Reproductive Health Management Programs

CHAPTER 93 Reproductive Health Management Programs



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.





SETTING GOALS AND MONITORING PRODUCTIVITY


The flock health cycle is composed of the following components:







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




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:









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.




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.







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.




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







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