Pregnancy and the rates of efficiency
Hit the right submission and conception levels for best results
Published 08/03/2011 | 05:00
The key to reproductive efficiency in dairy cows lies in submission and conception rates. In fact, pregnancy rate is a product of both. But what do we mean by these terms and what should we be aiming for?
- Submission rate: This refers to the proportion of cows that are calved more than 42 days with no uterine health issues that are submitted for AI over a defined period. In most cases, we're talking about the first three, six or nine weeks of the breeding season. Because a three-week submission rate equates to the length of the average oestrous cycle, the target three-week submission rate for eligible cows is 90pc.
The three key factors that affect submission rate are achievement of normal uterine environment, early resumption of cyclicity and a high efficiency of heat detection.
- Uterine environment: After calving, the uterus needs a minimum of six weeks to recover and be ready to support the next embryo. As a result, there is no point starting to breed cows before 42 days after calving.
- Resumption of cyclicity: Dairy cows that have had a normal calving event and are healthy and well managed return to normal cyclicity within 15-20 days of calving. The first heat should be observed from approximately day 25 after calving and then normally occurs at 18-24 day intervals thereafter. On average 50-80pc of cows within a herd fall into this category, with the balance of cows having delayed resumption of ovulation. The most common reasons for delayed resumption of cyclicity are excessive loss of body condition, and/or severe metabolic/disease insults in the early post partum period. Another category of cows are those that ovulate normally initially but subsequently develop an extended cycle. This problem is normally associated with some degree of a uterine infection that prevent oestrous cycles. Ovarian cysts may account for up to 5pc of cows with delayed resumption of cyclicity.
- Efficiency of heat detection: Detection of oestrus is a key part of achieving good submission rates on farms. However, heat detection is a management task and as such is carried out with variable accuracy and efficiency on different farms. Added to this is the fact that duration and expression of oestrus has actually decreased as cows have been selected for greater milk yield over the last decades. To effectively detect over 90pc of oestrous events within a herd, 4-5 times/day heat detection is required. Each period of observation needs to last for a minimum of 30 minutes and should be devoted purely to the observation of the cows. The true indicator of oestrus is standing to be mounted with all other signs being just secondary and may be associated with the period before, during or after oestrus itself. Farms with poor reproductive efficiency tend to have problems with both accuracy and efficiency of detection of oestrus. Poor accuracy leads to cows being inseminated at the incorrect time and will decrease conception rates to an individual service. Poor efficiency leads to oestrous events being missed, thereby extending the interval to return to pregnancy.
- Conception rate: This is affected by multiple farm factors. This includes timing of insemination. Optimal conception rates are achieved with AI around 12 hours after the onset of oestrus, assuming that it has been accurately determined by frequent observation. Semen quality, cow age and health, date since calving and the skill of the AI technician are also factors that contribute to conception rate success. Conception rates of up to 65pc for maiden heifers and 50pc for cows from a single insemination are achievable, but these targets are not met in many herds.
- Identification and treatment of problem cows: To maximise fertility in dairy herds, farmers should carry out pre-breeding heat detection from 18 to 20 days after calving to identify the normally cycling cows in the herd. All cows that are not seen in heat by day 42 should be examined by the vet. Some of these cows will be normal and cycling but their heats were just missed. Others will be problematic due to delayed resumption of cyclicity, persistent corpus luteum, cysts or uterine infections. It is these problem cows that your vet should be putting the effort into in order to get them into oestrus as soon as possible. These are also the cows that will give a return on investment of vet fees. Identification of the problem cows before the actual breeding season starts will mean that they can be treated on time and will minimize the number of cows not in calf at the end of the breeding season.
Professor Mark Crowe works in the Herd Health and Animal Husbandry department in the Veterinary Sciences Centre of UCD