Effects of relaxin on lactational performance in ovariectomized gilts.

In gilts, mammary lobulo-alveolar growth begins on about Day 80 of gestation and continues progressively until term. Relaxin in concert with estrogen plays a major role in promoting this mammary gland growth. The present study was conducted to determine the importance for lactational performance of prepartum relaxin-dependent growth of the mammary glands in ovariectomized gilts given progesterone to maintain pregnancy. Twenty-four gilts were either sham ovariectomized or bilaterally ovariectomized and assigned to four treatment groups: sham-ovariectomized control, ovariectomized progesterone-treated, ovariectomized progesterone- and (starting at Day 80) relaxin-treated, and ovariectomized progesterone- and (starting at Day 100) relaxin-treated. Piglets were delivered by cesarian section, and gilts were given uniform colostrum-replete foster litters (born of untreated mothers) to nurse from Day 1 to Day 28 of lactation. Prepartum mammary development appeared by visual examination to be greatly reduced in relaxin-deficient gilts. Stimulus of the mammary nipples by the nursing piglets, however, appeared to overcome relaxin-dependent differences in mammary development among treatments. There was no effect of treatment on the time piglets spent at the udder, piglet mortality, piglet weight at Day 21 of lactation, milk composition, mammary cross-sectional area, or sow weight change during lactation. We conclude that gilts devoid of circulating luteal relaxin can display normal lactational performance when given colostrum-replete foster litters.

Effects of relaxin administration in early gestation or prior to mating on uterine length and fetal survival in gilts.

The objective of this research was to determine the effect of administration of porcine relaxin to gilts during early gestation, or during the follicular phase of the estrous cycle immediately preceding mating, on the length of the uterus and consequently the number of surviving fetuses. Experiment 1 determined the individual and combined effects of 10 days of administration of relaxin (0.5 mg, 4 times daily), estradiol benzoate (1 mg, 2 times daily), and progesterone (50 mg, 2 times daily) on uterine wet weight and length in 58 ovariectomized 8-mo-old pubertal gilts. Relaxin alone had no effect on either uterine length or wet weight. Estrogen increased uterine wet weight, and this effect was augmented by relaxin. Progesterone increased uterine length, and this effect was augmented by estrogen. Combined treatment with progesterone, estrogen, and relaxin increased both uterine length and wet weight maximally. Experiment 2 determined the effects of relaxin administration in early gestation or prior to mating on uterine length and fetal survival in 75 unilaterally ovariectomized-hysterectomized gilts. Relaxin (0.5 mg, 4 times daily) was administered during three treatment periods, and uteri were collected on Day 40 of gestation. In this study, relaxin administration from Days 11 to 20 of gestation reduced the number of live fetuses (p = 0.01) and percentage survival (p = 0.01) and resulted in shorter uterine length (p = 0.01) and lower uterine wet weight (p = 0.03) than in controls, but did not affect length of uterus or uterine dry weight. Relaxin administration from Days 22 to 31 of gestation did not influence fetal survival, uterine length, uterine length per fetus, uterine wet weight, or uterine dry weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Variables related to the progress of parturition and probability of stillbirth in swine.

Sow and piglet variables related to probability of stillbirth and to viability score were analyzed in litters from 98 multiparous Yorkshire sows. Immediately after the birth of each piglet, viability was scored using Randall's method. Sow variables related to the probability of stillbirth were average birth weight of the litter (p = 0.0001), sow age (p = 0.001), sow condition score (p = 0.003), length of gestation (p = 0.005), and number of piglets in the litter (p = 0.01). Sow variables related to average viability score were average birth weight of the litter (p = 0.001), standard deviation in birth weight in the litter (p = 0.02), sow age (p = 0.03), sow condition score (p = 0.03), and length of gestation (p = 0.03). Piglet variables related to probability of stillbirth were piglet hemoglobin (p = 0.0001), position in the birth order (p = 0.0001), broken umbilical cord (p = 0.0004), and preceding birth interval (p = 0.0004). Piglet variables related to viability score were piglet hemoglobin (p = 0.0001), position in the birth order (p = 0.0001), broken umbilical cord (p = 0.0001), preceding birth interval (p = 0.0001), and birth weight (p = 0.004). Preceding birth interval was related to whether the piglet was live or stillborn (p = 0.0001), to position in the birth order (p = 0.003), and to the sex of the piglet (p = 0.03).The results demonstrated that sow and piglet variables were highly correlated to probability of stillbirth and to viability score. In addition it was also found that the probability of stillbirth was not associated with the duration of farrowing but with the number of piglets in the litter and piglet hemoglobin level. This study also found that lower weight piglets tend to have poor viability, but are not more prone to stillbirth as commonly suggested. These low viability piglets may survive if the necessary care is given during the farrowing process.

Effect of oxygen and neostigmine on stillbirth and pig viability.

In this experiment, 98 multiparous Yorkshire sows blocked on farrowing date were randomly assigned to four treatments in a 2 x 2 factorial arrangement. Oxygen inhalation (6 L/min) by the sow was tested in an effort to reduce stillbirth rate and improve pig viability. This study also tested the effect of increasing uterine contractions using neostigmine (5 mg) to determine whether simultaneous administration of oxygen to the sow could improve the inconsistent response of stillbirth rate to neostigmine. Pig viability was assessed using viability scoring and blood gas analysis of samples obtained from the suborbital sinus immediately after birth. The farrowings averaged 12.2 pigs/litter, 7.8% stillbirths, and 3.5% low viability (viability score < or = 6) pigs. Treatment had no effect on stillbirth rate or pig viability. Oxygen treatment increased pO2 (P = .0002), increased pCO2 (P = .02), and decreased pH (P = .02) in sow venous blood sampled after the birth of the last pig, but it had no effect on pig venous blood gases. Neostigmine treatment had no effect on either sow or pig venous blood gases. Oxygen treatment doubled the length of the first birth interval after the start of treatment (P = .003) but had no effect on remaining birth intervals. Neostigmine had no effect on birth interval. It is suggested that the effect of oxygen on birth interval is the reason for the lack of improvement in stillbirth rate.