- THE LACTATION CYCLE
Up to now we have looked at the product Milk and its composition. We have also looked up factors that can influence yield and composition. The mechanical removal of milk from the udder is also a very important aspect of dairying, which we will be looking at later. Because of the nutritional value of the product, we also will look at dairy hygiene and the value of dairying as a whole. We have also looked at some of the important breeds and their brief history. At this stage, we must now consider the most important unit of the factory, that is the dairy cows and the lactation cycle and what factors that influence the production of milk and to what extent these factors can be controlled by management.
The farmer and the cow are the two most important factors in profitable dairying. The farmer is responsible for the type of dairying that is carried out. He may make it an interesting and a profitable business, or he may allow it to be a job of drudgery with little returns for this work. A good herdsman is not only a lover of good cattle but also one who has the ‘know-how’ and the ability to get a satisfactory job done. The pay-off job in dairying is milking. The man handling the herd must be a good stockman. He must be able to relate the requirements of the animals to their individual outputs. He must see that the entire herd is well cared for and managed in a sound financial way. What is more, the herdsman must understand the lactation cycle and the trends he can expect during any lactation, as well as be able to assess the requirements of the animals in terms of their nutritional needs. When dealing with this aspect of the lecture, students should refer to the section on nutrition.
Although the lactation cycle will not be considered in any great detail, it will at least tell you what it is, and what the farmer can read into it in terms of management.
The Lactation Cycle represents, by definition, the milk production record of a dairy cow, from the time of calving, through to the dry period when she is not producing milk and prior to the onset of the next lactation period. In most cases, this is about 300 days. The lactation curve starts off relatively low and moves to a peak within 60 days after which this production slowly declines, to the end of the lactation period (300 days).
Figure 1: Shows the daily milk production in kilograms
DAIRY CATTLE –LEARNER GUIDE
You will notice from the diagram that the lactation commences only a few days (in fact, 4 days) after the calf is born. The reason for this is that the milk produced during that time is not fit for human consumption, and is called Colostrum.
The colostrum is a liquid containing mainly albumen and globulin, which are proteins required by the calf in the early stages of its life, for its defence. The lactation will then commence and proceed along the graph indicated. This graph has been represented as a straight line, but, in fact, it is not. The daily milk production of the cow can vary a great deal and this only represents the shape of the average trend observed in a number of lactations.
You will notice, too, that the lactation is only 300 days, on which date the cow is dried off and preparation commences for the next lactation, i.e. the birth of the next calf. You might be asking yourself where the bull comes into the picture. Well, you know already that the period of pregnancy or gestation is 270 – 300 days long. If you now look at the curve, you will notice that, if you count backwards from the expected time of calving, i.e. at 360 days, the cow should have been served at about 80 days after calving. The cow comes into season for the third time, and it is at this season, that she is put to the bull for the first time.
Now, if we have had a successful fertilisation, and the gestation period proceeds along the normal path, the calf will be born on day 360. However, this does not always happen, in exactly the same pattern and students who are familiar with dairying will have encountered this.
This period between two calvings is called the calving index and if this is a very low figure like 350 days, one might say that the management is good. If the calving index is high, like 400 – 500, then with this figure one would say that management of the herd is very bad. The object in dairying is to get a calf from the cow every year or at least two calves in three years.
If a cow persists in missing a conception when put to the bull, one must think strictly in terms of sending the animal to the butcher. She is not producing milk and she is costing a lot of money to keep, and one cannot afford to keep unproductive units in the dairy herd.
The total of the daily milk yields for the whole 300 day period is termed ‘the lactation yield’ and this can be used to measure the performance of the herd. The object here is to obtain a high average yield for the herd. Through careful management, this can be obtained. It is known for example, that the cow will increase her yield if she is fed properly. This is extremely important and can be controlled by management. One can also assume that, if you get rid of animals whose average lactation yield is low, and replace them with higher producing animals, the average for the herd will also be increased. This, however, is an extremely lengthy process, involving breeding and selection, and is not covered in this course. It is enough, however, that you should know that it can be done through
very careful and sophisticated management. The best method would appear to be to try and control the feeding as accurately as possible: the improvement in production will be quicker and more readily noticeable.