The Sunday News
Farming Issues Mhlupheki Dube LAST week I promised an article on managing a calf born to a dam with a dead udder. I will provide that article in subsequent instalments but today I have decided to tackle the issue of inbreeding and its effects in your herd. Inbreeding is loosely defined as the mating of closely related animals. This means you are mating animals that come from the same parental stock and hence they have a very closely related genetic makeup. While inbreeding has more negative consequences it does have positive uses especially by breeders. Pure breeders and line breeders use inbreeding to select for a trait which they seek to promote. One of the easiest ways to accomplish this goal is to use the bulls that express the desired trait to breed many cows, and then cross the progeny until the trait becomes fixed or uniform. I have no intention to submerge the reader in breeding and genetic jargon and therefore I will seek to relate this article to an average communal farmer and how inbreeding develops in his herd and what are the visible indicators of inbreeding depression. On the negative side inbreeding leads to a decline in phenotypic performance of animals in certain production characteristics, a phenomenon known as inbreeding depression. Inbreeding reduces heterosis (hybrid vigour) which is the advantage gained from crossing lines or breeds from unrelated gene pool. As the relatedness (homozygosity) increases due to inbreeding some deleterious recessive traits begin to manifest in your herd. These undesirable traits begin to show in your herd and the farmer cannot understand why his herd which used to be very productive is suddenly declining in performance. There are a number of important production traits in beef and dairy production and these tend to be affected by loss of hybrid vigour as a result of inbreeding. In dairy animals for example inbreeding severely reduces milk yields over time as the homozygosity of the stock increases. This is the single most important trait to dairy men. I have met smallholder dairy farmers whose main complaint is the low yields they are getting from their animals. Some farmers in Nyanga and Chipinge get as low as four litres of milk per day from an animal. This is the yield of an average indigenous beef not dairy animal! While there are a number of factors that can cause poor milk yields such as feed, inbreeding is the most important one. In beef production important production traits such as conformation, weaning weights, weaning age, age at first calving and post weaning gains are all affected by inbreeding. This means if you continue to use the same bull over a long period of time it will begin to mate with its offspring resulting in inbreeding depression. Sadly this is what obtains among most communal smallholder farmers. The same bull is used on the cows for more than 10 years. As a result your herd begins to express some unpleasant traits such as four-year- old animals with the size and weight of a weaner. If you go around communal farmers especially in Matabeleland North, you will see some animals which have the size of steers but on enquiry you will learn that these are fully grown oxen which have been used through three farming seasons! The inevitable result is that you will get very poor returns from suc animals when you eventually decide to sell them because you are selling old animals with the frame size of boys! How can you have a two-and-half-year-old steer that is the same size with your buck (impongo)? These are clearly some of the effects of inbreeding among communal herds. This is further compounded by the high bull to cow ratio. In communal areas the ratio is probably around one bull to a hundred cows. This means that herd is serviced by the same bull and if it is kept longer it will even mate with its offspring and the whole village has animals which are highly related genetically. As a rule of the thumb farmers need to rotate their bull after every three years. Take note that I said rotate not dispose because this can be highly impractical especially considering the cost of the bulls which I have previously described as demanding two arms and a leg. However farmers can rotate the bulls among themselves so that they continuously infuse new genetics into their herds. This is not easy either considering suspicions and uneasy relations among neighbours, but it can be done. Feedback [email protected] <mailto:[email protected]> cell 0772851275
