Estimated reading time: 8 minutes
- Profitable milk production and the genetic improvement of a dairy herd are directly dependent on effective reproduction management.
- An effective reproduction programme, along with sound calf- and heifer-rearing programmes, will ensure the maximum number of replacement heifers each year.
- Poor reproduction management and an intercalving period (ICP) of more than 365 days will mean more cows culled annually, fewer replacement heifers (which will limit selection), lower annual income, fewer bull calves sold, and greater veterinary and insemination expenses.
- Although ICP is used as a general reproduction norm for dairy herds, it can also be somewhat misleading, as an ICP cannot be calculated for cows that did not calve again. This is why producers must know how many of all potential cows calved annually.
- Easily identifiable cows are important for effective heat observation as this will ensure that any person handling the cows can report heats.
Profitable milk production and the genetic improvement of a dairy herd are directly dependent on effective reproduction management. Milk production is a secondary gender trait and depends on a cow yielding a calf. Genetic progress, in turn, is dependent on the progeny – heifers and bulls.
Heifers are reared in order to replace cows that are culled for a number of reasons. An effective reproduction programme, along with sound calf- and heifer-rearing programmes, will ensure the maximum number of replacement heifers each year. This article elaborates on some basic principles in respect of reproduction management.
Intercalving period (ICP)
This is the period between two successive calvings. The ICP of a herd is calculated on the basis of all second-plus lactation cows that have calved again. This is the general guideline used to quantify reproduction management. Poor reproduction management and an ICP of more than 365 days will mean more cows culled annually, fewer replacement heifers (which will limit selection), lower annual income, fewer bull calves sold, and greater veterinary and insemination expenses.
It is possible to achieve the theoretical optimal ICP of 365 days. The gestation period of a cow lasts approximately 280 days. The uterus will recover within approximately 20 to 40 days of a normal calving, at which time the cow will come into heat again. The mating period then lasts approximately 45 to 65 days which implies two to three mating opportunities in which she can reconceive.
As a rule, however, these norms are not achieved in dairy cows. They often contract uterine infections due to difficult calvings or a dirty calving environment, delaying the uterus’ recovery as well as first heat. Irregular and poor heat observation means that standing heat often goes undetected. Especially cows with high milk production levels exhibit fewer and shorter periods of standing heat.
Learn how to diagnose pregnancy in cows here.
Recording calving numbers
Cows will not conceive if erroneous insemination techniques are administered or low-quality semen is used. Therefore the open period (calving to conception date) often lasts longer than the optimal period of 85 days, and ICP is then longer than 365 days. Figure 1 illustrates the ICP distribution of 724 Jersey cows that calved again during a period of one year.
Figure 1: The intercalving period (ICP) of 724 cows over a one-year period.
This herd achieved an almost perfect average ICP of 367 days, as 62% of the cows calved again within a 12-month period and 84% within 13 months. Only 16% of the cows recorded an ICP longer than 13 months. Above-average management is maintained in this herd, leading to 87% of the cows calving again.
Although ICP is used as a general reproduction norm for dairy herds, it can also be somewhat misleading, as an ICP cannot be calculated for cows that did not calve again. This is why producers must know how many of all potential cows calved annually.
Other measures used to determine the standard of reproduction management include the number of days from calving to first insemination, the percentage of cows mated for the first time within 100 days post-calving, the number of open days (from calving to re-conception), the percentage of cows that conceived within 100 and 200 days of having calved, the number of inseminations per conception, the percentage of cows that conceived upon their first and third inseminations, and the number of cows (in second-plus lactation) that have calved again since the previous year.
It is important to estimate these measurements after each pregnancy test. Changes over time can be determined with the help of graphs. Effective reproduction management is influenced mainly by the following factors:
Easy identification
Easily identifiable cows are important for effective heat observation as this will ensure that any person handling the cows can report heats. This is usually done using brightly coloured eartags containing a legible cow number.
A normal heat cycle for dairy cows usually lasts about 21 days. During 16 of these days the cows have very little contact with other cows and during the other five days when they come into heat, they will seek each other out. Often, these cows will isolate themselves, sniff and ride each other.
The best sign of heat is when a cow stands still to allow other cows to ride her. These activities can occur during the day and more often at night. Observation studies have shown that a cow in heat will be ridden 50 times and more by other cows. However, these heat observations are complicated by the fact that 25% of cows are ridden less than 30 times a day. In addition, these sessions are much shorter and the heat activity usually take place at night, between 19:00 and 04:00.
Observe calm cows
Other signs observed during and after the heat period include restlessness; a clear mucous discharge from the vulva often smeared to the pinbones by the tail; a swollen vulva; dishevelled hair and scuff marks at the tail crest; mud on the sides of a cow that has been ridden; and lower feed intake and milk production.
Heat observation should preferably be done when the calves are calm, have finished feeding, and have been milked. Studies show that approximately 85% of all heats are observed during three 20- to 30-minute long heat observation periods at 08:00, 14:00 and 20:00. It is, however, very important that these heat observation periods are dedicated to searching for signs of heat and not for any other tasks.
The heat period lasts for about 12 to 16 hours, but can vary a lot. In approximately 20% of cows this period is shorter than six hours. Especially the high producers show shorter heat periods. It is important to pinpoint the onset of heat as it will determine the time of insemination.
Heat onset is regarded as the time between the current and previous heat observation, which is why regular heat observations allow for more accurate observation of the onset of heat. Cows are mated approximately 12 to 18 hours after the onset of the heat period which means that cows whose heat is observed in the morning, are often inseminated in the late afternoon.
Learn how to overcome fodder flow shortages in winter here.
Semen handling
Semen quality depends on correct storage and thawing, correct handling of the pistolet, and the insemination process in general. The inseminator is therefore a very important link in a successful reproduction management programme.
The tank in which semen is stored is filled with liquid nitrogen kept at a temperature of -196°C. This gas must be refilled regularly as the number of live sperm following thawing are strongly influenced by the level of liquid nitrogen in the semen tank. Sperm will die if the tank runs empty.
The frozen semen must be thawed in warm water immediately before insemination. According to research, the maximum number of live sperm is retained if the water’s temperature is 35°C. This temperature is very important as semen enters a damaging temperature zone during thawing. A temperature of 35°C allows for a shorter damaging zone and prevents sperm from becoming warmer than body temperature.
Semen is placed in the water container vertically as the lids that cover the straws can sometimes pop off. A special thermos flask is used to prevent the water temperature from cooling down. Semen can be kept in this water for longer (up to 15 minutes) although insemination should preferably be performed as soon as possible.
After thawing, the semen straw must be dried properly before placing it in the pistolet – this is because a few drops of water can alter the balanced salt concentration of the semen and sperm can then die due to osmotic shock. The pistolet must also be warmed slightly by holding it in the armpit for a few minutes before placing the semen straw in it.
The best place to deposit semen is just through the cervix, inside the uterus. If the semen is placed too deep in the uterus it may end up in a fallopian tube and no fertilisation will take place. Usually only half of the semen is placed this way, after which the pistolet is pulled back and the rest of the semen is deposited in the cervix opening.
Reproduction norms
Use the following norms to determine the reproduction management level of a herd:
- Age at first calving: 24 to 25 months.
- Intercalving period: 12 to 13 months.
- Number of days from calving to first insemination: 55 to 60 days.
- Number of days from calving date to conception (days open): 85 to 105 days.
- Number of inseminations per conception: 1,5 to 2.
- Percentage of cows that conceive at first insemination: 55 to 60%.
- Percentage of cows that conceive after three inseminations: 85%.
- Average days in milk: <185 days. – Dr Carel Muller, research fellow, Stellenbosch University
For more information, contact Dr Muller at careljcmuller@gmail.com.
