Abstract
Fecal microhistology and chemistry were used to evaluate botanical composition and quality of diets selected by Brangus cattle grazing Chihuahuan desert range in 3 seasons; fall: October, 1991; winter: January, 1992; and summer: July, 1992. Fecal samples were collected from 100 head in fall (58 2-8 year cows and 42 calves), 53 head (2-8 year-old cows) in winter, and 44 head (2-8 year-old cows) in summer. Paternal half sib analyses were used to estimate genetic and phenotypic variances and heritability estimates. Heritability is the proportion of total (phenotypic) variation which is due to additive genetic effects. The effect of sire within age was observed for percentage of Aristida spp. (P= 0.01), Sporobolus spp. (P= 0.09), total grasses (P = 0.02), Croton pottsii (Klotzsch) Muell.-Arg. (P= 0.03), and total forbs (P =0.02) in fall diets. The number of grass species in diets was also affected by sire (P=0.03). Heritability estimates were 0.87, 0.51, 0.78, 0.76, and 0.79 for percentages of Aristida spp., Sporobolus spp., total grasses, Croton pottsii, and total forbs, respectively. Heritability estimates for number of grass and forb species in fall diets were 0.68 and 0.26, respectively. Heritability estimates for winter samples were 0.40, 0.00, 0.37, and 0.27 for percentages of Sporobolus spp., total grasses, Yucca elata Engelm., and total shrubs, respectively. Heritability estimates for the number of grass and total species observed in winter diets were 1.11 and 0.47, respectively. Heritability estimates for percentages of Bouteloua spp., total grasses, Croton pottsii, Dalea spp., and total forbs in summer samples were 0.20, 0.55, 0.58, and 0.46, respectively. Heritability estimates for the number of grass and total species in summer diets were 0.49 and 0.79, respectively. These data suggest that genetic composition of beef cattle may affect diet selection under Chihuahuan desert conditions.
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