The genetic selection of animals bred to produce meat or milk has profoundly changed their metabolism. If they are animals destined to produce meat, a “metabolic setup” that favors the growth of muscle tissue and improves their quality will be rewarded, while if they are destined to dairy, the mammary gland has more metabolic priorities than every other tissue, although it is important as the immune and reproductive ones.
There is much knowledge about the production of ruminant milk, especially dairy cattle. All genetic selection, and now genomics, has had the priority in recent years of producing as much milk, fat, and protein as possible. First the morphological indices, and now also the functional ones, have “slowed down” this trend because the functional longevity and fertility, particularly of dairy cows, has been reduced to such a point that the economic advantage of producing milk, fat, and protein almost vanishes.
To better understand these concepts and to introduce metabolic diseases, the example of dairy cattle is very significant. How did geneticists prepare cows for productions that are now almost, and often exceed, 80 pounds and with milk that is constantly improving year after year? It is under everyone’s eyes that in recent months the Frisians (Holsteins), almost regardless of the average production, produce milk with more than 3.8% of fat and more than 3.15% of protein. There are now dairies, which are also very productive and do not have the food restrictions imposed by some PDOs, which deliver milk with more than 3.00% casein, something that was unthinkable a few years ago.
The human breast is the organ that allows the newborn child to grow up to food independence, which in natural conditions occurs at the 6th month of age. In dairy farms, this period lasts 60-90 days and is of fundamental importance for the species. Genetic selection has rewarded, with the advantage of access to the reproduction, the cows whose udder had the cells of the epithelium of the mammary alveolus less and less dependent on insulin and therefore able to acquire without its “intermediation” nutrients such as glucose, amino acids, and fatty acids. This “metabolic bullying” is attenuated when the cow is pregnant again because the uterus and the adipose tissue reacquire the priority dictated by the fetus.
In fact, milk production progressively goes down until the dry period. The pressing request of the industry to have milk with an ever-increasing percentage of fat and protein has imposed on cows another profound metabolic reorganization. To increase the availability of long-chain fatty acids for the udder, the aptitude to lose weight has been selected and, in order to have more amino acids, that of easily mobilizing the muscular reserves of “labile proteins”. Therefore, the modern dairy cattle, but also buffaloes, sheep, and goats that are very productive and have milk with a high concentration of casein and fatty acids, tend to have a lower response to the rise in blood sugar by insulin and tissues less sensitive to the action of this pancreatic hormone. This altered behavior of insulin, therefore, predisposes the animals to a greater lipo-mobilization which has positive effects on the percentage of milk fat. However, the increased inflow of non-esterified fatty acids (NEFA) to the liver greatly increases the risk of hepatic lipidosis and metabolic ketosis, both clinical and sub-clinical. The primary subtraction of amino acids, both essential and non-essential, due to the mammary synthesis of casein and other nutrients, very often induces secondary deficiencies of amino acids. This can lead to negative repercussions on the health of cows by acting on the export of triglycerides from the liver, on production (especially hepatic) of the hormone IGF-1, and on the full efficiency of the immune system, both humoral and cell-mediated.
Ruminants of high genetic potential (HMG) have a growth hormone (GH) level surely higher than that of a less selected animal. Among the multiple catabolic effects of this pituitary hormone is that of increasing the flow of blood and therefore the supply of nutrients to the mammary gland. Also, the hepatic blood supply is growing, and with it the clearance of estrogens and progesterone, an aspect that explains the reduced fertility typical of HMG animals. To understand the hormonal and metabolic structure of HMG ruminants, one can refer, even if very improperly, to what happens in the metabolism of a diabetic human by recognizing some aspects well known to both nutritionists and clinical veterinarians.
Figure 1: Some aspects of the metabolism of a diabetic human.
It is obvious that these hormonal and metabolic assets, primarily aimed at productive performance, have negative impacts on the health and fertility of ruminants both from milk and meat.
HMG animals require very accurate diets, management, environments, and management of infectious diseases, in order not to add serious risk factors to these potentially negative metabolic factors that could affect functional longevity, fertility, immunity, and even productive performance. Many of the problems affecting a dairy ruminant result from poor transitional management (the last three weeks of pregnancy and the first three weeks of lactation). Overcrowded and stressful environments in which the climate is not managed, and perhaps in the future the photoperiod, poor management of diets, and a lack of attention to the individual create a concatenation of etiological risk factors that can condition the prevalence of metabolic diseases that typically are concentrated in the transition phase: fertility, the full efficiency of the immune system, and productive performance. Metabolic diseases, which now account for 75% of the diseases that can affect a dairy cow, are intimately interconnected with each other. Consequently, if we want to reduce the excessive prevalence of one, we must also take care of all the others.
We believe that a deep knowledge of how the metabolism of animals subjected to genetic and genomic selection is changing can better direct the attention of farmers, veterinarians, and zootechnics on certain pathologies and how to prevent and treat them. Animals bred to produce food for humans are “metabolic athletes”, as William Chalupa has said; This ”athletic” dimension of ”food animals” has opened new points of view in nutrition, both basic and clinical, laying the foundations of nutraceutical applied to animal sciences which consist in using some nutrients as if they were drugs, useful both for therapy and prevention.For more information: firstname.lastname@example.orgOriginal article here.