Editing Meat (section)

== Animal growth and development ==

Several factors affect the growth and development of meat.

=== Genetics ===

{|class="wikitable" style="float:left; margin:10px"
|-
! Trait
! Heritability{{sfn|Lawrie|Ledward|2006|pp=17–22}}
|-
|Reproductive efficiency
|2–10%
|-
|Meat quality
|15–30%
|-
|Growth
|20–40%
|-
|Muscle/fat ratio
|40–60%
|}

Some economically important traits in meat animals are heritable to some degree, and can thus be selected for by [[animal breeding]]. In cattle, certain growth features are controlled by [[Dominance (genetics)|recessive genes]] which have not so far been excluded, complicating breeding.{{sfn|Lawrie|Ledward|2006|pp=17–22}} One such trait is [[dwarfism]]; another is the doppelender or "[[Myostatin|double muscling]]" condition, which causes [[muscle hypertrophy]] and thereby increases the animal's commercial value.{{sfn|Lawrie|Ledward|2006|pp=17–22}} [[Genetic analysis]] continues to reveal the mechanisms that control numerous aspects of the [[endocrine system]] and, through it, meat growth and quality.{{sfn|Lawrie|Ledward|2006|pp=17–22}}

[[Genetic engineering]] can shorten breeding programs significantly because they allow for the identification and isolation of [[gene]]s coding for desired traits, and for the reincorporation of these genes into the animal [[genome]].{{sfn|Lawrie|Ledward|2006|pp=17–22}} To enable this, the genomes of many animals [[genome project|are being mapped]].{{sfn|Lawrie|Ledward|2006|pp=17–22}} Some research has already seen commercial application. For instance, a [[Recombinant DNA|recombinant]] [[Bacteria|bacterium]] has been developed which improves the digestion of grass in the [[rumen]] of cattle, and some features of muscle fibers have been genetically altered.{{sfn|Lawrie|Ledward|2006|pp=17–22}} Experimental [[Cloning|reproductive cloning]] of commercially important meat animals such as sheep, pig or cattle has been successful. Asexual reproduction of animals bearing desirable traits is anticipated.{{sfn|Lawrie|Ledward|2006|pp=17–22}}

=== Environment ===

Heat regulation in livestock is of economic significance, as mammals attempt to maintain a constant optimal body temperature. Low temperatures tend to prolong animal development and high temperatures tend to delay it. Depending on their size, body shape and insulation through tissue and fur, some animals have a relatively narrow zone of temperature tolerance and others (e.g. cattle) a broad one. Static [[magnetic field]]s, for reasons still unknown, retard animal development.{{sfn|Lawrie|Ledward|2006|pp=22–23}}

=== Animal nutrition ===

The quality and quantity of usable meat depends on the animal's ''plane of nutrition'', i.e., whether it is over- or underfed. Scientists disagree about how exactly the plane of nutrition influences carcase composition.{{sfn|Lawrie|Ledward|2006|pp=25–30}}

The composition of the diet, especially the amount of protein provided, is an important factor regulating animal growth. [[Ruminant]]s, which may digest [[cellulose]], are better adapted to poor-quality diets, but their ruminal microorganisms degrade high-quality protein if supplied in excess. Because producing high-quality protein animal feed is expensive, several techniques are employed or experimented with to ensure maximum utilization of protein. These include the treatment of feed with [[Formaldehyde|formalin]] to protect [[amino acid]]s during their passage through the [[rumen]], the recycling of [[manure]] by feeding it back to cattle mixed with feed concentrates, or the conversion of petroleum [[hydrocarbon]]s to protein through microbial action.{{sfn|Lawrie|Ledward|2006|pp=25–30}}

In plant feed, environmental factors influence the availability of crucial [[nutrient]]s or [[micronutrient]]s, a lack or excess of which can cause a great many ailments. In Australia, where the soil contains limited [[phosphate]], cattle are fed additional phosphate to increase the efficiency of beef production. Also in Australia, cattle and sheep in certain areas were often found losing their appetite and dying in the midst of rich pasture; this was found to be a result of [[cobalt]] deficiency in the soil. Plant [[toxin]]s are a risk to grazing animals; for instance, [[sodium fluoroacetate]], found in some African and Australian plants, kills by disrupting the [[cellular metabolism]]. Some man-made [[pollutant]]s such as [[methylmercury]] and some [[pesticide]] residues present a particular hazard as they [[Bioaccumulation|bioaccumulate]] in meat, potentially poisoning consumers.{{sfn|Lawrie|Ledward|2006|pp=25–30}}

=== Animal welfare ===

{{See also|Animal welfare labelling}}

[[File:Animal Abuse Battery Cage 01.jpg|thumb|The welfare of farm animals such as hens in [[battery cages]] and other systems is debated.<ref>{{cite web |url=http://www.abc.net.au/news/2014-09-24/rspca-on-free-range-court-case/5769542 |title=RSPCA says egg industry is 'misleading the public' on free range |website=[[Australian Broadcasting Corporation]] |access-date=26 May 2015 |date=24 September 2014 |archive-date=1 November 2016 |archive-url=https://web.archive.org/web/20161101051034/http://www.abc.net.au/news/2014-09-24/rspca-on-free-range-court-case/5769542 |url-status=live }}</ref><ref>{{cite web |url=https://www.npr.org/sections/thesalt/2013/06/27/195639341/what-the-rise-of-cage-free-eggs-means-for-chickens |title=What The Rise Of Cage-Free Eggs Means For Chickens |website=[[NPR]] |access-date=26 May 2015 |archive-date=11 February 2021 |archive-url=https://web.archive.org/web/20210211010506/http://www.npr.org/sections/thesalt/2013/06/27/195639341/what-the-rise-of-cage-free-eggs-means-for-chickens |url-status=live }}</ref><ref>{{cite web |url=https://www.npr.org/sections/thesalt/2014/12/23/370377902/farm-fresh-natural-eggs-not-always-what-they-re-cracked-up-to-be |title=Farm Fresh? Natural? Eggs Not Always What They're Cracked Up To Be |website=[[NPR]] |date=23 December 2014 |access-date=26 May 2015 |last1=Kelto |first1=Anders |archive-date=3 November 2020 |archive-url=https://web.archive.org/web/20201103121635/https://www.npr.org/sections/thesalt/2014/12/23/370377902/farm-fresh-natural-eggs-not-always-what-they-re-cracked-up-to-be |url-status=live }}</ref>]]

Practices such as confinement in [[factory farming]] have generated concerns for [[animal welfare]]. Animals have [[List of abnormal behaviours in animals|abnormal behaviors]] such as tail-biting, cannibalism, and [[Abnormal behaviour of birds in captivity|feather pecking]]. [[Overview of discretionary invasive procedures on animals|Invasive procedures]] such as [[debeaking|beak trimming]], [[castration]], and [[Animal identification|ear notching]] have similarly been questioned.<ref>{{Cite journal |last1=Bartlett |first1=Harriet |last2=Holmes |first2=Mark A. |last3=Petrovan |first3=Silviu O. |last4=Williams |first4=David R. |last5=Wood |first5=James L. N. |last6=Balmford |first6=Andrew |date=June 2022 |title=Understanding the relative risks of zoonosis emergence under contrasting approaches to meeting livestock product demand |journal=[[Royal Society Open Science]] |volume=9 |issue=6 |page=211573 |doi=10.1098/rsos.211573  |pmc=9214290 |pmid=35754996|bibcode=2022RSOS....911573B }}</ref> Breeding for high productivity may affect welfare, as when [[broiler]] chickens are bred to be very large and to grow rapidly. Broilers often have leg deformities and become lame, and many die from the stress of handling and transport.<ref>{{cite web |url=http://www.ciwf.org.uk/farm_animals/poultry/meat_chickens/welfare_issues.aspx |title=Compassion in World Farming – Meat chickens – Welfare issues |publisher=[[Compassion in World Farming|Compassion In World Farming]] |access-date=22 October 2013 |archive-url=https://web.archive.org/web/20131023062150/http://www.ciwf.org.uk/farm_animals/poultry/meat_chickens/welfare_issues.aspx |archive-date=23 October 2013 }}</ref>

=== Human intervention ===

Meat producers may seek to improve the [[fertility]] of female animals through the administration of [[Gonadotropic cell|gonadotrophic]] or [[ovulation]]-inducing [[hormone]]s. In pig production, [[Domestic pig|sow]] infertility is a common problem – possibly due to excessive fatness. No methods currently exist to augment the fertility of male animals. [[Artificial insemination]] is now routinely used to produce animals of the best possible genetic quality, and the efficiency of this method is improved through the administration of hormones that synchronize the ovulation cycles within groups of females.{{sfn|Lawrie|Ledward|2006|pp=31–33}}

[[Growth hormone]]s, particularly [[Anabolism|anabolic]] agents such as [[steroid]]s, are used in some countries to accelerate muscle growth in animals.{{sfn|Lawrie|Ledward|2006|pp=31–33}} This practice has given rise to the [[beef hormone controversy]], an international trade dispute. It may decrease the tenderness of meat, although research on this is inconclusive, and have other effects on the composition of the muscle flesh.{{sfn|Lawrie|Ledward|2006|pp=35–39}} Where [[castration]] is used to improve control over male animals, its side effects can be counteracted by the administration of hormones.{{sfn|Lawrie|Ledward|2006|pp=31–33}} [[Myostatin]] has been used to produce [[Myostatin-related muscle hypertrophy|muscle hypertrophy]].<ref>{{cite journal |last1=Aiello |first1=D. |last2=Patel |first2=K. |last3=Lasagna |first3=E. |title=The myostatin gene: an overview of mechanisms of action and its relevance to livestock animals |journal=Animal Genetics |date=December 2018 |volume=49 |issue=6 |pages=505–519 |doi=10.1111/age.12696 |pmid=30125951 |s2cid=52051853 |url=https://centaur.reading.ac.uk/77388/1/Aiello_et_al_revised_not_highlighted.pdf }}</ref>

[[Sedative]]s may be administered to animals to counteract stress factors and increase weight gain. The feeding of [[antibiotics]] to certain animals increases growth rates. This practice is particularly prevalent in the US, but has been banned in the EU, partly because it causes [[antimicrobial resistance]] in [[pathogen]]ic microorganisms.{{sfn|Lawrie|Ledward|2006|pp=35–39}}