To investigate changes in muscle metabolism during lactation, serial biopsy of the triceps brachii was conducted in first-parity sows subjected to three degrees of selective protein mobilization through restriction of dietary protein intake (see Clowes EJ, Aherne FX, Foxcroft GR, and Baracos VE. J Anim Sci 81: 753-764, 2003). Muscle biopsies were taken 7 days before parturition and at 12 and 23 days of lactation. The following changes occurred after parturition, were progressive, and were significantly magnified in animals under the greatest degree of dietary protein restriction and hence of protein mobilization. Decreased RNA-to-DNA ratio (capacity for protein synthesis) was observed. The presence of increased expression of several elements of the ubiquitin proteasome proteolytic pathway suggested a robust catabolic response. However, as lactation progressed, and especially under conditions of increased dietary protein restriction, protein mobilization increased, muscle RNA-to-DNA ratio fell further, protease gene expression continued to rise, tissue free glutamine levels rose dramatically, and essential amino acid levels, especially branched-chain amino acids and threonine, fell to below prepartum levels.

Long limb bones were dissected from 30 Camborough x Canabrid pigs serially slaughtered at birth, 14, 28, 56, and 84 d of age to determine the growth patterns of long limb bones (humerus and radius for the forelimb and femur and tibia for the hindlimb) in relation to live weight from birth to 84 d of age, weighing up to approximately 31 kg. Relationships between individual long limb bone measurements (Y) and live weight or transformations of live weight (X) were evaluated using allometric analyses. Hindlimb bones tended to have higher growth coefficients than forelimb bones (P < .05), suggesting an anterior-posterior gradient of long limb bone growth. However, centripetal gradients of growth for long limb bones were not evidential(P > .05). Greater diameter growth compared with length growth of the long limb bones indicated that the differentiation in growth for diameter and length of the long limb bones was an effective response to the functional requirements of standing, walking, and running following birth.

Lactogenesis is triggered by a rapid decline in plasma progesterone concentration combined with a peak in plasma prolactin concentration; in mice, there is a concurrent loss of mammary progesterone receptors (Haslam and Shyamala, 1980). The aims of this experiment were to determine the pattern of change of progesterone receptor and prolactin receptor mRNA during late gestation and early lactation and to determine whether abundance of mRNA for the two receptors are related to each other, to plasma concentrations of progesterone and prolactin or to piglet performance.

It is considered that the rate of glucose uptake by the mammary gland is the main regulator of lactose synthesis (Threadgold and Kuhn, 1984) and hence the main factor determining milk production (Faulkner and Peaker, 1987). GLUT1 is the only glucose transporter that has been found in lactating mammary tissue (Burnol et al, 1990). The aim of this experiment was to determine whether GLUT1 mRNA could be detected in sow mammary tissue, to investigate how abundance of GLUT 1 mRNA in mammary tissue changed between late gestation, early lactation and established lactation, and to establish whether this was correlated with milk output and/or feed intake.

Sows attempt to meet the sudden and large metabolic demand of lactation by increasing their level of voluntary food intake. However, the voluntary food intake of most sows during lactation generally does not provide sufficient energy or protein to meet their requirements for maintenance and milk production. By providing multiparous sows with extra food during lactation (via a gastric cannula) they remained in an anabolic state, and both milk production and piglet growth were increased (Matzat et al., 1990). Do gilts respond in the same way as sows to extra food in lactation? Gilts are smaller than sows and would be expected to have a greater impetus for body growth because they have not reached their mature body size. If gilts are provided with extra food during lactation, they might partition more of it into body tissue and less into milk. Gilts, fitted with gastric cannulas, were used to test the hypothesis that they would respond differently from the sows of Matzat et al. (1990) to extra food in lactation.

One hundred and twenty Yorkshire pigs, equal numbers of gilts and barrows, with an initial average weight of 69 kg were used in the present experiment. The animals were treated with 2 mg d−1 of recombinant porcine somatotropin (rpST) either by daily injection or by slow-release implant, while the control animals were treated with a sham implant. The daily injection of rpST increased daily weight gain (P < 0.0001) and decreased feed/gain ratio (P < 0.0001) and daily feed intake (P < 0.0001). Barrows grew faster (P = 0.02) and ate more feed (P = 0.0001) than gilts. On reaching ~ 100 kg, all pigs were slaughtered, and 60 pigs (two from each pen) were randomly selected for carcass evaluation. Carcass lean content was increased (P < 0.0001) and carcass fat content was decreased (P < 0.0001) in animals treated with rpST by daily injection. Animals treated with rpST by the slow-release implant were not different from the control animals in terms of growth performance and carcass characteristics. No overt lameness was observed in any of the pigs in the experiment. However, rpST treatment, regardless of the method of administration, increased the incidence and severity of osteochondrosis and reduced glycosaminoglycan concentration in the cartilage of the weight-bearing area of humeral and femoral condyles. These changes were independent of enhanced growth rate and carcass lean content. The results indicated that somatotropin treatment predisposes pigs to osteochondrosis. Key words: Osteochondrosis, growth rate, growth hormone, joint cartilage, pigs

This study was undertaken to determine the concentrations of collagen and glycosaminoglycan (GAG) in different layers of joint cartilage of pigs. Effects of recombinant porcine somatotropin (rpST) treatment of pigs on cartilage composition was also examined. The results demonstrated that the concentrations of GAG uronic acid and collagen (measured as hydroxyproline) varied (P < 0.05) between different layers and were reduced (P < 0.05) by the rpST treatment. Key words: Osteochondrosis, articular-epiphyseal cartilage, hydroxyproline, glycosaminoglycan, recombinant porcine somatotropin, pigs

Nineteen sows culled because of impaired reproductive performance were examined postmortem for abnormalities of the femoral condylar cartilage. All animals had lesions of varying severity, including irregular articular surface, surface tears, and erosion of the cartilage. The etiology of these cartilage lesions is discussed in relation to confinement. Key words: Articular cartilage lesion, osteoarthrosis, confinement, sows

One hundred and fifty crossbred pigs (Camborough × Canabrid, equal numbers of gilts and barrows) at an average live weight of 64.2 kg were randomly assigned to diets containing 17 or 20% crude protein (with 0.8 or 1.1% lysine, respectively) and 0 or 20 ppm ractopamine. Pigs were slaughtered at an average live weight of 102.2 kg. Supplementation of ractopamine in pig diets significantly increased average daily gain (P < 0.005) and decreased feed to gain ratio (P < 0.001), with no effect on daily feed intake. Ractopamine feeding increased total lean (P < 0.001) and decreased total bone (P < 0.05) and total fat content (P < 0.001) of carcasses. The decreased fat content was largely due to the reduction of subcutaneous fat (P < 0.001). Cartilage visual scores and cartilage uronic acid concentrations of weight-bearing areas of humeral and femoral condyles were not affected by feeding ractopamine. Correlations between visual scores and uronic acid concentrations of joint cartilage and performance parameters and carcass characteristics were not significant. These results demonstrated that feeding ractopamine can increase pig growth rate and carcass leanness without detrimental effect on joint cartilage. Key words: Ractopamine, growth rate, uronic acid, cartilage, osteochondrosis, pigs

Pigs have developed the ability to store large reserves of protein, glycogen and fat in the body. The pig has also developed the ability to relate its nutrient intake, body composition and the level of tissue mobilization with the reproductive process. The possible physiological and endocrinological mechanisms by which genetically determined traits such as weight, fatness, growth rate or environmental cues such as nutrition affect the reproductive process have been extensively reviewed by Britt et al. (1988), Hughes and Pearce (1989) and Booth (1990). The concensus-is that nutrient intake (total feed, energy or protein) will affect the levels of substrates, hormones and neurotransmitters in the plasma, and these can influence the hypothalamo-hypophyseal-ovarian axis. In the longer term, nutrient intake will influence growth rate, body composition (protein and fat) and the extent of tissue mobilization. The level of anabolism or catabolism of body tissues will influence a host of plasma substrates, hormones and neurotransmitters which will in turn affect the function of the hypothalamus, hypothysis and ovary (Figure 1).

During their second lactation, 123 second-parity Yorkshire × Landrace sows were fed either 6 kg or 3 kg d−1 of a barley-soybean meal diet formulated to provide 12.5 MJ DE kg−1 and 16% crude protein (approximately 90 and 45% of National Research Council (NRC 1988) requirements). From 48 h after the onset of the post-weaning estrus, sows from each lactation feed treatment were allocated equally to receive the same diet at 3.6 kg or 1.8 kg d−1 (approximately 160 and 80% of NRC (1988) requirements), until slaughtered at 25 d of gestation. On days 4, 8, 12 and 16 of gestation, eight sows from each of the four feed level combinations were blood sampled at 15-min intervals for 4 h. Additionally, a further eight sows were sampled once on each of the above days. The lower plane of feeding during lactation resulted in a greater body weight and backfat loss (26.6 vs. 13.8 kg and 6.5 vs. 3.6 mm, respectively; P < 0.01 for both), an increased incidence of anestrus (21 vs. 8%; P < 0.05) and a longer and more variable interval to estrus (8.9 ± 0.4 vs. 6.0 ± 0.2 d; P < 0.01) than higher level feeding. There was no effect of lactation feeding level on ovulation rate (17.6 ± 0.3 vs. 17.7 ± 0.4 for sows having the higher and lower feed intakes, respectively). There was a main effect of lactation (P < 0.01), but not gestation, feeding level and an interaction between lactation and gestation feeding level (P < 0.02), on number of embryos and percent embryo survival. Embryo numbers and survival were reduced following lower plane feeding during lactation but were lowest following lower plane feeding during both lactation and gestation. There was no effect of sampling day on plasma LH concentrations but plasma LH was lower (P < 0.01) in sows on lower plane feeding during both lactation and gestation. The present data confirm an adverse effect of low plane feeding during lactation on subsequent sow reproductive performance and suggest that a reduction in plasma LH concentrations may be involved. These data fail to confirm any adverse effect on embryo survival of high plane feeding during the first 25 d of gestation. Key words: Sow, feed intake, LH, progesterone, reproduction

There is evidence that supplementation of most sow diets with vitamin E is necessary. The common recommendation for supplemental vitamin E in sow diets is 10–20 IU kg−1 diet. This level of vitamin E is adequate to meet needs of the sow for reproduction and to maintain body reserves of α-tocopherol over several parities. Reproducing females can tolerate lower dietary intakes of vitamin E if the levels of Se in the diet are adequate. If body reserves are maintained, the sow, through the colostrum and milk, can supply the neonate with the α-tocopherol required for normal growth and maintenance of tissue integrity. The neonatal piglet is dependent on the sow's colostrum for its α-tocopherol requirements as little placental transfer of vitamin E occurs during gestation. Placental transfer of α-tocopherol is resistant to dietary manipulation while colostral transfer can be enhanced by dietary supplementation. The dietary level of vitamin E in the sow gestation and lactation diet optimal for immune function in both sow and her piglet has not been established. Based on preliminary studies, the level needed is higher than that stated above for growth and reproduction. Enhancements in immune response have been observed with additions of 40–60 IU vitamin E kg−1 diet. This potential for enhancement of the sow's and piglet's immune response by dietary supplementation of vitamin E represents a possibility to improve pre-weaning survival of piglets.

Twenty-two ewes received either 30 μg GnRH or saline at the onset of estrus. Blood samples were obtained on days 1–7 (day 0 = estrus) and corpora lutea recovered surgically at day 7. There was no effect of GnRH on the number or weight of corpora lutea nor on the concentrations of progesterone in either corpora lutea or plasma. GnRH treatment caused an increase (P < 0.07) in luteal hCG binding capacity (0.66 ± 0.12 vs. 0.34 ± 0.12 nmol mg−1 protein). Key words: GnRH, estrus, corpora lutea, hCG binding

Estradiol-17β receptors (E2R) in 100 000 × g supernatant fractions from the hypothalamus and pituitary were determined for groups of five gilts, slaughtered at 4-wk intervals from 4 to 28 wk of age. Tissue samples were separated into the anterior hypothalamus (AH), the central hypothalamus (CH), posterior hypothalamus (PH), anterior pituitary (AP) and posterior pituitary (PP). After saturation binding assays were conducted, E2R concentrations were determined by Scatchard analysis. When expressed on a fmol mg−1 protein basis there was no increase in receptor concentration with age (P > 0.05); however, AP had higher concentrations of receptors than the AH, CH or PH (10.6 ± 1.4 vs. 6.5 ± 0.9, 6.7 ± 0.7 and 6.2 ± 0.6, P < 0.01). Posterior pituitary receptor levels remained low during maturation of the gilt with affinity constant (Ka) values similar to that obtained for the AP. Affinity constant values were found not to change with age; however, AP values were greater than that of the hypothalamus samples (55.2 ± 2.7 vs. 4.8 ± 0.2, × 108M−1). On a total tissue basis AH and CH had significant increases in receptor content from 4 to 28 wk (41.4 to 138.2 and 31.6 to 163.4 fmol, P < 0.05). It was also determined that the soluble protein content per gram wet tissue decreased with age in all regions of the hypothalamus and therefore may mask increases in receptor numbers. Keywords: Estradiol, receptor, gilt, hypothalamus, pituitary, swine

Fifty-five prepubertal Yorkshire × Landrace gilts were randomly assigned to one of six treatments involving the injection (i.m.) of estradiol benzoate (EB) at either 10 or 20 μg kg−1 body weight at gilt ages of 130, 150 or 170 d. Blood samples were taken by jugular vein puncture at 0, 24, and 36 h, and then at 6-h intervals until 84 h, after injection and assayed for plasma luteinizing hormone (LH) concentrations. The mean magnitude of the EB-induced LH peak was 6.1 ± 0.2 ng mL−1, and was not affected by treatment. Fifty-six percent of gilts ovulated in response to EB injection, and 34% had a subsequent ovulation. The initial ovulation rate was unaffected by EB dose, but was higher (P < 0.05) in 170 d (9.9 ± 1.0) compared to younger gilts (4.2 ± 1.1 and 5.5 ± 1.1 for 130-dand 150-d gilts, respectively). Subsequent ovulation rates were unaffected by treatment. It is concluded that EB treatment will usually induce a phasic release of LH from prepubertal gilts, but this release is not necessarily accompanied by normal estrous cyclicity. Key words: Estradiol, gilts, ovulation

In order to characterize the development of the adrenal axis by monitoring development of the circadian rhythm of cortisol, 10 gilts were blood-sampled serially for 24 h every 4 wk from 4 to 28 wk of age. Age at first estrus for sampled animals (199.6 ± 5.3 d, mean ± SEM) was not different (P > 0.05) from that of another group of 10 control gilts not blood sampled (203.4 ± 6.8 d). Cortisol profiles at 4 wk of age did not show a significant diurnal variation. At 8 and 12 wk, the profile showed the development of an afternoon trough. At 16 wk, an afternoon peak was present. At 20 and 24 wk, the continued development of peaks and a well-formed trough were evident and by 28 wk of age the profile was characterized by a large morning peak, small afternoon peak and an evening trough. Mean levels of total cortisol at 4, 8, 12, 16, 20, 24 and 28 wk were 25.3 ± 2.2, 37.4 ± 4.1, 40.1 ± 3.5, 26.8 ± 2.8, 20.6 ± 2.6, 38.3 ± 3.6 and 24.8 ± 2.9 ng mL−1, respectively. Profiles of biologically active cortisol appeared to closely mirror total cortisol profiles. Total cortisol levels at 8, 12 and 24 wk of age were higher (P < 0.05) than at other ages. These results indicate that in the gilt the circadian rhythm of cortisol undergoes gradual development reaching adult profiles at or shortly before first estrus. Key words: Adrenal, circadian rhythm, cortisol, cortisol binding globulin, development, gilt

The object of this study was to determine the effect of mixing stress on the development of osteochondrosis, using scanning electron microscopy. Sixteen litters of eight pigs per litter were randomly assigned to one of four different treatment groups involving combinations of preweaning handling and postweaning mixing stress. Before weaning, all pigs were subjected to normal handling procedures, but one of the groups was handled with exceptional care. After-weaning treatments involved various amounts of mixing stress varying from no mixing to mixing every month. All pigs received standard starter, grower and finisher diets ad libitum (19, 16 and 14% crude protein, respectively). Eight pigs from each of the four treatment groups were randomly selected for slaughter at 3, 4, 5 and 6 mo of age. After slaughter elbow and knee joints were examined grossly and histologically by light and scanning electron microscopy for evidence of osteochondrosis. Handling and mixing stresses had no significant effect on performance in the grower or finisher periods. Mixing stress had no significant effect (P > 0.05) on the average lesion scores of cartilage from any of the sites studied. No differences were apparent under light microscopy in the morphology of humeral and femoral condylar cartilage of pigs from any of the treatment groups. Under scanning electron microscopy the surface of normal porcine condylar cartilage appeared very smooth with numerous clusters of chondrocytes evidenced by small protrusions from the surface. Pigs from the two mixed treatment groups showed extensive surface wear (osteoarthrosis) at the age of 6 mo. The results indicated that mixing stress had little effect on the incidence of osteochondrosis but may be involved in the progression of osteoarthrotic changes with advancing age. Key words: Scanning electron microscopy, swine, osteochondrosis, mixing stress

Two experiments were conducted with 28-d-old pigs to study the effects of 0 or 8% added fat to the diet when constant nutrient to energy ratios were maintained. In exp. 1, 24 pigs were assigned to one of six treatments. Pigs were fed either ad libitum or restricted. Digestibility values were determined using fecal and terminal ileum collection methods. Only apparent ether extract digestibility increased (P < 0.001) with the addition of fat to the diet. Ether extract digestibility coefficients determined by the ileal collection method were significantly larger (P < 0.001) than those determined by fecal collection. In contrast apparent energy, dry matter and crude protein digestibilities based on ileal collection were significantly lower than the equivalent digestibilities based on fecal collection. The second experiment compared the performance and carcass composition of pigs fed the same diets as in exp. 1. Pigs 7 d after weaning contained less fat (P < 0.01), more water (P < 0.001) and more protein (P < 0.01) than pigs at weaning. Carcass composition of the pigs 7 d after weaning and at 20 kg liveweight were similar (P > 0.05). Feed conversion efficiency was improved (P < 0.001) by the addition of fat to the diet. Key words: Weaned pigs, fat, digestibility, performance, body composition

Eighty crossbred pigs at weaning were selected from 20, third-parity sows which had been fed either an adequate or restricted (50% of adequate) level of energy and protein during lactation for three consecutive parities. Pigs, in groups of four, were housed in 2.4-m × 1.5-m concrete-floored pens and fed standard starter, grower and finisher diets (19, 16 and 14% crude protein, respectively) ad libitum. Locomotory ability was recorded prior to slaughter at 100 kg liveweight. Sites in the elbow joint and distal ulna physis were examined for evidence of osteochondrosis. Pigs from restricted-fed sows were lighter at birth and weaning (P < 0.01) and had significantly higher rates of liveweight gain during the grower (7–60 kg) period than pigs from adequately fed sows. Locomotory ability, morphology under light microscopy and overall incidence of osteochondrotic lesions did not differ (P > 0.05) between pigs from the two sow nutrition regimes, nor between sexes. Osteochondrotic lesion score in the distal ulna physis was higher (P < 0.01) in pigs from restricted-fed sows and was weakly correlated (r = 0.16, P < 0.001) with the extent of maternal weight loss over the lactation period. Lesion scores for the lateral humeral condyle and proximal ulna were higher (P < 0.05) for pigs from adequately fed sows. The possibility of an etiological difference between physeal and articular-epiphyseal lesions of osteochondrosis is discussed. Maternal nutrition can not be ruled out as a factor in the etiology of physeal lesions. Key words: Swine, osteochondrosis, maternal nutrition, lactation

The objective of this study was to examine the development of the reproductive axis of the gilt with respect to development of the adrenal glands. Groups of five gilts each were slaughtered at 4-wk intervals from 4 to 20 wk of age. Organ weights as well as activity of the adrenal glands were determined by histometry to determine nuclear to cellular volume ratios and thickness of zones of the cortex. Weights of the heart, lungs, spleen, kidneys, pineal, thyroid and adrenals were found to increase with age while relative weight of these organs was constant or decreasing. In contrast, weight and relative weight of the whole reproductive tract, oviducts and uterus showed growth spurts, first at 16 wk and later at 28 wk of age. The ovaries had one growth spurt at 16 wk of age. An increase at 12–16 wk was also evident in profiles of estradiol and LH determined from blood samples collected from another group of gilts sampled at weekly intervals until first estrus (207.8 ± 3.3 d, mean ± SEM). Measurement of relative nuclear volume and thickness of the adrenal cortex zonation during development failed to provide any evidence to support the hypothesis that an increase in activity or growth of the adrenal gland is responsible for the growth spurts in the reproductive axis during development. Key words: Adrenal gland, adrenal axis, development, gilt, reproductive axis