Many producers are delaying breeding season this year to try and avoid severe winter weather. As we approach the breeding season, cows and heifers are faced with a variety of stressors from the metabolic pressure of providing for a calf to changes in environment. Stress during early pregnancy is well documented to cause embryonic death and loss of pregnancy. However, making strategic management decisions during the fragile two months after breeding can help minimize those losses.
Transporting cows to summer pasture oftentimes coincides with the breeding season. Especially, if cows or heifers are artificially inseminated and need to be near working facilities during that time. It is important to plan transportation, or other stressors, strategically to prevent early pregnancy loss and reducing overall pregnancy rates.
Research conducted at Colorado State University has found that transporting cattle between days 5 and 42 post insemination can result in a 10 percent reduction in pregnancy. When cattle are loaded into a trailer and transported to a new place, they may become stressed and release a cascade of hormones that can alter the uterine environment making it less ideal for supporting a pregnancy.
Prior to day 5, the embryo is still in the oviduct and protected from changes in the uterine environment. After day 42, the embryo has implanted into the uterine wall and is less susceptible to changes in environment. While transporting on days 5 to 42 pose the greatest risk, waiting to haul cows and heifers until a week or two after day 42 may help prevent late embryonic loss. Some general guidelines for when to transport pregnant cows and heifers post breeding:
• Recommended time to haul: Days 1 to 4 or after day 60
• Risk of pregnancy loss: Days 5 to 55 or 60
Another key to minimizing pregnancy loss when transportation is necessary is to avoid hauling cows on excessively hot days — approximately 90 degrees to 110 degrees, and 40 percent humidity or more. Research conducted at Oklahoma State University found that cows exposed to heat stress 8 to 16 days after breeding had decreased progesterone concentration, increased prostaglandin concentrations and reduced embryonic weights.
A 2 to 2-1/2 degree increase in rectal temperature — representative measurement of body temperature — for as little as nine hours has been found to reduce embryo development. Planning to haul cows on days with more moderate temperatures can help reduce stress on heifers and cows and ultimately prevent early pregnancy loss.
It is well established that deficiencies in protein and energy at breeding time has detrimental effects on fertility. Traditionally, it is recommended that cows should be at a BCS of 5 and first calf heifers should be at a BCS of 6 at calving for optimal reproductive performance. Managing cows and heifers to be on a positive plane of nutrition at the time of breeding is essential for the establishment of pregnancy.
Studies at University of Nebraska have found that thin cows, that are on an increasing plane of nutrition and gaining weight, can have equivalent pregnancy rates as cows in moderate condition that are maintaining their body weight at breeding. However, thin cows that are determined to be losing condition can have a reduction in pregnancy rates up to 30 percent, which may be a result of embryonic loss or anestrous at the time of breeding. Having a sound nutritional program is key to optimizing reproductive function during the breeding season.