Melatonin administration during the follicular phase and early pregnancy to minimize seasonal infertility in swine

Melatonin;Gilt;Sows;Seasonal infertility

Sbaraini-Arend, Lidia ; Miller, David J., ; ,Wheeler, Matthew B. ; Knox ; Robert V.

关键词: Melatonin;    Gilt;    Sows;    Seasonal infertility;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/99535/SBARAINI-AREND-THESIS-2017.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

It is well documented that fertility in pigs is reduced in summer and fall compared to winter and spring. Termed as seasonal infertility, problems with follicular development and corpora lutea formation and other unknown factors can combine to delay puberty in gilts, increase wean to estrus interval in sows, and increase rates of pregnancy failure and reduced litter size. The array of seasonal problems associate with the confounded effects of both heat stress and changing photoperiod. Although the modern domesticated pig is considered a “non-seasonal” breeder, its ancestor, the European wild boar, and other well characterized seasonal species, breed seasonally in response to changing photoperiod and hot temperature. Perception of photoperiod through the pineal gland alters patterns of melatonin which modulate the hypothalamic-pituitary axis and function of the ovary to control reproduction. Seasonal infertility problems are then at least partially mediated, through the seasonal changes in the duration of nighttime secretion of melatonin, which is shortest in summer and slowly increases into fall. Because both photoperiod and heat stress are associated with seasonal infertility, two studies were designed to test whether short-term supplemental melatonin given to mimic the extended nighttime melatonin pattern observed in the peak fertility season of winter, could improve fertility in summer and fall under periods of heat stress. In both studies, exogenous melatonin was fed during proestrus and into early gestation, coinciding with the follicular and early luteal phases. Experiment 1 was performed in a single replicate using prepubertal gilts (n=36). Females were randomly assigned by age and weight and allocated in a 2 x 3 factorial treatment design to receive Melatonin (MEL, 5mg) or Control (CON, placebo) once a day while housed in one of three environmental rooms (32 °C) that provided: 1) 8 h of light and heat (8H); 2) 16 h light and heat (16H); or 3) 24 h light and heat (24H). All gilts received an i.m. injection of P.G. 600, fence line boar exposure, and artificial insemination at estrus. Following P.G. 600, ovaries were assessed by ultrasound and reproductive tracts collected to assess pregnancy, litter size, fetal and placental measures at 33 days of gestation. Continuous and categorical data were analyzed using the GLM and GENMOD procedures of SAS for the main effects of treatment and room. Temperature, humidity, ammonia and light intensity for all the three rooms were assessed. There was no effect of MEL or room on estrus (91.6 ± 11.8%), or on follicle development (14.3 ± 1.5 large follicles/gilt in 91.6 ± 15.9% of the gilts). However, there was a tendency (P = 0.08) for MEL to improve pregnancy rate compared to CON (87.8% vs. 63.3%) but with no effect of room. The number of fetuses, healthy fetuses, abnormal fetuses and placental efficiency were not affected. The results of this study suggest that P.G. 600 alleviates the effects of heat stress on expression of estrus but only melatonin had beneficial effects on maintenance of pregnancy.Experiment 2 was conducted at a 6,500 sow commercial farm in 12 sequential replicates starting from mid-summer and continuing into early-fall. In Expt. 2a, gilts (n = 420) that had expressed a second estrus were assigned by weight to receive once daily oral MEL (3 mg) or CON during the late follicular into the late luteal phase. In Expt. 2b, parity 1 (P1) sows (n = 470) were assigned by lactation length and backfat to MEL or CON during similar reproductive phases. Data were analyzed for the main effects of treatment, season (4 wk periods) and their interaction. In Expt. 2a there was no effect of MEL on age at 3rd estrus (203 ± 1.3 d), follicle size on 7th day of treatment (5.0 ± 0.3 mm), estrous cycle length (22.6 ± 0.4 d) or return to estrus (9.2 ± 4.0%).However, season affected number of follicles and gilts expressing estrus within 23 days (P = 0.03). There was no effect (P>0.10) of MEL or season on farrowing rate (80.0 ± 4.9%) or total born pigs (13.6 ± 0.4). In Expt. 2b, although there was no effect of MEL on follicle size (5.4 ± 0.3 mm), number (15.4 ± 1.2), or wean to estrus interval (8.9 ± 2.4 d), MEL reduced estrus expression within 7 d of weaning by 8.5% compared to CON (73.5 vs. 82.0%, respectively).There was no effect of MEL on farrowing rate (83.0 ± 4.5%), but there was an effect of season (P = 0.001). Neither MEL nor season influenced total born (13.0 ± 1.3). In addition, environmental measures classified as lower or higher for lighting intensity, temperature, humidity in breeding and gestation, associated with fertility measures of estrus, pregnancy and litter size in both gilts and sows. In Expt. 2, although there was clear evidence of seasonal fertility failures in gilts and sows, MEL treatment did not improve fertility effects in mature gilts, but the short-term MEL reduced and delayed estrus expression in parity 1 sows. It is possible that differences in the lighting and thermal environments for various periods of time prior to breeding might have affected the response to treatment in sows and gilts. The results of this experiment demonstrate season effects on commercial farms and that these change during summer and fall. Further, evidence of lighting and temperature effects on fertility during the different production phases is new, and has not been scientifically reported before, although much anecdotal evidence and opinion is accessible. Lastly, the studies show that short term MEL can affect seasonal fertility. In order to help to alleviate seasonal infertility problems affecting the meat production globally, further studies in the follicle and luteal periods are needed to better understand how melatonin might be minimizing its effects on seasonality.