Cow comfort: 6) Reproduction

Reproduction is a necessary and important part of milk production. Without regular calvings when the cow produces milk to feed her calf, it would be impossible to produce the desired amount of milk. It is also important to produce sufficient heifer calves as replacement animals to allow herd size to be maintained or expanded. Average replacement rates are between 20 to 25 percent. If replacement needs are higher, it indicates problems and possible poor cow comfort.

Today, it is most common to use artificial insemination (AI) instead of a bull. AI increases control over reproduction and enables the dairy farmer to use semen selected from global genetic breeding programmes to increase the genetic gain. However, it also simultaneously increases the need for good planning, well structured working routines and very good observation. Another way to get a cow in calf is to use the embryo transfer technique. So far this is relatively uncommon, but it is expected to increase in importance. The main advantage with embryo transfer is that it is possible to generate more calves from a good cow.

The oestrus cycle

As long as a cow or heifer is not pregnant she will normally have a 21-day oestrus cycle. The length of the oestrus cycle may vary but it usually ranges from about 17 to 24 days. A heifer normally has an oestrus cycle slightly shorter than a cow. The cycle will continue until the cow is in calf. After calving, cows normally undergo a 20 to 30 day period when oestrus cycles do not occur. This period can increase in high yielding cows, unable to take in enough energy to fully cover milk production. The cow will protect herself and will wait to get in oestrus again.

Oestrus cycle chart:

 

Source: DeLaval 2001; Efficient Dairy Herd Management.

The oestrus cycle is controlled by a complex system involving different hormones produced in the brain and ovary. The diagram above shows a simplified picture of how two of these hormones, oestrogen and progesterone, vary depending on where the cow is in the oestrus cycle. Some cows do not follow the normal oestrus cycle. For example a cow can be unoestrus, which means her ovaries do not function on the regular 17 to 24-day cycle and are therefore not observed to be in heat. Other cows may suffer from ovarian cysts. These cows will show heat at very short intervals and the period that they are in heat will last three to four days.

Reproductive management

Depending on breed, the optimal age for first calving is around two years. Then ideally a cow gives birth to a calf every year, meaning every 365 days. Research by the Swedish Association for Livestock has shown that sub-optimal calving intervals cause substantial economic losses to dairy farmers – second in importance only to mastitis. Milking cows in late lactation are less profitable due to the decline in production over the milking cycle. A long calving interval means milking less profitable cows due to the decline in production, fewer calves, and too many cows with low feed conversion efficiencies. Therefore, successful reproductive management has a significant impact on the herd’s overall performance and the net income. Well managed reproduction also reduces the risk of expensive involuntary culling.

Distribution of controlled Swedish herds in relation to calving interval and production level

Average calving interval (days) Production level (kilogram og milk/cow/year)
  -4499 4 500-5 499 5 500-6 499 6 500-7 499 7 500-
<365 6% 7% 7% 9% 11%
365-377 18% 20% 28% 36% 43%
378-392 23% 28% 34% 36% 33%
393-408 18% 22% 19% 14% 10%
>409 35% 23% 12% 5% 3%

Source: SHS; Swedish Association for Livestock, breeding and production.

The time of the calving interval that is possible to influence by management is the open days. These days are determined by the voluntary waiting period (VWP) and the breeding window (BW). Missed heats are a common reason for undesirably long calving intervals. With improved heat detection rate (HDR) and conception rate (CR) via better management and improved timing of inseminations, it is possible to obtain a significantly shorter calving interval.

Factors affecting the calving interval:

 

Source: DeLaval 2001; Efficient Dairy Herd Management.

Detecting heat

The most sexually intensive period of the oestrus cycle is during standing heat, which lasts for approximately 18 hours. In loose-housing herds, this period is indicated by the cow in heat standing immobile when mounted by another cow or bull. The duration of heat varies from animal to animal, but approximately 10 to 12 hours after the end of standing heat, the egg is released (ovulation) and the heat ends.

Reproductive activity table:

  • Bellowing
  • Increased activity
  • Walking the fence line
  • Licking/Sniffing
  • Swelling and reddening of the vulva
  • Mounting other cows
  • Lower milk yield
  • Reduced feed intake

Developed from Basics of reproductive function, www.milkproduction.com

Manual heat detection

Manual heat detection relies on manual observations in the barn. The cows and heifers should be observed for oestrus two to three times per day, with all observed heats recorded whether the animal is bred or not. The records provide the manager with information to anticipate future heats, which will make it easier to distinguish if a cow is really in heat or not. Most mounting occurs between 18.00 and 06.00 so it is therefore important to check for heat during these hours. To facilitate planning and record keeping, a cow calendar is often used. This can be either manual or computerised. The disadvantage with manual detection is that it is very time demanding and requires people with the ability to observe the right signs. This is particularly important when there are no distinct signs of heat. By using progesterone testing or other tools on the market, the detection rate can be improved.

Automatic heat detection

Another way to identify cows in heat is to monitor their activity. Cows can be up to eight times more active than normal while in heat. The activity can be monitored automatically by using activity meters attached to the neck band or leg. By comparing the amount of activity with the last observed heat, actual milk yield and feed consumption, a reliable indication of heat is obtained. An activity meter will generate significant time savings and improve calving intervals through better heat detection. For instance, a study 1) has shown that the daily cost for extended calving intervals is Euro 3 while the cost for each heat missed is Euro 61.

 

Timing of insemination

With artificial insemination, the timing of the insemination becomes important. The optimum time for insemination depends on when the ovulation occurs in relation to the heat and for how long the semen is viable. Most semen remains viable for about 24 hours. The ovum’s life is only about four hours, a very short moment of opportunity. It is therefore preferable that viable semen is present in the sample during ovulation. As illustrated below, ovulation normally occurs about 30 hours after the start of standing heat.

Factors affecting the calving interval:

 

Source: DeLaval 2001; Efficient Dairy Herd Management.

There are two main rules for the timing of insemination. Traditionally the AM/ PM rule was the one dairy producers followed. This rule dictates that cows and heifers first observed in heat in the morning should be bred late in the afternoon. Likewise, cows and heifers first observed in heat in the afternoon should be bred the following morning. This is still a good rule, but many producers have now successfully gone to once-a-day insemination. This rule dictates that cows and heifers first observed in oestrus in the afternoon or the following morning, should be bred later that day.