The reproductive efficiency of the herd is a major component of sustainable cattle management. The profitability of dairy and beef cattle farming is influenced by the milk yield and the healthy growth of the calves. For both cases, optimizing reproductive efficiency depends upon achieving a high submission rate of cows to artificial insemination or natural service and a high pregnancy rate. The reproductive goal for cows is to produce a healthy, live calf each year, with the desired genetic traits, born at the right time, and without calving problems. Cattle breeding may rely on natural service or the use of reproductive biotechnologies, including artificial insemination (AI) and embryo transfer (ET), which have increased livestock sustainability and herd health while facilitating genetic advancements at a cost-effective rate.
Various parameters are used to evaluate cattle's reproductive performance. Some of these terms can be challenging, and acronyms are often misinterpreted; therefore, this article aims to provide clarifications and help readers become familiar with these complex concepts.
The first calving marks the beginning of a heifer's productive life. When it is delayed, overall dairy cow production is decreased. The average age at first calving is calculated by dividing the total age of all heifers at their first calving by the total number of first calving in a 12 month period. For dairy cows, the ideal age at first calving is around 22 to 23 months.
Time in days for an individual cow between one calving and the next. It should only be used as an initial indicator of reproductive issues on the farm as it does not account for cows that fail to calve a second or subsequent time. This limitation may result in an overestimation of the herd's actual reproductive performance.
Average calving interval in days of all cows in a herd at any given time. It provides an overview of the fertility dynamics for a herd calving year-round.
Number of days from the time a cow calves until her first service. It is the average of all cows in the herd receiving a first service. The measure combines the effects of Voluntary Waiting Period (VWP) and Submission Rate (SR), which will be described later. Short intervals – under 50 days – compromise pregnancy rates, and can lead to milk losses, as it requires drying them off with excessive milk in the udder, increasing the risk of mastitis. Longer intervals may help improve it, but excessive long intervals indicate considerable economical losses and the risk of calving over-conditioned cows.
Time in days from calving to the service at which a cow gets pregnant. Herd CCI is the average performance of all pregnant cows in the breeding season. A short CCI is a good index of effective reproductive management, indicating a well-planned voluntary waiting period, good submission for first AI either from the application of fertility programs, or a good heat expression and detection and a high pregnancy per AI, as well as a good re-synchronisation strategy for open cows. It typically ranges between 80 and 150 days.
Percentage of cows that conceive after a service. Four general factors determine CR in a herd: cow fertility: any cow-related factors that influence the establishment of pregnancy, including factors such as inadequate nutrition and environmental stress; bull fertility: quality of semen used for AI; accuracy of heats: timing of AI relative to oestrus or ovulation; artificial insemination efficiency: factors affecting pregnancy rates due to AI technique.
Number of cows in a defined period (usually 12 months) that are sold, died or transferred out of the herd before starting another lactation as a percentage of the total number of cows calving in the period.
Average number of days from calving to conception for cows that successfully conceive, and from calving to culling for those that do not. It is a reliable indicator for assessing reproductive efficiency as it takes into account the culled animals that did not conceive. It is influenced by the voluntary waiting period, the heat detection rate, the conception rate, and the overall herd health and nutrition.
Pregnancy losses occur at various stages of gestation, with the highest rate of loss typically observed in the first month of pregnancy establishment most of them happening before the pregnancy could be diagnosed by common methods (around day 28), and lower rates of loss later in gestation.
Losses before day 24 are classified as Early Embryonic Loss (EEL), those between day 24 and 42–50 as Late Embryonic Loss (LEL); losses detected after day 50 are considered foetal loss.
Since pregnancy loss is common, cows diagnosed as pregnant between days 25 and 60 of gestation should undergo one or more confirmation tests to verify pregnancy or detect loss. Pregnancy loss can be detected through direct methods, such as transrectal ultrasonography or palpation, or indirect methods, including measurement of pregnancy-specific glycoproteins (pregnancy associated glycoprotein PAGs).
Reproductive technology that involves the synchronization of the animals of the herd through the use of hormones (injection or insertion of a progesterone releasing intravaginal device PRID) to be artificially inseminated over a controlled timeframe. It allows AI to be performed without requiring heat detection, and significantly improves the pregnancy rate.
This technology regardless of the different strategies utilised relies on the ability to control the emergence of a follicular wave, the control and the induction of luteolysis and the induction of a timed ovulation primed by the deposition of semen in the reproductive tract of the cow/heifer.
FTAI supports the efficiency of the operation through easier calving, shortened breeding and calving seasons, reduced incidence of postpartum anoestrus, improved fertility and a more consistent and healthy line of calves.
Protocol that allows for embryo transfer without the need for oestrus detection. Most current FTET protocols are follow the same basic concepts of FTAI programs and rely on progestin-releasing devices combined with oestrogens or GnRH and prostaglandins, which control and synchronize follicular wave dynamics and ovulation, the embryo is then transferred 7 days after the induced ovulation in the second half of the ipsilateral horn to where the ovulation has occurred.
Proportion of cows that are accurately identified as being in heat out of those eligible during a specific period (normally of 21 days). It accounts for missed heats (cows not detected in heat) and false positives (cows incorrectly identified as in heat).
The time, in days, between two services or oestrous events in an individual cow or in a given herd. Most cows should fall between 20 and 24 days. If this period is increased, it may indicate lost pregnancies or poor heat detection.
Pregnancy rate simply is the percentage of animals which get pregnant out of all the animals which are eligible to get pregnant during a specific time interval normally calculated every 21 days. It is the combination of CR% and 21d HDR% it is one of the most accurate parameters to be used to judge the fertility of a given herd.
The most used measure of heat detection. It represents the proportion of eligible cows to be bred during a 21 or 24-day period that actually are bred. It is a key indicator of the effectiveness of heat detection in a herd, and it is calculated early enough in the season to provide a timely indication of problems to enable appropriate action to be taken. In well-managed, year-round calving herds, this rate should exceed 70%.
Time planned period after calving during which cows are not bred. As it is a planned measure, it helps prevent animals from being served too soon. This period can vary across herds or seasons but typically ranges from 50 to 77 days in most dairy herds, and its variability is derived by the strategies used for first breeding, herds relying on heat detection should anticipate the VWP, while herds that systematically using fertility programs for first AI can delay the VWP as they are ensuring 100% SR at the given time.