Why our zebu cattle are getting smaller

Dear Daktari, I am still attached to my indigenous zebu animals despite having some exotic dairy crosses.  As such, I have Zebu herd that I take lots of pleasure in. Now my worry is the ever diminishing body size of zebus. What is causing this? I am only seeing this trend with our local cows and not the exotic ones.   [Jackson Waliaula, Bungoma County]

Dear Waliaula, thank you for reading The Smart Harvest. I can relate with your love for zebu cattle. You are not alone. I am still struggling to convince my mother to change over to exotic crosses. She has maintained her love for her zebus and she has own good reasons; they are hardy and easy to feed she says. On the low milk production, she says they produce just enough for her subsistence use.

You are right in your observation that our zebu is decreasing in size. Mr John Kanyanya a great friend from Mumias makes a joke that today five zebus can be carried on a small Datsun Pickup like they are goats.   Growing up, we used to take pleasure in the big zebu bulls and cows we used to graze. Today, it is becoming rare to spot a well built zebu bull or cattle.

Blame it on inbreeding and feeds 

The main reason for the vanishing size of zebus is the inbreeding problem. How has this come about? Again if you go back to history you will observe that grazing lands have dwindled very fast. We longer have communal grazing grounds where cattle from different villages gathered to graze and in the process naturally control inbreeding.

Today, land is fragmented and to avoid conflicts people are keeping animals much closer to their chests on their small pieces of lands and inbreeding is normal. They are oblivious of the negative effects of inbreeding. Second, good body comes with good feeding, most of those keeping zebus are tethering them on trees the whole day and not supplementing this merger feeds hence denying the body the most needed nutrients to grow.

In breeding is the mating of animals that are closely related. Off course all members of a breed are related inbreeding is generally used for the mating of cattle that are more closely related than the average of the breed. Geneticists have formulas for calculating this.

The science behind it

Inbreeding has negative effects that result from animals receiving identical genes from each parent. If the parents are related, it is more likely that they have genes that are identical. Receiving identical genes from each parent is said to be homozygous for that pair of genes. This would be desirable if the gene the individual received from each parent leads to superior performance. However, most animals carry undesirable genes that usually remain hidden unless the animal is homozygous. An inbred animal is more likely to be homozygous for any gene, so the animal is more likely to express undesirable genes, and hence, undesirable traits.

However inbreeding can have some benefits but only if the breeder understands how to monitor it and is willing to sacrifice some performance in the process.

Disadvantages of inbreeding

With it, you get smaller size animals with lower fertility, high probability of defects or genetic conditions, slower growth and high offspring mortality. Inbreeding reduces the chances of improving a trait. 

[The writer is a veterinary surgeon and the head of communications at the Food and Agriculture Organisation of the United Nations (FAO) Kenya. The views expressed here are not necessarily those of FAO]