Reproductive Health Management Programs

CHAPTER 93 Reproductive Health Management Programs



PAULA I. MENZIES


Throughout North America, many systems are used for managing sheep, from the traditional annual spring lambing with fall marketing of lambs off pasture, to managing several lambing groups per year, to marketing lambs year round. The basic principles for a reproductive health management program remain the same but need to be fine-tuned with each producer’s limitations and goals in mind.



FACTORS TO CONSIDER IN DESIGNING A PROGRAM



• Types of products to be marketed
• Meat (light lamb, heavy lamb, mutton)

• Wool (fine wool, specialty spinner’s wool)

• Milk (length of lactation, seasonal production versus year-round production of milk)

• Purebred breeding stock

• Type of markets

• Specific local market (e.g., Easter “new crop” lambs)

• Processing plant’s time constraints on cheese production

• Cash flow requirement (may dictate year-round production)

• Forward contracting constraints from regional abattoirs

• Seasonality of markets

• Relationship between lambing and marketing—how old are lambs when they reach market weight?

• Frequency of lambing

• Nutritional/housing/pasture constraints on lambing
• Producer motivation and skills

• Capable of managing a complicated management scheme

• “Weekend” farmer interested in lifestyle farming


TYPES OF REPRODUCTIVE MANAGEMENT SYSTEMS



• Annual lambing in season (Fig. 93-1)

• Spring grass

• Early spring or late winter confinement lambing

• Annual lambing out-of-season

• Fall lambing

• Frequent or accelerating lambing

• Three lambings in 2 years (Fig. 93-2)

• Cornell Star (five lambings in 3 years) (Fig. 93-3)

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Fig. 93-1 Annual lambing in season.


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Fig. 93-2 Three lambings in 2 years.


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Fig. 93-3 The Cornell Star: Five lambings in 3 years.



SETTING GOALS AND MONITORING PRODUCTIVITY


The flock health cycle is composed of the following components:


• Monitoring on-farm productivity

• Goal setting

• Implementing strategies to achieve those goals

• Monitoring the response to the strategies and the effect of outside factors on flock productivity

• Setting goals again

It is a continuous process for which the backbone is monitoring and goal setting.



Guides for Goal Setting



• Regional production averages

• Breed production averages

• Best expected productivity for specific management system and breed

• Producer’s past performance and analysis of limitations on productivity


Record-Keeping Systems


Monitoring requires a functional record-keeping system and the ability to easily turn the data into information useful in the monitoring and management of productivity and health. Examples of common sheep record-keeping systems include head counts at specific intervals (e.g., number at breeding, number of ewes lambing, number of lambs weaned or marked), lambing diaries, individual animal paper records, and computerized on-farm sheep management systems.


An ideal sheep record-keeping system should have the following characteristics:


• Flexible and powerful enough to suit the multitude of diverse management systems

• Easy to use

• Efficient, requiring only a few minutes a day to update

• Streamlined, minimizing the number of places the data need to be recorded

• Designed to produce usable action lists (e.g., ewes ready to lamb, lambs to be weighed, culling lists, animals to be vaccinated) that can be used in the barn, by the chute, or at the weigh scale

• Capable of monitoring reproduction, health and production performance and producing usable and meaningful analysis reports

• Compatible with regional, breed organization, or national production and health improvement schemes

It is unlikely with a flock size greater than 60 ewes that action lists and analysis reports can be produced easily and in a timely manner with any paper system. If individual animal records are to be kept, then it is necessary for the progressive producer to move to a computerized management system.



Information to Be Recorded



• Accurate numbers of animals at breeding, lambing, and weaning. Each ewe should be uniquely identified, and data pertaining to its performance are recorded at breeding, lambing, and weaning, as well as lamb or ewe morbidity, mortality, and culling

• Unique identification can be in the form of ear tags, tattoos, computer chips, or temporary paint branding

• Ram in and ram out dates, artificial insemination dates

• Ewes marked by ram marker harness during breeding. Color of marker can be changed every 14 days to record rebreedings

• Observed abortions with diagnosis if available

• Lambing diary: ewe ID, lamb IDs, sex, status at birth (live/stillborn), assisted lambings, periparturient disease (e.g., pregnancy toxemia, vaginal prolapse, ring womb)

• Body condition score (BCS) at different stages of production

• Outcome of lamb rearing: died (age and diagnosis), marketed, or retained, or sold as breeding stock

• Fostered, artificial reared, supplemented on ewe

• Weaning weights (or weights recorded at other times if on national or regional record of performance [ROP] program)

• Prophylactic or preventive flock level treatments (e.g., anthelmintic dosing, vaccinations, hormones) and individual animal treatments

• Removals from the flock: involuntary culling including death, euthanasia, culling due to disease, and voluntary culling


MEASURES USED IN REPRODUCTIVE MANAGEMENT



Body Condition Score


BCS is a subjective evaluation of muscle development and fat cover and is a management tool rather than an outcome measure of productivity. Routine scoring of ewes and rams helps the producer make nutritional management decisions. If BCS is used correctly, many nutritional mistakes can be corrected before problems begin. See Figure 93-4 for an overview of a commonly used sheep scoring system. Sheep need to be handled in order to be accurately scored because of wool cover and because of breed differences in muscling and fat deposition. A maternal trait/dairy-type ewe (e.g., Finnish Landrace, Rideau, Romanov) will not carry the lumbar muscling of a meat trait breed (e.g., Suffolk, Texel) and may carry more internal fat. Practice and understanding of breed differences will allow a producer to accurately score both types. Ideally, one operator should perform all the scoring, because correlation between different scorers was poor, but with high intraobserver repeatability, in a 1998 study by Calavas and associates (see Bibliographic References at the end of the chapter). The sheep should be palpated over the spinous and transverse processes of the lumbar vertebrae, ribs, and shoulder and the muscles of the “twist” (hind legs and rump). This can be best done in a sheep race, with a drafting gate at the end to separate off the thin animals for special feeding. Goals for BCS and nutritional demands at the different stages of the production cycle are profiled in Figure 93-5.


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Fig. 93-4 Commonly used body condition scoring system for sheep.


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Fig. 93-5 Goals for body condition scores at different stages of production.


(From Body condition scoring of sheep. Ontario Ministry of Agriculture and Food Factsheet, May 1985.)



Ram-to-Ewe Ratio


Factors used to determine the appropriate number of fertile breeding rams for the number of ewes include the age and experience of the ram (e.g., experienced versus maiden ram), ovulatory versus nonovulatory season, terrain (hill versus paddock), estrus synchronization in the ewe flock, length of ovulatory season of breeds being used, and fertility of those breeds during the nonovulatory season. Recommended ratios for common production situations are presented in Box 93-1.



Box 93-1 Recommended Ram-to-Ewe Ratios


With some highly fertile rams on range conditions, ratios of up 1:80 to 1: 100 have been used with success.



Recommended Ram-to-Ewe Ratios






























Mature ram in breeding paddock 1:40 ewes
Yearling ram in breeding paddock 1:25 ewes
Mature ram with maiden ewes 1:30 ewes
Mature ram on rough or barren terrain 1:30 ewes
Mature ram in flock synchronized with ram effect (transition) 1:20 to 1:25 ewes
Teaser ram used to synchronize flock (transition) 1:40 ewes
Mature ram in synchronized flock in season 1:15 to 1:20 ewes
Clean-up ram after synchronization (second cycle) in season 1:30 ewes
Mature ram in synchronized out-of-season flock 1:6 to 1:10 ewes


Length of the Breeding and Lambing Period


The length of the breeding period—that is, period of exposure to the ram—will equal the length of the lambing season plus or minus approximately 3 days. Short, intense lambing seasons are useful for concentrating labor requirements, making more uniform feeding practices, and improving lamb survival. In season, the normal duration of estrus in sheep is 17 days. So a 42-day breeding period is sufficient to achieve excellent conception rates in cycling ewes exposed to capable rams.


The practice of synchronization of estrus commonly is used to induce estrus during the transition period (3 to 6 weeks before the ovulatory breeding season), as well as out of season. Synchronization also can be used during the ovulatory season to shorten the breeding period even more. Figure 93-6 summarizes how the different methods of estrus synchronization can result in a tighter lambing period. If ewes are synchronized with sponges or prostaglandins in season, the breeding season will be 48 hours, optionally followed 10 to 12 days later with a clean-up ram for 6 days to catch repeating ewes. Out-of-season, synchronized ewes will have a breeding season of 48 hours.


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Fig. 93-6 Effect of estrus synchronization on length of lambing period.


(Data from Henderson DC [ed]: The veterinary book for sheep farmers. Ipswich, UK: Farming Press Books, 1990, p 118.)



MEASURES OF PERFORMANCE: CALCULATION, INTERPRETATION, AND GOALS



Calculating Measures of Performance


Flock productivity is measured by calculating either ratios, proportions, or rates. A ratio compares measures that do not share any animals (e.g., ram-to-ewe ratio). For both proportions and rates, the numerator is the number of sheep that are affected (e.g., lambed, culled, died, treated) and the denominator is the number of sheep that are at risk of being affected (e.g., to lamb, the ewe must have been exposed to the ram). A rate also requires a specified time period (e.g., day, month, year, breeding season, birth to weaning) during which the animals were at risk. For example, culling rate is the proportion of sheep that were culled in 1 year (as defined in Herd Health: Food Animal Production Medicine, edited by O.M. Radostits, p. 53; see Bibliographic References).



Reproductive Measures of Performance


The following parameters measure different aspects of reproductive performance. Not all measures should be used in any one flock. A variety are presented here because it is important that parameters be clearly defined, as well as the method of calculation. The language of measuring reproductive performance in sheep is variable and not as well defined as with dairy, beef, and swine performance (as discussed in Herd Health, p 107).


The goals reported here will vary greatly depending on the management system and breeds used but are appropriate for most North American conditions. A schematic of these parameters is presented in Figure 93-7. Possible causes of reproductive failure are summarized in Box 93-2. Data from a 1996 survey conducted by the U.S. Department of Agriculture (USDA) (see Bibliographic References) are included where relevant. Table 93-1 summarizes data from Ontario flocks in the Sheep Flock Improvement Program and is useful for comparison with the USDA data.


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Fig. 93-7 Schematic of parameters used to measure reproductive performance.



Box 93-2 Causes of Reproductive Failure in Sheep


BCS, body condition score; eCG, equine chorionic gonadotropin; MGA, megestrol acetate.



Causes of Reproductive Failure in Sheep








Ram Failure Ewe Failure

Failure to mate

Crayon failure
• Harness does not fit properly

• Wrong type of crayon

Lack of libido
• Disease

• Low BCS

• Photoperiodic effect

Reluctance to breed
• Infectious balanoposthitis (“pizzle rot”)

• Contagious ecthyma of the penis or prepuce

• Lame (footrot, poor conformation)

Experience/age of male
• Too young or too old

Ram-to-ewe ratio
• Too few rams for season, terrain, breed, synchronization, age

Behavior
• Inter-ram aggression

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