Increase Lamb Crop by Testing for Pregnancy

Geri Parsons and Cleon Kimberling, Optimal Livestock Services
Reviewed by: Jay Parsons, University of Nebraska-Lincoln and Bill DeMoss, Mountain Vet supply
(Previously published online with Agriview: September 5, 2019)

(Image Source: U.S. Lamb Resource Center)

Pregnancy detection in the ewe provides the opportunity to adjust nutritional and lambing management to save on feed and labor costs. The old adage that “one open ewe takes the profits of five producing ewes” may be true when all costs are calculated. Early determination of fetal numbers and gestational stage gives the option of sorting for nutritional demands in late pregnancy and early lactation. Without that information, the single-bearing ewe is being fed too much or the twin-bearing ewe too little. Open ewes are robbing the pregnant ewes of necessary nutrition. Grouping according to gestational stage will also save on labor and allow for better utilization of facilities and biosecurity.

The key in any type of business is producing an end product, or more simply put, production. The economic benefit of pregnancy testing in cattle, whether it be beef or dairy, has been proven time and time again. The product at the farm or ranch level from a cow is the calf and milk. Individual production must be taken into account in those businesses; it boils down to pounds of meat or milk produced per cow. That’s not only looked at annually but also throughout the lifetime of the cow. The earlier one can tell if there’s a viable pregnancy, the more potential for greater profit.

Pregnancy diagnosis in cattle is conducted via rectal palpation by a veterinarian palpating the uterine tract for the presence of a fetus and determining age based on the size of the fetus. Due to the size of the ewe, that hasn’t been an option. That left ewes being pregnancy-tested, often referred to as bagging, to some degree at shearing, with questionable accuracy. Or ewes that haven’t lambed with group one are put in with group two, and so on until the end of lambing season. That was the case until ultrasound technology became more affordable, making it more beneficial to utilize.

Use pregnancy-testing methods
Marker paint — For a smaller more intensively managed breeding system, the use of marker paint, or a harness on a ram, can provide limited information on the pregnancy status of a ewe. It’s not foolproof because not all ewes marked will become pregnant and remain pregnant. Recording each marked ewe is required on a daily basis. Grease or chalk must be reapplied as needed, changing the color at 14-day intervals. A ewe may continue to be re-marked even though she may already be pregnant. That’s common with an aggressive ram, certain ewes or tight quarters. A noted benefit of using markers is the potential to see a ram-breeding problem earlier if all ewes continue to re-mark.

Blood testing — Blood testing is another method for pregnancy-checking ewes. Measuring blood-progesterone concentration has been trialed several times. A pregnancy-specific protein B may also be tested for in the blood after 30 days of pregnancy with relative success. That will provide an idea of pregnancy status. But it doesn’t indicate fetal numbers or stage of the pregnancy. Some false negatives may occur if the ewe is about 30 days pregnant.

Ultrasound — Ultrasound imagery is the most reliable form of pregnancy-checking the ewe. More information will be gained by the producer, giving him or her the tools to make better management decisions. Ultrasound technologies were developed through the scientific study of sound waves. The older A-mode ultrasound technology doesn’t produce an image. It’s widely available; in recent years it has made a comeback in sales due to marketing. It has a beep or light that goes on when the pregnancy is detected. What’s being detected is fluid. Therefore accuracy is quite variable. The B-mode ultrasound technology has the capability of producing an image. Waves are transmitted from crystals in the handheld ultrasound probe to and from the specific body tissue forming the ultrasound image in gray-scale on the screen. The denser the tissue the lighter or whiter the tissue appears, such as bone, whereas liquid appears black on the image. Although ultrasound equipment was initially developed and used in human medicine, the development of equipment for use on animals has been slow because of great costs, portability and durability.

Ultrasound provides information
Pregnancy-checking the ewe with an ultrasound can provide beneficial information.

Pregnant or open ewes – Save feed for pregnant ewes; they are the ones that need it. Cull all open ewes as soon as possible to save on feed, labor and medicine costs.

Ewes that are consistently open shouldn’t be retained. Without a lot of medical intervention, testing or hormonal therapy, those ewes won’t become pregnant. Rid the farm of those barren ewes now.
Healthy animals are less labor intensive, saving time, medicine, and money. When a ewe has aborted, or is a poor doer, they often have chronic problems preventing them from becoming pregnant. An ultrasound image may detect the problem, depending on the severity of inflammation and damage. Producers are encouraged to cull those ewes to clean the herd.
Stop the spread of disease and cut costs. When debilitating or reoccurring problems are present it’s a great time to pregnancy test and cull open ewes.
If producers incorporate nonseasonal breeding, it’s advantageous to know the pregnancy status as early as possible allowing open ewes to be put back into the breeding group sooner.

Fetal counts — Efficiently manage the proper care and nutrition of the pregnant ewe depending on the number of lambs she’s carrying. A ewe carrying multiple lambs requires 25% more nutritional energy than ewes carrying a single. Proper nutrition can prevent fetal loss and difficult lambing, poor colostrum, poor milk production, poor mothering and pregnancy toxemia.

Single-bearing ewes can be lambed on the field or pasture, with or without the use of a dog or donkey, with little oversight or labor.
Ewes with multiple lambs can lamb in a shed, receiving the added care for greater lamb survival.
Some ewes with single lambs can be utilized for grafting of a triplet.

Gestational dates — The diameter of the fetal thorax or head can be used to estimate the number of days pregnant.

Use that information to group animals according to when they will lamb when space is limited in the shed or corral for the close group.
Use the estimate to group according to nutritional needs.
It’s useful to have estimated-day pregnant when a ewe is marked multiple times by a ram.
That’s important information for 4-H or FFA shows and the purchase of a bred ewe.

Test early
The earlier producers are able to pregnancy-check the ewe, the earlier she can be managed correctly. Whether to cull, feed accordingly or put into a different breeding group, the advantages of ultrasound will save time and money.

The best time to schedule a flock’s ultrasound is when the ram is turned out with the ewes. Timing is important when counts and dates are needed. But there are limitations to the information an individual ultrasound technician can provide based on the technician’s experience, the ultrasound machine used, the facility, the amount of help provided and the timing of the scanning after mating.

Producers should be prepared to follow any requests of the ultrasound technician prior to pregnancy-checking ewes to ensure scanning accuracy. Fetal death loss does occur and will vary greatly between producers, which can be the result of poor nutrition. Producers should be observant; notice what and how much animals are eating. They should also watch for signs of illness, injury and stress. Helpers on the farm or ranch should also know what’s going on and why.

Ultrasound technology is the most useful and practical method for pregnancy-checking the ewe. The earlier in the pregnancy the ewe can be scanned, the earlier she can be properly managed to avoid problems. Pregnancy-checking will save time, medicine, and labor all adding to the bottom line. It will provide valuable information to help producers determine which animals to retain and which animals to cull based on lack of productivity or the presence of disease.