Performance, chemical body composition, and energy balance of 70-kg pigs as affected by dietary restriction in young age

The study was carried out on 20 gilts from 15 to 70 kg. From 15 to 25 kg the animals were fed a starter diet at three feeding levels: group C, 100; group D l , 85; D2, 60% of intake. From 25 to 70 kg the animals were fed a grower diet at the standard feeding level. During restriction, the D l and D2 pigs grew slower than the C pigs (382, 240 vs 512 g/day) and reached 25 kg 8 and 23 days later, respectively. During realimentation, both D l and D2 pigs utilized feed more efficiently and grew faster than controls. Overall performance (15-70 kg) indicates that D l pigs grew at similar rate and D2 significantly slower than the C pigs (670, 677, 565 g/day) but both previously restricted pigs utilized protein more efficiently. The D l group showed a full compensatory response.


INTRODUCTION
Temporarily underfed animals can grow faster during subsequent stages of their growth (Donker et al., 1986;Stamataris et al., 1991;Bikker, 1994). However, this response depends on many factors (Ryan, 1989) and sometimes animals are unable to fully compensate for age and weight lost during underfeeding (e.g. Campbell andBiden, 1978).
The aim of this study was to test the hypothesis that the compensatory response of previously underfed pigs is connected with better protein deposition as well as protein and energy utilization.

MATERIAL AND METHODS
A study was carried out on 20 Polish Landrace gilts growing from 15 to 70 kg. At 15 kg the pigs were divided to three groups and up to 25 kg {restriction phase) fed the same diet: the C (control) nearly ad libitum, group Dl, 85% and group D2, 60 % of the intake of the C pigs. From 25 to 70 kg {realimentation phase) all pigs were fed at the standard feeding level (1.44 MJ ME/kg 0 -75 ).
The starter diet used during the restriction phase contained 12.9 MJ ME and 9.9 g of lysine per kg and comprised (%): protein concentrate, 20; cereals, 77; and mineral components, 3; The grower diet fed to animals during realimentation was based (%) on rapeseed meal as the main source of protein, 25.0; cereals, 71.6; mineral components, 3; and synthetic lysine, 0.4; and contained 12.4 MJ ME and 11 g of crude lysine. Apparent digestibility (indirect method with Cr 2 0 3 ) of nutrients was determined on animals in the middle of each phase of the study.
At 15 kg four pigs were slaughtered as the "zero" group, the rest at 70 kg. The pigs were slaughtered after 16 h of fasting. After slaughter, the body were analyzed for protein and fat content (AOAC, 1994). Daily deposition of protein and fat was established from the difference between the final and initial content of these body components.
Statistical analyses were performed by one-way analysis of variance ANOVA using Statgraphics version 6.0 Plus software.

RESULTS
The performance of the pigs during the subsequent growth period is given in Table 1. Decreasing the feed consumed by animals inhibited the growth rate of the Dl and D2 pigs as compared with the control pigs (382 and 240 vs 512 g/day) and worsened their feed conversion ratio as well (29.4, 35.0 vs 26.9 MJ ME/kg gain). Consequently, these pigs reached 25 kg 8 days (group Dl) and 23 days (group D2) later than the control (C) pigs. Protein digestibility was not affected by the severity of the restriction and amounted on average to 79.6%.
During growth from 25 to 70 kg, the Dl and D2 pigs utilized energy more efficiently than the C pigs (29.3, 33.3 vs 35.6 MJ ME/kg gain), however, a significant difference (P<0.01) was detected only between the D1 and C pigs. The growth rate of the D2 and Dl pigs was faster as compared with the C pigs (886 and 780 vs 732 g/day, respectively). The severity of the previous restriction did not influence the apparent protein digestibility of the diet (on average 75.3%).
During the overall period of growth (15-70 kg), the gain of the Dl and C pigs was similar (670 and 677 g/day, respectively), but the D2 pigs gained more slowly (565 g/day, PO.01). The feed conversion ratio in the Dl and D2 pigs was better Performance of the pigs A,B,c_p <0>0 i than in C (31.9, 26.5 vs 34.0 MJ ME/kg gain), but a significant difference was detected only between the D2 and C pigs. When the final age of the pigs was compared it was found that the D1 pigs were only slightly older than the C (144 vs 141 days, difference insignificant)) while the D2 pigs were significantly (PO.01) older (159 days). The final protein content in the body did not differ significantly between groups (Table 2). However, the D1 and D2 pigs had even less fat compared with the C pigs (11.15 and 11.60 vs 12.97 kg), but a significant (PO.05) difference was detected between the Dl and C pigs only. A tendency (PO.07) to improve the proteimfat ratio in the body of the Dl and D2 pigs as compared with the control animals was detected (0.97 and 0.92 vs 0.80, respectively).
Protein and fat content in the body of the pigs at 70 kg The C and Dl pigs deposited a similar amount of protein daily (102 and 105 g, respectively) and significantly more (P<0.01) than the D2 pigs (87 g), (Table 3). However, the efficiency of digestible protein (protein consumed/protein deposited) was the best in the Dl pigs (50.7 %), slightly worse in the D2 pigs (47.2 %) and the worst in the C pigs (43.7%) but a significant difference (PO.01) was detected only between the C and Dl pigs. Daily energy intake (Table 3) by the pigs varied from 23.0 MJ (the C), 21.3 MJ (the Dl) to 18.7 (the D2). The C and Dl pigs deposited a similar amount of energy as protein and significantly more than the D2 pigs (2.4 and 2.5 vs 2.1 MJ/day). However, the Dl and D2 pigs deposited less (PO.01) energy as fat compared with the C pigs (4.7 and 4.2 vs 5.6 MJ/day) but no differences between groups of pigs in energy utilization were detected.

DISCUSSION
Decreasing the energy intake inhibited the growth rate of animals to the same extent as in a previous study on compensatory growth, in which feed intake had been decreased to a comparable extent (e.g., Campbell et al., 1983). Positive growth of the most severely underfed pigs during the restriction phase indicates that young animals have a great adaptive capacity to temporary nutritional deficiency, which is connected with a reduction in their maintenance requirements due to the smaller size of internal organs (Koong et al., 1982).
Similarly to the results of our study, significantly higher growth rates of pigs previously underfed in terms of energy intake had been observed in the studies by Donker et al. (1986), Stamataris et al. (1991) and Bikker (1994). However, only a few studies have been carried out on sheep (e.g., Winter, 1976;Thornton et al., 1979). In them, animals recovered their weight and age lost during the restriction phase similarly to the Dl pigs in our study. Data concerning the growth rate of the D2 pigs showed a decrease of their daily gain during the subsequent four weeks of realimentation, which might have resulted from the intensive recovery of the size of their alimentary tract, which usually takes place in the first period after the change from restriction to realimentation (Ryan, 1989). Intensive recovery of metabolically active organs increases protein turnover and, as a consequence, the maintenance requirement of animals (Koong et al., 1985) therefore, less energy can be assigned for growth.
The energy balance of the pigs during growth from 15 to 70 kg indicates that previously underfed pigs deposited more energy as protein and less as fat and that the energy efficiency in such growing pigs is not significantly worse than in the pigs fed adequately throughout their growth period.
The severity of the restriction of the D2 pigs was too high and those pigs grew significantly more slowly, but utilized protein slightly better than controls. These findings agree with those presented by Stamataris et al. (1991) and Bikker (1994) who applied a similar severity of the restriction but used animals at a different age. It should be pointed out that from 15 to 70 kg, previously weakly underfed pigs grew at similar rates and deposited similar amounts of protein despite lower energy intake, but protein utilization was even better than in the control animals. The similar average protein deposition of the previously weakly underfed and control pigs indicates that during the realimentation phase, previously weakly underfed pigs must have deposited a greater amount of protein in the body as compared with the control (Stamataris et al., 1991;Bikker, 1994).

CONCLUSIONS
Temporary underfeeding of young pigs increased their growth rate during the subsequent stage of growth and influenced their overall performance. Temporarily underfed pigs are able to show compensatory growth (recovering weightfor-age) but this response is influenced by the severity of the previous underfeeding.
Overall performance of previously underfed pigs indicates that the compensatory response can be connected with higher protein deposition and better protein utilization.