Author
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Chase, Chadwick - Chad |
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OLSON, T - UNIVERSITY OF FLORIDA |
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Submitted to: Florida Cattleman
Publication Type: Trade Journal Publication Acceptance Date: 10/23/2006 Publication Date: 10/26/2006 Citation: Chase, C.C., Olson, T.A. 2006. Effect of Frame Size on Reproductive and Maternal Performance of Brahman Cattle. Florida Cattleman. 71(1):70,72,74. Interpretive Summary: The effect of frame size on reproduction is an important consideration in both purebred and commercial cowherds. Although it now seems to be recognized (but is still not well documented) that increased frame size negatively affects reproductive performance in beef cows, not long ago, the tallest cows and bulls were the show winners and those sires with the heaviest yearling weights (or growth rates) were the most popular. Use of these selection criteria in breeding programs can result in increases in frame size of replacement heifers and subsequently as cows can negatively affect the reproductive performance of the cowherd. We report on a 10-year study conducted at STARS using the Brahman cowherd that was divided into small, medium, and large frame size groups and bred to similar frame size Brahman bulls. Results from this study clearly show that frame size affects reproductive and production performance in Brahman cattle. Selection of Brahman cattle for larger frame size (taller hip height) delayed puberty and reduced fertility in young females. The depression in fertility and productivity associated with increased frame size was most evident in first- and second-parity dams and not in mature dams (third- and greater parity). Although increased nutrition may be able to overcome some of these depressions, the associated costs could be extremely high particularly when the body condition of young lactating large frame size cows is trying to be increased through added nutrition. Although reproduction was better for small frame size cattle, reduced growth potential and the possibility that progeny would not have adequate carcass weight for slaughter all must be considered for a given management/marketing situation. Therefore, the optimal cow frame size would appear to be one of moderate size for a particular situation based on the ability of cows to maintain an adequate body condition when managed under commercial conditions and to produce progeny capable of producing acceptable carcass weights. Technical Abstract: The effect of frame size on reproduction is an important consideration in both purebred and commercial cowherds. Although it now seems to be recognized (but is still not well documented) that increased frame size negatively affects reproductive performance in beef cows, not long ago, the tallest cows and bulls were the show winners and those sires with the heaviest yearling weights (or growth rates) were the most popular. While it may be advantageous to select for growth rate, it is known that selection for increased growth rate is accompanied by an increase in frame size due to the correlation between the two traits. These increases in frame size of replacement heifers and subsequently as cows can negatively affect the reproductive performance of the cowherd and the economics of the ranching enterprise. We report here results conducted with Brahman cattle that will be useful to breeders and commercial producers of Brahman and Brahman-crossbred cattle, but are also applicable to the British and European breeds. A 10-year study was initiated in 1984 by Dr. Tim Olson, University of Florida, and was conducted at the STARS. The Brahman cowherd was divided into small, medium, and large frame size groups and bred to similar frame size Brahman bulls (i.e., small to small, medium to medium, and large to large). Heifers were raised as replacements and entered into the herd to calve as 3-year-olds. By the end of this study, we observed large differences in frame sizes among cows. Large frame size heifers reached puberty 39 days later than small, and 46 days later than medium frame size heifers. There was no difference in age at puberty between small and medium frame size heifers. Because heifers were bred to calve first as 3-year-olds, conception rate for first-parity was high across all frame size groups (92%). Conception rate for second-parity cows was only 41% for large frame size cows, which was lower than for small (66%) and medium (69%) frame size cows. Conception rate for third- and greater parity cows, was similar for medium and large frame size cows, but both were less than for small frame size cows. Conception rate increased with increased body condition score. For second-parity cows, conception rates were 17, 69, and 89% for body condition scores 3, 4, and 5, respectively. These results indicate that the nutrient demands of young (second-parity) large frame size cows could not be met under the station’s conditions. This was reflected in low conception rates in young (second-parity) large frame cows with low (~3) body condition scores. Calf survival from first-parity cows was similar for small and medium frame size cows but was over 30% less for large frame size cows. Calf survival did not differ among frame size groups for second- or third- and greater parity. Weaning rates were lower for large frame size cows compared to small or medium frame size cows at both first- and second-parity. This may be explained because for first-parity, large frame size cows had lower calf survivability and for second-parity, large frame size cows had a lower conception rate. Weaning rates for third- and greater parity cows did not differ among frame sizes. Production per cow (lbs. of calf weaned per cow exposed) for first- and second-parity were greater for small and medium frame size cows than large frame size cows. Although large frame size cows had calves with heavier weaning weights this could not make up for the lower numbers of calves weaned. Production per cow for third- and greater parity did not differ among frame size groups. Results from this study clearly show that frame size affects reproductive and production performance in Brahman cattle. Selection of Brahman cattle for larger frame size (taller hip height) delayed puberty and reduced fertility in young females. The depression in fertility and prod |
