Breeding Management

Primarily for economic reasons, mares are bred to have their foals during the months of January through May

(Northern Hemisphere). However, horses are long-day breeders that have optimal reproductive success from April through July. The equine reproductive cycle is entrained to daylength (photoperiod); therefore, estrus can be induced earlier in the year by using an artificially lengthened photoperiod. The daily schedule should provide approximately 16 hours of light (natural plus artificial) and 8 hours of darkness. This schedule should begin around the first of December, allowing time for the mare to go through the transitional phase and enter the first ovulatory cycle in mid-to-late February. The artificial lighting program should continue until the mare is determined to be safe in foal. Artificial lighting programs are sometimes used with gestating mares to ensure a return to cyclicity after foaling. Stallion owners may also consider an artificial photoperiod if the majority of their stallion's book will be bred early in the breeding season, but this is not recommended if most of his mares will be bred later (April June).

Exogenous hormonal treatments may be beneficial in managing the reproductive cycle of the mare. The most frequently used treatments are prostaglandin (for shortening the luteal phase between ovulations), human chorionic gonadotropin (for ensuring ovulation of a large pre-ovulatory follicle), and progestins (for preventing estrus or for early pregnancy maintenance).

Time of breeding is determined by evaluation of the following criteria: 1) intensity of estrus (Fig. 2); 2) patency of the cervix; 3) uterine environment; and 4) follicular status. All of these criteria are indicative of the mare's physiologic readiness for breeding. They provide a checklist for the breeder to ensure that the mare is inseminated at the optimal time for conception. Mares that do not meet these criteria may not be candidates for breeding.

The method of breeding plays a significant role in the timing of insemination of the mare. When multiple inseminations are possible, initial inseminations tend to be made slightly earlier during estrus. The interval between inseminations in the mare should be 48 hours, the length of time that spermatozoa remain viable within the female reproductive tract. For hand-mating or if semen is limited, timing the insemination as close to ovulation as possible is paramount to the success of breeding. Conception rates in the mare are increased when sperm are within the female reproductive tract prior to ovulation,[6] providing adequate time for capacitation. For situations in which only one insemination or breeding is possible, it is important to use all information available to optimize chances for conception and to inseminate close enough to ovulation that only one insemination is necessary.

A significant factor related to successful artificial insemination is the number of motile spermatozoa used

Score Description

1 Poor. The horse is extremely emaciated. Spinous processes (backbone), ribs, and tailhead project prominently. Bone structure of the withers, shoulders, and neck easily noticeable. No fatty tissue can be felt anywhere.

2 Very Thin. Horse is emaciated. Slight fat covering over base of spinous processes and transverse processes of lumbar vertebrae feels rounder. Spinous processes, ribs, hips, and tailhead are prominent. Withers, shoulders, and neck structures faintly discernable.

3 Thin. The spinous processes stand out, but fat covers them to midpoint. Very slight fat cover can be felt over the ribs, but the spinous processes and ribs are easily discernable. The tailhead is prominent, but individual vertebrae cannot be seen. Hips are visible but appear rounded. The withers, shoulders, and neck are accentuated.

4 Moderately Thin. The horse has a negative crease along its back, and the outline of the ribs can just be seen. Fat can be felt around the tailhead. Hip bones cannot be seen, and the withers, neck, and shoulders do not look obviously thin.

5 Moderate. The back is level. Ribs cannot be seen but can be easily felt. Fat around the tailhead feels slightly spongy. The withers look rounded, and the shoulder and neck blend smoothly into the body.

6 Moderate to Fleshy. There may be a slight crease down the back. Fat around the tailhead feels soft, and fat over the ribs feels spongy. There are small fat deposits along the sides of the withers, behind the shoulders, and along the sides of the neck.

7 Fleshy. There may be a crease down the back. Individual ribs can be felt, but there is noticeable fat between the ribs. Fat around the tailhead is soft. Fat is noticeable at the withers, the neck, and behind the shoulders.

8 Fat. The horse has a crease down the back. Spaces between the ribs are filled with fat so that the ribs are difficult to feel. The area along the withers is filled with fat, and fat around the tailhead feels very soft. The space behind the shoulders is filled in flush, and some fat is deposited along the inner buttocks. There is noticeable thickening of neck.

9 Extremely Fat. The crease down the back is very obvious. Fat appears in patches over the ribs, and there is bulging fat around the tailhead, withers, shoulders, and neck. Fat along the inner buttocks may rub together, and the flank is filled in flush.

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Fig. 2 During estrus, the mare demonstrates a number of signs indicating that she is receptive to the sexual behavior of the stallion. (View this art in color at www.dekker.com.)

for breeding. Traditionally, the minimum insemination dose using fresh semen has been 500 x 106 sperm cells. The number is doubled when the semen has been preserved in a cooled environment (1 billion). Samper[7] stated that there was no consensus on the minimum number of progressively motile sperm when using frozen semen due to the wide variation in freezing success among stallions. He did indicate that insemination doses ranging from 600 800 x 106 sperm with 30 35% motility seemed to provide the highest pregnancy rates.

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