EFFECTS OF COW SIZE AND MILK YIELD ON BEEF COW PRODUCTION EFFICIENCY

ABSTRACT

EFFECTS OF COW SIZE AND MILK YIELD ON BEEF COW

PRODUCTION EFFICIENCY

Gertrude S. Aboagye, M.Sc. Supervisor;

University of Guelph, 1976 Dr. J.W. Wilton

Data on 5 groups of cow and Angus-sired first-calf pairs representing

year and season of calving subclasses were analysed within

groups for effects of cow size and milk yield on 180-day weaning weight

and efficiency of production. There were 15, 20, 22, 32 and 38 covrcalf

pairs in groups 1 to 5 respectively. There were 3 criteria for

size: height at withers, post-calving weight and length of cow. The

milk criteria were 180-day milk yield and 180-day milk fat yield.

Efficiency was estimated as the ratio of calf weaning weight to total

TDN consumption of cow and calf during lactation. Interactions between

the effects of milk and size were examined and the data were analysed

for relationships between the various criteria for cow size and milk

yield.

Milk yield was generally positively associated with the various

measures of cow size. With regard to 180-day weaning weight, interactions

between height at withers and total milk yield were significant

in 2 of 4 groups. When efficiency was considered, interaction was significant

in 1 of 4 groups. The effect of sex was generally non-significant.

Regression coefficients of 180-day weaning v/eight on height

at withers where cows were classified into low, medium and high classes

within group ranged from -4.7 to 5.7 Kg/cm. The regression coefficients

were generally positive and significant indicating an increase in

weaning weight associated with increased height at withers. When

efficiency estimates were regressed on height at withers, the

regression coefficients were very low and generally negative.

Regression of 180-day weaning weight and efficiency on total milk

yield for the different height classes showed that both 180-day

weaning weight and efficiency increased with the amount of milk

produced by the dam.

There was no interaction effect between total milk yield and

post-calving weight of cow on 180-day weaning weight and efficiency

in any of the 5 groups. Regressions of 180-day v/eaning weight on

weight of cow were positive and significant in 4 of 5 groups indicating

an increase in weaning weight associated vtith increased weight

at calving. Regressions ranged from -0.1 to 0.4 Kg calf weight/Kg

cow weight. None of the regressions of efficiency on post-calving

weight was significant.

Interaction between total milk yield and length of cow was

significant in 1 of 5 groups. When fat yield was considered, there

was no interaction effect between yield of fat and the 3 size criteria

in any of the 5 groups, but fat yield had a significant effect on both

180-day weaning weight and efficiency in 3 of 5 groups.