Get 'Em Bred and Keep 'Em
by Mel DeJarnette, director of technical research, Select Sires Inc.
A.I. breeding problems can be classified into two fairly broad categories: fertilization failure and embryonic death. Most of my articles focus on semen handling, heat detection and estrous synchronization to improve fertilization rates. However, research suggests that with normal semen quality and appropriate timing of inseminations, fertilization rates will exceed 80%. The difference between the fertilization rate and your pregnancy rate is due to early embryonic death. It's time to dedicate an article to keeping cows pregnant once fertilization occurs.
When you mention embryonic death, most people immediately think of abortion and aborted fetuses. However, embryonic mortality rates are highest in the first few weeks after breeding; before a recognizable fetus is fully developed. Data compiled by Sreenan and Diskin (1986) suggests fertilization rates approach 90% while actually pregnancy rates will decline to 60% by day 19 after insemination (Figure 1).
During the period of maternal recognition (days 16-19 after estrus), hormonal communication between the developing embryo and the uterus is essential for recognition and maintenance of the pregnancy. When the embryo and uterus fail to communicate, the corpus luteum (CL) is regressed resulting in the animal returning to estrous. While embryonic death is often associated with an extended inter-estrus interval (25-35 days), this may not always be the case. If embryonic death occurs early enough (< 7="" days),="" the="" animal="" will="" likely="" return="" to="" estrus="" at="" a="" normal="" 18-24="" day="">
The potential reasons for very early embryonic death (< 3="" weeks)="" are="" numerous,="" difficult="" to="" define="" and="" often="" not="" clearly="" understood.="" in="" general,="" it="" appears="" that="" any="" type="" of="" stress="" on="" an="" animal="" can="" increase="" rates="" of="" embryonic="" mortality.="" typical="" sources="" of="" stress="" that="" can="" affect="" reproduction="" include="" high="" milk="" production,="" poor="" nutrition,="" heat,="" disease="" and="">
Obviously it would not be economically advisable to decrease milk production in order to get better pregnancy rates. However, it's important to keep in mind that there may be interactions among different sources of stress. Thus, the high producing cows in a herd will be more sensitive to stress arising from other sources.
Minimizing stress from all sources is essential to maintenance of high levels of production and reproduction.
Animals on a poor plain of nutrition, as reflected by low body condition scores, have been shown to have reduced pregnancy rates and altered levels of several important reproductive hormones including LH and progesterone. Progesterone is essential to maintenance of the pregnancy and may be closely associated with the ability of the embryo and uterus to communicate. Use body condition scoring on a routine basis to monitor the effectiveness of your nutrition program. Cows should calve in at a body condition score of about 3.5. Energy dense postpartum rations should be used to minimize negative energy balance and body condition loss. Cows should lose no more than one point of body condition after calving before they start to regain weight. Work with your nutritionist to develop a complete nutrition program tailored for cows at various stages of lactation and production levels.
Work with your veterinarian to establish a sound herd health program addressing all diseases of relevant concern in your geographic region. Remember, to be effective, all vaccines require time to work before they can establish immunity.
Also, many vaccines can cause an elevation in body temperature which can result in reduced fertility. Thus, make sure all vaccinations are completed at least three weeks prior to the VWP. When vaccinating pregnant animals, make sure all vaccines are approved and recommended for use in these animals.
Mastitis and high somatic cell counts are signals of a reduced immune system and have been associated with reduced reproductive performance. In addition to production of a high quality dairy product, proper hygiene and sanitation procedures in the milking parlor may go a long way in improving reproductive performance as well.
Heat stress can have extreme effects on early embryonic development. Your first line of defense against heat stress is to focus on estrous synchronization and heat detection in the spring to get cows pregnant before hot weather arrives. A more advanced fetus is less sensitive to heat stress.
Recent research (Drost et al., 1999) found embryo transfer of frozen-thawed embryos obtained from super-ovulated cows may lend itself to improved summer time fertility, however, frozen IVF embryos failed to demonstrate any positive effect on fertility. Keep cows as cool as possible by use of shade, sprinklers and plenty of cool clean water. Some research suggests that the 24 to 48 hours before and after estrus are extremely important for establishment of pregnancy. Any preferential cooling animals in estrus receive during this time will likely be worth the investment.
Stress from fear or excitement may also cause reproductive problems. Keep animals as calm as possible any time you handle them but especially at breeding and for the following several weeks. Avoid isolation of individual animals. Cows are social creatures that often get anxious and excited when separated from the herd. If a single animal must be isolated for breeding, herd health, etc., place another animal with her to help keep her calm. If animals must be transported after breeding, research found that transport at two weeks after A.I. reduced pregnancy rates by 12% compared to transporting animals within one to four days after A.I.
GnRH and Problem Breeders
Gonadotrophin releasing hormone (GnRH) has long been used to treat problem breeding cows. Most commonly known as Cystorelin, injections of GnRH to problem breeders (>3 services) at the time of estrus (+24 hours) appears to help these animals develop a more competent CL, higher levels of progesterone, and may increase conception rates by 5-15%. GnRH at estrus does NOT appear to have a cost effective benefit in first or second service animals.
Beware that injections of GnRH at the time of estrus has been associated with an increased incidence of twins. However, GnRH used in estrous synchronization protocols (Ovsynch or Select Synch), also appears to be good therapy for problem cows and does not appear to increase the incidence of twinning.
Don't Shoot Yourself in the Foot!
Prostaglandins (PGF) have become an increasingly important component of dairy herd reproductive management programs. However, pregnant animals injected with this hormone will abort. Accurate recording keeping systems are essential to ensure that previously inseminated or pregnant animals are not inadvertently injected with prostaglandin.
Oxytocin, which is often used to encourage milk let down in slow milkers, has been shown to stimulate muscle contractions and PGF production in the uterus. Recent research (LeMasters et al., 1999) found that 100 IU injections of oxytocin at 8 hour intervals on days 5-8 after mating resulted in increased PGF secretion, short estrous cycles, and higher rates of embryonic mortality. Although the level of oxytocin use in this study is relatively high, these data suggest it might be wise to avoid oxytocin injections during the first few weeks after breeding.
Reinsemination of pregnant animals can wreak havoc on your conception rates. In the study shown in Figure 2, animals were inseminated based on observed standing estrus. Half of the animals were then reinseminated 12-24 days later without regard to estrous expression. Animals were palpated for pregnancy 40 days after the initial A.I. Pregnancy rates were 40% for control animals and only 4% for the reinseminated cows. These results suggests that reinsemination of pregnant animals during the first few weeks of gestation will result in abortion/early embryonic death 90% of the time. This may be a major source of poor fertility in herds that breed cows exclusively on chalk markings or other secondary signs of estrus. Extreme caution must be exercised when interpreting secondary signs of estrus in repeat animals. If a thick mucous plug is encountered, practice mid-cervical semen deposition. Would you believe that some herds may improve pregnancy rates if they simply quit inseminating so many cows?
Don't ignore the possibility that your hormone injection schedule or your heat detection and breeding program may be causing abortions in your herd. To do so would be "Shooting yourself in the foot".