HEAT STRESS ▶▶▶


Nutritional solutions for sows under heat stress


Increasingly, pig farms will have to cope with warmer temperatures. High temperatures can cause heat stress, with production disadvantages being the outcome. How does that work in practice – and what can be done about it? Professor Bruno Silva explains.


BY VINCENT TER BEEK, EDITOR, PIG PROGRESS F


or Professor Bruno Silva, the combination of “heat stress” and “pig production” does not hold many se- crets. He is professor in swine nutrition and environ- mental adaptation at the Federal University of Mi-


nas Gerais (UFMG/ICA), in Montes Claros, Brazil. Minas Gerais is located north of Rio de Janeiro and São Paulo – en- tirely in a tropical zone. If any place is ideal for learning how to deal with hot temperatures and their effects on pig and sow performance, it is there. Recently he featured in a webinar organised by Lallemand Animal Nutrition, titled “Nutritional solutions for lactating sows under heat stress”. Bottom line: efficiency is compro- mised every time environmental temperatures create a situ- ation that is above or below particular threshold values. He said, “Nutrients have to be diverted to maintain the preser- vation of the animals’ natural or constant temperature.”


Inefficient thermoregulatory process Pigs are highly susceptible to heat stress because they have a very inefficient thermoregulatory process, Prof Silva said. “They are very dependent on convective and conductive heat losses and on breath frequency, because they lack functional sweat glands.” Modern pigs, he added, have a high meat percentage, a high protein turnover; hence their metabolism produces more heat as well. Heat stress induces several changes, Prof Silva said. “Not only from a physiological or behavioural point of view, but also from a metabolic point of view. Because in the end, the animal has to survive; it has to adjust its metabolism to the new challenge.” On a gut level, he said, the combination of all these heat stress factors can contribute to a rupture of the tight junc- tions, that is, a leaky gut. That will not only decrease the


10 ▶PIG PROGRESS | Volume 36, No. 5, 2020


efficiency of digesting nutrients, but will also increase the susceptibility of the animal to immune challenges.


Reducing feed intake One of the pig’s most effective measures to reduce heat pro- duction is to reduce feed intake, Prof Silva said. In order to understand that in more detail, he introduced the concept of “Thermal Effect of Feed” (TEF), that is, the contribution of feed to heat. The digestion of proteins, he said, generates more heat than does carbohydrates and fats, for instance. “The extent to which feed intake is reduced is directly relat- ed to metabolic rate and also to the productive stage.” Young sows, he said, eat at least 20% less than adult sows under heat stress conditions, because they have a lower in- testinal tract capacity. “But when we look at the impact of reducing feed intake as a consequence of not having the possibility of thermoregulating – then you will see that the adult sows suffer more.” Prof Silva showed figures gathered by the university’s swine research facility (NEPSUI). On average, he said, sows during 24 days of lactation eat about 22% less in summer than in winter. He said, “Until the end of the first week, the feed in- take is the same. What makes the difference after seven days is actually that the piglets start demanding more nutri- ents from the sow. But due to the fact that the sows are under heat stress, they will not be able to increase milk production.” Prof Silva also commented that sows have a nocturnal eat- ing pattern. Irrespective of the season, sows tended to con- centrate their feed intake between midnight and 10am in the morning. That happened to 75% of total feed intake in summer and 81% of total feed intake in winter.


Endocrine changes How do sows adjust their metabolism under heat stress? That happens through changes in their hormonal profiles, Prof Silva explained. For instance, studies have shown an impact on thy- roid hormones, a change in cortisol levels and in insulin levels. This translates to a negative impact on milk production. He showed data from his own recent research on modern sow lines, showing a 19% reduction of milk yield when tempera- tures increased from 23˚C to 35˚C. That relates to the mam- mary gland having a relatively high temperature, that is, it contributes a larger part to heat production.


PHOTO: VINCENT TER BEEK


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