Thirty-seven pigs were used to evaluate the effects of age and weaning on the level of protease in the gastric mucosa and trypsin, chymotrypsin, amylase and lipase in the pancreas. There was a positive allometry of the pancreas and gastric mucosa associated with age and with weaning to a solid diet. Increases with age in total activity of chymotrypsin, trypsin, amylase and gastric proteases were due to increases in both tissue weight and enzyme activity per gram of tissue. A general depression in pancreatic enzymatic activities, but not in gastric proteolytic activity, was found during the first week following weaning. Forty pigs were used in a second trial to evaluate the effects of age and weaning diet on the same digestive enzymes. Total activity of all enzymes assayed increased with time postweaning. Increases in total activity of lipase and chymotrypsin were due primarily to increased pancreatic weight postweaning. Amylase, trypsin and gastric protease increases were due both to increased tissue weight and increased activity per gram of tissue. There were no effects of diet on the weight of gastric mucosa or the level of activity of the gastric proteases. Pigs fed a diet containing 20% whey had larger pancreases (P less than .10) at slaughter and a greater, but nonsignificant, mean activity per gram of pancreas for all pancreatic enzymes. It appears that the pig has sufficient pancreatic and gastric enzyme activity so that performance should not be limited, with the possible exception of the period shortly after weaning. However diet digestibility and subsequent pig performance may be more directly related to the extent of release of these enzymes into the intestine and the conditions that exist therein.
Regression analysis was used to evaluate the effects of gilt age and body composition at first breeding on sow performance over three parities. Eighty-seven Yorkshire x Landrace F1 gilts were used. Variation in age and body composition at first breeding was obtained by breeding gilts at puberty, second, or third estrus and by providing those gilts bred after puberty one of four nutritional regimens from puberty until breeding: 1) 2.7 kg/d of a 14.3% CP, 3.5 Mcal ME/kg diet (H), 2) maintenance ME and CP/d (M), 3) half-maintenance ME and CP/d (1/2M), and 4) M or 1/2M until anestrus, then 2.27 kg/d of a 14.0% CP corn-soybean meal diet until first breeding. Body composition at first breeding was determined using live weight, backfat thickness, and deuterium oxide space as variables in prediction equations. All females were treated similarly after first breeding. Age and body composition at first breeding were not related (P > .10) to litter size at birth or weaning in parities 1, 2, 3, or overall. Increasing age at first breeding was related to small increases in pig birth weights (P < .001) in parity 1 and average pig weaning weight (P < .001) in parities 1, 2, and overall. Body composition of gilts at first breeding was not related (P > .10) to pig birth weights and was inconsistently related to pig weaning weights in parities 2 and 3 (P < .001). Females heavier at first breeding remained heavier (P < .01) throughout the experiment. Age and body composition at first breeding were not different (P > .10) for gilts completing three parities (n = 53) compared with gilts failing to complete three parities (n = 34). Results show no large effects of gilt age or body composition at first breeding on sow productivity and longevity over three parities.
The relationship between body composition and the occurrence of puberty was evaluated using 93 Yorkshire x Landrace gilts. At approximately 60 d of age gilts were purchased and placed in a heated confinement unit where they were housed for the duration of the study. Ad libitum access to feed was provided throughout the study. Gilts were moved, mixed, and initially exposed to mature boars at approximately 120 d of age to encourage the earliest possible occurrence of puberty. Empty body weights of water, fat, protein, and ash at puberty were estimated using a deuterium dilution technique and prediction equations developed for this gilt population. There was considerable variation in age, weight, and all measures of body composition at puberty. Gilts were 138 to 240 d old and weighted 64.9 to 150.8 kg. Backfat thickness ranged from 17.5 to 44.0 mm. Gilts were composed of 32.4 to 64.3 kg of water, 15.6 to 53.9 kg of fat, 9.03 to 20.56 kg of protein, and 1.24 to 3.10 kg of ash. The coefficient of variation for fat to lean ratio at puberty was 15.39%. Linear and quadratic regressions showed that lifetime (birth to puberty) growth rate was not related to age at puberty (P > .10). Based on the variation in body composition observed it was concluded that the occurrence of puberty in gilts given ad libitum access to feed during rearing and initially exposed to mature boars at approximately 120 d of age was not related to certain minimum threshold amounts of body tissues or to a specific rate at which body tissue reserves were accumulated.
Thirty-seven Duroc x (Yorkshire x Landrace) (DYL) and 21 Yorkshire x Landrace (YL) gilts were used to develop equations that predict body composition of replacement-age breeding swine. Before slaughter, gilts were weighed, ultrasonically scanned for 10th rib backfat thickness, and infused with D2O (.25 g/kg live weight). The D2O space (kilograms) was calculated from body water D2O concentration determined at equilibrium (150 and 210 min after infusion). Regression models predicting empty body (Eb) components for DYL and YL groups were fitted using all possible variable combinations (D2O space, live weight, and[or] backfat depth). Variables selected in best-fit models for Eb water, protein, fat, and ash for data from DYL gilts differed from variables selected from data from YL gilts. Average prediction errors (kilograms; [predicted residual sum of squares divided by n]1/2) of best-fit equations were 2.37, 2.03 (Eb weight), 2.36, 1.66 (Eb water), 1.07, .47 (Eb protein), and 2.76, 2.89 (Eb fat) for DYL and YL data sets, respectively. Cross-validation by applying DYL equations to YL data, and vice versa, resulted in larger prediction errors. Likewise, larger errors were obtained when equations published elsewhere were applied to DYL and YL data sets. No cited source provided a set of equations that consistently minimized prediction errors of all Eb components of both DYL and YL gilts. Results indicate that prediction equations using D2O space, live weight, and(or) backfat thickness are accurate in estimating body composition only in animals physiologically resemble the population in which the equations were derived.
An experiment using comparative slaughter was conducted to examine the relationship between occurrence of nutritionally induced anestrus in postpubertal gilts and chemically determined body composition and body composition changes. Thirty-nine Duroc x (Yorkshire x Landrace) gilts, each having experienced three or more estrous cycles, were used. Nine gilts were chosen randomly, weighed, ultrasonically scanned for 10th rib backfat thickness, and slaughtered to determine initial body composition. Remaining gilts were allotted randomly to five dietary treatments, four characterized as severely energy restrictive (RES; .25, .50, .75, and 1.0 mcal of ME/d) and a control (3.4 Mcal of ME/d). Dietary treatments provided equal amounts of protein (50 g), minerals, and vitamins daily. Individual serum progesterone levels were determined every 3 d using RIA and gilts were considered anestrous when concentrations were < 1.0 ng/mL for four consecutive samples (9 d). All RES gilts became anestrous, and gilts restricted more severely tended (P = .22) to do so more quickly. Days to anestrus were 66.0 +/- 12.0, 77.4 +/- 13.1, 84.5 +/- 12.0, and 86.5 +/- 12.0 for treatments .25, .50, .75, and 1.0, respectively. Among RES treatments there were no linear, quadratic, or cubic effects of ME intake (P > .10) on the quantity of body protein or fat lost, or on the quantity of body protein or fat remaining at anestrus. However, individual body protein and body fat contents of RES gilts at slaughter revealed that anestrus occurred at a wide range of body compositions, from 13.4 to 20.2 kg of protein and .36 to 27.0 kg of fat. This wide range of individual values suggests that estrous activity in the mature gilt is not controlled by specific threshold levels of body reserves.
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