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The lysine requirement of the lactating sow was examined in two Latin-square experiments using multiparous sows, in mid lactation, each of which suckled a litter of 10 piglets. The lysine requirement was examined by the addition of supplementary synthetic lysine to a basal diet deficient in lysine, to give dietary lysine levels of 6·4 to 17·2g/kg dry matter. The adequacy of the lysine supply was judged by the responses of plasma lysine, plasma and urea-nitrogen, urinary urea-nitrogen and milk composition. Intersecting linear regression lines were fitted to the treatment means. The responses of urinary urea-nitrogen, in the two experiments, indicated that the lactating sow required approximately 48·5 g dietary lysine per day while the response of plasma lysine indicated a requirement of approximately 51 g lysine per day. Plasma urea and milk composition were less useful as indicators of the nutritional adequacy than were urinary urea-nitrogen and plasma lysine.

Data on the effect of postpartum feeding methods on sow and litter performance and the incidence of lactation failure in the sow are presented. One hundred and sixteen sows were allowed either ad libitum consumption within 16 h postpartum (AL) or restricted to a gradual increase in feed, starting with 0.45 kg on Day 0 and increasing to 0.91 kg each day reaching ad libitum by Day 6 of lactation (R). The AL sows consumed more feed from Day 0 to Day 6 (P

To determine the role of prolactin in the suppression of ovarian activity during lactation in the sow experiments were performed to investigate a possible inhibitory action of prolactin at the pituitary level. Therefore the LH-response to an intravenous injection of 25 μg synthetic LH-RH was measured in the 1st, 2nd and 3rd week of lactation. The compound was injected under high and low concentrations of prolactin in the peripheral blood, the latter achieved by removal of the piglets 6 h before administration of LH-RH. The results showed no difference in the effect of LH-RH injected at high or low prolactin levels. However, although the mean prolactin concentrations in the 1st, 2nd and 3rd week of lactation were similar, the results clearly demonstrated an increase in LH-response as lactation proceeds. The low responsiveness of the pituitary shortly post partum was also observed when the preparturient rise of prolactin was suppressed by treatment with bromoergocryptine. Injections of LH-RH in the last week of gestation given before and after the physiological increase of PRL, which occurred about 48 h before delivery, all showed low LH-response. It is obvious from the presented data that the LH-response to an intravenous injection of 25 μg LH-RH is in no way correlated with the prolactin levels at the time of treatment.

Plasma relaxin levels were measured in animals at different stages of lactation and related to the amount of nuzzling and suckling behavior exhibited by the piglets. Only in some acute suckling episodes was relaxin secreted rapidly and episodically in spiteof normal pigletand sow behavior and interaction. However, when the piglets were removed from the dams 6 h before suckling, the sows were very restless and the relaxin response to suckling was delayed. Oxytocin injection in lactatingbut nonsuckled sows caused an episodic secretion of relaxin similar to suckling itself. The source of relaxin in the lactatingsow may be the old corpus luteum, since progesterone levels increasedacutely,somewhat reflectingthe profileof relaxinincrease over the suckling episode. BIOLOGY OF REPRODUCTION 33, 705-714 (1985)

The injection of small amounts of oxytocin into the lactating sow has shown that the minimum quantity required to evoke a response in a normal adult animal is of the order of 0·05 i.u. If the injection is prolonged, the dose must be increased to produce a response. Large doses (0·8–1·0 i.u.) given at widely different rates produce multiple ejection pressure graphs with two or more peaks.

Measurements of intramammary pressure changes in the sow following intravenous injection have shown that the milk-ejecting action of vasopressin and acetylcholine is similar to that of oxytocin. Doses up to 0·4 mg. of histamine produced no measurable effects within the mammary gland.

Using an electronic pressure recording system, pressure changes in the sow's mammary gland in response to injections of oxytocin and whole pituitrin have been recorded. The results suggest that an injection of oxytocin within physiological range may pass round the circulatory system twice, resulting in a small secondary pulse of pressure. Slow injections over periods of the order of 8–16 sec. are shown to produce a double rise in pressure, the two phases of which are of the same order of magnitude, suggesting a contraction followed by a period of relaxation and a further contraction.

SummaryAcetylcholine was shown to cause the let-down of milk in the intact lactating sow. The time interval from injection to milk let-down was believed to indicate direct action upon the mammary gland, although action on the pituitary may also occur. The let-down effect was augmented by the anticholine-esterase action of prostigmine. Small amounts of carbaminoylcholine, a derivative, had let-down action similar to acetylcholine.

It has been shown that a dithiocarbamoylhydrazine, ICI 33828, inhibits the milk-ejection reflex in lactating rats without significantly altering milk formation (Benson & Zagni, 1965), and that oxytocin treatment can overcome the milk ejection inhibition caused by ICI 33828 in the sow (Gerrits, Johnson & Kraeling, 1965). Because the site of action of the ICI 33828 compound is believed to be at the pituitary or hypothalamic level, we have directed research effort to establishing the effect of this compound on various pituitary hormones. This brief communication is presented to demonstrate further, using a larger number of sows, that exogenous oxytocin can overcome the inhibitory action of ICI 33828 on milk ejection. Ten crossbred sows were assigned to this study as pairs dependent on the time of farrowing. One sow in each pair was then assigned to 100 mg/day of ICI 33828 and the other as control with no ICI 33828 treatment. ICI 33828 treatment began on Day 10\m=+-\2post partum, but the measurement of milk ejection was not begun until Day 14\m=+-\2post partum. Piglet weights determined before and after suckling were used to assess the effectiveness of the milk ejection response. Piglets were kept in separate pens and were randomly assigned within a pair of sows to suckle every 4 hr for 30 to 40 min. Six suckling measurements over a 48-hr period were made every 8 hr per pair of sows. The 4-hr suckling period without measurement was included to eliminate carry-over effects of the previous treatment period. The number of piglets assigned per sow within a pair was constant throughout the entire experiment and ranged from three to eight between pairs. The mean litter weight increase after suckling was used for further analyses. At three of the six measurement periods, the sow received a 30 i.u. intramuscular injection of oxytocin (Norden's Purified Oxytocic Principle). The other three measurements were made without prior oxytocin injection. The oxytocin injections were randomly assigned. Therefore a typical assignment per sow might be NM NO NM NO NM NO where denotes a non-measurement suckling, M a non-oxytocin suckling measurement, and 0 a suckling measurement after oxytocin. Analysis ofvariance revealed that the ICI 33828 compound reduced milk ejec¬ tion (P

The milk-ejecting activity of the hormones of the posterior-pituitary gland is well known and has been adequately reviewed (1). Most of the published information deals with the lactating dairy cow. In the course of work at this Station involving the lactating sow as a basis for assay of the milk-ejecting hormones (2, 3), data have been collected on the effect of a standard dose of oxytocin. Our normal assay procedure (2) involves giving the animal a preliminary dose of 0·5 unit of oxytocin. Thus over one lactation we have been able to record the time between injection into the ear vein and the onset of milk let-down, and the period during which milk may be obtained by simple hand-milking, for a number of sows. Braude & Mitchell (4) have published figures for the milk let-down effects of doses of oxytocin ranging from 1 to 10 units. The following results were obtained with &5 unit. All sows used were of the Berkshire breed.

Ten gilts were examined for peripheral plasma levels of progesterone and oestrogens 3 weeks before and up to 8 weeks after parturition. The sows were slaughtered at different intervals after parturition and the ovaries were examined. Peripheral plasma levels of progesterone decreased dramatically from about 8ng/ml two days before parturition to about 2 ng/ml on the day before parturition. After parturition the mean progesterone level was about 1.5 ng/ml. Maximum oestrone levels of about 7 ng/ml were obtained two days before parturition. After parturition the level dropped to below 0.1 ng/ml. Three sows showed high levels of oestradiol (75–440 pg/ml) without signs of heat during the lactation. In no case were ovulated follicles or periodic corpora lutea registered.

A study by Turker & Kiran (1969) revealed that single retrograde intraarterial (i.a.) injections of prostaglandin E1 (PGE1) did not produce a change in milk-ejection pressure in the lactating rabbit, but could inhibit the milk-ejection response to oxytocin. The minimal dose range of PGE1 required to produce an inhibition of milk-ejection pressure by oxytocin was 0\m=.\1to 1 \g=m\gPGE1 i.a. Halder, Maiweg & Grosvenor (1970) showed that PGE1 could abolish the milk-ejection activity of oxytocin in the rat. A study by McNeilly & Fox (1971) indicated that PGE1, PGE2, PGF1\g=a\ and PGF2\g=a\,all possessed inherent milk-ejection activity in the guinea-pig. They found that in no case did the i.a. injection of any of these four prostaglandins in amounts up to 30 \g=m\gcause any decrease in, or inhibition of, the milk-ejection activity of oxytocin in the guinea-pig. In connection with the agalactia syndrome in swine, the present study was undertaken to determine if any of the prostaglandins showed an inhibitory effect on oxytocin activity, or could be used to treat those cases of milk-ejection failure that would not respond to oxytocin therapy. The in-vitro method described by Van Dongen & Hays (1966) and adapted by Parkash & Anderson (1972) for biological assay of oxytocin was adapted to lactating sow mammary tissue. Mixed breed sows of 150 to 250 kg body weight with a first, second or third litter of approximately 1 week of age were procured from local swine producers. The sows were maintained in free stalls and were fed the standard University farrowing ration containing 15 % protein. The sows each had from six to twelve piglets nursing at the time of purchase and throughout the experiment. Only

It has been suggested that calmodulin, a calcium-binding protein, has a functional role during milk secretion. High levels of calmodulin are present during lactation in rat mammary glands and a substantial increase has been observed in the bovine mammary gland prior to parturition. In the sow, regressed glands involute while suckled glands remain highly active even though they are under the same hormonal influence. In this study, tissue samples were taken from suckled and regressed glands of the same sow at both peak and late lactation. Calmodulin and total protein were measured in tissue homogenate supernatants. Residual milk was apparent in regressed glands during mid lactation but not in the same glands by late lactation. Calmodulin levels in tissue were the same for both suckled and regressed glands. There was a slight but non-significant increase in the tissue calmodulin level from peak to late lactation. Protein levels declined significantly from mid to the late stage of lactation. There was no change in protein level between the suckled and regressed glands. Calmodulin may be responsible for casein phosphorylation and/or the mediation of prolactin action on the gland. The precise regulatory mechanisms relating hormonal control to calmodulin levels during lactation need further investigation.

Dietary lipid supplementation benefits the prolific and high-producing modern lactating sow. A comprehensive review of recent studies showed that lipid supplementation increases average daily energy intake, which is partitioned for lactation as indicated by greater milk fat output and improved litter growth rate. Recent compelling findings showed that addition of particular lipids during lactation improved the subsequent reproductive outcome of sows. Such benefits were related to the level of dietary essential fatty acids (EFA, linoleic acid, C18:2n-6; and α-linolenic acid, C18:3n-3) during lactation. Lactation diets without supplemental EFA resulted in a pronounced negative balance (intake minus milk output) of linoleic (-25.49 g/d) and α-linolenic acid (-2.75 g/d); which compromised sow fertility (farrowing rate 75 % and culling rates 25 % of weaned sows). This phenomenon seems to be increasingly important with advancing sow age because of a progressive reduction of body EFA pool over successive lactations. The net effect of supplemental EFA during lactation was to create a positive EFA balance, which improved the subsequent reproduction of sows. Adequate linoleic acid intake improved the proportion of sows that farrowed in the subsequent cycle (Farrowing rate (%) = [(-1.5 × 10(-3) × linoleic acid intake (g/d)(2)) + (0.53 × linoleic acid intake (g/d)) + (45.2)]; quadratic P = 0.002, R(2) = 0.997, RMSE = 0.031). In addition, increasing linoleic acid intake increased the number of pigs born in the subsequent cycle (total pigs born (n) = [(9.4 × 10(-5) × linoleic acid intake (g/d)(2)) + (0.04 × linoleic acid intake (g/d)) + (10.94)]; quadratic P = 0.002, R(2) = 0.997, RMSE = 0.031). Supplemental α-linolenic acid resulted in a rapid return to estrus (sows bred: sows weaned = 94.2 %; wean-to-estrus interval = 4.0 d) and achieved a high retention of pregnancy (sows pregnant: sows bred = 98 %). Collectively, we conclude that a minimum dietary intake of 10 g/d of α-linolenic acid, simultaneous with a minimum of 125 g/d of linoleic acid should be provided to ≥ 95 % of the sows; thereby, achieving a maximum sow reproductive efficiency through multiple mechanisms that include rapid return to estrus, high maintenance of pregnancy and large subsequent litter size in mature sows, that appear to be susceptible to EFA deficiency.

Keeping sows in single housing systems with farrowing crates can affect animal health and welfare. The aim of this study was to investigate the behaviour and health of lactating sows kept in a novel group housing system which could be easily installed on commercial farms. The housing system had five farrowing pens without crates, a common area and an area only available for piglets. Data from 25 sows were collected in five batches. Sows’ location and activity, suckling behaviour and floor soiling were analysed by video or direct observation. Skin lesions were determined using a lesion score. Group housing of sows did not increase the number of skin injuries, since the lesion score decreased during the housing period (19.2 vs. 16.3 vs. 12; p

Background Previous studies suggested that supplementation of lactating sows with β-hydroxy-β-methylbutyrate (HMB) could improve the performance of weaning pigs, but there were little information in the muscle fiber type transformation of the offspring and the subsequent performance in pigs from weaning through finishing in response to maternal HMB consumption. The purpose of this study was to determine the effect of supplementing lactating sows with HMB on skeletal muscle fiber type transformation and growth of the offspring during d 28 and 180 after birth. A total of 20 sows according to their body weight were divided into the control (CON, n = 10) or HMB groups (HMB, n = 10). Sows in the HMB group were supplemented with β-hydroxy-β-methylbutyrate calcium (HMB-Ca) 2 g /kg feed during d 1 to 27 of lactation. After weaning, 48 mixed sex piglets were blocked by sow treatment and fed standard diets for post-weaning, growing, finishing periods. Growth performance was recorded during d 28 to 180 after birth. Pigs were slaughtered on d 28 (n = 6/treatment) and 180 (n = 6/treatment) postnatal, and the longissimus dorsi (LD) was collected, respectively. Results The HMB-fed sows during lactation showed increased HMB concentration (P