Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Livestock species play a major role in economic development worldwide. Until recently selecting animals for breeding was done by personal judgement and observation of phenotypes or of pedigree data. In this way people have been guiding the evolution of domestic animals for about ten thousand years. This method has been quite successful but there have been some drawbacks; e.g. in dairy cattle increased milk yield has been accompanied by a decrease in reproductive efficiency. With the advent of genomics, our increased knowledge should lead to marked improvements in performance in both milk yield and reproductive efficiency, as well as many other features.
Biological processes that influence performance
The performance of cattle is influenced by a wide variety of factors and is a prime example of the nature versus nurture debate: a beef animal may have the genes for large muscles (nature) but if it is not fed properly (nurture) it will not have a high live-weight gain.
Hormone levels are also important as they control the growth, development and productivity of all animals. Prolactin and oxytocin are important in the control of milk production, while growth hormone affects live-weight gain. Hormones are of course genetically determined. The use of artificial growth promoters is now banned in the European Union.
If animals have a disease they will not perform at optimum levels and it has been shown that routinely dosing cattle with antibiotics increases their live-weight gain.