Page 80 - The Welfare of Cattle

bIoteChnoLoGY and anIMaL WeLfare 57

single-nucleotide variants. A small fraction of these mutations have been selected owing to their
beneficial effects on phenotypes of agronomic importance. None of them is known to produce ill
effects on the consumers of milk and beef products, and few impact the well-being of the animals
themselves.
Although gene editing can be used to introduce virtually any DNA sequence into genomes,
many applications will likely result in animals carrying desirable alleles with sequences that origi-
nated in other breeds or individuals from within that species, for example, an edit to correct diseases
and disorders that have a genetic basis. There is a need to ensure that the extent of regulatory over-
sight is proportional to the unique risks, if any, associated with novel phenotypes.

aNIMaL WeLFare aSPeCtS OF BreeDING

Genetics may not be obviously connected with agricultural sustainability, and yet the impor-
tance of animal genetics in contributing to the interplay between the environmental, social, and
economic goals of sustainability should not be underrated. Genetic gains are both permanent and
cumulative meaning that gains made in 1 year will be transmitted to subsequent generations without
further endeavor or expenditure. Genetic improvement has been an important component of the
tremendous advances in agricultural productivity that have occurred over the past 50 years.
Traditional breeding programs focused on production traits such as milk yield, growth rate,
and meat yield. Key social goals such as food safety, food quality, environmental protection, and
animal welfare were not overtly included in breeding objectives. Recently, more selection emphasis
has been placed on functional traits that are not directly associated with production outputs includ-
ing traits that could lead to improved animal welfare. Several authors have discussed approaches to
incorporate “sustainability traits” into breeding objectives. As might be predicted from the rather
broad definitions of sustainable animal breeding, approaches vary depending upon which compo-
nents of sustainability are under discussion.
Some important examples where functional traits have been added to breeding objectives include
the incorporation of fertility and disease resistance traits into dairy cattle selection indexes, and the
inclusion of leg traits into poultry breeding. Table 7.4 shows the ten dairy traits that are currently
included in the US dairy selection index with the year that each trait was introduced.
It can be seen that production traits (milk and fat) were the first traits incorporated into selection
programs. As time went on, more functional traits were included to widen the scope and redirect
the emphasis of breeding programs. At the current time, production traits represent 35% emphasis
of the dairy selection index, with the remaining 65% placed on functional traits. Figure 7.4 shows
table 7.4 Year that Genetic rankings Began and emphasis Placed on Dairy traits in 2010 US National
Dairy Selection Index
Year trait Current Selection
trait added to Index Index emphasis (%)
1. Milk 1935 0
2. Milk fat 1935 19
3. Milk protein 1977 16
4. Calving ability 1978/2006 5
5. udder shape and support 1983 7
6. feet and leg conformation 1983 4
7. body size/weight 1983 −6
8. Productive life/longevity 1994 22
9. Mastitis susceptibility (somatic cell score) 1994 −10
10. daughter pregnancy rate/fertility 2003 11