Page 121 - The Welfare of Cattle

98 the WeLfare of CattLe

the fact that polled Holstein sires have lower estimated breeding values for milk production when
the polled allele is introgressed and that is estimated to result in a loss of $252 per lactation cycle.
In the Holstein breed, only 6% of dairy sires produce commercially available seedstock
carrying the POLLED gene and it could take more than 20 years of breeding to achieve a frequency
of 50% polled animals (Dorshorst, 2014). Therefore, genetic biotechnology is being implemented
to accelerate efforts to achieve hornless cattle, particularly in dairy cattle (see Carlson et al.,
2016). The need to utilize biotechnology to enhance welfare is also receiving pressure from cor-
porations like Wal-Mart, Starbucks, Nestle, and Kroger because they have prioritized a reduction
of dehorning practices into their animal welfare policies and supply chain producer requirements
(Swanson, 2015).
Genome editing using transcription activator-like effector nucleases (TALENs) to introgress the
polled allele into the genome of bovine embryonic fibroblasts has been used to produce a genotype
identical to what is achievable using natural mating, but without negative effects on lactation in
dairy cows (Carlson et al., 2016). The researchers used TALEN-stimulated homology-dependent
repair to produce four cell lines either homozygous or heterozygous for the polled allele10. Each
of the four lines was cloned by somatic cell nuclear transfer and full- term pregnancies were estab-
lished for three of the four lines. Five calves were polled and the homozygous introgression of the
polled allele into the calves was confirmed and there were no “off-target” effects associated with
introgression of the polled allele that might affect lactation.
Carlson et al. (2016) propose that genetic improvement of livestock using TALENs, or other
genome-editing methods, is an alternative to transgenic methods for genetic improvement of live-
stock using variation that is already present in species without the admixture that can result from
classic breeding methods. They caution that their results do not demonstrate that the introgression
of polled alleles into elite animals would be without risk to the economics of milk production by
dairy cows in the United States.
Castration. Castration of cattle is performed to reduce inter-animal aggression, improve human
safety, avoid the risk of unwanted pregnancies, and enhance product quality and production effi-
ciency. Castration may be accomplished by surgical removal of the testes, use of a rubber band to
inhibit blood flow to testes or by crushing the spermatic cord that includes blood vessels to the testes.
However, immunological castration is also possible. One approach was to immunize calves against
Gonadotropin Releasing Hormone (GnRH) that stimulates the pituitary gland to release Luteinizing
Hormone (LH) and Follicle Stimulating Hormone (FSH). Robertson et al. (1982) immunized 10
Holstein calves against GnRH and found that five calves responded poorly in terms of produc-
ing antibodies to GnRH. However, the other five calves responded with high-antibody titers, low
concentrations of testosterone in serum, involuted testes, reduced libido and semen production,
and docile behavior. The immunocastration effect lasted approximately 6 months before the calves
exhibited behaviors of intact males. Temporary immunocastration did not affect weight gain that
was improved over that for castrated steers. Carcass traits were similar for immunocastrated and
castrated calves, but the lean content in all ten calves subjected to immunocastration was greater
than for steer carcasses.
Marti et al. (2017) reported on an immunocastration study that initially included 493 bulls of
which 476 remained in the study for 133 days. Meat quality (carcass fat-cover, marbling, tenderness
score, pH), marbling, and other meat quality characteristics were assessed and related to testicular
function and concentrations of testosterone in serum in immunized bulls. The results of Marti
et al. (2017) have been corroborated by others who reported that bulls immunized against GnRH
had carcasses more likely to grade choice. Cook et al. (2000) did not report an improvement in
meat tenderness when bulls were vaccinated with another GnRH vaccine; rather they found that as
the response to GnRH immunization increased, meat tenderness also increased. Similarly, Ribeiro
et al. (2004) collected rib dissection data and found that the carcass composition of vaccinated ani-
mals and castrated animals had more fat and less muscle than carcasses of intact bulls.