During drought, our focus is generally on what we don’t have and can’t do. Culling a portion of the cow herd is often needed during extended drought. And while parting with those cows can be painful for a number of reasons, it also provides an opportunity to reshape the herd. The standard recommendation to begin the process is to cull the four O’s: open, old, ornery and odd balls.
Today, culling the open cows can really go far beyond just pregnant and open. Pregnancies as early as 30 days can be identified with ultrasound and fetal size can be measured to stage pregnancies. This would be most accurate when done from 30 to 120 days of gestation. Use of ultrasound can also allow gender to be determined. The earliest gender can be differentiated is day 55 to 60 of conception. An optimum time period to target fetal sexing is 60 to 85 days of gestation and no later than 110 days as the pregnant uterus drops out of reach. Sexing fetuses does take a high degree of skill with an ultrasound machine. Fortunately, more and more veterinarians have incorporated ultrasound equipment into their practice.
Staging pregnancies allows for the retention of cows that would calve in a relatively short period of time. A tightened calving season can have tremendous advantages. The range in subsequent calf weaning weights should be decreased and result in a more uniform group to manage or market. When the nutritional requirements of the first cow to calve and the last cow to calve are more similar, more timely changes can be made in ration quality and quantity. Thus minimizing the days of under and over-feeding that occurs with long calving seasons. When it comes to rebreeding the following year, more cows would be “early calvers” that should rebreed promptly given adequate condition at calving. Cows with a tight calving season would respond well to synchronization of estrus and AI, perhaps using gender sorted semen to get the calves desired. In addition, information on stage of pregnancy could be used to retain cows that fit a targeted calving season.
Older cows that can no longer retain body condition or have feet or leg issues would be easy culls. When deeper culling is needed, mouthing to look at teeth can be used to age cows but some type of record on actual age would be valuable if one was forced to make cuts into the middle aged cows.
Culling the ornery or mean cows should be routine. When deeper cuts are needed, notes or other information on any handling issues or excess nervousness during handling would be useful to include in decisions. Several scoring methods are available to evaluate the disposition of your cows.