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Breed-Type x Forage Interaction for Mature Weight and Rate of Maturing
for Angus, Brahman, and Reciprocal Cross Cows
B. A. Sandelin, 1 A. H. Brown, Jr., 1 M. A. Brown, 2 Z. B. Johnson, 1 and A. M. Stelzleni 1
Story in Brief
Mature weight (A) and rate of maturing (k) were estimated in 177 Angus, Brahman, and reciprocal cross cows
grazing Bermudagrass (BG) or endophyte-infected tall fescue (E+) to evaluate breed-type x forage interactions. Data
were collected every 28 d until approximately 18 mo of age and then at prebreeding, postcalving, and weaning of calf.
Mature weight and k were estimated using Brody’s model. Data were pooled over year and analyzed by the general linear
model (GLM) procedure of SAS. Models for A and k included the independent variables of breed-type, forage and
breed-type x forage interaction. There was a significant (P < 0.01) breed-type x forage interaction for A, but not for k.
Angus cows had greater (P < 0.01) mean A on E+ than did Angus x Brahman cows on BG. Angus x Brahman cows grazing
BG had lower (P < 0.05) mean A than did Brahman x Angus cows grazing BG or E+ and Brahman cows grazing
BG. Angus cows had a slower (P < 0.05) mean k than Angus x Brahman and Brahman x Angus cows, and Angus x
Brahman cows had a faster (P < 0.05) mean k than Brahman x Angus and Brahman cows. These data suggest that the
choice of breed-type is important for maintaining a crossbreeding program, in that mature size and rate of maturing are
critical to the match of animal requirements to available production resources.
Introduction
The growth parameters of mature weight (A) and rate of
maturing (k) have been shown to be of biological importance
to the efficiency of beef production. These parameters are
major determinants of the amount of energy needed to grow
and mature properly. The availability of adequate production
resources often hinders the level of efficiency needed to sustain
this level of energy. These parameters may be useful to
producers who are trying to find the ideal animal to match
available resources. There have been numerous papers that
deal with the calculation of A and k in many breeds of cattle,
however, a review of literature found a limited amount of
growth curve data for crossbred cattle. Problems associated
with endophyte-infected tall fescue (E+) have been extensively
documented. The objective of this study was to look at
the interaction of breed-type x forage for the growth parameters
of A and k in Angus, Brahman, and reciprocal cross cows
grazing common bermudagrass or endophyte-infected tall
fescue.
Experimental Procedures
Base Herd Development. Eighty purebred Angus and
80 purebred Brahman heifers born in the spring of 1985 were
purchased from approximately 20 different sources per breed
in the fall of 1985 and winter of 1986. Of these heifers, 32
and 30 different sires were represented in Angus and
Brahman breeds, respectively. Heifers were stratified according
to source and assigned at random to one of four 36-acre
BG pastures and one of four 36-acre ‘Kentucky-31’ E+
pastures.
Stocking rate for each pasture within forage environment
ranged from 19 to 24 head, with approximately equal
numbers of Angus and Brahman. Heifers were managed as
commercial replacement heifers to gain approximately 0.80
lb/d by supplementing with cottonseed meal, corn, and E+ or
BG hay according to visual estimates of forage DM availability
and normal quality curves for either BG or E+.
Normally, supplemental feed was provided from late
November to late April for both forage treatment types; supplemental
grain (2.0 lb per animal per day) was continued in
the E+ treatment into late fall and early spring in an attempt
to moderate potential toxicity from the forage. Minerals were
fed free choice throughout the year.
Heifers were bred as 2-yr-olds to calve at 3 yr of age to
preclude introducing parity differences into the study due to
the low percentage of purebred Brahman reaching sexual
maturity at 15 mo of age. They were bred during 75 d breeding
seasons. Five sires of each breed were used in this study.
Sires were rotated among breeding pastures in both forage
treatments to prevent confounding of sire and forage effects,
and breed of sire was alternated in a breeding pasture to facilitate
sire of calf identification.
Study Animals. Calves were born from late February to
late May each year. Weights were taken, and calves were
tagged at birth. The post-weaning backgrounding environments
were designed to imitate two commercial situations: 1)
a warm season, dormant forage environment (BG) and 2) a
cool-season forage environment (E+) where growing forage
is available for a portion of the evaluation period and supple-
1 Department of Animal Science, Fayetteville
2 USDA-ARS, Grazinglands Research Laboratory, El Reno, OK
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