What Happens After Summer?
Analysis of the Main Issues Encountered in Late Summer and Autumn.
It is well known that the decrease in milk production and productivity during the summer months is a combination of unfavorable environmental conditions (heat and humidity) and the extension of the average lactation days (Graph 3). Consequently, one might expect an increase in production as temperatures start to drop, around late August and September. However, this does not happen!
We will now examine the various aspects of what we can define as autumn syndrome in dairy cows.
Analyzing the data for Italy (Graphs 1 and 3), it is evident that August, September, October, and November are the months with the lowest production. In contrast, in the southern hemisphere (particularly looking at delivery data from New Zealand), these are the most productive months of the year (Graph 2).
Several factors influence the lack of milk production: heat stress, photoperiod, management of heifers, and the presence of fresh cows. In this article, we will analyze the first two conditions.
Heat Stress
Heat stress can be defined as the set of forces related to high temperatures that induce changes in the animal at various levels (from subcellular to macroscopic); these changes help the animal adapt to physiological alterations.
As documented in various studies worldwide, the effect of high temperatures on both dairy and beef cattle causes significant economic losses. As is now known, to determine the state of heat stress, a formula (found in all livestock management books) is used that relates two specific parameters: temperature and humidity:
Since the 1980s, it has been believed that a dairy cow experiences heat stress at a THI of 72 (for example, THI of 72 = 27°C and 30% humidity). However, with genetic improvements that have allowed for high-producing and highly efficient animals, setting this threshold at 72 no longer makes sense. According to current knowledge, a THI threshold of 68 is more accurate, which translates to 22°C and 50% humidity.
From a metabolic point of view during high summer temperatures…
the dairy cow tries to dissipate as much heat as possible; one of the physiological strategies it can use is peripheral vasodilation: this promotes increased blood flow to the external areas and thus greater heat dissipation.
Baumgard from Iowa State University has shown that an increase in peripheral vasodilation corresponds to a phenomenon of vasoconstriction at the intestinal level, with villi contraction and reduced nutrient absorption capacity.
This reduced blood flow at the visceral level leads to poor oxygen availability and consequently alters the integrity of the intestinal absorptive surface. The same research also highlighted that the reduced milk production is due 50% to decreased voluntary intake and 50% to the effect of heat stress on the histological changes in the intestine.
During heat stress, the decreased intake of dry matter, combined with the loss of rumen buffering capacity, increases the risk of acidosis.
The association between reduced blood flow to the enteric system and ruminal and intestinal acidosis extends the condition of digestive fatigue, including increased oxidative stress. The latter induces an imbalance between the production and removal of peroxides and free radicals, causing cell death and tissue damage.
In situations of heat stress, even at the ruminal level, the bacterial flora loses efficiency, worsening microbial protein synthesis, fiber digestion, and unsaturated fatty acid biohydrogenation, resulting in decreased milk quality.
All these issues not only worsen production performance but also have a negative impact on the cow’s health.
In this situation, the administration of antioxidants has shown positive results by neutralizing free radicals, improving the animal’s metabolic state, and normal rumen functionality. Antioxidants, due to their ability to protect cells from the toxic and degenerative effects of free radicals and peroxides, help restore the oxidative balance in heat-stressed cows. This action also positively affects dry matter intake during the summer period.
Discover the Normoterm line, ideal during the summer period:
Photoperiod
The photoperiod, or the duration of daylight hours, has a significant influence on the behavior and milk production of dairy cows and affects the autumn syndrome in dairy cows.
Light or darkness stimuli pass through the eye bulb and travel along the optic nerve to modify the activity of the pineal gland or epiphysis. This gland acts as an internal clock, sensitive to the duration and intensity of light.
The pineal gland secretes melatonin, the hormone that regulates the sleep/wake cycle and influences the immune system, reproductive system, and lactation. However, not all stages of a dairy cow’s life respond the same way. Let’s examine the differences between lactation and dry periods.
Lactation Phase
During lactation, the highest milk production occurs when daylight is increasing, particularly when light hours exceed 14 hours. In fact, exposure to light prevents melatonin secretion for most of the day and promotes the secretion of prolactin and IGF-1, two hormones that influence mammary gland activity. Research has shown an increase in production in lactating cows exposed to long photoperiods compared to animals in natural conditions.
Graph 5 (from Geoffrey and Dahl, 2001) summarizes 9 studies that recorded significant positive effects on production following exposure to 16 hours of light per day. With a positive photoperiod, moreover, metabolism and the immune system are more efficient.
Dry Period
In contrast to lactating cows and heifers, the group of dry cows and pre-calving heifers seems to achieve better results after exposure to a short photoperiod with only 8 hours of light daily (Miller et al., 2000).
Graph 6 (from Geoffrey and Dahl, 2001) shows the difference in production in the subsequent lactation of 2 groups of dry cows (equivalent production in the previous lactation) exposed to LDPP – long photoperiod with 16 hours of light and 8 hours of darkness per day (line with pink squares) and SDPP – short photoperiod with 8 hours of light and 16 hours of darkness per day (line with red squares).
Exposure for 2-3 weeks before calving to a short photoperiod for these animals seems to act as a sort of reset of their ability to respond to increased light hours after calving.
In conclusion, manipulating the photoperiod, that is, the duration of light exposure for lactating cows, can reliably provide benefits to production, milk yield, fertility, growth, and immune system efficiency.
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