Altrenogest treatment during late pregnancy did not reduce colostrum yield in primiparous sows

The decrease in circulating concentrations of progesterone is the lactogenic trigger in many species. The aim of the present study was to determine the effect of an orally active progestogen, altrenogest, administered in late gestation, on lactogenesis in sows. Gilts were treated with altrenogest (20 mg/d) from d 109 to 112 of gestation (ALT112, n = 6) or d 113 (ALT113, n = 8) or were not treated (control, n = 9). Colostrum production, estimated from the BW gains of the piglets, was measured during 24 h starting at the onset of parturition. Colostrum samples were collected at the onset of parturition until 48 h later. Jugular blood samples were taken from d -8 prepartum until d 3 postpartum. Altrenogest treatment extended the gestation length of ALT113 sows in comparison with control sows (116.3 vs. 114.7 d; P < 0.05). Litter size and litter weight at birth did not differ between groups (P > 0.1). Estimated colostrum yield was not reduced in altrenogest-treated sows compared with control sows (4.20 kg) and tended to be greater in ALT112 (4.73 kg) than in ALT113 sows (3.74 kg; P = 0.09). Altrenogest reduced endogenous progesterone concentrations during the 2 d prepartum in ALT113 relative to control sows (P < 0.05), likely because luteolysis occurred earlier in relation to parturition in ALT113 sows. Altrenogest reduced estradiol-17beta concentrations during the 2 d prepartum in ALT113 (P < 0.05) and ALT112 (P < 0.1) sows. Altrenogest treatment did not influence the timing of the prepartum peak of prolactin in relation to parturition. The ALT113 sows had lesser (P < 0.05) concentrations of lactose in plasma and a lesser Na:K ratio in colostrum after parturition than Control and ALT112 sows, indicating that the junctions between their mammary epithelial cells were tighter. Concentrations of colostral IgG in sows that received altrenogest tended to be less than in control sows (P = 0.08). In conclusion, altrenogest administered from d 109 to 112 or 113 of pregnancy did not affect lactogenesis in sows, possibly because the treatment delayed farrowing and main hormonal changes without affecting the relative chronology of these changes.

Carcass Composition and Resistance to Fasting in Neonatal Piglets Born of Sows Immunized against Somatostatin and/or Receiving Growth Hormone-Releasing Factor Injections during Gestation

Thirty-eight gestating sows were either immunized against somatostatin (SRIF) and/or injected with growth hormone-releasing factor (GRF). Treatment effects on carcass composition and resistance of newborn piglets to a 60-hour fast were investigated. Protein content of carcasses at birth was increased in piglets of sows receiving GRF or immunized against SRIF, however, when sows received both treatments there was a reduction in carcass protein content (p = 0.01). Other carcass components were unaltered by treatments, and none of the treatments affected metabolic or endocrine profiles of piglets at birth. Concentrations of GH, IGF-I (p less than 0.01), glucagon and cortisol (p less than 0.05) increased linearly with duration of fast, whereas glucose values decreased. Resistance to fasting was unaltered in piglets from any treatment thereby suggesting that exogenous GRF and/or SRIF immunization of sows during gestation are unlikely to improve survival of newborn piglets.

Effect of age on the behavioral and physiological responses of piglets to tail docking and ear notching

Neonatal piglets are often subject to potentially painful processing procedures such as tail docking and ear notching during the first few days after birth. However, these procedures may influence the development of suckling behavior and passive transfer of immunoglobulins, especially if done within the first day postpartum. The objective of this experiment was to compare the effects of processing piglets during the first 24 h versus at 3 d of age on suckling and pain-related behavior, the passive transfer of immunoglobulins, and growth. Six piglets per litter from 20 litters (n = 120 piglets) were used in a 3 x 2 complete block design. Piglets were weighed at birth and assigned to 1 of 3 treatments (balanced by birth weight): control (unmanipulated), sham processed (manually manipulated), and processed (tail docked and ear notched) at 1 of 2 ages (1 or 3 d of age). Vocalizations were recorded during the procedures, and piglets were observed after the procedures for pain-related behavior. Suckling behavior was observed for 6 h on each of d 1 to 4. Colostrum samples were collected after the birth of all piglets (before first suck), and blood samples were collected on d 5 to examine concentrations of immunoglobulins (IgA and IgG) and IGF-I. Body weights were measured at birth and on d 5 and 14. During the procedures, processed piglets, regardless of age, vocalized at a greater frequency (P < 0.001) and produced more high frequency calls (P = 0.016) than sham-processed piglets. All piglets on d 1 produced more high frequency calls than all piglets on d 3 (P = 0.047). Immediately after the procedures, sham-processed and processed piglets spent less time lying and more time standing than control piglets (P < 0.001), whereas processed piglets jammed their tail between their legs more than sham-processed or control piglets (P < 0.001). Lying, standing and tail posture were not influenced by age, nor were there age by treatment interactions. Piglets on d 1 trembled more than piglets on d 3 (P < 0.001), and this tended to be exacerbated by processing (P = 0.076). There was no effect of treatment or age of treatment on suckling behavior. Processed piglets had decreased IgG serum concentrations compared with sham-processed and control piglets (P = 0.029), although there was no interaction between treatment and age of treatment (P = 0.67). Whereas tail docking and ear notching do appear to result in short-term pain and modulated immune status, processing on d 1 appears neither better nor worse than processing on d 3.

Feeding flaxseed to sows during late-gestation and lactation affects mammary development but not mammary expression of selected genes in their offspring

Mammary gland composition and mammary gene expression were measured in pubertal gilts whose dam were fed a control (CTL) diet or a diet with a 10% supplement of flaxseed (FS) during late-gestation and throughout lactation. Parenchymal weight expressed as a percentage of body weight tended to be greater in offspring from FS compared with CTL sows (P < 0.1) and to contain less fat (P < 0.1). Offspring from FS sows had more parenchymal protein, whether expressed as a percentage (P < 0.05) or total amount in tissue (P ≤ 0.05), than offspring from CTL sows. No changes (P > 0.1) in mammary gland expression of the studied genes were observed with dietary treatment. Key words: Flaxseed, gene expression, gestation, mammary development, offspring, porcine

Nutritional, hormonal, and environmental effects on colostrum in sows

It is widely recognized that an early and high intake of colostrum is a major determinant of piglet survival during the early suckling period. The production of colostrum, however, is very variable among sows and the factors affecting this variability are not well known. Factors such as number of parity and genotype do seem to influence colostrum yield and composition. The endocrine status of the sow also affects the process of colostrogenesis and changes in the sow endocrine status can have an impact on quantity and quality of colostrum produced. Indeed, induction of parturition seems to play a role. Nutrition is undoubtedly a major factor that could be used as a tool to alter colostrum composition, with fat content being the most affected. Feed ingredients, such as yeast extracts and fermented liquid feed, were recently shown to alter colostrum composition, yet more research is needed to substantiate these effects. Very few data are available on the influence of environment on colostrum production; results suggest that heat stress has negative effects on colostrum composition. Considering the importance of colostrum for the survival, growth, and immune resistance of piglets, it is obvious that research on the development of new management systems is necessary to improve yield and composition of colostrum.

Review: Current knowledge on mammary blood flow, mammary uptake of energetic precursors and their effects on sow milk yield

Dietary availability of nutrients to the mammary gland is a major limiting factor for sow milking potential. Nutrient availability to the udder is estimated by measuring mammary arteriovenous differences, which are affected by blood flow as well as circulating concentrations of nutrients. Mammary blood flow can be measured either directly or indirectly. Even though it is influenced by numerous factors, such as time since feeding, postural behavior, vasoactive substances, ambient temperature and litter size, authors report that the amount of plasma required to produce 1 kg of milk for a litter of 12 pigs ranges from 490 to 1050 L at peak lactation. Blood glucose is the major precursor for lactose synthesis and reported extraction rates of glucose by the mammary gland vary between 20 and 31%. Other metabolic precursors, such as triglycerides, phospholipids, acetate, propionate and lactate are also used for milk synthesis. There exists a discrepancy between estimates of energetic efficiency depending on the type of study conducted (metabolism vs. mammary balance). Endocrine status of the sow may affect mammary nutrient availability. There still exists a gap in our knowledge on relative mammary uptakes of energetic compounds other than glucose and on glucose transporter systems in porcine mammary tissue. The need for such information is of particular importance due to the increased milking demands currently made on lactating sows. Key words: Blood flow, lactation, mammary gland, nutrient uptake, sows

Influence of genotype on metabolic variables, colostrum and milk composition of primiparous sows

Composition of colostrum and milk in first-parity sows from four genetic lines, namely, synthetic Belgian Landrace/Pietrain (B), Duroc (D), Landrace (L) and Yorkshire (Y) were determined. Circulating concentrations of leptin, IGF-I, glucose and FFA were also measured in sows. Differences in colostrum and milk composition were observed between genotypes, but did not generally seem related to variables in blood. Colostrum and day-2 milk from D sows contained more protein (P < 0.05) and less lactose (P < 0.1) than that from sows of other genotypes. Results suggest that selection strategies to improve the composition of milk and colostrum of sows from European breeds could be a useful tool to increase their lactation potential. Key words: Colostrum, lactation, milk composition, sow

Effects of dietary supplementation with flax during prepuberty on fatty acid profile, mammogenesis, and bone resorption in gilts1,2

The possible role of dietary flax on pre-pubertal development of mammary glands and bone resorption was investigated in gilts. Fifty-seven gilts were fed 1 of 4 diets from 88 d of age until slaughter (d 212 +/- 1). Diets were control without flax (n = 14); 10% flaxseed supplementation (n = 13); 6.5% flaxseed meal supplementation (n = 15); and 3.5% flaxseed oil supplementation (n = 15). All diets were isonitrogenous and isocaloric. Jugular blood samples were obtained on d 78 and 210 to establish the fatty acid profile and to determine the concentrations of prolactin, estradiol, and cross-linked N-telopeptides of type I collagen. At slaughter, the mammary glands were excised, parenchymal and extraparenchymal tissues were dissected, and the composition of the parenchymal tissue (protein, fat, DM, and DNA) was determined. Histochemical analyses of the mammary parenchyma were performed, and fatty acid profiles in the extraparenchymal tissue were evaluated. Dietary flax increased (P < or = 0.001) the concentrations of PUFA and decreased those of SFA (P < 0.01) and MUFA (P < or = 0.001) in plasma and extraparenchymal tissues, which was largely due to the inclusion of 10% flaxseed or 3.5% flaxseed oil (P < or = 0.01) but not 6.5% flaxseed meal. Circulating concentrations of prolactin and estradiol were unaltered by treatments (P > 0.1), but concentrations of cross-linked N-telopeptides of type I collagen tended to be greater (P < 0.1) in flax-supplemented gilts. The DM content of parenchymal tissue was the only mammary compositional value affected, showing an increase with flax addition (P < 0.05). No change (P > or = 0.1) in the bromodeoxyuridine labeling index or estrogen receptor localization was observed with treatments. Dietary supplementation with flax as seed, meal, or oil, therefore, brought about the expected changes in the fatty acid profile but had no beneficial effects on mammary development or bone resorption.

Mammary gland involution and endocrine status in sows: Effects of weaning age and lactation heat stress

The effects of lactation length and/or heat stress on endocrine status of sows and indicators of mammary involution at weaning were studied. Twenty-eight first parity Yorkshire × Landrace sows were housed at 21 (CTL) or 29°C (HS) throughout lactation. Within each temperature group, half the sows were randomly assigned to a weaning age of 22 (W22: CTL, n = 7; HS, n = 8) or 44 d (W44: CTL, n = 6; HS, n = 7). Litter size was standardized to 10 or 11 on day 2 and to 9 on day 23 of lactation. Blood and milk samples were collected on days -1, 1, 2 and 3 relative to weaning (day 0). Concentrations of prolactin, IGF-I and lactose were measured in both fluids and concentrations of Na, K and IGFBP-5 were measured in milk. Standard milk composition was also determined. Lactose was lower (P < 0.001) and protein greater (P < 0.05) in all milk samples from W44 compared with W22 sows. Percentages of milk fat and dry matter were lower (P < 0.05) in W44 than in W22 on days 2 and 3 post-weaning. Milk lactose was reduced (P < 0.05) with heat stress on days 2 and 3. The day before weaning, concentrations of prolactin in blood (P < 0.001) and lactoserum (P < 0.01) were lower and those of IGF-I in lactoserum were greater (P = 0.01) in W44 than in W22. Values of IGFBP-5 in milk were drastically lower (P < 0.001, more than a fourfold difference), those of Na greater (P < 0.001) and those of K unchanged (P > 0.1) for W44 compared with W22. Post-weaning, evidence of leaky tight junctions (increased milk Na, decreased K) was evident a day earlier (2 vs. 3) in W44 compared with W22 and was most marked in HS. In support, plasma lactose concentrations increased transiently on the same day in HS W44. The greater Na/K ratio in W44 compared with W22 taken together with increased plasma lactose particularly in HS shows that mammary epithelial cell tight junctions become leaky as lactation advances. Weaning age therefore has an impact on milk variables which are indicative of the status of mammary involution in sows and some of these effects are exacerbated by heat stress. Key words: Heat stress, lactation length, mammary involution, sows, weaning

Hormonal response to dietary L-arginine supplementation in heat-stressed sows

The response of key metabolic hormones to dietary arginine supplementation in heat-stressed lactating sows was determined. Sixty-three sows were exposed to a thermoneutral (TN = 20°C) or hot (HT = 29.4°C) environmental temperature, and were fed diets containing 0.96% (control, C), 1.34% (medium, ME) or 1.73% (high, HI) arginine. Blood samples were obtained 2 h postprandially on days 7, 14, and 21 of lactation and concentrations of insulin, glucose, growth hormone (GH) and prolactin were determined. Arginine supplementation increased insulin concentrations (P < 0.01) on day 14 of lactation, had no effect (P > 0.1) on glucose, and decreased (P < 0.05) GH with ME compared with C diets. There was a temperature × diet interaction (P < 0.05) for prolactin, with values being greater for the C compared with the ME and HI diets at 29.4°C, but being lower at 20°C.There was no effect (P > 0.1) of temperature alone on any of the measured variables. Results indicate that arginine supplementation may mediate improvements in nutrient utilization by regulating the metabolism of both insulin and GH in lactating sows. Key words: Arginine, growth hormone, heat stress, insulin, lactation, prolactin, sow

Colostrum production in swine: from the mammary glands to the piglets

Abstract

An early and high intake of colostrum is a major determinant of survival during the early suckling period, when most losses occur. Indeed, piglets are born devoid of body fat and are dependent on colostrum as their sole energy source. Colostrum also has other essential roles for the developing piglet; most importantly, it provides passive immunity and nutrients to the piglet and permits thermoregulation. It also stimulates gastrointestinal development, muscle protein synthesis and the development of active immunity. Neonatal swine can efficiently use colostrum since they have a remarkable capacity to deposit large amounts of fat and can also absorb intact immunoglobulins for 24 h postnatally. The production of colostrum, however, is very variable between sows and the factors affecting this variability are not well known. Such studies are most difficult to carry out since it is not easy to estimate colostrum yield. Indeed, the various methods that can be used tomeasure colostrum yield all have several drawbacks. The endocrine status of the sow undoubtedly affects the process of colostrogenesis and the underlying mammary changes associated with it. The composition of sow colostrum is well known, yet it is only recently that the presence of numerous bioactive compounds which can either protect piglets from infection or modulate their metabolism was detected in colostral secretions. There are indications that the composition of colostrum can be altered by some management components but further studies are necessary in that area.

Joint working with hospice teams: a renal collaborative approach

There are over 600 million people in the world aged 60 years and over. This figure is expected to double by 2025 and to reach 2 billion by 2050 (1). Population ageing is characteristically accompanied by an increase in the burden of chronic non-communicable diseases such as diabetes, cardiovascular disease, cancers and renal failure. As a consequence, pressures on health systems worldwide will increase (1). Data produced by the National Renal Workforce Planning Group in 2002 (2), predicted that the demand for renal replacement therapy (RRT) will continue to rise beyond 2010 for many reasons one of those being demographic changes with an aging population. This will also have an impact on the numbers of patients predicted to commence dialysis and transplantation (Table 1). With this higher projection of patients requiring RRT, there is a need to look at new ways of working.

Effects of prolactin inhibition during late gestation on the immunity of gilts and foetuses

The goal of the present study was to determine the effects of inhibiting prolactin (PRL) synthesis for three consecutive 20-d periods during the second half of gestation, on the immune status of gilts and their foetuses. Crossbred gilts were randomly assigned as controls (n = 12) or received 10 mg of bromocriptine orally three times daily from days 50 to 69 (BR50, n = 12), days 70 to 89 (BR70, n = 12), or days 90 to 109 (BR90, n = 12) of gestation. All gilts were injected subcutaneously with ovalbumin (OVA) on days 53 and 72 of gestation. Blood samples were collected on days 50, 60, 70, 90 and 109 of gestation to evaluate the antibody response. Cellular immunity, as measured by lymphocyte proliferative response and production of interferon-γ, was characterized on controls and BR50 gilts until the end of gestation. Six foetuses from five litters per treatment were selected and their thymus and spleen were excised and weighed. Splenocytes and thymocytes were assayed to characterize lymphocyte sub-populations and to evaluate splenocyte responses to mitogenic stimulation. Average spleen weight in foetuses from BR90 gilts was significantly lower (P < 0.05) than that of foetuses from control or BR70 gilts. In all gilts treated with bromocriptine,percentages of CD4+ and CD8+ lymphocyte populations in foetus spleens were numerically reduced compared with those obtained in foetus from control gilts but the differences were not significant. In BR50 gilts, inhibition of PRL synthesis did not affect the proliferative response of lymphocytes to mitogenic stimulations compared with control group, but tended (P = 0.13) to increase the production of interferon-γ. A time effect showed that production of interferon-γ by leukocytes was reduced (P < 0.02) on days 80 and 100 compared with days 50 and 70, regardless of bromocriptine treatment. The antibody response of gilts to OVA was not affected by bromocriptine treatments. In conclusion, inhibition of PRL synthesis by bromocriptine did not significantly affect immune response of pregnant gilts. In foetuses, although the differences between treatments were not significant, data suggest that the foetal development of immune tissues seems to be impaired by bromocriptine treatment. Key words: Bromocriptine, prolactin, immunity, pregnancy, sow

Impacts of dietary protein level and feed restriction during prepuberty on mammogenesis in gilts

The possible roles of dietary protein level and feed restriction in regulating mammary development of prepubertal gilts were investigated. Cross-bred gilts were fed a commercial diet until 90 d of age and then divided into four nutritional regimens based on two pelleted diets (as-fed basis): a high-protein diet (HP = 13.8 MJ of ME, 1.0% total lysine, 18.7% CP) and a low-protein diet (LP = 13.8 MJ of ME, 0.7% total lysine, 14.4% CP). Nutritional regimens were as follows: 1) HP ad libitum until slaughter (n = 22, T1); 2) HP ad libitum until 150 d of age followed by LP until slaughter (n = 20, T2); 3) LP ad libitum until slaughter (n = 21, T3); and 4) HP with a 20% feed restriction until slaughter (n = 19, T4). Gilts were weighed, their backfat thickness was measured, and jugular blood samples were obtained on d 90, 150, and at slaughter to determine concentrations of prolactin, IGF-I, leptin, and glucose. Gilts were slaughtered 8+/-1 d after their first or second estrus (202.7+/-14.5 d of age). Mammary glands were excised, parenchymal and extraparenchymal tissues were dissected, and composition of parenchymal tissue (protein, fat, DM, DNA, protein/DNA) was determined. The T4 gilts weighed less (P < 0.01) and had less backfat (P < 0.01) than did gilts on other treatments on d 150 and at slaughter. Treatments had no significant effects on prolactin, IGF-I, or glucose concentrations, but there was a treatment x day interaction (P < 0.01) for leptin, with concentrations being lower at slaughter in restricted-fed (T4) vs. LP (T3) gilts (P < 0.05). There was less extraparenchymal mammary tissue (P < 0.01) in T4 gilts than in gilts from the other groups and a tendency (P = 0.13) for the amount of parenchymal tissue to be lower in T4 gilts. In conclusion, a lower lysine intake during prepuberty did not hinder mammary development of gilts, but a 20% feed restriction decreased mass of parenchymal and extraparenchymal tissues. The effect of feed restriction on extraparenchymal tissue is most likely associated with the lower fat deposition.

Growth-hormone-releasing factor given to early-pregnant Genex-Meishan and Large White gilts: Effects on growth, carcass, meat quality and histochemical traits of the progeny

The objective of this study was to determine the effects of growth hormone-releasing factor (GRF) given in early gestation on post-weaning performance, carcass and meat quality and histochemical properties of two pig genotypes. Large White (LW, n = 10) and Genex Meishan-derived dam line (GM, with 50% Meishan genes, n = 10) gilts were treated during gestation with either saline injections (control, n = 5 LW and 5 GM), or 6.6 µg kg-1 of a GRF analog (n = 5 LW and 5 GM), given thrice daily from days 18 to 33 of gestation. After birth, at 56 d of age, four piglets (two barrows and two gilts) each from 20 litters were selected, allotted into individual pens and grown to slaughter weight (108.2 ± 2.3 kg). Feed intake was measured daily and pigs were weighed weekly. Prenatal GRF treatment had a detrimental effect (P < 0.05) on daily gain in both genotypes, but did not affect carcass quality. Significant interactions between GRF, genotype and sex (P < 0.01) for colour traits of the longissimus (L) and semimembranosus (SM) muscles and between GRF and genotype (P < 0.01) for shear force of the L muscle were found. GM pigs had lower growth rate (P < 0.01), higher feed intake (P < 0.05), fatter and shorter carcass (P < 0.001) than LW. L and SM muscles from GM pigs were less exudative (P < 0.05) than LW. L muscle from LW had higher percentages of slow oxidative (SO) (P < 0.001) and fast oxidative glycolytic (FOG) (P < 0.01) fibres but lower percentage of fast glycolytic (FG) fibres (P < 0.001) than that of GM. The results suggest that GRF given in early lactation reduces post-weaning growth of pigs from either breed, but does not affect carcass quality. GM pigs have poorer carcass quality than LW. Key words: Gestating gilts, growth hormone releasing factor, growth, carcass characteristics, meat quality traits, muscle fibre, pig

Gene expression of leptin, leptin receptor, prolactin receptor and whey acidic protein in mammary glands of late-pregnant gilts from two breeds

In order to identify genes which are essential for pig mammary gland development, mRNA levels of prolactin receptor (PRL-R), leptin, leptin receptor and whey acidic protein (WAP) were measured in parenchymal tissue of 110-d-pregnant gilts. Thirteen Upton-Meishan (UM) and 14 Large White (LW) pregnant gilts and 5 non-pregnant control gilts (2 LW and 3UM) were used. PRL-R and WAP mRNA levels were higher in pregnant than in non-pregnant gilts (P < 0.05). Leptin mRNA levels were higher in UM than in LW gilts (P < 0.05), but this breed effect was not seen when leptin mRNA levels were corrected for percent fat in parenchyma. Correlations were found between concentrations of IGF-I in plasma and PRL-R (P < 0.01) and WAP (P < 0.05) mRNA levels in UM gilts. Serum prolactin (PRL) was correlated with leptin mRNA levels in the overall (P < 0.05) and LW (P < 0.05) populations of gilts, while estradiol was associated with leptin receptor mRNA in UM gilts (P < 0.05). The mRNA levels of all studied genes were positively correlated with mammary parenchymal and extra parenchymal weights in UM gilts, whereas these variables were only correlated with PRL-R and WAP gene expression in LW gilts. The presence of leptin and leptin receptor mRNA in parenchymal tissue suggests a paracrine role for leptin in mammary tissue of late-pregnant gilts. These results also suggest that the PRL signalling pathway is fully active at the transcriptional level in the mammary gland of gilts at 110 d of pregnancy. Key words: Genetics, pig, mammary glands, Meishan, mRNA

Use of recorded nursing grunts during lactation in two breeds of sows. I. Effects on nursing behaviour and litter performance

The impact of exposing lactating sows and their litters to recorded sow nursing grunts played at different intervals during lactation was studied. Yorkshire × Landrace (YL) and 25% Meishan (MH) primiparous sows were divided into three groups (n = 14): (1) no playback, (2) playbacks at 35-min intervals (GR35), and (3) playbacks at 40-min intervals (GR40). Recordings were played from day 110 of gestation to day 27 of lactation. Nursing behaviours, incidence of nursings without milk ejection (NPN), nursing interval and proportion of nursings induced by playbacks were measured on days 6, 18 and 26 of lactation. Litter size was standardized to 10 ± 1 piglets within 48 h of birth and piglets were weighed weekly. Mean nursing intervals, excluding NPN, were shorter for MH than for YL sows (P < 0.001). The increase in mean nursing interval between days 6 and 18 was greater in GR40 than in GR35 or controls (P < 0.01) and, when excluding NPN, the mean nursing interval decreased in GR35 on day 18 (P = 0.01). The occurrence of NPN decreased as lactation advanced (P < 0.001) and was lower for MH than YL sows on day 26 (P < 0.001). Between days 6 and 18, the proportion of nursings initiated by playbacks increased (P < 0.05) and the duration of milk ejection decreased (P < 0.001). In MH sows, controls had longer milk ejections than GR35 (P < 0.05) whereas, in YL sows, controls had shorter milk ejections than GR40 (P < 0.05) and GR35 (P = 0.06). Piglet growth was not affected by treatments or breed (P > 0.1). In conclusion, exposing sows and their litters to recorded sow nursing grunts played at 35-min intervals reduced nursing intervals on day 18 of lactation only, without affecting piglet performance. Key words: Auditory stimulus, behaviour, lactation, litter performance, Meishan, sows