Reproductive Performance (RP) in dairy herds continues to be a major issue. While experts suggest that herds should strive for a pregnancy rate of greater than 20%, Virginia's average for DHIA herds is currently 14.1%, indicating potential for improvement.
Unfortunately, improving reproduction is rarely as simple as improving one thing - usually a variety of factors need attention in order to improve RP. At its simplest, improving the RP of a dairy requires the timely administration of semen to a cow with a healthy uterus at the correct time of the estrus cycle. What sounds simple when boiled down to one sentence actually encompasses most aspects of dairy management.
Days open remains a useful tool in diagnosing the weak link in herd RP and there are four components: the voluntary waiting period, heat detection, conception rate, and culling. This issue discusses the voluntary waiting period (VWP), which is an often overlooked area of reproductive performance.
Sixty days has been the standard VWP for years. As reproductive problems increased on dairy farms an attempt was made to lower the VWP to 45 days to improve reproductive management. While good in theory, this practice rarely lead to improvement in RP. In most cases the conception rate in these herds for cows from 45-60 days in milk (DIM) was less than 15%. One of the main issues this early in lactation is uterine health. In a recent study, 44% of the cows still had subclinical metritis at 45 DIM. Many factors have been blamed for uterine problems post calving. These factors include: subclinical hypocalcemia, dirty calving environment, and selenium deficiency. Recent studies have shown that excessive negative energy balance precalving may be the single most important factor in cows developing metritis post-calving. Putting the information from these studies together reveals that a successful reproduction program must begin even before a cow calves.
Heat Detection presents a real challenge on modern dairy farms. The simple answer to heat detection has always been to spend more time watching cows for signs of heat. The problem is that there are many tasks competing for time around the dairy. Add the fact that the modern dairy cow only shows heat for about 8 hours and heat detection can be a real challenge. None of this changes the fact that in order to avoid losing cows from semen deficiency, cows must be found in heat. There are three ways to improve heat detection.
The first way is to put more emphasis on heat detection. There are many ways to accomplish this goal. One person on the farm must be put in charge of heat detection. The old saying "if it's everyone's job it's no one's job" is apt when it comes to heat detection. While everyone can help with heat detection, having one person who is ultimately responsible will improve the program's success rate.
The second option to improve heat detection is to use one of the timed artificial insemination (TAI) protocols like Ovsynch. Since all synchronized cows are inseminated, heat detection for that cycle will be 100%. One of the big misconceptions in TAI protocols is that they eliminate heat detection. While they do eliminate heat detection for the cycle the cows were synchronized, as many as 70% of these cows will likely not conceive and thus will be coming in heat 18-23 days later.
The final method of improving heat detection is to simply put a bull in with the cows. Bulls are often considered to have 100% heat detection. When young, fit, and healthy this fact is close to true. The problem with bulls on dairy farms is that they must be managed to ensure that they maintain healthy feet and legs and are free of other health problems. The most common mistakes with bull breeding herds are having too few bulls for the number of cows and not monitoring bulls for health problems.
It is no secret that the conception rate continues to decline on dairy farms. At one time the goal for conception rate was >50%. Over time that goal fell to >40% and now herds that utilize total AI are getting 25%-35% of their cows pregnant from each service. Experts continue to argue over and work on the causes of low conception rate. Many of these problems are larger than individual dairy farms. With regards to conception rates on their farm, the most important factors dairymen can address are ensuring that the cows that are inseminated are truly in heat and the timing of breeding within the heat period.
With heat detection being such a big problem on most farms there is a tendency to call cows in heat when only the most minor of secondary signs of heat are detected. If these cows are not in heat then the chance of these cows becoming pregnant is zero. In the quest to improve heat detection make sure that you are not over zealous and call too many cows in heat that are not truly in heat.
The second factor is timing of breeding after finding cows in heat. Excellent work by Dr. Ray Nebel showed that cows are most fertile when inseminated 4-16 hours after the first standing heat. The problem when finding a cow in heat on the farm is you never know if this is the first standing heat or not. While the AM-PM rule works, when combined with the typical management systems on many farms it has the potential to result in cows being inseminated too late after their first standing heat. Take for example, a cow that is observed to be in sanding heat at 4 a.m. when cows are being gathered to be milked-this may be the first standing event for that cow or the cow may have been in heat all night. If this cow is not inseminated until after the evening milking it will be 13-23 hours after her first standing heat event. If the cow is inseminated after the morning milking then it would be 3-12 hours after the first standing event. Carefully consider how your management interacts with the timing of breeding after the cow is first detected in heat.
When evaluating reproductive records it is important to look at culling, as well. Excessive culling of cows for reproductive reasons can lead to good-looking reproductive records while actual reproductive performance is in need of improvement.
By the same token trying to expand the dairy herd may lead to keeping cows in the breeding herd for as long as possible. These cows may have an apparent negative impact on reproductive records when compared to another farm.
It is important to take these other factors into account when evaluating your reproductive records. Work closely with your veterinarian and all members of your management team to measure, monitor, and manage the reproductive performance on your dairy farm.
By John Currin, Extension Dairy Veterinarian
Dairy Pipeline newsletter (January, February, March 2009)
Virginia Cooperative Extension