Nutritional measures to prevent heat stress in pigs in summer
Heat stress refers to the sum of nonspecific physiological responses made by an organism in an extreme high-temperature environment to the thermal environment. With the development of intensive high-density rearing methods, the decline in sow reproductive performance caused by heat stress has become increasingly serious.
Heat stress causes severe body weight loss in sows, prolongs the interval from weaning to return to estrus, reduces the number of ovulations, lowers the conception rate, reduces the embryo survival rate, decreases the number of piglets born per litter, causes sows not to come into estrus, and may even shorten the useful life of sows. In addition, during heat stress in lactating sows, feed intake is low, which leads to insufficient milk production, thereby affecting piglet growth and pre-weaning survival rate.
Provide high-quality protein
Protein and lysine in the diet of lactating sows are key factors affecting their reproductive performance. Low dietary protein during lactation prolongs the interval from weaning to return to estrus in sows. Under heat stress, pigs' requirement for protein increases, but excessively high crude protein increases the heat increment of sows, making them feel hotter. Therefore, in hot weather, providing lactating sows with high-quality protein and supplementing essential amino acids can effectively meet their needs and reduce body weight loss.
The daily lysine requirement of lactating sows should exceed 60 grams, and the corresponding dietary lysine content can be calculated according to the actual feed intake of the sows. Threonine is insufficient relative to milk production and mammary gland growth. Therefore, for sows with low feed intake and large body weight loss, threonine becomes a potentially key limiting amino acid.
During the 21-day lactation period, for sows with body weight loss of 75-80 kg, the ratio of threonine to lysine in the diet should be increased to 75%. 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, when body weight loss is greatest (75-85 kg), threonine may become the first limiting amino acid; however, under other body weight loss conditions, lysine may still be the first limiting amino acid; when body weight loss is minimal, valine may become the second limiting amino acid after lysine. It has been reported that increasing the arginine level in the diet of heat-stressed sows from 0.96% to 1.73% can reduce body weight loss in lactating sows and improve feed utilization, but has no significant effect on sow feed intake or piglet growth performance.
Increase the energy concentration of the diet during lactation
When the energy concentration of the sow diet is increased, sow feed intake tends to decrease, and the final energy intake is similar. However, when a high-fat diet is used, sow energy intake generally increases. According to thermodynamic principles, under high-temperature conditions, a greater heat increment can lead to reduced feed intake. Compared with carbohydrates and proteins, fat has lower heat expenditure and higher energy content, so increasing the energy concentration by adding fat to the diet is more beneficial for heat-stressed lactating sows. Feeding heat-stressed sows a high-fat diet can shorten the interval from weaning to return to estrus in sows. For the composition of short-chain fatty acids in breast milk, do not use oils with excessively high ratios of saturated fatty acids and long-chain fatty acids. In addition, in summer, be sure to prevent the added fat from being oxidized or becoming rancid, and it is recommended to add antioxidants at the same time.
Except in cases of heat stress, it is not advisable to add fat to the diet of lactating sows, because fat cannot produce the insulin secretion-promoting effect that starch does. On the contrary, adding fat to the diet of lactating sows reduces plasma insulin levels and luteinizing hormone secretion.