Overcrowding and presence of fresh cows

13 September 2023

What happens after summer?

Analysis of the main issues observed in late summer and autumn. Part II

Alteration of the estrous cycle, with a consequent concentration of calvings toward the end of summer and autumn, very often leads to overcrowding and certainly to an increase in the number of fresh cows.

As shown in graph 7, the calving pattern is concentrated between late August and throughout autumn. The high number of calvings results in a large number of fresh cows; these animals will almost certainly face an energy deficit, which becomes more pronounced the more poorly the transition period is managed.

In fact, during this period, cow intake does not reach the levels required to meet productive and metabolic demands, generating a negative energy balance with a consequent risk of ketosis onset (Graph 8).

To compensate for this energy deficiency, the animal reacts by mobilizing its body reserves, especially adipose tissue—both visceral and subcutaneous—resulting in the release of non-esterified fatty acids (NEFA) into the bloodstream.

One of the main sites where NEFA are utilized for energy production is the liver cells (hepatocytes). To be used, these fatty acids must enter the mitochondria and be processed through the Krebs cycle; however, along this pathway they must overcome several “bottlenecks,” where deficiencies of specific molecules can compromise their complete utilization for energy purposes. Within the hepatic cell, NEFA bind to molecules such as coenzyme A to enable their transport into the mitochondria.

The transport of NEFA–acyl-CoA across the mitochondrial membranes requires an enzyme (carnitine acyltransferase), making carnitine a limiting factor. The Krebs cycle, which is glucose-dependent, also requires certain “complementary” factors (vitamin B12) that catalyze the various chemical reactions. If, due to excessive fatty acid influx into the mitochondria or a deficiency of carbohydrate-derived metabolites, the process is not completed, ketone bodies are formed and released into the bloodstream.

In addition, in cases of excessive mobilization, fatty acids reaching the liver can be re-esterified and accumulate as triglycerides within hepatic cells, leading to a serious condition: hepatic lipidosis (steatosis), i.e., a pathological accumulation of fat in the liver that severely compromises its functionality.

From a metabolic standpoint, the fresh cow may also develop significant health disorders (Table 1). Limiting the incidence of these diseases is extremely important, not only because they represent a cost for the farm, but also because there is a negative correlation between these conditions and the resumption of productive activity, as already highlighted by Opsomer in 2000. For example, cows with major body condition score (BCS) variations during the first month of lactation have a 19-fold higher risk of increased days open compared with cows showing only moderate weight loss.

Also noteworthy is the increased incidence of mastitis and elevated somatic cell counts (Graph 9). Therefore, optimal hygienic–sanitary management becomes even more critical, including the use of high-quality post-dipping solutions based on iodine or chlorine dioxide.