Nutritional measures to prevent heat stress in pigs in summer

Heat stress refers to the sum of non-specific physiological responses of organisms in extreme high temperature environment to heat environment. With the development of intensive high-density feeding, the decline of sow fertility caused by heat stress becomes more and more serious.

Heat stress caused severe weight loss, prolonged interval from weaning to reestrus, decreased ovulation, conception rate, reduced embryo survival rate, litter size, sow non-estrus, and even shortened sow life span. In addition, low feed intake during heat stress in lactating sows can lead to insufficient lactation, thus affecting piglet growth and pre-weaning survival.

Provide high quality protein

Dietary protein and lysine are key factors affecting reproductive performance of lactating sows. Diets low in protein during lactation lengthen the interval between weaning and reestrus. The protein requirement of pigs increases under heat stress, but high crude protein will increase the body heat of sows and make sows feel hotter. Therefore, when the weather is hot, providing nursing sows with high-quality protein and supplementing essential amino acids can effectively meet their needs and reduce weight loss.

Lysine requirement of lactating sows should exceed 60 grams per day. Lysine content of feed can be calculated according to actual feed intake of sows. Threonine is insufficient relative to milk production and mammary gland growth. Therefore, threonine is a potentially critical limiting amino acid for sows with low feed intake and high body weight loss.

For sows with a weight loss of 75 - 80 kg, the ratio of threonine to lysine in the diet should be increased to 75% during the 21-day lactation period. For sows with minimal body weight loss (0 - 8 kg), the ratio of threonine to lysine in the diet can be reduced to 60%. For sows fed a typical corn-soybean meal diet, threonine may be the first limiting amino acid at the time of maximum body weight loss (75 - 85 kg), but lysine may remain the first limiting amino acid at other body weight losses, and valine may be the second limiting amino acid after lysine at the time of minimum body weight loss. It has been reported that increasing arginine levels in the diet of heat-stressed sows from 0.96% to 1.73% can reduce body weight loss of lactating sows and improve feed utilization, but has no significant effect on sow feed intake and piglet growth performance.

Increase dietary energy concentration during lactation

When the dietary energy concentration of sows was increased, the feed intake of sows tended to decrease, and the final energy intake was similar. However, energy intake of sows generally increased when high fat diet was used. According to thermodynamic principle, at high temperature, more body heat gain can lead to lower feed intake. Fat has lower heat consumption and higher energy content than carbohydrate and protein, so increasing energy concentration by adding fat to diet is more beneficial to heat-stressed lactating sows. Feeding heat stressed sows with a high fat diet can shorten the interval between weaning and reestrus. The composition of short-chain fatty acids in breast milk does not use saturated fatty acids and long-chain fatty acids, which are too high in oil and fat. In addition, summer must prevent added fat from being oxidized or rancid, it is recommended to add antioxidants at the same time.

Fat should not be added to the diet of lactating sows, except in cases of heat stress, because fat does not produce insulin secretion similar to starch. In contrast, fat supplementation in the diet of lactating sows decreased plasma insulin levels and luteinizing hormone secretion.