Vet on call: The trouble with growing dairy herd from two cows

Most dairy farmers don’t consider the intricacies of establishing a dairy herd, apart from the main issues of building the dairy unit and buying the starter stock.

From experience, what many do is start with the first cow and keep breeding to build the herd. Others believe once you have the first cow, you just keep buying new ones and breeding the existing ones.

Sometime in 1997, Karanja from Murang’a told me he wanted to build a dairy herd from two pedigree Friesians and he would not introduce any new female genetic material from outside.

It was only the bulls that would be different. When I cautioned him that would be an uphill task, he asked me why, because according to the Bible, the whole human population came from only one man and woman.

My answer was that science and faith operate in two different realms that defy convergence. I explained the science of breeding and population growth for animals like cattle that rarely give birth to more than one offspring worked against building a large herd from two cows. Furthermore, even one cow with a starling performance can only give birth once in a year.

Well, Karanja started the farm and for the last 22 years, there has not been any other introduction of a new cow from outside. Last week, a young potential farmer from Kiambu, planning to start dairy farming, approached me with a concept similar to Karanja’s and my advice was the same. It is not a good idea to attempt to build a large dairy herd from only two cows.

I explained to Kamau that theoretically, one can build a large herd from two cows. However, there are many factors apart from breeding that will frustrate the venture and stunt growth of the herd number at some point in time. Scientifically we call this the population stable state.

This situation arises when the number of animals getting into the herd every year and those exiting are roughly the same.

DYNAMICS OF BUILDING A HERD

Therefore, even with annual births of heifer calves, the population still remains the same or declines. In Karanja’s case, the population stabilised with 35 head of cattle from the initial two cows about five years ago.

Since that time, the herd swings between 25 and 40 dairy cattle of different ages and genders. The bulls are raised and slaughtered for meat while the heifers are raised as replacement stock.

Since starting the farm, Karanja has never sold any of his heifers. They always enter the herd and become breeding cows. Kamau was perplexed by the state of affairs and wanted to know why then the herd does not grow beyond 40 animals.

To know the number of animals that have been born on the farm, the original two cows were labelled 1 and 2. All other animals are given a serial number followed by a notation associating them with their mother such as KF6D1.

This means it is the sixth cow on Karanja Farm and is a daughter of Cow No.1. A bull would read KF6S1 to mean the sixth animal on Karanja Farm and is a son of Cow No. 1.

From the numbering, the records show Karanja Farm has raised about 100 cattle in the last 22 years. Currently, there are only 27 cattle on the farm.

Kamau told me he had difficulties understanding why so many animals had been born but there were only 27 on the farm currently. I fully explained to him the dynamics of building a herd from two initial cows. It is much more complicated than the story of Adam and Eve.

To start with, if the cows have given birth to 100 animals over the last 22 years, Kamau had to appreciate that in the best breeding programme, 50 per cent of the calves would be bulls, which have to be removed from the farm for slaughter at the age of 15 to 18 months.

That leaves only 50 female animals on the farm. There is also the normal mortality in any zero-grazing dairy cattle population.

NEW SYSTEM WAS POOR

It is about one per cent per year in the best of times. That means the farm would lose half a cow per year making 11 cows for the last 22 years the farm has operated.

That leaves the farm with 28 animals. Interestingly, Karanja’s farm has 27 cattle currently meaning the management of the farm has been very good and the population will not grow beyond the stable state unless new cows are bought from outside.

Other factors that contribute to population stable state are unexpected higher than normal mortality, breeding difficulties and ageing of cattle resulting in culling.

On Karanja Farm for instance, there was a five-year period at one time without any cattle death. However, in 2017 and early 2018, the farm suddenly lost seven cattle in six months due to poor disease detection.

The farm management had changed and the new system was poor in detecting sick animals. The source of hay had also been changed and it happened the new grass was heavily infested with disease-carrying ticks. Animals got infected with East Coast Fever, Babesiosis and Anaplasmosis but the reports always reached me when the diseases were too advanced for the animals to recover.

I revised the disease detection system, retrained the workers and changed the hay source back to the original supplier.

The animals were also washed with acaricides twice per week and the problem was resolved. To avoid high mortalities, a farm should have a policy of disease detection three times a day and prompt reporting of sick animals to the veterinary doctor.

At the end of the discussion, Kamau decided he would establish his dairy herd through a mix of breeding his own animals and buying others until he had a breeding population that would keep his herd growing to attain his planned population of 200 milking cows.