Linda Benedict, Derouen, Sidney M., Turpin, J Mike | 8/4/2009 11:31:27 PM
Sidney M. DeRouen and J. Michael Turpin
Most commercial cow-calf herds in Louisiana and in the southeastern United States include fewer than 100 animals and consist of crossbred combinations of Brahman, British, Continental and possibly dairy breeds. The first-cross Brahman has been recognized as one of the more productive brood cows throughout the southern United States because of superior adaptability and productivity in hot, humid weather.
Crossbreeding is widely recognized as an excellent management tool for improving productivity because of heterosis. Heterosis is the superiority exhibited by crossbred individuals for a particular trait, such as weaning weight, compared to the average of straightbred animals. The effects of crossbreeding can accumulate. Even though only a small level of heterosis may be realized for a single trait, the effects tend to be additive so that an increase in overall productivity can range from 9 percent to 28 percent.
A major disadvantage of traditional crossbreeding systems is that the producer must use several breeding pastures or artificial insemination. For producers with cow herds of fewer than 100 animals, this is not feasible. Another limitation is the difficulty of producing suitable replacement females of the desired breed composition. It is almost impossible to produce the optimum market steer calf and the ideal replacement heifer from the same mating system because carcass characteristics and maternal traits are antagonistic.
In this crossbreeding study, the main objective was to compare straightbredand composite-sired progeny that vary in percentage of Brahman inheritance. In addition, British (Angus) and Continental (Gelbvieh) sire breeds were evaluated along with their Brahman derivative counterparts, which are Brangus (5/8 Angus-3/8 Brahman) and Gelbray (5/8 Gelbvieh-3/8 Brahman). In this report, progeny produced from these matings were evaluated for potential as market calves.
Mating systems, preweaning management
A total of 503 calves were weaned from both spring and fall calving seasons over a four-year period. First cross (F1) Brahman x Hereford cows were sorted by cow age and were randomly allotted each year to one of eight breeding groups. Groups of cows were exposed each year to either Angus, Gelbvieh, Brangus or Gelbray sires. All together, 29 sires were used — nine Angus, seven Gelbvieh, six Brangus and seven Gelbray. The Angus- and Gelbvieh-sired offspring had 1/4 Brahman inheritance, whereas Brangus- and Gelbray-sired offspring had 7/16 Brahman inheritance.
Spring-calving cows were exposed to bulls from May 1 through June 30. Calves were born from early February through mid April in 1993 through 1996, with weaning occurring in late September of each year. Cows and calves were placed on bermudagrass pastures during the preweaning period. Before bermudagrass became available for grazing, cows were fed bermudagrass hay and an energy supplement (3 to 5 pounds per head per day of ground corn).
Fall and late-summer calving cows were exposed to bulls from October 15 through December 14. Calves were born from late July through early October 1993 through 1996, with weaning occurring in mid April of the subsequent year. Calves were weaned at this time so that they could be placed into a stocker grazing program on bermudagrass pastures in late April. During the preweaning period, cows and calves grazed bermudagrass until it became dormant. Thereafter, cows were fed with bermudagrass hay and an energy supplement (3 to 5 pounds per head per day of ground corn). No grazing of cool-season annuals, such as ryegrass, was employed for either calving system during the preweaning period.
Cows were tested for pregnancy about 60 days after the end of the breeding season, and open cows were reassigned to the alternate calving season to allow the production of as many calves as possible. Cows that were open after a second consecutive breeding season were culled. All male calves were castrated at birth. Creep-feeding was not practiced. Recommended health and management practices were followed on the cows and calves.
Calving season and calf sex effects
Fall-born calves were 2 pounds heavier at birth than spring-born calves. Average daily gain for spring-born calves, however, was 0.45 pound greater than for fall-born calves. This resulted in a 14-pound-heavier actual weaning weight and a 90-pound-heavier adjusted 205-day weight for spring-born calves. It is important to note that the majority of the preweaning period for the fall-born calves occurred when the bermudagrass was dormant. Cows and calves in this calving system were provided freechoice bermudagrass hay and 3 to 5 pounds of ground corn per cow. Under this type of nutritional program, the growth potential of fall-born calves was apparently hindered, resulting in substantially lower preweaning weight gains compared to spring-born calves. Male calves were 3 pounds heavier at birth and 22 pounds heavier at weaning and had greater preweaning gains than female calves.
Sire breed effects
Figure 1 shows the performance of preweaning traits of crossbred calves by sire breed. There was no change in rank of sire breed between the two calving seasons. The range in birth weight – from 77 pounds for Angus-sired calves to 82 pounds for Gelbvieh-sired calves – did not vary among sire breeds. Rate of average daily gain was similar among sire breeds (1.77 to 1.83 pounds per day). Actual weaning weight ranged from 495 pounds for Angus-sired calves to 466 pounds for Gelbray-sired calves and was similar among sire breeds. When weaning weight was adjusted to an age-constant basis (205-day weight), the variation among sire breeds was reduced (443 to 453 pounds).
Estimated market value (at 75 cents per pound) of calves, if sold at weaning, would be $371 for Angus-, $358 for Gelbvieh-, $352 for Brangus- and $350 for Gelbray-sired calves based on actual weaning weight. The Brangus- and Gelbray-sired calves may possibly be discounted because of level of Brahman inheritance. A possible explanation for the lack of variation in preweaning performance due to sire breed could be that the maternal ability of the F1 Brahman x Hereford cow tended to mask any differences in growth potential among these breeds.
In this study, an attempt was made to sample individual sires of each breed that would be representative of the type of bulls used by commercial cattle producers in this state. However, because only 29 bulls were sampled, true representation of the average of each respective sire breed may not have been attained.
In conclusion, calf performance was statistically similar among straightbred and Brahman-composite bulls when mated to F1 Brahman x Hereford cows. Angus- and Gelbvieh-sired calves were numerically heavier at weaning, resulting in increased market value compared to Brangus- and Gelbray-sired calves.
A long-term objective of this study includes evaluation of female productivity. Brangus and Gelbray bulls producing calves with 7/16 Brahman inheritance would not be ideal sire breed types when marketing at weaning but would be suitable sires to consider for producing replacement heifers. These calves will be evaluated for potential as replacement heifers, stockers, feeders and for carcass merit.
Sidney M. DeRouen, Associate Professor, and J. Michael Turpin, Research Associate, Hill Farm Research Station, Homer, La.
(This article was published in the summer 1999 issue of Louisiana Agriculture.)