Benchmarks for a Good Lamb Crop
Performance Targets for Replacement Ewe Lambs

Introduction

The theme of this year's seminar is "Building Blocks for Productive Flocks", generally meaning that if the replacement females are managed and grown out well, they are the foundation of the flock's future years' productivity. Conversely, poorly managed and poorly grown-out replacements have a negative impact on the flock's future productivity for many years.

This paper is meant to challenge Ontario's sheep producers to do a better job of raising and managing replacement females. Average production is not good enough as a benchmark when we set production targets.

Production targets will differ between production systems. The appropriate production system is best chosen only after the producer chooses which market(s) is to be targeted, and the one that best matches the resources of the farm and operator.

For the purposes of this discussion, the focus will be on annual pasture lambing and accelerated lambing production systems.

Why Set Production Targets?

Production targets identify what you want to achieve, and when you want to achieve it by. They should be based on the market that a producer has decided to meet. Management, growth and performance targets of the replacement ewe lambs are "sub-targets" of the main production targets of the operation. These sub-targets are really check stations along the way, to ensure that everything is on track so that the main targets can be achieved.

Production targets set to meet a particular market would include number of lambs within a weight range; a specific degree of finish, and a set date.

It becomes obvious that there are a number of management practices that will need to be well understood and fine-tuned to meet the production targets. These include:

• mating management to achieve a high ovulation and breeding (conception) rate within a short period of time;
• understanding the feed requirements (pasture or supplementary) to achieve optimum growth rates of the lambs;
• knowing the lambs' genetic ability;
• and understanding the flexibility within the sub-targets in order to be able to speed up or slow down lamb growth rate to achieve the ultimate target.

Breeding Targets

In all lamb production systems it is important to have high lambing percentages. The key components to achieve high lambing percentages include:

• ewes must be ovulating;
• ovulation rates must be high;
• conception rates must be high;
• rams must be fertile and aggressive breeders;
• a condensed lambing period

Infertile, or subfertile rams are often the cause of poor conception rates. Remember too, that early embryonic losses affect lambing percentages. Keep handling procedures to a minimum during the breeding season, and 20 - 30 days afterwards to minimize this loss.

A condensed lambing period (consequently condensed breeding period) is also desirable from the standpoint of labour efficiencies, feed and health management, as well as to produce uniform groups of lambs. In a 21 day lambing period, all lambs are plus or minus 10 days from the average aged lamb in the group.

Weight of replacement ewe lambs at breeding will influence the conception rate achieved, since puberty and time of first cycling activity are tied to body weight. Flocks that are expanding will keep a higher percentage of replacement ewe lambs. Conception rate will be lower, since there will be a higher percentage of lambs at or below the target weight of 65 percent of the mature ewe body weight. As well, flocks where nutrition and management are short-changed would expect lower conception rates since fewer replacements would have achieved the target breeding weight by 7 months of age.

Feeding Management to Achieve Growth Targets

In order that replacements reach 65 % of mature ewe body weight by breeding time, moderate growth rates need to be achieved. Refer to Christoph Wand's paper on Replacement Ewe Lamb Production for details on feeding management.

Effect of Season on Breeding Performance

As seasonal breeders, sheep's ability to breed throughout the year can be broken down into four phases:

• transitional pre-breeding
• breeding season
• transitional post-breeding
• anestrus

Characteristics of reproductive performance in each of these phases are outlined below.

Transitional Pre-breeding (August - September)	Results in:
fertility (number of ewes cycling) is lower ovulation rate is low	low conception rate low lambing percentage
fertility increases ovulation rate peaks in mid-October/early November	high conception rates high lambing percentage
Transitional Post-breeding (February - April)
fertility decreases (fewer ewes cycling) ovulation rate declines	low conception rate low lambing percentage
Anestrus Period (May - August)
fertility ceases in most sheep ovulation rate is very low	very low conception rates low lambing percentage

Replacement ewe lambs begin cycling later and quit cycling sooner compared to mature ewes. Subsequently, expected conception rates and lambing percentages will be lower for them, and more so, during the transitional periods.

The Replacement Ewe Lamb as a First Time Lamber

If it is the intention to keep lambs from first time lambers as flock replacements it is recommended that these first time lambers are run, and managed as a separate flock. Here are a few important reasons:

• Their nutritional needs are substantially different from mature ewes, as they are still growing themselves.
• Their milk production is lower, so their lambs grow at a slower rate.
• They do not compete efficiently with the mature ewe flock.
• They are more susceptible to internal parasites than the mature flock as their immunity is still developing.

Their lambs are at a distinct disadvantage to reaching targets by breeding time. Considerations of early weaning, or creep feeding can help offset these challenges.

Producers who are unable to manage the replacement ewe lambs separately might consider using a terminal breed ram of small to medium size for breeding to improve survival and growth rates of lambs.

Differences Between Production Systems

For the most part, any differences in the performance targets listed, between the two production systems, can be related back to two factors - breed choice and season of year for lambing (breeding).

Most successful accelerated lambing systems rely on prolific ewe breeds or crosses as their base genetics. Prolific breeds are recognized for having the following traits:

• high fecundity (lambing percentage)
• early maturity
• extended breeding season

These traits allow replacement ewe lambs from prolific breeds to cycle and breed at lighter weights, to have higher conception rates, and higher lambing rates compared to non-prolific breeds. As well, mortality rates are also higher in prolific breeds, since birth weight decreases with increased number of lambs per litter.

Pasture lambing flocks tend to rely on breeds and breed crosses that have the following traits:

• very strong mothering ability
• excellent foraging ability
• medium fecundity

Extended breeding season is not as important for pasture based flocks since breeding time is chosen to target lambing to coincide with pasture growth. Because fecundity is not as high, lamb mortality targets are lower in pasture systems compared to accelerated lambing systems. Recognize that these are average mortality targets, since weather during lambing can contribute to mortality rates as happened in the spring of 2002. This type of weather is the "one in 10 year" worst case scenario.

Mortality rates of lambs from first time lambers are higher than mortality rates of lambs from mature ewes. Generally, first time lambers take longer to lamb, are slower cleaning off their lambs, and more reluctant to allow lambs to nurse. This applies equally to all production systems.

Economics (Cost-Benefit)

Every management decision must include the economic impact - what is the cost? What is the benefit? This pertains equally to management and performance of the replacement ewe lamb flock. Feed costs account for the highest portion of operating expenses, and are expected to remain high this feeding season. A balanced approach to improvements in the feeding program will ensure that unnecessary expenses are avoided.

Comparison of Good Production Performance with Average Performance for two 60 ewe startup flocks (Alberta, 1994)

Total feed per ewe per year .80 Tonne

Average Performance
Live lambs born	160%
Lamb mortality	18%
Lambs raised to market weight	132%
Market weight of lambs	105 pounds
Total feed per ewe per year	.80 Tonne
Net profit	($3,551)
Net profit per ewe	($59.19)
Net cash flow per year	($1,995)

Good Performance
Live lambs born	190%
Lamb mortality	10%
Lambs raised to market weight	171%
Market weight of lambs	110 pounds
Total feed per ewe per year	.66 Tonne
Net profit	$466
Net profit per ewe	$7.76
Net cash flow per year	$1,951

Although not specific to replacement ewes, this table shows the impact of good production performance on net profit compared to average performance levels. These numbers are from a Cost of Production Study of Alberta operations in 1994.

Conclusion

Performance targets are difficult to achieve unless real measures are taken and evaluated. Producers are encouraged to:

• weigh lambs at weaning and calculate average weight by sex
• calculate necessary weight gain to achieve target breeding weight
• weigh and condition score replacement ewe lambs prior to breeding time
• weigh and condition score first time lambers at a specific time after lambing that coincides with some other handling procedure
• weigh and condition score first time lambers at weaning
• track total feed used and cost of feed; conception rates; lambing percentages; mortality rates and growth rate of their lambs

Use these data to fine-tune your management so that next year's replacements will have every opportunity to perform at the desired levels.

The following table provides some performance targets and their ranges for replacement ewe lambs.

Reproduction Targets for Replacement ewe Lambs in Two Production Systems

Reproduction Targets for Replacement Ewe Lambs in Two Production Systems

		Annual Pasture		Accelerated
		Target	Range	Target	Range
Age @ Breeding (months)		7	7-9	7	6-12
Wt @ Breeding (% of mature ewe wt)		65%	60-70	65%	55-80
Length of Breeding Period (days)		21	17-35	21	17-35
Wt @ Weaning (pounds)		60	55-70	50	35-60
Age @ Weaning (months)		3.5	2.75-4	2	1.5-2.5
Average Daily Gain-Weaning to Breeding (pounds)		0.4	0.25-0.5	0.35	0.2-0.6
Conception Rate (In Season) %		80	>65	80	>70
Conception Rate (Out of Season) %		-	-	30	>20
Lambing Percentage (Prolific)		1.6	>1.2	1.6	>1.2
Lambing Percentage (Non-prolific)		1	>0.8	1	>0.8

Mortalities		Non-prolific		Prolific
Lambs	% Stillborn	7	7-9	7	6-12
	% Birth to 10 Days	65%	60-70	65%	55-80
	% 10 Days to Weaning	21	17-35	21	17-35
	% Weaning to Market

		Annual Pasture		Accelerated
Mortality in Adult Ewes (%)		2	1-5	4	2-5
Confined (In Addition to Annual or Accelerated)		2	-	2	--
Outwinter (In Addition to Annual or Accelerated)		0	-	0	-

Conception Rate = number of ewes lambing/number of ewes exposed to ram
Lambing Percentage = number of lambs born/number of ewes lambing
Lamb Crop = conception rate x lambing percentage

References

AgVentures - Ag. Business Profile: Commercial Sheep Production. 1999. Alberta Agriculture. Agdex 430/830-1.

Achieving Production Targets for Prime Lamb. 2000. Department of Agriculture, Western Australia.

Reducing the Seasonality of Prime Lamb Production. 1998. E.J. Grennan, Teagasc Research Centre, Ireland.