heifer	220		480	550	0.70	38.2	6.4
Bull	240		560	700	0.88	45.9	7.7
Rising 2 year old slaughter by Nov/Dec (250 days)
Steer	400		600	650	0.80	32.1	5.4
Heifer	360		520	550	0.64	26.8	4.5
Bull	420		650	700	0.92	37.1	6.2
Systems > the April/April year – Weaner bull (purchased Nov, 455 days)
Bull	100		420	600	0.70	37.2	6.2
Beef cows
	Average liveweight		Annual loss/gain	Weaning %	Weaning weight
Hard Hill	400		30	82	175	39.6	6.6
Easy Hill	475		40	85	210	42.2	7.0
Good Hill/Flat	550		40	86	250	44.6	7.4

DEER

The variation in size between different genotypes of deer is considerably greater than for sheep and cattle. This is reflected in a very large range of stock unit values for breeding systems (Table 13) and for adult stags (Table 14). In contrast to this, there is much less variation in the stock unit values for various one-year venison finishing systems on account of the target slaughter weights being similar for all genotypes (Table 15).

Animals in a two year system, (mainly red deer rather than hybrids or elk) will spend an additional 5 months (April - August) for those animals slaughtered in for the early spring premiums (Sept) or 9 months if slaughtered after velveting as 2-year olds. The ME requirements for these periods would add 0.7 and 1.5 RSU respectively to the above figures.

Table 13: The influence of hind liveweight, fawn weaning weight and hind genotype on energy requirements of deer breeding systems.

	Hind liveweight (kg)
		Reds 80 100 120			Hybrids 120 140 160			Elk 230 250 280
Weaning Weight (kg)	RSU (6 GJ ME)
40	1.3
50	1.3		1.5
55	1.4		1.5	1.7	1.9	2.1	2.2
60	1.4		1.6	1.7	1.9	2.1	2.3
65			1.6	1.8	1.9	2.1	2.3	3.1
70				1.8	2.0	2.1	2.3	3.1	3.3
80								3.2	3.3	3.6
90								3.2	3.4	3.7
100									3.5	3.7
110										3.8

Table 14 Annual energy requirements for different genotypes of adult stag

	Red	Hybrid	Elk
Liveweight (kg)
average	200	300	400
gain	25	35	45
loss	30	40	50
GJ ME/year	11.6	15.7	19.3
RSU	1.9	2.6	3.2

Table 15: The liveweight (LWT, kg), liveweight gain (LWG, g/day), annual ME requirement and RSU values of three typical one-year venison production systems

Month	Red deer LWT LWG % present			Hybrids LWT LWG % present			Elk LWT LWG % present
Mar	47	150	100	55	200	100	80	220	100
Apr	52	150	100	61	175	100	87	200	100
May	56	150	100	66	150	100	93	150	100
Jun	61	80	100	71	100	100	97	120	100
Jul	63	80	100	74	100	100	101	120	100
Aug	65	120	100	77	120	100	104	150	100
Sep	69	175	100	80	200	100	109	300	100
Oct	74	250	100	86	300	100	118	400	100
Nov	82	250	100	95	350	100	120	400	50
Dec	89	250	100	106	350	100	120	350	30
Jan	97	150	100	106	275	50	120	300	20
Feb	101	150	75	106	230	30	120	200	10
Mar	106	120	50	106	200	20	120	150	0
Average	74	160		84	212		107	235
Annual ME (GJ)			8.26			8.97			8.84
RSU			1.4			1.5			1.5
Bold values represent target slaughter liveweight

 

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