Steven D. Lukefahr, Professor
Department of Animal & Wildlife Sciences
Texas A&M University-Kingsville 78363
Commercial livestock producers often use sire and dam breeds of recognized merit to produce crossbred offspring for market. In fact, the majority of chickens, beef calves, hogs and lambs produced in the U.S. for meat are crossbred. The crossbreds give more efficient performance and greater profits. For example, in swine, Yorkshire sows with breed strengths for large litter size, high milk production and excellent mothering ability are commonly mated to Duroc boars with breed strengths for rapid body gains, good feed conversion, minimal backfat and lean carcasses. Such a combination of breed strengths is referred to as breed complementation. The crossbred pig will also express hybrid vigor, which is an additional benefit of crossbreeding. In Europe, the sophisticated use of commercial sire and dam breeds to produce crossbred fryer rabbits is widely practiced. Major rabbit breeding companies exist which develop and sell parental hybrid lines to commercial producers for the purpose of crossbred fryer production.
Development of the Breed
In the July issue of the Journal of Animal Science, an article described the development of a terminal sire breed in the U.S. (Lukefahr et al., 1996). The breeding project began in 1986 when purebred Californian (CAL), Champagne d'Argent (CHA) and Flemish Giant (FG) rabbits were obtained from reputable commercial and fancy breeders from several states and received at Alabama A&M University, Huntsville, AL. As shown in Figure 1, FG bucks were mated with CAL and CHA does to produce two first-cross (F1) lines. Bucks and does of both F1 lines were then crossed to produce a composite, second-cross (F2) population. This resulted in all F2 rabbits being 1/2 FG, 1/4 CAL, and 1/4 CHA. This breed composition was used to assemble genes from the three breeds for sire traits: rapid and efficient body gains, high dressing percentage and high meat-to-bone ratio. In such an F2 population, it is expected that all possible gene combinations can occur. Thus, a great deal of variation can arise for all observable traits. Many different coat colors appeared in this generation and there was substantial variation in body size and type and growth rate among fryers.
During the long-term breeding program, rabbits were fed a commercial diet. Litters were weaned at 28 days of age by removing the dam from the rearing cage. During the 28- to 70-day postweaning phase, growth, feed consumption and survival rates were monitored. At 71 to 73 days of age, one or two rabbits from each of 240 litters were randomly sampled for evaluation of dressing percentage, meat-to-bone ratio and other carcass traits.
As early as the F1 generation, superior growth and meatiness were clearly observed. The F1 rabbits had large body frame size and plenty of muscle to portray a desirable commercial meat-type animal. The F2 population was next separated into two genetic lines: selected and unselected. This was done to measure genetic progress for the sire traits in each generation. Next, there was one generation of random mating in both lines (generation 0). For the next five generations, rabbits in the selected line with the heaviest body weights at 70 days of age were saved as replacements. No attention was paid to coat color or other characters. Replacements for the unselected line were chosen at random. There were a total of 1,616 rabbits from 336 litters (sired by 121 bucks and reared by 321 does) produced in this phase of the breeding program. Under intense selection, considerable genetic progress was achieved in the selected line (Figure 2). By the fifth generation, the average 70-day body weights of selected rabbits were 4.9 lb, while those of the unselected line were 4.5 lb. In addition, genetic improvements in weaning weight, daily weight gains and meat-to-bone ratio were also confirmed in the selected line.
Between 1988 and 1994, commercial producers in 12 states used bucks from the selected line at Alabama A&M University to produce crossbred fryers. These large bucks were mostly mated with New Zealand White (NZW) purebred or CAL X NZW crossbred does. Many producers reported that their crossbred fryers reached market size about a week earlier than purebred NZW fryers. In a two-year experiment at Alabama A&M University involving 460 litters, total 70-day market weights of NZW litters averaged 27.8 pounds compared to 29.7 pounds for litters sired by select line bucks and reared by NZW or CAL X NZW does (Khan and Lukefahr, 1996).
In 1994, Dr. Lukefahr moved to Texas A&M University-Kingsville and took rabbits with the best genetics from both the selected and unselected lines. In Texas, the two lines were crossed to expand the genetic base. Selection efforts continue to further refine this improved genetic line. The name "Altex" (Al from Alabama and tex from Texas, and pronounced "all-tex") has recently been given to this new commercial sire breed. In terms of color, fryers possess a white pelt. Soon, all Altex rabbits will be white with dark points - a simple recessive gene retained from the CAL foundation breed. This "genetic stamp" will avoid confusion between the white (albino) variety of the FG, and will avoid confusion between the smaller body size and lighter mature weight features of the CAL (Photo 1).
Use of Terminal Sires
Altex bucks and does may first be mated by 6 months of age. Mature body weights typically exceed 13 pounds in both sexes. It is advised that when Altex bucks are used in a commercial crossbreeding program that all offspring be sold for meat. This breeding practice is called a "terminal crossbreeding". In other words, replacements should not be saved because less efficient production would be expected. Specifically, an Altex X NZW sire may produce less growthy fryers than an Altex sire, and the Altex X NZW dam may consume more feed, produce less milk and wean fewer offspring than a NZW dam. A commercial breeder may simply obtain another Altex buck from a nucleus herd source when a replacement is needed. Replacement does can be purchased from reputable purebred NZW breeders or other commercial sources. This process in itself leads to improved production efficiency because the breeder is relieved of the responsibility and time involved in making selections and in occupying cage space for young, home-grown replacement bucks and does. Lastly, it is emphasized that the Altex is a commercial breed, being developed according to sound genetic principles of selection for economic traits.
A second nucleus unit of Altex stock was established last year at Southern University and A&M College, Baton Rouge, LA. Breeding stock (bucks and does) are available in Louisiana and Texas from both universities cited. Rabbits are sold with complete pedigree and performance trait information. Interested breeders may contact either Dr. Lukefahr or Dr. McNitt for further information concerning purchases, breeding and management of Altex stock.
Khan, M.A., and S.D. Lukefahr. 1996. Breed type comparisons for postweaning litter traits in rabbits. In: Proceedings of the 6th World Rabbit Congress, Toulouse, France. 2:299-304.
Lukefahr, S.D., H.B. Odi, and J.K.A. Atakora. 1996. Mass selection for
70-day body weight in rabbits. Journal of Animal Science, 74:1481-1489.
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