Causes of Declining Laying Rate in Laying Hens and Prevention and Control Measures
At present, for more than 30 batches and over 60,000 laying hens received for diagnosis, epidemiological investigation, clinical symptom analysis, pathological necropsy and treatment effect observation were carried out. The main types are as follows
??? 1. Causes:
?1. Poor flock development and poor uniformity
The main manifestations are: ① Insufficient tibia length. Tibia length is one of the most important indicators of whether laying hens meet production requirements, but many chicken farmers do not know this indicator during the rearing process. Because they overemphasize cost, they do not feed qualified complete feed as required, resulting in feed nutrition not meeting standards; they neglect brooding management, causing the tibia length of chicks before 8 weeks of age (brown-shell laying hens require a tibia length of 82mm at 8 weeks of age) to fail to meet standards; some farmers have brooding and rearing houses that are too small, resulting in excessive density, which prevents tibia length from reaching standards. The tibia length of laying hens at 8 weeks of age is very important, and there is a saying that 8 weeks determines the whole life; because of the above factors, by the time laying begins at 18 weeks of age, a considerable number of hens in the flock have a tibia length of less than 100mm: the normal tibia length of brown-shell laying hens should reach 105mm,} and some are even less than 90mm. ② Body weight fails to meet standards, and uniformity is too poor. In flocks with poor uniformity, the laying peak often delays by 2 to 3 weeks and only appears 9 to 10 weeks after laying begins. Practice has shown that for every 3% increase or decrease in flock uniformity, the average annual egg production per hen increases or decreases by 4 eggs accordingly. If a flock with 90% uniformity is compared with one with 70% uniformity, the difference in egg production alone is more than 20 eggs, and at current prices, the income difference per hen is 8 to 10 yuan, and flocks with poor uniformity also have high mortality and cull rates, an unsatisfactory laying peak, short duration, and poor overall benefits. ③ Poor sexual maturity. Because sexual maturity is inconsistent, different individual production patterns arise within the flock, and individual hens have different laying peaks, so the laying peak is not prominent and lasts only a short time, and the laying rate curve is also relatively flat.
In flocks with the above conditions, the combs are pale, body weight is low, feathers lack gloss, and there is malnutrition; some have a "little chubby" body shape. The flock delays laying, and in the early laying period soft-shelled eggs, white-shelled eggs and malformed eggs increase; laying rises slowly, and there are many prolapsed hens; diarrhea is likely to occur. Necropsy shows that internal organs are small, elasticity is reduced, follicle development is delayed, and the internal constitution unique to high-yielding hens is absent.
?2. Sequelae of nephropathogenic infectious bronchitis
Chicks that have suffered from nephropathogenic infectious bronchitis within 3 weeks will cause a significant increase in "big-bellied hens" after maturity. Because their follicle development is not affected, after laying begins the mature follicles cannot be laid normally and fall into the abdominal cavity, causing severe yolk peritonitis and reflexively increased androgen secretion, so the flock shows signs such as red, thick combs, leading to a large number of low-producing "false hens" and serious economic losses. In flocks where chicks have been vaccinated against nephropathogenic infectious bronchitis, or in chicks that developed the disease after 3 weeks of age, the sequelae of nephropathogenic infectious bronchitis are significantly milder than in chicks not vaccinated and those that developed the disease within 3 weeks, that is, the sequelae of nephropathogenic infectious bronchitis are directly related to whether vaccination was given and the age at which chicks developed the disease. Practice has shown that if nephropathogenic infectious bronchitis occurs at 1 to 3 weeks of age, it causes destruction of the oviduct, and the proportion of "false hens" formed is relatively high, which can reduce the laying rate of hens after maturity by 10% to 20%; if nephropathogenic infectious bronchitis occurs at 4 to 10 weeks of age, the "false hens" formed will be reduced, and it can reduce the flock's laying after maturity by about 7% to 8%; if nephropathogenic infectious bronchitis occurs at 12 to 15 weeks of age, the flock's laying rate after maturity is reduced by about 5%; after laying flocks develop KIB, it can also cause a decline in laying, but generally not more than 10%, and after recovery from the disease they can return to close to the original laying level, and "false hens" are rarely formed.
Necropsy: the oviduct is small, ruptured and edematous. In some, the oviduct is enlarged, with accumulated fluid reaching more than 1200g, becoming a "big-bellied hen". Ultimately death occurs due to yolk peritonitis.
????3. Effects of infectious rhinitis and tumor diseases
In flocks suffering from chronic infectious rhinitis before laying, the time to laying is obviously delayed, and the rise to the laying peak is slow. The author once encountered a case in which a flock with chronic infectious rhinitis had still not laid eggs at 30 weeks of age. In flocks suffering from tumor diseases (Marek's disease, avian leukosis, reticuloendotheliosis), symptoms such as pale and shrunken combs, emaciation, long-term diarrhea, and tumors in internal organs occur, causing the flock's constitution to decline and making it impossible to begin laying on schedule or to reach the laying peak.
????4. Use of inferior feed and long-term drug abuse
Some chicken farmers believe that replacement pullets are just "building the frame", and as long as the chickens are fed enough, it is fine. They often do not pay attention to feed quality, stocking density, etc., resulting in poor development of replacement flocks. Some chicken farmers use drugs excessively or abuse drugs for a long time, and even use drugs that inhibit ovarian development or seriously affect laying hen production, such as aminopyrine, analgin, dexamethasone, prednisone, etc., causing the flock not to lay eggs or to be unable to reach the laying peak.
5. Chick quality problems
Because of stage diseases in breeder chickens or other reasons, commercial chicks are congenitally deficient, the flock develops poorly, and laying performance after maturity is poor.
?6. Other factors
Management factors such as placing 3 hens per cage while some place 4, unreasonable or uneven beak trimming, unreasonable lighting, nipple drinker pressure being too low and causing insufficient drinking water for the flock, and poor ventilation can all cause laying hens to delay the start of laying or fail to reach the required laying peak.
????2. Prevention and control measures
????1. Scientific management and complete nutrition
In order to make the flock reach or approach the standard body weight, high-nutrition feed is generally used from 1 to 42 days of age (some farmers use complete broiler chick pellet feed from 1 to 14 days of age and layer chick pellet feed from 15 to 42 days of age), and tibia length is measured and body weight is recorded regularly. The final feed change time is determined according to the tibia length and body weight of brooding and rearing hens. If the two indicators do not meet standards, the feeding time of high-nutrition feed can be extended. When chicks have many stresses such as vaccination, beak trimming, transfer between houses and disease, normal flock development will be affected. It is recommended to formulate a rearing plan with the flock body weight slightly higher than the recommended standard. In daily rearing, the flock should be adjusted in time in combination with vaccination and weighing, and chickens with lagging development should be given strengthened rearing to ensure good body weight and uniformity. The various physical indicators of chicks at 8 weeks of age basically determine the production level after maturity, and this is the top priority of the entire rearing process. Therefore, there is a saying that 8 weeks determines the whole life.
?2. Advocate high-temperature brooding, reduce the temperature difference between day and night, and eliminate the occurrence of nephropathogenic infectious bronchitis