Long-term, but not short-term, treatment with somatotropin during pregnancy in underfed pigs increases the body size of progeny at birth1

Abstract

Treatment of pigs with porcine ST (pST) in early to mid-pregnancy increases body weight and length of their fetuses by mid-pregnancy, but this increased weight may not persist to birth. We investigated the effects of short- (25 d) and long-term (75 d) treatment with pST, and interactions between long-term pST treatment and crude protein content of diet, in restricted-fed gilts. In both experiments, Large White x Landrace gilts were bred at first estrus to Large White x Duroc boars and allowed to farrow naturally. In the first experiment, gilts were fed 1.8 kg/d of a diet containing 13.5 MJ DE/kg of DM and 15.05% CP (as-fed basis) throughout pregnancy, and were injected daily with 0, 2, or 4 mg pST from d 25 to 50 of pregnancy. Maternal treatment with pST from d 25 to 50 of pregnancy did not affect the number of piglets born per litter or progeny size at birth. In the second experiment, gilts were injected daily with 0 or 2 mg of pST and fed 2.2 kg/d of a diet containing 14.5 MJ DE/kg and either (as-fed basis) 16.6% (0.81% lysine) or 22.2% CP (1.16% lysine) from d 25 to 100 of pregnancy. All gilts were then fed 3.0 kg/d of the lower protein diet from d 100 of pregnancy to farrowing. Treatment with 2 mg pST/d from d 25 to 100 of pregnancy increased live weight of all gilts during the treatment period (P = 0.016), but the change in maternal live weight from d 25 to 100 of pregnancy was only increased (P = 0.001) by pST in gilts fed the higher protein diet. Live weight of gilts 1 d after farrowing was increased by pST treatment (P = 0.007), but was not altered by protein content of diet during pregnancy. In gilts fed the lower protein diet, but not in those fed the higher protein diet, pST treatment decreased maternal backfat depth during treatment (P < 0.020) and 1 d after farrowing (P = 0.002). Treatment with pST during pregnancy did not affect the number of piglets born per litter but independently increased body weight by 11.6% (P < 0.001) and length by 3.4% (P = 0.005) of progeny at birth and decreased (P < 0.01) the negative effect of litter size on body weight at birth. We conclude that in feed-restricted gilts, fetal weight gains in response to 25 d of pST treatment before mid-pregnancy are not maintained to term but that treatment with pST during most of pregnancy increases progeny size at birth and reduces maternal constraint of fetal growth.

Responses to maternal GH or ractopamine during early–mid pregnancy are similar in primiparous and multiparous pregnant pigs

“…Increased fetal growth in pGH-treated dams in the present study is consistent with reports from previous studies of pGH in gilts, in which both placental and fetal growth increases have been reported at the end of treatment (Kelley et al 1995, Sterle et al 1995, Gatford et al 2000. Although litter average progeny birth weights or near term fetal weights are not increased when maternal pGH treatment stops around mid-pregnancy (Rehfeldt et al 1993, 2001b, Kelley et al 1995, Okere et al 1997, Gatford et al 2004, fetal and subsequent progeny development is altered and progeny from pGH-treated dams have larger muscles after weaning (Kelley et al 1995, Gatford et al 2003. In contrast with previous reports of greater progeny muscle development and placental length responses to pGH in small than in large littermates (Sterle et al 1995, Rehfeldt et al 2001a,b, Rehfeldt & Kuhn 2006, we found greater fetal growth responses to pGH in heavier littermates than in lighter littermates.…”

Obstetric and neonatal outcomes to recombinant porcine somatotropin administered in the last third of pregnancy to primiparous sows

“…The increased neonatal size observed in the present study was consistent with that reported elsewhere in the literature (Rehfeldt et al 1993, Gatford et al 2004). This effect may have relevance to the prospect of using ST during pregnancy to treat intra-uterine growth retardation in humans, especially in the light of accumulating evidence of the adverse impact of low birth weight in adult life.…”

“…In addition, the placenta produces a variant of ST that progressively replaces pituitary ST in the maternal circulation from midgestation (Frankenne et al 1988), and has been correlated to birth weight in humans (Evain-Brion et al 1994, McIntyre et al 2000. In addition, fetal growth induced by maternal treatment with ST during early to mid-gestation may not necessarily be maintained to term (Gatford et al 2004), whereas treatment during the late or greater part of gestation has been related to increased piglet size at birth, as occurred in the present study.…”

“…In a study administering ST to sows at different gestational ages, it was observed that administration during early pregnancy induced the formation of significantly more muscle fibers in the semitendinosus muscle of fetuses; when given from days 50 to 64 of gestation there were no beneficial effects on fetal development, and when given from days 80 to 94 there were higher body weights and advanced stage of maturity at birth (Rehfeldt et al 1993). The link between ST administered during pregnancy and an increased neonatal size in pigs was also confirmed by Gatford et al (2004). Despite ST not crossing the placenta (Fholenhag et al 1994), the metabolic effects directly induced by this hormone in the pregnant sow could alter fetal adaptation at birth and increase neonatal death.…”

Nutritional programming: prenatal nutritional effects on the regulation of growth and metabolism

“…So far efforts to manipulate maternal nutritional status centred on short periods before mating because a moderately high level of nutrition results in a maximized rate of ovulation. Since the 1970's it is also known that litter size and birth weight of pigs are relatively insusceptible to varied levels of maternal dietary protein intakes during gestation (Mahan and Mangan, 1975;Gatford et al, 2004) but it is uncertain whether gestational protein levels below or above sows' requirements have effects on performance traits later in life. In this context it is of interest that lower birth weight piglets (< 1.2 kg) from otherwise normal litters have later on lower daily gains, higher body fat contents, lower muscle mass and higher drip losses (Kuhn et al, 2003).…”