| dc.description.abstract | The main purpose of this study was to understand the type of dairy cattle that can
be optimally used by smallholder farmers in various production environments such
that they will maximize their yields without increasing the level of inputs. Anecdotal
evidence and previous research suggests that the optimal level of taurine inheritance
in crossbred animals lies between 50 and 75% when considering total productivity in
tropical management clusters. We set out to assess the relationship between breed
composition and productivity for various smallholder production systems in Tanzania.
We surveyed 654 smallholder dairy households over a 1-year period and grouped
them into production clusters. Based on supplementary feeding, milk productivity and
sale as well as household wealth status four clusters were described: low-feed–lowoutput
subsistence, medium-feed–low-output subsistence, maize germ intensive semicommercial
and feed intensive commercial management clusters. About 839 crossbred
cows were genotyped at approximately 150,000 single nucleotide polymorphism (SNP)
loci and their breed composition determined. Percentage dairyness (proportion of
genes from international dairy breeds) was estimated through admixture analysis with
Holstein, Friesian, Norwegian Red, Jersey, Guernsey, N’Dama, Gir, and Zebu as
references. Four breed types were defined as RED–GUE (Norwegian Red/Friesian–
Guernsey; Norwegian Red/Friesian–Jersey), RED–HOL (Norwegian Red/Friesian–
Holstein), RED–Zebu (Norwegian Red/Friesian–Zebu), Zebu–RED (Zebu–Norwegian
Red/Friesian) based on the combination of breeds that make up the top 76% breed
composition. A fixed regression model using a genomic kinship matrix was used to
analyze milk yield records. The fitted model accounted for year-month-test-date, parity,
age, breed type and the production clusters as fixed effects in the model in addition
to random effects of animal and permanent environment effect. Results suggested that
RED–Zebu breed type with dairyness between 75 and 85% is the most appropriate
for a majority of smallholder management clusters. Additionally, for farmers in the feed intensive management group, animals with a Holstein genetic background with at least
75% dairy composition were the best performing. These results indicate that matching
breed type to production management group is central to maximizing productivity in
smallholder systems. The findings from this study can serve as a basis to inform the
development of the dairy sector in Tanzania and beyond. | en_US |
