Morgan

Cloning in the Cattle and Sheep Industry
Most farmers and ranchers use cloning as advancement in their program. Cloning can offer farmers advantages by the farmers selecting the animal that has passed down the most superior genetics and that has performed the best in everyday environmental settings. Also, it can give them advantages on selling high-quality meat and dairy products for the dairy cattle producers. Ranchers has the advantages by hand picking the highest quality in the sires or dams genetic makeup by making an exact replica for breeding purposes in the commercial industry and/or the stock show industry.

Cloning of cattle and sheep does not harm the animal in any shape or form but it may put a little environmental stress on them due to all of the handling and testing of the animal. When you clone an animal this doesn’t mean you are changing the animal by altering their genetic makeup or genetically engineering them, it just means you are getting an exact replica of that particular animal you have chosen. When an animal is cloned, it alters their immune system somehow and where they do not get sick as often and they become parasite resistant so you spend less money on veterinary visits. Another important reason why cloning is in the livestock industry is for strict breeding purposes so the cloned animals can breed and produce animals for meat purposes.

Cloning has been part of our world for over three or four decades. Hans Dreisch performed the first successful reported case of cloning in 1894, which he cloned a sea urchin by isolating blastomeres. In 1902, Dr. Hans Spemann split the embryo using a strand of hair from his newborn son, and the resulting cells grew into normal adult salamanders. 1928 Dr, Spemann was at it again by conducting the first ever conducted nuclear transfer. This proved that the nucleus of an early embryo cell could lead to the growth of a separate organism and creating a clone of the DNA donor. Twenty-four years later, Robert Briggs and Thomas King used nuclear transfer on northern leopard frogs. They removed the nucleus from a blastula cell and then replaced the nucleus from an egg. In 1995 the first animal, two domestic sheep named Meagan and Morag, was cloned by using differentiated embryo cells was found to be starving the differentiated cell of nutrients, causing it to enter a suspended state of cell division. Ian Wilmut and Keith Campbell in the Roslin Institute at Edenburgh, United Kingdom accomplished this. Finally on July 5, 1996 the famous Dolly was born using a differentiated adult cell by Wilmut and Campbell. The cell she was cloned from was received from the udder of a six-year-old Fin Dorset ewe. (Seraphin, 2007)

Cloning of cattle and sheep is accomplished by first and foremost selection of the animal you would like to clone. This is based on the animals breeding performance, genetic makeup in his or her offspring, and whether or not it can handle the stress it has put on it due to the whole process. One of the many reasons why selection is important factor in cloning is due to not many of the carriers have a high birth rate of live progeny. When it came to cloning Dolly, scientist tried 277 times before they were successful in producing one live offspring (Edwards, 2003).

Some reasons that animals are being cloned are for the production of their cells that have been genetically engineered for the purposes of human medicine. In sheep when they are genetically engineered they carry the genetic information to make the human clotting factor IX in their milk, which is an important for therapeutic treatment for hemophiliacs (Eenennaam, 2006). Also, in some cases there are possibilities that cloned animals are disease resistant and have improved in milk composition. Also, frozen tissue samples are being used for the preservation of endangered species and help to save some species when they are on the verge of extinction. In many cases why cloning is used is to breed the cloned animal and their progeny is used for meat purposes. The Food and Drug Administration has not passed to use the actual cloned animals for human consumption (Eenennaam, 2006). The FDA’s Center for Veterinary Medicine is ultimately responsible for the evaluation of the food safety and the health of animal’s implication of cloning, as well as its environmental impact.

There are many ways to clone an animal but in cattle and sheep there are only a select few. Mainly there are only four main methods for producing clones number one individually separation of embryonic blastomeres up to the four- cell stage, number two embryo bisection at the morula or blastocyst stages, number three tetraploid of embryo complementation, and number four nuclear transfer or nuclear cloning (Wells, 2003). The first two cloning methods rely on the inherent cellular totipotency of very early embryonic cells, which limits the number of viable embryos and offspring that can be obtained. They share identical mitochondria and genomic DNA as the embryonic cells generate the entire conceptus (Wells, 2003). The third method of cloning has only been accomplished in a mouse where the pluripotent embryonic stem cells combined with tetraploid host embryos result in offspring comprise solely from the differentiated derivatives of the original embryonic stem cells and with the tetraploid cells contributing to the extra embryonic lineages developing into the placenta (Wells, 2003). The fourth and final method, which was used to clone Dolly and the most common by the majority of producers, is nuclear transfer or nuclear cloning. Cloning by nuclear transfer using mammalian somatic cells, however, it can be inefficient in all species in which live clones have been produced is usually a 0–10 live births after transfer of 100 cloned embryos (Tian, 2003). These developmental defects have been attributed to incomplete reprogramming of the somatic nuclei. The process by nuclear transfer usually proceeds as cells are collected from the selected donor and cultured in vitro or a petri dish. A matured oocyte is then enucleated and a donor cell is transferred into the enucleated oocyte. The somatic cell and the oocyte are then fused and the embryos are allowed to develop to a blastocyst in vitro. The blastocyst can then be transferred to a recipient and cloned animals are born after completion of gestation (Tian, 2003).

Due to nuclear transfer having difficulties in producing live clones, some studies show that a process known as serum starvation is used to improve the live progeny ratio while the majority of others show that it is not necessary. Serum starvation induces quiescence of cultured cells, arrests them at the cell cycle stage of G0 (Tian, 2003). Some laboratories have debated to whether inducing quiescence is required for a successful transfer or is it redeemed as unnecessary. P. Cibelli debates on that the G0 was unnecessary and those animals could be produced from cycling cells. In his study actively dividing the fibroblasts were used for nuclear transfer and for example, four calves were born from twenty-eight embryos transferred to eleven recipients due to the 56% of cycling cell in the G1 stage. (Cibelli, 1998). In many different studies, it was shown that the quiescence is not necessary for success of nuclear transfer due to the fact that the cells are not subjected to serum starvation, which can produce live clones. Which the question still remains with many laboratories which cell cycle to use, G0 or G1 imparts a higher nuclear transfer efficiency (Tian, 2003). The question will remain unanswered until a debated large-scale nuclear transfer studies can be conducted (Tian, 2003).

Another reason why nuclear transfer might fail is due to failure of the placenta to develop and function correctly. This is caused by most early pregnancy failure before placentome formation are attributed to an inadequate transition from the yolk sac to allantoic derived nutrition, with poor allantoic vascularization in sheep (Wells, 2003). In cattle, 50-70% of pregnancies at day 50 are lost throughout the remainder of gestation. These losses occur despite the presence of abundant fetal cotyledonary tissue, however this tissue fails to interact with the maternal caruncles to form functional placentomes (Wells, 2003).

In conclusion, cloning of cattle and sheep is still a long ways away from being perfected but we are on the right tract to master the art of cloning. As you can see there are still numerous experiments that need to be conducted to validate the multiple hypothesis there are with nuclear transfer of somatic cells. In my personal opinion I believe that cloning of all animals is very beneficial to us due to the markets in all livestock prices are increasing tremendously and rapidly where farmers and ranchers are being forced to sell out and having a rapid decrease on the meat market. By having the cloning option we can clone the dams that have shown the greatest performance and using her progeny for meat purposes.

References
Eenennaam, Allison Van, PhD. "Livestock Cloning." Livestock Cloning. University of California Department of Animal Science, Mar. 2006. Web. Nov. 2012. <http://animalscience.ucdavis.edu/animalbiotech/Outreach/Livestock_cloning.pdf>.

Seraphin, Rebecca. "History of Cloning." History of Cloning. University of California Davis, 2007. Web. <http://cosmos.ucdavis.edu/archives/2007/cluster7/seraphin_rebecca.pdf>.

Edwards, J. L., F. N. Schrick, M. D. McCracken, SR Van Amstel, F. M. Hopkins, M. G. Welborn, and C. J. Davies. "Cloning Adult Farm Animals: A Review of the Possibilities and Problems Associated with Somatic Cell Nuclear Transfer." Cloning Adult Farm Animals: A Review of the Possibilities and Problems Associated with Somatic Cell Nuclear Transfer. AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, 2003. Web. Nov. 2012. <http://animalscience.ag.utk.edu/utcloneproject/pdf/aji_064a%2062303.pdf>.

Wells, D. N. "Cloning in Livestock Agriculture." Cloning in Livestock Agriculture. Reproductive Technologies Group, AgResearch, PB 3123, Hamilton, New Zealand, 2003. Web. Nov. 2012. <http://www.clonesafety.com/cloning/peer-reviewed-research/articles/Wells_Cloning_in_livestock_agriculture_2003.pdf>.

Cibelli P, Stice SL, Golueke PJ, Kane JJ, Jerry J, Blackwell C, deLeon FAP and Robl JM: Cloned transgenic calves produced from non-quiescent fetal fibroblasts. Science 1998

Tian, Cindy X., Chikara Kubota, Brian Enright, and Xiangzhong Yang. "Cloning Animals by Somatic Cell Nuclear Transfer – Biological Factors." Reproductive Biology and Endocrinology. Bio Med Central, 13 Nov. 2003. Web. Nov. 2012. <http://www.biomedcentral.com/content/pdf/1477-7827-1-98.pdf>.