Subcutaneous Backfat Thickness Research Articles

Serum leptin concentrations, luteinizing hormone and growth hormone secretion during feed and metabolic fuel restriction in the prepuberal gilt

Two experiments were conducted to determine 1) the effect of acute feed deprivation on leptin secretion and 2) if the effect of metabolic fuel restriction on LH and GH secretion is associated with changes in serum leptin concentrations. Experiment (EXP) I, seven crossbred prepuberal gilts, 66 ± 1 kg body weight (BW) and 130 d of age were used. All pigs were fed ad libitum. On the day of the EXP, feed was removed from four of the pigs at 0800 (time = 0) and pigs remained without feed for 28 hr. Blood samples were collected every 10 min from zero to 4 hr = Period (P) 1, 12 to 16 hr = P 2, and 24 to 28 hr = P 3 after feed removal. At hr 28 fasted animals were presented with feed and blood samples collected for an additional 2 hr = P 4. EXP II, gilts, averaging 140 d of age ( n = 15) and which had been ovariectomized, were individually penned in an environmentally controlled building and exposed to a constant ambient temperature of 22 C and 12:12 hr light: dark photoperiod. Pigs were fed daily at 0700 hr. Gilts were randomly assigned to the following treatments: saline (S, n = 7), 100 ( n = 4), or 300 ( n = 4) mg/kg BW of 2-deoxy-D-glucose (2DG), a competitive inhibitor of glycolysis, in saline iv. Blood samples were collected every 15 min for 2 hr before and 5 hr after treatment. Blood samples from EXP I and II were assayed for LH, GH and leptin by RIA. Selected samples were quantified for glucose, insulin and free fatty acids (FFA). In EXP I, fasting reduced (P < 0.04) leptin pulse frequency by P 3. Plasma glucose concentrations were reduced (P < 0.02) throughout the fast compared to fed animals, where as serum insulin concentrations did not decrease (P < 0.02) until P 3. Serum FFA concentrations increased (P < 0.02) by P 2 and remained elevated. Subcutaneous back fat thickness was similar among pigs. Serum IGF-I concentration decreased (P < 0.01) by P 2 in fasted animals compared to fed animals and remained lower through periods 3 and 4. Serum LH and GH concentrations were not effected by fast. Realimentation resulted in a marked increase in serum glucose (P < 0.02), insulin (P < 0.02), serum GH (P < 0.01) concentrations and leptin pulse frequency (P < 0.01). EXP II treatment did not alter serum insulin levels but increased (P < 0.01) plasma glucose concentrations in the 300 mg 2DG group. Serum leptin concentrations were 4.0 ± 0.1, 2.8 ± 0.2, and 4.9 ± 0.2 ng/ml for S, 100 and 300 mg 2DG pigs respectively, prior to treatment and remained unchanged following treatment. Serum IGF-I concentrations were not effected by treatment. The 300 mg dose of 2DG increased (P < 0.0001) mean GH concentrations (2.0 ± 0.2 ng/ml) compared to S (0.8 ± 0.2 ng/ml) and 100 mg 2DG (0.7 ± 0.2 ng/ml). Frequency and amplitude of GH pulses were unaffected. However, number of LH pulses/5 hr were decreased (P < 0.01) by the 300 mg dose of 2DG (1.8 ± 0.5) compared to S (4.0 ± 0.4) and the 100 mg dose of 2DG (4.5 ± 0.5). Mean serum LH concentrations and amplitude of LH pulses were unaffected. These results suggest that acute effects of energy deprivation on LH and GH secretion are independent of changes in serum leptin concentrations.

Transfer of an ovine metallothionein-ovine growth hormone fusion gene into swine.

An ovine metallothionein-1a (oMT1a)-ovine growth hormone (oGH) fusion gene was microinjected into 400 pig zygotes, the zygotes were transferred into recipient females, and 15 founder transgenic pigs were born. Of 12 transgenic pigs assayed, five expressed high levels of oGH (> 900 ng/mL plasma), one expressed low levels of oGH (10 to 30 ng/mL), and six did not express oGH. Dietary supplementation with 2,000 ppm of zinc for 6 d induced a 20-fold increase in plasma oGH in the transgenic pig with low expression but did not induce expression in the six transgenic pigs with no constitutive oGH expression. The average daily gain of five transgenic pigs with elevated oGH was similar to that of non-transgenic littermates during a 9-wk feeding trial (P = .52). The liver, kidney, adrenal, and thyroid weights were all significantly heavier for the oGH-expressing transgenic pigs than for non-transgenic littermates. Total carcass fat, longissimus muscle fat, subcutaneous backfat thickness, and loin eye area were lower and carcass protein and water content and beta R fiber area of longissimus muscle were higher in the transgenic pigs with elevated oGH than in their littermate controls (P < .05 for each). The data indicate that even though the oMT1a promoter was more inducible by zinc than was previously reported for the mouse MT promoter in swine, the former provided a higher level of oGH expression than the mouse MT promoter.

A STUDY OF ULTRASONIC PROBING TECHNIQUES FOR SWINE II. PREDICTION OF CARCASS YIELD FROM THE LIVE PIG

In order to examine the effect of probe site and pig weight at probing on ultrasonic machine and operator accuracy, 227 pigs were probed for subcutaneous backfat thickness at 80, 90, 100 or 110 kg. Ultasonic probe sites were 5 cm off the midline on the midback at a point aligned with the root (B1) or the apex (B2) of the curve of the last rib. Loin sites were defined as 15 cm posterior to B1 (L1) or directly above the stifle joint of the hind leg (L2) of a pig standing normally. A third midback measurement was defined as for B1 but 6 cm off the midline (B3). The value of layer 2 or total backfat depth measurements at these five sites in predicting carcass dissectible fat and lean tissue content were examined. The best combinations of probe sites included L1 and either B1, with R2 of 0.41, 0.70, 0.72 and 0.78 or B2 with R2 of 0.38, 0.70, 0.71 and 0.76 for 80-, 90-, 100-, and 110-kg pigs, respectively, when total backfat was used to predict percent dissectible fat of carcass. These results indicate that carcass yield cannot be predicted adequately at 80 kg and that the optimum probe weight was between 90 and 100 kg. However, the additional expense associated with performance testing pigs at weights greater than 90 kg cannot presently be justified. The R2 for either B1 + L1 or B2 + L1 when fat depth of layer 2 was measured at 90 kg was 0.66. The greatest consistency between operators was observed when fat depth of layer 2 was measured. Key words: Swine, ultrasonic probe, slaughter weight, carcass yield