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Accueil du site → Doctorat → États-Unis → 1994 → Diet botanical and fecal chemical composition of three breeds of cows on semidesert rangeland

New Mexico State University (1994)

Diet botanical and fecal chemical composition of three breeds of cows on semidesert rangeland

De Alba Becerra, Ramiro

Titre : Diet botanical and fecal chemical composition of three breeds of cows on semidesert rangeland

Auteur : De Alba Becerra, Ramiro

Université de soutenance  : New Mexico State University

Grade : Doctor of Philosophy (PhD) 1994

This study was conducted in south-central New Mexico, to evaluate diet botanical, fecal nitrogen and phosphorus contents of three breeds of cattle and to determine seasonal effects on plant nutritive values. Barzona, Brangus and Beefmaster cows were studied during August and November of 1991 and during January, June and November of 1992. Fecal samples were subjected to chemical and microhistological analyses to estimate diet quality and species composition. Twenty plant species were identified in the diets ; among dietary species, grasses were dominate for all three cattle breeds during all seasons. Major dietary forage plants were dropseeds, threeawns and black grama. Black grama was the most abundant forage plant ; dropseeds and threeawns were second and third in importance. Although the availability of black grama was greater than dropseeds, the three breeds showed a significant preference for dropseeds. Croton pottsii was the forb with highest availability and was the most consumed by the three breeds. Brangus selected more total shrubs than Barzona and Beefmaster (P =.0007). Barzona ate more threeawns than Brangus and Beefmaster (P =.0191). Black grama (P =.0370) and Sphaeralcea coccinea (P =.0091) were consumed in higher proportions by Barzona and Beefmaster than by Brangus. Barzona selected more mesquite than Brangus and Beefmaster (P =.00091). In diet diversity there was a significant difference among breeds and seasons. During winter, the Shannon-Weinner index indicated greater diversity for Brangus and Beefmaster than Barzona. In fall 1992, Barzona and Brangus obtained greater diversity than Beefmaster. Fecal nitrogen concentration was higher with Brangus compared to Barzona and BeefMaster (P $<$ 0.05) during summer 1991. In June 1992, fecal nitrogen concentrations were higher in BeefMaster diets compared to those for Barzona (P $<$ 0.05). The analysis of variance from regression indicates a significant relationship between fecal nitrogen and phosphorus. The R-square was 0.82. The correlation between fecal nitrogen and phosphorus was 0.94, 0.90 and 0.83 for Beefmaster, Brangus and Barzona, respectively. From a practical standpoint, my study showed no definite advantage of any breed studied in diet botanical composition or in diet quality. Animal behavior and physiology appear to better explain productivity differences among the cattle breeds studied than diet botanical composition and quality.

Mots clés : Diet, botanical composition, Biological sciences, Livestock


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